chapter one background studies -...

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel___________ for Naval applications__________________________

CHAPTER ONE

BACKGROUND STUDIES

1.1 Introduction

Till date modem industries mainly focused on light and high performance materials

for static and dynamic machine structures by single step fabrication technique [1]. But

due to complex shape, size, heterogeneous materials, fabrication has become complex

and unable to fabricate machine structures by one step casting [2]. Machine parts are

cast separately and joined to form their final shape. Joining of the part / materials is

one of the vast area which includes permanent joints such as welding [3], brazing [4]

and soldering [5] and temporary joints such as mechanical fasteners [6], adhesive

bonding [7], and riveting [8]. Latter methods (temporary joints) are used for only light

and frequently loading structures. In the former methods welding is especially used

for rigid and permanent structures which are exposed to dynamic / variable loading

environment [9]. On the other hand brazing and soldering are generally used for

electrical equipments [10]. As industrial machine structures are huge and complex in

nature, casting of these machine parts need more attention and special tailored made

fixtures are necessary and become more expensive [11]. Casting parts need secondary

operations such as removal of extra materials and unwanted materials using

machining centers. Hence majority of machine parts are fabricated by joining of

different cast structures. Some of the dynamic structures require relative motion with

respect to rigid structures. The type of joint is dictated by the applications of the final

assembly, strength requirement, type of the materials used, type of interaction of

forces involved among the subassemblies, geometry of the components and cost

issues [12]. Presently welding is one of the most important joining techniques in

industries. More than 50% of joining of structures depends on different welding

techniques [13].

1.2 Purpose of Welding

Variety of joining processes are available for engineering applications such as

welding [14], solid state welding [15], brazing [16], soldering [17], mechanical

fastening [18] and adhesive bonding [19]. Since many of the industrial applications

involve use of metals and alloys, welding as a joining process has gained popularity

R V Center for Cognitive Technologies, R V College of Engineering, Bangalore-59. 1

over other methods, as it is efficient, economical, reliable, rigid, repairable, and can

be performed quickly [20]. Other methods of joining processes such as solid state

welding though may yield good strength among metals or alloys but it is expensive

and demand highly cleaned surfaces [21]. It is limited to specialized applications such

as in aerospace and automotive industries. On the other hand, brazing, soldering and

adhesive bonding though are comparatively cheaper, the joint strength is low [22].

Joints formed by mechanical fastening are a result of friction or mechanical

interlocking. These joints are best suited for components which involve frequent

disassembly for maintenance purposes. Creating a mechanical joint involves

additional manufacturing process like hole-drilling, reaming, bolting, washer / rivet

placing, tightening / hammering. These methods are used only in sheet metal working

where minimum loading conditions apply [23]. Among all joining processes, the arc

welding is the most preferred method for heavy static and dynamic structures due to

their rigid and good bond between the structures.

1.3 Novel Welding Techniques

Every day industries develop new manufacturing designs or concepts to replace older

version to improve their functional performance and also to increase specific strength

of the structure [24], Presently, conventional welding such as arc welding is used in

more than 75 % of the times in all type of industries due to simplicity and cost

effectiveness [25]. The new design of machine structure with complex joints, use of

dissimilar alloys for diverse environment has made conventional welding techniques

obsolete and hence is unable to fulfill the service requirements [26].

1.3.1 Underwater Welding

Several researchers suggested Laser Beam welding (LBW) technique to repair

underwater offshore structures, cross continental pipelines by any of the two

techniques such as dry [27-29] and wet underwater welding [30] technique. In wet

underwater welding LBW is preferred due to low heat input, high cooling rate, small

heat affected zone and lower residual stresses [31]. Xudong Zhang et al have

suggested using LBW to repair underwater structures as the input power is transmitted

through optical fiber and hence welding is flexible and location of weld is precise

inspite of problems like effect of water on weld metallurgy and absorption of water by

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel__________________________ for Naval applications__________________________


laser beam [32]. Other researchers [33-35] endorsed wet water welding using self

shielding flux cored arc welding (FCAW) due to its low cost compared to other

welding techniques wherein extra engineering vessels and shielding gas has to be

installed at the time of welding [36]. On the other hand Nixon et al [37] have

developed dry hyperbaric chamber to overcome the difficulties such as influences of

arc behavior, metal transfer, welding metallurgy and mechanical properties. [38].

1.3.2 Welding in Space

Welding in space presents unique challenges such as microgravity and vacuum. Paton

et al[F39] through their studies have concluded that vacuum condition in space are

favorable for welding process since there are no problems such as base metal

oxidation and absence of other contaminants in the atmosphere, hence base metal

covering by flux and inert gas are also not required. Though Milo Nance et al[40]

proposed both electron beam welding (EBW) technique and laser beam welding

(LBW) technique for space welding applications both do not require filler metal (low

payload for the space flight) but the laser beams are inherently dangerous as laser

pointing some other direction can harm other structures or welder himself. Also,

power requirements for LBW process is more than EBW. McKannan and Monroe et

al [41-43] studied microstructure of weld joint of three materials such as tantalum,

SS304, and 2219 T87 aluminum after welding by EBM technique in space and

reported that all the weldments showed significant grain refinement compared to the

same metals being welded on earth. Also in pure metals like tantalum, no solid phase

transformation was noticed. Block-Bolten et al [44] have suggested gas tungsten arc

welding or tungsten inert gas welding (GTAW/TIG) technique for space

environments but maintaining constant gas supply through compressed gas cylinders

(excess payload) for arc stability will be a problem.

1.3.3 Friction Stir Welding

The inherent problems in fusion welding of metals such as resolidification, formation

of secondary phases, porosity, hydrogen embrittlement and liquation cracking may

not be fully eliminated in spite of taking great care [45]. Hence, friction stir welding

(FSW) is preferred as the alloy is not melted during the process, joints with lower

distortion and lower residual stresses can be obtained. Hence the mechanical

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications

R V Center for Cognitive Technologies, R V College of Engineering, Bangalore-S9. 3

properties of the joint are superior to other joining processes. Thomas and Dawes [46-

48] have successfully demonstrated welding of similar and dissimilar metals by

means of FSW. A non-consumable rotating tool with pin and shoulder is used for

joining in FSW. Various researchers [49, 50] have shown applications of FSW in

many fields of engineering such as aerospace, automotive and defense applications.

1.3.4 Electron Beam Welding

Electron beam welding (EBM) is used for fabricating structures which have to pass

stringent quality, strength and joint reliability tests [51, 52]. Several researchers [53-

58] have reported good weldability between similar and dissimilar metal joints due to

its highly dense and sharply focused beam of electrons (100-kV, 10-mA). Cam et

al[53] have showed that joining rate is higher in EBM welding technique compared to

other fusion welding techniques [54]. Its narrow heat affected zone (HAZ) [55],

minimum distortion[56,57] and welding in vacuum [58] eliminates the problem of

oxidation in the weld joint.

1.3.5 Laser Beam Welding Technique

Several studies [59-61] have reported use of laser beam welding technology in joining

new materials in the field of automobile and aerospace. Weichiat et al[62] in their

study on laser welding of martensitic steel have reported the fine quality weld seam

deep penetration, high speed and small heat affected zone attributed to its low heat

input per unit volume, high density power, sharply focused beam and delivery of

beam at the precise position by optic fiber.

1.4 Welding in Closed Place

Several researchers have discussed the different types welding used to weld or repair

structures within enclosed space such as interiors of boilers, ships and submarines.

Welding techniques such as gas metal arc welding/metal inert gas welding

GMAW/MIG [63, 64], laser beam welding [65, 66], submerged arc welding

(SAW)[67], flux cored arc welding (FCAW) [68], shielded metal arc welding

(SMAW)[69] and others are used. Lesnewich et al [70] have reported good quality

weld joints in primary tubing of power plant made of Cr-Mo steel by MIG welding

technique with gas mixtures of He, Ar, and COj. The productivity of the welding is



also high in MIG welding. Missori et al [71] in their findings have reported the use of

transition joint Ni-Cr-Fe filler metal to obtain good quality weld between austenitic

stainless steels and ferritic low alloy steels by means of pulsed laser beam welding in

the main steam lines of thermal power plant. Kabir et al [72] have proved that good

quality welds free from porosity were obtained when welding Ti alloy by laser

welding technique. Kanjilal et al [73] have reported that in SAW welding of low

carbon steel, mechanical properties of the weld primarily depended on the welding

parameters and quality of the flux used to submerge the electrode. Cary et al [74] have

reported FCAW as one of the popular welding process among fusion welding

techniques due to its high productivity, good quality welds, low fume generation,

effective utilization of electrode materials, low distortions and residual stresses. Raja

et al [75] have reported the applications of FCAW welding in steel fabrication, public

works (e.g. bridges), naval works, boiler making, tube/pipe welding, heterogeneous

assemblies, and others. Cary et al[76] have reported SMAW as simplest in terms of

equipment requirements among all the welding techniques and is used for all types of

manufacturing, construction and repair/maintenance type of applications. Technical

guide from Hobart Brothers Co [77] reports though primarily the welding in SMAW

is dependent on the skill of the welder, by careful control of welding parameters, good

quality welds can be achieved and was demonstrated in the construction of submarine

pressure hull sections and high-pressure oil/gas pipe lines.

Several researchers [78-79] have reported scope of closed welding techniques, quality

of the weld joints, its effect on the mechanical properties and ongoing effort to further

improve the quality of the weld but very few researchers have made attempts to

quantify and document the various types of weld fumes and its adverse effects on the

welders and the people in the welding area vicinity. As per the estimates of Bureau of

Labor Statistics (US) [80], worldwide, there are more than two million welders

working in hazardous conditions. Zimmer and Biswas et al [78] reported the

formation of gaseous and aerosols byproducts generated from the electrode or flux

materials at the time of welding which react with air and become particles of

respirable size. These airborne particles, when inhaled cause respiratory disorders and

affect the health of the welders by causing asthma and in some conditions even lung

cancer. Occupational Safety and Health Administration (OSHA) in its annual report

[81] have suggested use of safety equipments such as gloves and mask during



welding, but these equipments affects the welder’s productivity. Other solution

proposed by OSHA is by providing exhaust systems. Though exhaust systems protect

the welders from harmful fumes, such solutions become expensive and impractical

when the welding is done in closed or interiors of a ship or a power plant. Wittczak et

al [82,301] have reported the presence of heavy metals such as Cr, Mn, Ni, Fe in the

welding fumes and they are responsible for causing respiratory disorders such as

metal fume fever, bronchial asthma, chronic obstructive pulmonary disease,

pneumoconiosis and lung cancer.

Inspite of the advances in welding, there are equal number of problems to be

addressed in both open and closed environment welding processes. Technical notes of

Miyachi Unitech Ltd (US) [83] reports five prominent sources of problems in

welding. They are

1. Weld materials

2. Electrode materials

3. Welding technique

4. Power input

5. Fumes.

Wrong welding technique [84], wrong selection of electrodes and base materials [85]

leads to weld defects such as cracks, porosity, oxidation, distortion of the weld joint,

brittle welds, residual stress accumulation along the weld joint, harmful fumes

generation etc. In case of harmful fumes generation, installation of exhaust systems at

the place of welding does not provide 100% removal of poisons gases. Hence in the

present research work effort to reduce the adverse effects of weld fumes has been

addressed specifically carcinogenic hexavalent chromium fumes generation during the

welding of stainless steel is attempted.

1.5 Different Types of Welding Electrode

1.5.1 Coated Electrodes

As per American Society of Materials (ASM) handbook vol 6 [86] welding electrodes

are classified broadly as non consumable and consumable electrodes. Technical notes

by ESAB [87] have defined non consumable electrode as an electrode which does not

become part of the finished weld but is used to strike an arc and melt the filler and

base metal such as in case of TIG welding technique, whereas [87] consumable

electrode is defined as an electrode which becomes part of finished weld such as in



case of SMAW, MIG, etc. Consumable electrode can be further subdivided into

coated electrode and bare or wire electrode. Based on the coating, electrodes (for low

and mild alloy steel) can be classified into four types.

1) Cellulosic electrodes

2) Rutile electrodes

3) Iron oxide silicate

4) Basic electrodes.

As per welding guide of Bohler [88] it is reported that, 1) Gas shielding cellulose

electrodes contain 30 per cent of organic material such as alpha flock, wood flour or

other cellulose. At the time of welding, voluminous gas shield of H2, CO and CO2

gives good protection for the molten weld metal, hence good weld metal properties,

excellent penetration, suitable for all welding positions and requires direct current

(DC). As per the welding electrode product information from Sandvik materials

technology centre, it is reported that, 2) Rutile electrodes [89] contain 50% Titania or

Ti02, and is known to give good arc stability, low operating voltage is low, and can

be used with alternating current (AC). At the time of welding, hydrogen, oxides of

carbon, nitrogen, together with an acidic slag protect the weld from the air

contamination. Other advantages include easy slag control, low spatter, medium

penetration and high deposition rate, good mechanical properties, good weld

appearance but low ductility. As per the training materials information from Lincoln

electric company it is reported that, 3) Iron oxide silicate coated electrodes [90] apart

from welding give low gas shielding but high supply of acidic slag which results in

intense slag metal reaction. Due to high oxygen availability and low carbon in the

weld region, the strength of the weld is good and ductile. The electrodes can operate

for both AC and DC. Fluidity of the slag being more, the welding in vertical position

is difficult but nevertheless the weld profile obtained at the time of weld is concave

and good in appearance especially for fillet weld. Other advantages are high

deposition rate, good penetration and low spattering, but low notch ductility. 4) Basic

electrodes [91] also called as low hydrogen or lime-ferritic or lime-fiuorspar

electrodes have high limestone (CaCOs), fluorspar (Cap2) contents. Also present are

clays, asbestos and other minerals which are mixed with very minimum contents of

water to ensure very low hydrogen contents in the weld deposit. Some of the

advantages of using such type of welding electrodes are good ductility, high notch



toughness, good weld soundness is good, high resistance of the weld to hot and cold

cracking and hence suitable for welding higher strength steels such as high carbon or

high sulphur containing steels. It is less sensitive to plate quality.

1.5.2 Wire or Bare Electrodes

As per the technical information brochure of CMW metallic company [92] and hand

book of welding from ESAB [87] it is reported that many or several non ferrous

materials welding is usually done by TIG welding and electrodes used are bare or

wire electrodes. Various manufacturers around the world manufacture bare wire or

welding electrode alloy material suitable to weld that particular alloy, such as copper

wires with alloying elements Si to weld bronze, copper-silicon, copper-phosphorous

and copper-aluminum alloys. As per ESAB hand book [87] on welding it is reported

that aluminium wire with presence of alloying elements like Fe, Cu, Mn, Si, Zn, Cr,

Ni, Ti, Zr, Li, Pb is used to weld their respective aluminum alloys grades ranging

from Ixxx to 7xxx . The weld strength and ductility are found to be good. Varying

diameter of wires from 1-5 mm welding wire or rods are used to weld aluminum

alloys. As per the welding alloy group product catalogue [93] nickel based welding

electrodes such as ENi6182, ENi6082, ENi6625 are used to weld Nickel based alloys

such as Udimet, Inconel 738L, Hastelloy A2, Nimonic alloys, waspoly etc. As per the

author’s opinion, the weld strength depends on various factors like alloy elements

addition, pre and post heat treatment of the weld plates and electrodes wires. The sizes

of the wire to be used for specific application are available in the product catalogues

of the different manufacturers. The welding strength obtained is high, ductility of the

weld joint and resistance to stress corrosion cracking is also high.

1.5.3 Tubular Electrodes

Many manufacturers produce tubular electrodes primarily for hard facing purpose. As

per the catalogue of Inter group [94] of companies, tubular electrode come in different

sizes starting from 6 - 1 2 mm dia. Specific type of tubular electrodes are

recommended for specific substrate. As per the authors [94, 95] claim, such tubular

electrodes can deposit at high rate carbide particle on any given substrate such as mild

steel, cast iron, stainless steel, etc. The mix of matrix (austenite, martensite matrix)

and carbide particles gives the hard facing wear resistant and toughness for external


R Center for Cognitive Technologies, R V College of Engineering, Bangalore-S9. 8

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel

impact loads. Other advantages reported by the authors [94, 95] are low dilution rate,

high alloy concentrations, little or no slag formation and no moisture pickup during its

storage.

1.6 Welding Rod Manufacturing

Several welding electrode manufacturing firms such as ESAB[96], AdorFontech [97],

L&T [98], Lincoln [99] have proposed almost similar methods to manufacture

different types of welding electrodes.

1.6.1 Tubular Welding Electrode Manufacturing

Lincoln Global Inc in its patent No “US7807948 B2” [100] has proposed a

methodology of manufacturing tubular welding electrodes. As per the patent

document [100] the manufacturing process involves a sheet of metal of appropriate

width so as to obtain a tube of desired diameter which is first straightened and

flattened. The sheet is then bent into a V-shape or U-shape with the help of roller

channels. Fill materials are poured on the V/U bent sheet. The sheet is then closed to

form a circular cross section and finally is tube drawn. The drawing process not only

welds the sheet together but also helps in adhering of the fill material permanently

within the tube. Different fill materials can be poured to obtain different electrodes.

Figure 1.2, shows flow chart of manufacturing process of the same. For the ease of

drawing, lubricants are applied intermittently.

1.6.2 Wire Electrode Manufacturing

Some of the welding electrode manufacturing firms such as ESAB[96], AdorFontech

[97], L&T [98], and Lincoln [99] have developed similar techniques to manufacture

bare wire or wire electrode. As per the manufacturing manuals [96-99] of these

companies, the wire electrode of required alloy is usually taken in the form of a coil

of 6-8 mm diameter and then straightened. Later, the wires are pulled through series

of dies to gradually reduce the wire cross-section by 1mm. After achieving the

required diameter, required lengths of wires are cut and quality inspection is

performed. Wires are checked for its diameter, straightness and for defects formed

during wire drawing. The defective products are recycled based on the type of defects

R V Center for Cognitive Technologies, R V College of Engineering, Bangalore-59.

detected and good quality electrodes are sent for packaging. Figure 1.3 shows the

flow chart of wire manufacturing process.


Figure 1.1: Flow chart of the manufacturing of Tubular welding electrode

1.6.3 Flux Cored Electrode Manufacturing

Eureka Systems and Electrodes Pvt Ltd (ESEPL) [101], a Chennai based firm has

proposed flux cored electrode manufacturing methodology. As per the project report

[101], manufacturing of flux cored welding electrode can be divided into three stages.

First stage involves wire extrusion and straightening process, second stage involves

flux preparation process and third stage involves flux coating on the electrode and

simultaneously extrusion (for adherence of flux to welding rod) followed by baking

and air drying. The flow chart of flux cored electrode making is shown in Figure 1.1.

Intermittent quality checks in between various stages of manufacturing are performed

to achieve high quality welding electrodes.


1.6.4 Wire Electrode Manufacturing at Research and Development Stage

Some researchers [102] have suggested using wire Electric Discharge Machine

(EDM) for manufacturing of novel welding electrode developed in the laboratory or at

research and development (R&D) stage. As per Li Li et al [103] wire electrode

development at R&D stages usually involves small quantities of welding electrodes to

be produced and hence wire EDM manufacturing is suitable. Though the

manufacturing process is time consuming and expensive, it is free of defects.

Different diameter wires and lengths can also be achieved with good accuracy. Based

on the weldability studies of new electrode and its materials properties, a suitable wire

fabrication method can be evolved. In the present work, wire EDM machine was used

to manufacture novel wire electrodes.

Wire Coil (Quality control (QC) Approved) (5.5,6, 6.5 & 7/8 mm Dia)


Figure 1.2: Flow chart of manufacturing of wire electrode


Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel_________________________ for Naval applications_________________________

W ire Coil (QC Approved)Raw Materials (QC Approved)

Ferro Alloys & Ceramic material/ Powders

Figure 1.3: Flow chart of Flux cored electrode manufacturing


1.7 Welding Electrode Materials Characterization Studies

Various researchers [104, 123, 135, 143] suggested different methods to evaluate

material properties such as X-ray NDT inspection of electrode material, materials

property prediction by simulation techniques and experimental determination of phase

transformation using Differential Scanning Calorimeter (DSC). Destructive

techniques to determine materials properties have also been suggested such as tension

test, hardness tests, and impact tests. Some authors [143] have investigated

microstructure using optical / scanning electron microscope (SEM) / transmission

electron microscope (TEM) techniques to study grain boundaries, primary and

secondary phases of welding materials. Energy dispersion spectroscopy (EDS),

electron probe micro analysis (EPMA) and X-ray diffraction (XRD) are most

prominent methods [144] to determine the chemical composition of micro

constituents in the weld alloys.

1.7.1 Weld Alloy Defects Inspection Methods

Several researchers [104-106] suggested using non-destructive methods (NDT) such

as ultrasonic (UT) and radiography (RT) to check for casting defects of the electrode

material developed by casting technique. Tian Yuan et al [104] suggested X-ray

techniques as one of the most popular techniques used to identify casting defects such

as shrinkage porosity, voids, cracks, blow holes and sand inclusions. Damn et al [105]

used X-ray techniques to identify defects in metal casting / plates of maximum

thickness of 200 mm. Wang et al [106] reported use of x-ray to identify the micro and

macro pores in aluminum castings. Yi Sun et al [107] reported use of fuzzy logic for

pattern recognition to identify weld defects on real time in case of digital real time

radiography technique. Hayens et al [108] have suggested use of X-ray to identify

surface defects (surface cracks) which otherwise was done by other techniques such

as dye penetrate test (DPT), magnetic particle inspection (MPI) and eddy current

inspection technique (ECIT). Antoni et al [109] have developed a new pulse echo

technique based ultrasonic inspection procedure to identify defects in powder

metallurgy based materials. Young-Sang et al [110, 111] reported use of ultrasonic

based immersion and waveguide based sensor for visual inspection of reactor core and

internal components of sodium faced fast reactor. Several researchers [112, 113] have

recommended variety of NDT methods such as DPT, MPI, ECIT, RT, UT for weld



quality inspection to ensure that the structures meet the design requirements. Among

variety of techniques Gang Wang et al [113] recommended UT and RT tests for

identification of subsurface defects such as crack, porosity and slag inclusion for the

weld joints. Further they [113] developed, via image processing technique, an

automated system for identification of different types of welding defects using fuzzy

k-nearest neighbor and multi-layer perceptron neural networks classifiers. Liao et al

[114, 115] suggested fuzzy reasoning based expert system for identification of weld

defects in radiographic images. Several researchers have suggested using machine

vision for automatic inspection [116, 117] of welding defects, weld defect analysis

[118,119], detection of welding defects [120] and analysis of radiography [121-122].

In the present work. X-ray technique is used to identify the defects in new materials

and weld joint due to its wide acceptability, ease and low cost.

1.7.2 Materials Properties Simulation Studies

Several researchers have opinions that alloy development is expensive and time

consuming [123-127] process. Newer materials are constantly developed to meet

aggressive service conditions such as high temperature, highly corrosive environment,

and to withstand various forces on the materials. Modem alloys [124] have as many

as 15 elements and understanding the interaction among themselves, is too complex to

understand. Alloy designers [125] use thermodynamic based tools such as Thermo-

Calc, FACTSage, MTDATA, Pandat and JMatPro to construct phase diagram,

simulate thermo-physical, mechanical and other materials properties. Fu et al [126]

studied the role of Al contents on formation of y' precipitates and compared it with

experimental studies. Guo et al [127] used JMAT PRO to modeled multi component

material like cast iron, Ni-based super alloy 713 and Aluminum alloy ADC 12 for

properties such as density and volume change with respect to temperature and other

thermo physical properties which are critical for casting simulations. Guo and

Saunders et al [128] have calculated high temperature strength and generated stress-

strain curves for Al A319 using JMATPRO to study the deformation simulation.

Different authors have reported, predicting materials properties through different

softwares, such as Chen et al. [129] reported breakthroughs in thermodynamic

calculations using PANDAT software, Kao et al. [130] simulated thermal properties

of electronic materials. Nataraj et al [131] generated phase diagram and simulated


R V Center for Cognitive Technologies, R V College of Engineering, Bangaiore-S9. 14

mechanical properties of novel Cr-free nickel based material for welding applications.

Other authors [132-134], reported breakthrough in research work due to reliable and

correct prediction of materials properties such as melting temperature, strength and in

many cases the solidification behavior of the alloy. In the present work, JMAT Pro

materials property simulation software is used to predict the properties. The wide

usage of the software in the scientific community for research and development

purpose and availability of nickel database are the reasons for the selection of this

software in the current work.

1.7.3 Experimental Method of Determinination of Phase Transformation Studies

Many researchers [135-142] have suggested several experimental techniques to

determine phase transformations such as XRD, energy dispersion X-ray analysis

spectroscopy (EDXA), EDS, X-ray flourosence spectroscopy (XRP) and DSC. Meng

et al [135] reported the significance of solidification or cooling rate of alloy or weld

joint, as it affects the grain size of the microstructure which in turn has a profound

effect on the mechanical properties. Dobrzanski et al [136] have suggested use of

differential scanning calorimeter (DSC) technique among various thermal analysis

techniques, as the most popular due to its accurate method of determination of phase

change, solidification range and cooling curve during the alloy solidification. Rojas et

al [137] reported identification of different primary and secondary phases in 9% Cr

heat resistant steel, based on the alloy composition through DSC techniques. Young-

Sun Kim et al [138] through DSC studies concluded that addition of some alloying

elements (Bi & C) has an effect on the onset of solidification and range of

solidification on Sn-Zn-Bi alloy system. Seo et al [139] studied the solidification

sequence of different phases in IN792 + Hf using DSC technique. Zhai et al [140]

performed studies on liquidus and enthalpy of fusion in Cu-Sn alloys across all the

composition range. Naffakh et al [141] performed studies on solidification path,

micro-segregation of alloying elements in the interdendritic regions, solidification

temperature ranges, to predict the formation of secondary structures and the

castability behavior of four newly developed as-cast nickel based superalloys using

DSC. Nurveren et al [142] studied the changes in the phase transformation

characteristics at different heating / cooling rates by means of DSC measurements for



four NiTi alloys. In the present work, DSC method of determining phase

transformation is done due to its accuracy and availability of the equipment.

1.7.4 Microstructure Characterization of Electrode Materials

Several researchers [143-145] have reported microstructure characterization as an

NDT technique to study the relationship between microstructure of an alloy and its

mechanical properties. The study of relationship between the microstructure and

mechanical properties has attracted great interest over several decades [143], owing to

improvement in microscopy technology and demand for tailor made materials. As per

“ASM vol 10: Materials Characterization”, microstructure characterization [144] of

nickel based alloys involve 1) Study of morphology, volume fraction, location and

distribution of primary phases (grain), secondary phases and precipitates by means of

optical micoscopy/SEM/TEM. 2) Identification of chemical composition of phases by

means of EDS and XRD. Various researchers have characterized the alloys for

determining size and volume fraction of primary phases, secondary phases, carbide

phases and deleterious phases using optical microscopy (OM), SEM and TEM.

Several researchers [145-151] characterized the alloys using XRD and EDS to

determine chemical and elemental composition of each microconstituent in an alloy

system. Many researchers [152-158] have characterized the alloy, using SEM, to

study the effect of heat treatment, mechanical loading on the morphology, volume

fraction of different phases and on phase transformation in different alloys. Xuebin et

al [159] and Stevens et al [160] have studied the effect of solution treatment on the

dissolution of y' gamma prime in IN738LC nickel alloy using SEM.

1.7.5 Mechanical Properties Characterization of Alloy Material

Many researchers [161-170] suggested destructive methods to determine the

mechanical properties of electrode material with tests such as tension, compression,

hardness, fatigue, creep, wear and impact. Balikci et al [161] reported the importance

of determining mechanical properties for design of structures which can operate

satisfactorily in severe working environments. Some of the desirable material

properties include high temperature stability and strength, resistance to corrosion,

good impact toughness and wear resistance, good fatigue and creep strength.

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel._______________________ for Naval applications__________________________


1.7.6 Hardness Testing Studies

WAN Wen-juan [FI62] characterized newly developed Ni-Co AEREX350 for

hardness using for Rockwell test. Nader El-Bagoury reported the effect of aging in

nickel based super alloy IN738LC on the hardness using Vickers hardness testing.

Gerald et al reported mechanical characterization methodology of ATI Allvac 718Plus

a commercial by available nickel based alloy using microhardness tester, by applying

a load of 500g, dwell time 20s, specimen size 10 mm x 10 mm xlO mm, as per

standard EN ISO 10002 using hardness testing machine EMCO-Test, M4C-025-G3M.

Sushanta et al [166] characterized Al-M g-Si alloy for micro hardness measurements

on samples 10 mm x 10 mm x 10 mm using a load of 100 g with indenter dwell time

of 15s.

1.7.7 Toughness Measurement Studies

Shuangqun Zhao et al [163] reported measurement of toughness of inconel alloy for

aged specimens with V-notch at room temperature. Edward et al [168] of special

metals corporation reported impact toughness test methodology for nickel alloys 686,

925, 725 and 725HS using American Society of Testing materials (ASTM) Test

Method E992.

1.7.8 Tension Measurement Technique

Gupta et al [165] reported the methodology of tension tests for Al-Li alloy samples

treated under various heat treatment conditions, with strain rate of 1 mm/min,

specimen size of 120 mm, gauge length 32 mm and gauge diameter 12 using ASTM

E8 standard and INSTRON universal testing machine (UTM). Sushanta et al [166]

characterized Al-Mg-Si alloy by tensile strength, yield strength and ductility at strain

rate of 5X10“ /s using ASTM E8 standard and specimen gauge diameter 12 mm.

Sheldon Winkler [167] et al studied the effect of heat treatment on the mechanical

properties of Nickel Chrome base alloy using Instron UTM at strain rate of

0.5 mm/min. Also determined were material stress at 0.2% and 0.02% offsets in a

stress strain curves, yield strength. Ultimate Tensile strength (UTS) and % elongation.

These experiments were performed for various heat treatment conditions which

mimicked annealing, homogenizing and solution treatment conditions. The test

specimens used were as per ASTM standards A370 with a gauge length of 1 cm.

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications ___________


1.7.9 Fracture Studies

Several researchers [163, 165, 170] have also reported the fracture studies of the new

alloy developed to understand the mode of failure on tensile tested or impact tested

specimens. Shuangqun Zhao et al [163] reported fracture studies of Inconel alloy 740

using SEM. Fractography studies to determine the presence of secondary precipitates

in the voids of the fractured surface and analysis of the surface texture to determine

the failure mode were also presented. Gupta et al [165] reported the fracture studies of

Al-Li alloy using SEM by means of crack initiation spot, nature of crack propagation

and crack length. Guo-hua et al [170] have reported fractographic characteristics and

mechanisms of the fracture in the near eutectic Al-Si piston alloys. Post failure

analysis was conducted on the fracture surface using a SEM with EDS attachment. In

the present work mechanical characterization of nickel alloy welding materials for

tensile strength, impact and hardness tests and failure mode were investigated.

1.8 Characterization of Weld Joints

Vander Voort et al [171] have reported microstructure studies of weld interface for

dissimilar welding using optical microscope / SEM / TEM. Naffakh et al [172]

reported that dissimilar weld interface microstructure consists of four regions 1. Base

metal (BM), 2. Heat affected Zone (HAZ), 3. Fusion zone (FZ) and 4. Weld metal

(WM). In order to view this microstructure in optical microscope and SEM, ASM

Volume 9 - Metallography and Microstructures [171] has reported detailed procedures

to prepare specimens for microstructure studies. As per Vander Voort [173], specimen

preparation method is classified into three steps 1.Grinding, 2.Polishing, 3.Etching.

Several authors [174-181] have suggested different reagents such as Marbles reagent,

70 ml H3PO4 + 30 ml H2O, Villela’s reagent, 10% perchloric acid and 90% methanol

etc, as etchants to selectively etch specific type of micro constituent of an alloy. Some

of the authors [182-185] have also suggested electrolytical etching, as the process is

quick and not much specimen preparation is required (such as grinding and

polishing). Vander Voort has [171] reported specimen sizes of the weld joint required

for microstructure characterization to be about 25 mm x 25 mm x 6 mm.


R y Center for Cognitive Technologies, R V College of Engineering, Bangalore-59. 18

1.8.1 Effect of Welding on Base Metal Characterization

Many researchers [186-188] have reported characterization of base metal portion of

the weld joint using optical microscope, SEM, TEM and focussed ion beam (FIB)

using SEM [186]. They have also reported the chemical analysis of the alloy such as

primary phases, secondary phases and carbide precipitates using XRD, EDS, X-ray

elemental mapping, and electron probe micro analysis (EPMA) techniques [187], Lee

et al [188] have reported the characterization of base metal stainless steel SS304L

using optical microscope/SEM for grain morphology, presence of secondary

precipitates (carbides) in grain boundaries, annealed twin and presence of ferritic

phase. Bala Srinivasan et al [189] have reported the characterization of duplex

stainless steel (of grade IINS 31803) for determining amounts of austenitic phase and

ferrite phase. Also characterization of carbon steel (of grade IS 2062) for amounts of

ferrite and pearlite phases and grain morphology using optical microscope was

undertaken. Ravi Shankar et al [190] have reported characterization of two base metal

Zircaloy-4 and SS304L for grain morphology and presence of secondary precipitates.

Some researchers have also reported the characterization of heat effected zone (HAZ)

using optical microscope and SEM. Naffakh et al [172] have reported the changes of

grain morphology of the HAZ due to heat transfer from weld pool at the time of

welding using optical microscope. Lee et al [188] have reported the changes in the

grain boundary chemical composition due to diffusion of some elements at the time of

welding using EDS. In conclusion, it was clear that base metal characterization is very

essential to use OM and SEM for morphological studies and XRD for chemical

analysis of micro constituents. Hence in this research work all base metals are

characterized for both microstructure and chemical anysis done using OM, SEM,

XRD and EDS.

1.8.2 Fusion Metal Characterization

Several [172, 187, 188] researchers have suggested characterization of the weld

region as important part of weldability studies as it corelates the structure and

mechanical property of the weld joint. In this direction Belloni et al [191] studied the

a-chromium principal precipitates in HAZ and FZ of dissimilar weld joint between

Inconel 657 and stainless steel 310 using EDS and SEM. Caironi et al [192] reported

segregation studies of elements like Nb in interdendritic regions of FZ of dissimilar



weld using SEM and EDS. Dupont et al [193] have reported calculation procedure of

determining dilution levels of electrode material in base metal using optical and SEM

with the expression as shown in Eq. 1.1. This is done by measuring individual

geometric cross-sectional areas of the deposited filler metal and melted base metal.

Dilution of the weld joint is given by the ratio of the melted base metal (Abm) to the

total melted cross sectional area of the filler metal and base metal (Abm+ Afm)

combined

A .


D = bm

fin

Various authors [172, 187, 188, 190] have reported weld microstructure for base

metal, FZ, and WM in case of dissimilar welding using optical microscope / SEM and

TEM. Several researchers [194-197] have reported carbon migration studies from

lower Cr base metal to higher Cr base metal in a dissimilar welding between carbon

steel pipe and SS304 using EDS attached to SEM equipment. Changheui et al [198]

reported dendrite structures, their location, direction and spacing in the FZ of

dissimilar welding between low alloy steel and SS 316 stainless steel using optical

microscope. Sireesha et al [199] studied recrystallization with extensive grain

boundary migration behavior of FZ in dissimilar welding between 316LN austenitic

stainless steel and alloy 800 using optical microscope. Devendranath et al [200] have

also reported the microstructure studies of dissimilar welding as a NDT technique to

identify welding defects such as porosity, cracks, segregation, formation of secondary

precipitates, dilutions using SEM, OM studies. From the above literature survey, it is

evident that microstructure study of the weld interface provides valuable information

about the structure which can be correlated to mechanical properties. Hence in the

present work optical microscopy and SEM are used in the characterization of weld

interface.

1.8.3 Weld Joint Preparation for Mechanical Studies

Many researchers [199] have reported mechanical testing of dissimilar weld joints as

an important characterization technique to study the weldability of dissimilar weld

joints. Sireesha et al [199] have reported tension tests, micro hardness tests across the

weld joints, impact tests, longitudinal varstraint testing and three point bend tests as

some of the important tests to evaluate mechanical properties of dissimilar weld

R V Center for Cognitive Technologies, R V College of Engineering, Bangalore-S9. 2 0

joints. Sireesha et al [199] further reported that nickel based electrodes 316, 16-8-2,

Inconel 182, and Inconel 82 were used to weld with two base plates (SS316LN and

alloy 800) of 12 mm thick with double V groove edge preparation and included-angle

of 70°. Bala Srinivasan et al [189] have reported using Duplex stainless steel (DSS)

electrode E2209 and austenitic SS electrode E309 to weld 5 mm thick plates of DSS

of UNS31803 grade and boiler grade plain CS IS 2062. They further reported that two

base plates of dimensions 200 mm x 80 mm x 5 mm were used for producing the

joints with a 70° single V groove edge preparation followed with a root face/gap of 2

mm. Lee et al [188] reported using several grades of Inconel Welding Electrode of

152 series with gradual increase of Ti percentage to weld two base plates (SUS 304L

and alloy 690) of dimensions 80 mm x 70 mm x 6 mm. The beveled test plates to be

welded together were arranged to form an 80° V groove with a 3.2 mm root opening

gap and a 1 mm root face. To achieve good quality welds, many researchers [188,

189, 199] have reported solution annealed treatment for base plates before welding.

Sireesha et al [198] have reported the welding parameters as current = 100 A, voltage

= 11.5 V and travel speed = 4.2 mm/s. Naffakh et al have reported the welding

parameters in the range of 95A-135A, 12-26 volts, 0.77-3 mm/s welding speed.

0.83-2.3KJ/mm heat input for various combinations of weld electrode and base metal,

also heat input calculations were done using the equation E W , where E= welding

voltage, I is the current, V is the welding speed. Ravi Shankar et al [190] have

suggested to wire cut the specimen required for various tests from the main welded

plates. In the present work weld plate dimensions and welding parameters were

selected as per respective ASTM standards.

1.8.4 Tensile Studies

Several researchers have reported tension test as one of the important mechanical tests

to characterize mechanical properties such as UTS [172], yield strength [188] and

ductility [178] of the weld joint. Specimen sizes generally preferred for tensile testing

are 140 mm x 25 mm x 1.5 mm with a weld bead width ranging from 2.4 to 3.3mm

[202], button-head type cylindrical all-weld and transverse tensile specimens (28.6

mm gauge length and 4 mm gauge diameter) [201], test specimens machined and

prepared as per ASTM E-8 standards with gauge diameter of 7.5 mm and gauge

length of 72 mm [190], a nominal specimen width of 30 mm and mandrel diameter of


R V Center for Cognitive Technologies, R V College of Engineering, Bangaiore-S9. 21

91 mm [203] and also with specimen dimensions of length 140 mm, gauge length 60

mm, plate width 20 mm and plate thickness 6 mm, root gap opening 3.2 mm [188]

were also reported. The tests were generally conducted at room temperature at various

strain rates of 5.4 x lO s [198], 1.2 mm/min [172], 2.4 x lO /s [201], Taban et al

[203] have also reported tensile tests carried on longitudinal section of the weld joints.

Ravi Shankar et al [190] have reported three point bend test on specimens machined

and prepared as per ASTM standard with 8 mm diameter and 120 mm long, load

applied exactly at the interface supported at a distance of 60 mm apart from the

center. Naffakh et al [172] reported conduction of varstraint tests to determine hot

cracking susceptibility of dissimilar weld at various strain rates of 1%, 2% and 4%. In

the present work, tensile test procedures as per ASTM E-8 standard were followed.

1.8.5 Hardness Studies

Several researchers [204,302,303] have suggested hardness tests across the dissimilar

weld joints to report microstructural heterogeneities. Xiu-Bo Liu et [204] have

reported microhardness test as one of the important property for wear and abrasive

dynamic structures. Magnabosco et al [205] have reported the variation of hardness

across weld joint due to the effect of dilution of electrode materials with base metal

and effect of several passes of welding. Bala Srinivasan et al [189] have reported the

presence of harder microconstituents, such as carbide precipitates and martensite

through hardness measurement in FZ of a dissimilar welding between Unified

numbering system (USN) 31803 and (International systems) IS 2062 steels. Several

researchers [201, 199,304] have reported Vickers hardness testing as popular hardness

measurement techniques and suggested specimen sizes of 30 mm x 10 mm x 6 mm

[201], load of 500 g [201], lOOOg [205], 2000g [189] and dwell time of 20s [201], 30s

[205] as procedures for hardness testing. In the present work, hardness of the weld

zone was determined by applying a load of 500 g and 30s dwell time was considered.

1.8.6 Impact Studies

Several researchers [172,189, 198, 206] have reported impact studies as one of the

characterization techniques for dissimilar weld joint. Sireesha et al [198] have

reported room temperature toughness for a dissimilar weld joint between 316LN

austenitic stainless steel and Alloy 800 using impact studies. Bala Srinivasan et al



[189] and Muthupandi et al [206] have studied the low temperature (-40°C) impact

toughness and room temperature impact toughness on dissimilar weld joint between

IS 2062 and UNS 31803. Naffakh et al [172] have studied the room temperature

impact toughness of dissimilar joint between AISI 310 austenitic stainless steel to

nickel-based alloy Inconel 657 using Charpy impact tester. Taban et al [203] studied

the effect of notch (2 mm deep) position, such as on the weld metal, HAZ, face and

root side of the weld joint at -20°C and at room temperature for a dissimilar weld joint

between 12% Cr modified Ferritic Stainless Steel and Carbon Steel S355. For impact

tests several researchers have used standard specimens sizes of 55 mm x 10 mm x 10

mm [178, 198, 203], and sub-size specimens (3 x 10 x 55 mm^) [189] using charpy

impact tester machine. In the present work standard specimen sizes at room

temperature using charpy impact testing machine was used for studying the impact

toughness of various weld joints.

1.8.7 Fracture Studies

Several researchers [207-209] have reported fracture studies of the weld joints to

study the mode of failure using SEM. Li and Congleton [207] have reported the

fracture in the dissimilar welding joint between low plain carbon steel and austenitic

stainless steel due to carbon migration from low carbon steel to austenitic stainless

steel in a simulated corrosive environment using SEM. Joseph et al [208] have

reported a case study of an in-service failure of a dissimilar weld joint in a steam

generator using SEM. Bala Srinivasan et al [189] have studied crack propagation by

impact testing machine on a dissimilar weld joint through optical microscope and

SEM. Liang et al [209,305] studied the fracture surfaces of Ni-Cu and Ni-Cu-Ru

electrodes welding with SS304L using SEM and OM. The authors reported ductile

modes of fractures with its characteristic dimples formation in the HAZ region of the

base metal which were exposed to air, but weld samples exposed to corrosive fluids

like NaCl showed low ductile mode failures or underwent stress corrosion cracking

due to embrittlement of the base metal in the corrosive fluids. Lee et al [188] reported

the fracture studies of tensile tested specimens of a dissimilar welded joint SS304L

and alloy 690 using SEM. They further reported ductile mode of failure at the fusion

zone of the weld joint. Changheui et al [198] reported ductile mode of failure with

presence of dimples on fractured surface from the weld specimens taken from the



bottom portion of a 40 mm thick weld joint where as top portion of the weld joint

specimens showed shear-stretch mode of failure with high toughness values. The

dissimilar weld joint between low alloy steel and stainless steel was welded by

Inconel 82/182 filler metal and fracture surface was studied under SEM at different

magnifications such as lOOX and 500X [198]. In the present work fractured surfaces

of the dissimilar weld joint was analysed by SEM at magnification of lOOX, 500X etc.

1.9 FEM Welding simulation Studies

Various authors [210-222] have reported Finite Element methods (FEM) based

welding simulation techniques which are in agreement with experimental studies.

Various authors [210-222] worked FEM based weldability studies on the following

parameters

1) Temperature distribution around the weld joint,

2) Type and magnitude of longitudinal and transverse residual stress distribution

around weld joints and

3) Magnitude of the distortion of the weld joint.

Many investigators have compared analytical with and experimental methods to study

and predict welding residual stresses. With the advancement in computer technology

and numerous improvements in numerical techniques, analyzing residual stress in

welded structures using FEM has gained popularity. Earlier, Norton and Rosenthal

[210, 211] measured residual stresses by the X-ray diffraction technique. Also Pange

and Pukas [213] presented hole-drilling and strain gauges to determine residual

stresses. Cheng et al, [212] investigated the residual stresses due to surface treatment

using the compliance method which can measure a rapidly varying compressive stress

under the interface which even the X-ray technique would fail to detect. Also, Muraki

et al, [214] developed FEM based elasto-plastic model to predict thermal stresses and

heat source movement to simulate welding. Kuang and Atluri [215] used a moving-

mesh finite element technique to study the effect on temperature field due to a moving

heat source. Shim et al, [216] developed an analytical method for predicting

distribution of residual stresses due to multi pass welding across the thickness for a

thick plate using FEM. Chidiac et al, [217] presented the iterative procedure to

determine the thermal cycle required for different types of welding simulation through

non-linear heat transfer analysis. Josefson [218] estimated residual stresses in a multi

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications__________________________

R V Center for Cognitive Technologies, R V College of Engineering, Bangalore-S9. 2 4

pass weld and in a spot-welded box beam with SOL VIA and ABAQUS commercially

available FE-codes through non-linear analyses. Yang and Xiao [219] proposed an

analytical model to examine the residual stress distribution across the weld of panels

welded with mechanical constraints. Furthermore, Ueda and coworkers [220-222]

presented a novel measuring method of three-dimensional residual stresses (based on

the principle which is simplified by utilizing the characteristics of the distribution of

inherent strains induced in a long welded joint). Residual stresses during welding are

unavoidable and their effects on welded structures cannot be disregarded. Design and

fabrication conditions, such as the structure thickness, joint design, welding

conditions and welding sequence, must be altered so that the adverse effects of

residual stresses can be reduced to acceptable levels. In this work, the residual stresses

are determined during one-pass arc welding in a steel plate using ansys finite element

techniques.

1.10 Experimental Determination of Residual Stress Using XRD

Many researchers [223] have reported residual stresses in welded structures promote

brittle fracture, fatigue, stress corrosion cracking and reduction in buckling strength

[224] of base plate. Several researchers [223, 224, 225, 226] have reported destructive

and non-destructive methods of measurement of residual stresses. Destructive method

of residual stress determination was done by Pang and Pukas et al [224] by a

technique called stress-relaxation methods using strain gauge techniques. NDT

approach followed by Chang and Teng, et al [225], calculated residual stresses using

finite element methods. Chandra et al [226] in the weld bead measured residual stress

using XRD techniques. They [225, 226] reported XRD method as an accurate method

to measure the residual stress in a thin surface layer. As per Robbins [227], residual

stress changes the atomic spacing of the weld joints. Such stressed materials change

the angular position of the diffracted X-ray beam due to change in atomic spacing

which in turn is the measure of residual stresses. Joseph et al [228] determined

residual stress using X-ray diffraction technique for a dissimilar weld joint between

2.25Cr-lMo ferritic steel and (American Iron and Steel Institute) AISI type 316

stainless steel with and without Inconel-82 buttering on the ferritic steel side. Spiess et

al [229] have reported the calculation method of determination of residual stress using

X-ray diffraction technique using sin v(/ -method. B. Chen et al [230] compared



experimental results (XRD technique) with numerical algorithm (FEA simulation) of

residual stress distribution in the welding slot area of a Cr21Ni6Mo9 stainless steel

pipe. Omar Hatamleh et al [231] applied XRD technique to determine residual stress

distribution on a surface of FSW sample of aluminum alloy 2195 and 7075 after it had

undergone surface treatment. They further reported that small sample size of 10 mm x

10 mm X 10 mm is required for this investigation. In the present work X-ray

diffraction technique was used to determine the residual stress in different type of

weld joints as this technique is reported to give accurate measurements.

1.11 Applications of Dissimilar Welding

1.11.1 Power Plants

Modem power plant boilers operate at 1050°C and make use of two or more materials

/alloys. Outer pipes made of comparatively low cost stainless steel 310 are joined to

pipes made of high cost Inconel 657 [232]. Though pipes made of Inconel 657 are

expensive, they are known to be stable at high temperatures, resistant to highly

oxidizing and carburizing environments.

1.11.2 Nuclear Power Plants

In fast breeder nuclear reactor ferrite and austenite steel tubing is joined by a

transition joint such as nickel based alloy 800. Ferrite steel P91/T91 is a precipitate

strengthened steel used for modules where high temperature and superior creep

properties are the requirements and SS310 is an austenitic structural steel suitable for

sodium environment [233-237]. Also, the transition joint alloy 800 provides a

gradation of Co-efficient of Thermal Expansion (CTE) between two base plates

thereby providing a better distribution of thermal stresses. Zircaloy-4 is dissimilar

welded with AISI type 304L by friction welding [238]. Zirconium and its alloys

exhibited outstanding corrosion resistance in nitric acid environment. In fast reactor

reprocessing facilities, zircaloy-4 is used as a candidate material for dissolvers and

evaporators [239-244].

1.11.3 Earth Moving Excavators

The buckets of the excavators are fabricated with low alloy steel due to its low cost,

better toughness and strength but have low resistance to corrosion. During excavation

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications_____________


of the earth the teeth of the excavator buckets are exposed to moisture and mineral

salts in the earth and hence prone to corrosion and abrasion. By weld overlaying

(cladding) the teeth with nickel based alloy, life of the teeth is not only prolonged but

rendered corrosion resistant [245].

1.11.4 Cryogenic Applications

Normally 8-9% Nickel based steel such as SS308L and SS316L are used for

cryogenic applications due to their balanced austenitic structure. For cryogenic

applications, weld joint with 156 MPa fracture toughness is the requirement. Joints

obtained with special electrodes containing high Nickel (25%) and high nitrogen

(0.18%) contents are free of delta ferrite and non metallic inclusions such as carbides

and nitrides [246].

1.11.5 Other Dissimilar Welding Applications

Sun et al [247] have reported that industries adopt dissimilar welding as it is

advantageous both economically and technically. They also reported that dissimilar

welding provided possibility of flexibility in design as each material can be used

efficiently and benefit in functional way due to their specific property. They further

added that, materials possessing large variation in properties create problems such as

residual stress, cracks etc, in weld joint but efforts are on to mitigate this problem.

Several researchers have studied dissimilar joints as it finds applications as a

transition joint [248] which accommodates the co-efficient of thermal expansion

between two materials with widely varying CTE properties. Bhaduri et al [249] have

done a comparative study between two, nickel based filler materials alloy 800 and

Inconel 182 welded between ferrtite steel and 9Cr-lMo steel. The study was done to

select the best filler material among the two as weld joint failed in service due to

thermal stresses along the weld fusion line. Several researchers [250-255] have

recommended use of nickel based filler materials to weld ferritic steel and austenitic

steel as they prevent carbon migration from ferrtic steel side towards austenitic steel

thus avoiding degradation of the properties. Due to its wide application and major

benefits, in the present research work, it was decided to use nickel based Cr-free

welding material as filler alloy to weld stainless steel.

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications__________________________

R V Center for Cognitive Technologies, R V College of Engineering, Bangalore-59. 2 7

1.12 Role of Alloying Elements in Welding Electrode

Many researchers [256-258] have studied the role of alloying element on the weld

alloy as it affects the weld quality in terms of mechanical strength, ductility and

corrosion reistance. Several authors [256,265] have reported that the selection of

dissimilar welding electrode is based on the base metals to be welded and the alloying

element present in the welding electrode. Choi et al [260] have reported that alloying

elements have a direct effect on the microstructure and thereby on mechanical

properties. Many researchers [256-257,261] have reported nickel-based weld filler

metal majorly consists of elements such as Fe, Mn, Mo, Co, Nb, C, B, Al, Si, Cu, and

minor content of S, P, Pb. Investigations of Scrimgeour et al and Shoemaker et al

[257, 268] have shown that adding of C and Al has a certain graphitizing effect on the

partially fusion zone (PFZ) of arc welded ferritic ductile iron. The strength and

elongation of weld metal decreases with more addition of carbon content (0.2 to

2.91%) and Al promotes precipitation strengthening. Further, they also reported that

width of the carbide layer decreases with the increase of Al content in the weld.

Addition of Ti content helps to improve the mechanical properties of weld metal.

Various authors have reported [256-257, 260, 262,264] the effect of Ti. They reported

that Ti forms carbides (TiC) which improves the strength and elongation of the weld

metal in stainless steel. Many researchers [257-259,261,263-265, 268-269] have

suggested use of Fe with Ni to reduce overall alloy cost. They also reported that Fe

additions in Ni not only provides improved resistance to H2SO4 (sulphuric acid) when

concentrations are greater than 50% but also increases the solubility of carbon, which

improves resistance to high-temperature carburization. Daniel et al [266,271] reported

that though increase in copper content increases corrosion resistance of nickel alloy,

its segregation in interdendritic region promotes solidification cracking. Numerous

authors [257, 258-259,261, 263-265,268-269] have reported that presence of iron

increases the weld metal strength due to solid solution strengthening. They further

stated that, if Fe content is less than 20%, fusion of the weld metal to base metal will

be weak due to segregation of Fe to inter-dendritic cores and thereby increases the

hardness of the transition zone. Several authors [257,262,268] have recommended

addition of manganese to nickel alloy benefits the weld metal significantly, such as

improvement in ductility of the weld joint, improved resitance to weld cracking,

formation of much stable compound MnS compared to FeS thereby mitigating the

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications __________

R V Center for Cognitive TeiJinologies, R V College of Engineering, Bangaiore-S9. 28

harmful effect of sulfur in stainless steel welding. Adachi et al and Shoemaker et

al[257, 264] have investigated and reported the effect of various levels of Titanium

addition on the weld microstructure, fusion zone (FZ) microstructure and mechanical

properties of dissimilar nickel-based alloy 690 and SUS 304L SS weldaments. They

further reported the beneficial use of addition of Ti on the increase in hardness of the

FZ, Ti-Fe compound rather than pure Ti-powder additive. Also elongation increased

while the tensile strength remained constant. Addition of Ti promotes formation of

TiC and TiNi inter-metallics. As per William Smith, addition of Mo and Co [270,302,

303] enhances the solid solution strengthening in the weld region. Futher they

reported that Co discourages the solubility of elements such as Al and Ti at low

temperature enabling the formation of greater amount of precipitates strengthening

phases for a given amount of Al and Ti in the weld region. Different authors

[261,263,265,268-269] have reported that Cr not only increases the resistance to stress

corrosion cracking but also enhances the weld hardness in the transition region of the

weld joint.

1.13 Regulations on Hexavalent Chromium Emission

Environmental and occupational safety awareness is increasing day by day. Various

findings are reported by researchers around the world about ill effects of inhaling of

the welding fumes by the welders. Occupational Safety and Health Administration

(OSHA) in United states of America (US) in its latest rulings has drastically reduced

the permissible exposure limit of harmful hexavalent Cr" fumes by the welders to

5|ig/m^ from 52|xg/m^ [78, 81]. This ruling is a direct result of findings that welders

are at high risk of developing respiratory disorders such as asthma, nasal and skin

damage and in certain conditions may even lead to lung cancer. Regulations like these

already exist in European Union, Canada and Australia. Similar regulations are also

expected to come into effect in third world countries such as India and China. This

regulation clearly presents an engineering challenge especially for stainless steel

welding industries. Hence OSHA has recommended use of Cr-free welding electrodes

for stainless steel.




1.14 Research Gap

After an extensive literature survey, it was found that few researchers have worked

towards the development of Cr-free filler material for welding stainless steel.

Research gaps in welding of stainless steel by Cr-free welding electrodes are listed in

this section.

1. No research work focused to develop Cr-free welding electrode based on

multiple alloy elements (Ni, Mo, Fe, Cu, Co, Al, Ti, B, P, S, Si, and Mn) as

they can substitute Cr based properties such as good mechanical strength and'v

corrosion resistance.

2. Only few research works utilized simulation tools (JMAT Pro, Thermocalc

and MTDATA) for development of novel alloys. Developing novel alloys in

conventional methods are tedious, time consuming and high cost processes.

3. Effect of solutionzing treatment on the electrode materials properties are yet to

be investigated as solutionzing treatment improves the properties of electrode

such as ductility of the materials (and reduction of brittleness).

4. No research work has involved investigation of effect of precipitation

hardening on the electrode materials and its effect on weld properties. Though

precipitation hardening enhances the hardness or mechanical properties of

stainless steels and nickel based super alloys, its effect on welding needs to

explored.

5. Although the residual stresses degrades mechanical strength but No research

work focused on residual stresses induced by Cr-free electrode during stainless

steel welding.

6. Generally, weld joint suffers due to environmental corrosion (galvanic

corrosion). Hence there is scope for study on weld joint corrosion and methods

of protection in reducing and oxidizing environments are limited.

7. All mechanical structures generally are subjected to fatigue or cyclic load

Hence there is scope for fatigue studies of the weld joints.

8. In industries, they follow pre heat treatment of base plates and post heat

treatment of the weld joint to avoid welding defects but none of the works till

date have been investigated and effect of the same on the welding joints.

9. Presently, the simulation of welding is one of the significant research areas to

do state of art research using commercial or tailor made softwares for


Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel

investigating the effect of welding sequence, joint type and welding

parameters.

Although research in welding has grown enormously, still there is lot of scope for

doing research in welding. The present research work addresses points 1, 2, 3 and 5

as mentioned above.

1.15 Research Objectives

After extensive literature survey and discussions on dissimilar welding in chapter 1, it

is clear that reduction of hexavalent chromium fumes in the welding of stainless steel

is difficult without the use of Cr-free filler rod, so the order of the day is to develop

new Cr-free filler material.

The main objectives of the research work are,

> Development of new Cr-free nickel based weld alloy filler material.

> Prediction of phase transformations of weld alloys prepared, using JMATPro

material simulation software.

> Characterization of newly developed weld alloy for its microstructure and

mechanical properties.

> Evaluation of mechanical properties and microstructure of welded joints.

> Determination of residual stresses and distortion in the weld joints using

elemental birth and death technique.

> Experimental determination of residual stresses using XRD techniques.

1.16 Research Methodology

Present research work methodology can be divided into two stages

1. Weld alloy synthesis and its characterization

2. Weld joint characterization.

1.16.1 Nickel Alloy Synthesis and Characterization

> Prediction of various properties of electrode materials such as metallurgical

and mechanical properties, using JMATPro-material property simulation

software.

> Electrode alloy synthesis using an induction furnace

R V Center for Cognitive Technologies, R \/ College of Engineering, Bangaiore-S9. 31

> Identification of casting defects such as shrinkage porosity, cracks, blow holes

etc by exposing to X-rays as per ASME standards

Evaluation of mechanical properties of as-cast and solution treated material

such as Yield Strength (YS), Ultimate Tensile Strength (UTS) and hardness as

per ASTM standards and fracture studies using micrographs generated by

SEM

> Microstructure characterization of as-cast and solution treated materials such

as grain size, morphology, secondary phase distribution etc, using optical

microscopy and SEM.

> Identification of various phases using XRD techniques

1.16.2 Weldability studies

> Base metal and filler rod preparation using wire EDM. Specimen preparation

for welding , deciding on welding parameters based on weld trial runs

> Weld quality inspection by exposing weld joints to X-rays as per ASME

standards.

> Evaluation of mechanical properties of the weld joint such as tensile tests,

UTS, YS, ductility, impact and hardness profile across the weld joint.

> Determination of mode of failure or fracture studies on tensile tested

specimens using SEM

> Microstructure characterization of the weld joints such as Heat Affected Zone

(HAZ), Fusion Zone (FZ), Partially Mixed Zone (PMZ) and Unmixed Zone

(UZ) using SEM and Optical microscope

> Determination of residual stresses and distortion in a weld joint based on the

temperature distribution using FEM and XRD techniques.

Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steelfor Naval applications ____________________


Development and Characterization of Novel Cr-Free Electrode for Welding Stainless Steel_________________________ for Naval applications_________________________

1.16.3 Flow Chart of Methodology of the Research Work

Nickel Based Alloy Characterization andits Weldability Studies

Alloy Synthesis

Alloy Characterization

Microstructural Mechanical Properties

SEM XRD Ootical JMATPro Simulation UTS YS % Elongation Hardness Fracture

Filler Material Development

Welding of Base Plates

Microstructural Studies Mechanical Prooerties FEM Simulation

SEM

UTS YS % Elongation Hardness Fracture

Ootical EDS Stress Distortion

Result and Discussion

Conclusion & Future Scooe

Figure 1.4: Shows the flow chart of the methodology of the research work


1.17 Oi^anization of Thesis

In the present dissertation work, the main focus is weldability studies between newly

developed nickel based Cr-free electrodes and stainless steel. The weldability study

includes weld joint strength, ductility, hardness and impact toughness. Chapter one

gives detailed description of concepts of welding, types of welding, elsewhere studies

on weldability of stainless steel, background of the problem and it concludes with

objectives and methodology of the research work. Chapter two describes in detail,

the simulation procedures to predict phase diagram, cooling curves and phase stability

of the newly developed electrode material, experimental methods and procedures

employed to evaluate mechanical and microstructural properties of various versions of

nickel weld materials and dissimilar weld joints with stainless steel. Chapter three

presents the discussion of alloy characterization and Chapter four involves

weldability studies of weld joints which include results of weld joint microstructure,

mechanical properties of weld joint and fracture studies. Chapter five presents FEM

simulation results to predict the residual stress, distortion in a weld joint and

comparison of the results with experimental methods and finally, Chapter six

consists of summary of the key findings of the research work and proposes the scope

of the future work followed by references, publications and appendix.



chapter one background studies -...

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