review global progress on welding consumables for hsla steel

© 2014 ISIJ 1472

Review

ISIJ International, Vol. 54 (2014), No. 7, pp. 1472–1484

Global Progress on Welding Consumables for HSLA Steel

Tianli ZHANG,1)* Zhuoxin LI,2) Frank YOUNG,3) Hee Jin KIM,4) Hong LI,2) Hongyang JING1) andWolfgang TILLMANN5)

1) School of Materials Science and Engineering, Tianjin University, 92 Weijin Road, Nankai District, Tianjin, 300072 China.2) College of Materials Science and Engineering, Beijing University of Technology, 100 Ping Le Yuan, Chaoyang District,Beijing, 100124 China. 3) The Lincoln Electric Company, 22800 Saint Clair Ave Cleveland, Ohio, 44117 United States.4) Reliability Assessment Center for Metallic Materials, Korea Institute of Industrial Technology, 35-3 Hongchonri, Ibjangmyun,Chanansi, 331-825 Korea.5) Institute of Materials Engineering, Technische Universität Dortmund, 2 Leonhard Euler Street, Dortmund, 44227 Germany.

(Received on November 15, 2013; accepted on March 17, 2014)

This paper reviews the global progress on welding consumables for high strength low alloy steel. Thenumerous aspects, such as the toughness and cleanliness of weld metal, the new removal mechanismsof impurity elements and the crack resistance of weld metal, are discussed. To meet increasing environ-ment requirements, the fumes and life cycle assessment of welding consumables are also discussed.Finally, future trends in the development of welding consumables for high strength low alloy steel arepointed out.

KEY WORDS: high strength low alloy steel; welding consumables; toughness; cleanliness; impurity; crackresistance; fumes; life cycle assessment.

1. Development of HSLA Steel and its Welding Con-sumables

The properties of steel have undergone profound changesin recent years, improving steel cleanliness (i.e. the massfraction of impurity elements (S+P+O+N+H) in steel) to alever lower than 250×10–6, and even lower than 100×10–6.Rolling technologies such as the thermo-mechanical controlprocess and deformation induced ferrite transformation canget finer grains, and 2 μm ferrite grains have been obtainedin micro-alloyed steel. High strength and toughness steelplates (tensile strength is 600–1 000 MPa, and yield strengthis 400–800 MPa) are stably produced.1,2) Ultrafine grainedsteel is widely used. Nanotechnology has been applied inultrahigh-strength and ultrahigh-toughness steel has beensuccessfully produced. The changes in the technologies ofsteelmaking and steel rolling are a challenge for weldingconsumables and the joining technology.

The market for steel and corresponding welding consum-ables is also influenced by world economy. Table 1 showsoutputs in recent years and predictions for the future of steelin the main regions and countries of world.3) According toa research report from Euro Strategy, world steel consump-tion will amount to more than 2 billion tons in 2017.

In 2009, total consumption and the percentages of differ-ent welding consumables in the main regions and countriesof world were as shown in Fig. 1. The consumption of weld-ing consumables increased with increased use of steel. Theproportion of welding consumables consumed differed

because regions may differ in their level of economic andtechnological development. Overall, the general require-ment for world welding consumables tends to be higherstrength, higher toughness, more cleanliness, more energy-saving, more environment-friendly, and higher efficiencyand automation.4) Welding consumables have developedfrom traditional Mn–Si alloy system to Ti–B alloy systemsthat can obtain inclusions with proper feature parameters toinduce acicular ferrite (AF) nucleation. New alloy systemsin welding consumables can obtain more and finer AF,which could further improve properties of weld metal. High-performance flux cored wire (FCW) and solid wire occupyincreasing proportions, while the percentage of stick elec-trode continues to decrease. Ultra-low hydrogen (<3 ml(100 g)–1) and high toughness welding consumables arewidely used in important engineering structures. Weldingspatter and fume continue to decrease, while the weldingoperative performance has continually improved. However,at present the actual contents of impurities and mechanicalproperties including fatigue strength of weld metal stillshow a large discrepancy when compared with some steels(see Table 2).

2. Main Research Progress in Welding Consumablesfor HSLA Steel

Phase transformation of high strength low alloy (HSLA)steel weld metal is complicated, and its final microstructuredepends on the chemical composition and cooling rate ofweld metal. The optimal microstructure for high propertyweld metal is obtained more AF, duo to the character withfine grain size, high density dislocation in grain, large-angle

* Corresponding author: E-mail: [email protected]: http://dx.doi.org/10.2355/isijinternational.54.1472

ISIJ International, Vol. 54 (2014), No. 7

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grain boundaries, and the interlocking structure with eachother, which have larger resistance against crack formationand propagation.5) Therefore, the nucleation mechanismsand influencing factors of AF have been investigated.Unfortunately there is no general agreement regardingnucleation mechanisms and control measures of AF untilnow, so the engineering applications of AF in welding con-sumables design cannot be controllable. Nevertheless,research on AF nucleation and its influence is still effectivein welding consumables design. Also, as the requirementsfor cracking resistance and fatigue properties of weldingjoint become higher, diffusible hydrogen (HD) contentdecreases to 2.8 ml (100 g)–1, and cold and hot crack resis-tance get further improved. The design of welding consum-ables performance is now mainly focused on furtherimproving all-position welding operative performance, spat-

ter, fume and high efficiency. Market demands for weldingconsumables are as shown in Fig. 2.6)

2.1. Toughness of Weld Metal for HSLA Steel2.1.1. Mechanisms of AF Nucleation

There are various opinions about the four mechanisms ofAF nucleation in weld metal:5,7–13)

(1) High energy inert matrix nucleation theory: The the-ory states that inclusions, as the inert nucleation surfaces,reduce the activation energy to promote AF nucleation.However, Sarma et al.11) argued that though providing theexternal surfaces needed for nucleation, inclusions cannotbe equivalent to grain boundaries. The activation energyneeded for heterogeneous nucleation of ferrite at the inclu-sion surfaces is usually higher than that at high angle aus-tenite grain boundaries. However, while activation energy

Table 1. Outputs in recent years and predictions for the future of worldwide crude steel (million metric tons).3)

Country 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2017

China 179.7 215.1 282.9 353.2 419.1 489.3 500.3 567.8 626.7 674.0 800.0

Japan 107.8 108.5 112.7 112.5 116.2 120.2 118.7 87.5 109.6 110.0 155.0

Russia 59.8 62.7 65.6 66.1 70.8 72.4 68.5 59.9 64.0 67.0 90.5

America 91.6 90.4 99.7 94.9 98.6 98.1 91.4 58.1 80.6 92.7 114.0

India 28.8 31.8 32.6 45.8 49.5 53.1 55.1 56.6 66.8 93.4 160

Korea 45.4 46.3 47.5 47.8 48.5 51.5 53.6 48.6 58.5 62.6 82.7

Asia 391.7 431.7 486.0 573.5 647.5 732.8 743.1 790.0 897.9 979.0 1 270.0

Europe 206.6 209.2 222.0 217.8 231.9 239.9 229.1 167.0 201.9 201.8 285.6

North America 122.9 123.2 133.0 126.0 131.5 131.2 124.5 82.3 111.8 125.2 158.1

South America 40.8 43.9 46.2 45.5 45.3 48.5 47.3 37.8 43.8 45.9 62.0

Africa 15.7 16.6 16.5 17.5 18.1 19.1 17.1 15.2 17.2 17.5 24.3

Oceania 8.3 8.0 7.7 8.7 8.7 8.6 8.4 6.0 8.2 8.5 11.6

CIS 100.4 105.9 111.2 112.8 119.6 119.5 114.3 97.5 108.4 108.0 153.3

Middle East 12.4 13.7 13.6 14.6 14.8 15.7 16.7 17.2 19.0 20.0 25.9

World 898.8 952.2 1 071.5 1 144.4 1 247.3 1 345.8 1 326.5 1 219.7 1 414.0 1 505.9 2 000.0

Fig. 1. Total consumption and percentage of different welding consumables in main regions and countries in 2009.

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for heterogeneous nucleation of ferrite on inclusions is lessthan that for heterogeneous nucleation, the ratio willdecrease with an increase in the inclusion diameter andreaches less than 1.0 as shown in Fig. 3.7,11,12) Therefore, ascenters of heterogeneous nucleation of AF, the size andnumber of inclusions are important for improvement ofweld metal microstructures.

(2) Coherent boundary nucleation theory: The theorystates that good lattice matching between AF and inclusionsreduces activation energy for nucleation. Due to the con-straint of the reproducible orientation relationships betweenaustenite and ferrite, it is difficult for inclusions and ferrite,ferrite and austenite to achieve suitable orientation relation-ships. Thus, the AF firstly nucleates at an inclusion surfaces.Figure 4 shows the lattice matching for TiC and WC with

δ -Fe respectively.11) It is shown that the disregistry betweenδ -Fe and TiC is lower than that between δ -Fe and WC.Therefore, TiC is more favorable for AF to nucleate.

(3) Thermodynamics driving nucleation theory: The the-ory states that inclusions deplete hardening elements such asC, Mn and Si from the austenitic matrix and thereforeincrease the thermodynamic driving force for ferrite nucle-ation at inclusion surfaces. The influence of Mn in the Mn-depleted zone (MDZ) to energy barrier for ferrite nucleationat the inclusion surface is shown in Fig. 5.11) It can be seenthat activation energy for heterogeneous nucleation of ferritedecreases with a decreased Mn content in the MDZ. There-fore, the nucleation of ferrite with diameters larger than1 μm nucleates at very low contents (about 0%) of Mn morefavorably on the inclusion surfaces than on austenite grainboundaries.

(4) High strain energy nucleation theory: The theory stat-ed that the thermal expansion coefficients (Δα) of austeniteand inclusions are different, so there are thermal stresses ontheir interface, which can reduce the activation energy fornucleation of ferrite. Figure 6 shows the relationshipbetween Δα of different inclusions in an austenite matrixand the probability of nucleation of AF on inclusions.11) Itcan be seen that the difference in the Δα between austeniteand MnS or Fe-oxides is lower with respect to other inclu-sions. The tessellated stresses induced by the iron matrixnear the inclusions are very small, so MnS and Fe-oxideshave no influence on AF nucleation. The probability of AFnucleation on inclusions increases with an increase in the

Table 2. Comparison of S, P contents and mechanical properties between steels and welding consumables.

SteelTypical steel properties Welding

consumableTypical weld metal properties

S/% P/% TSa/MPa YSb/MPa AKVc/J S/% P/% TSa/MPa YSb/MPa AKVc/J

Q460 0.004 0.008 720 460 189@-20°C E7015 0.010 0.012 490 390 120@-20°C

D36 0.009 0.011 559 454 184@-20°C E71T-1 0.011 0.014 540 450 100@-20°C

WDL610D 0.006 0.013 740 490 150@-40°C E9015-G 0.008 0.013 620 520 110@-40°C

N610E 0.002 0.010 645 600 262@-20°C E71T-1 0.008 0.011 650 520 65@-20°C

X65 0.005 0.017 550 470 240@-40°C E71T-1 0.006 0.150 640 535 53@-40°C

X70 0.003 0.012 656 532 300@-30°C E71T8-Ni1 0.003 0.013 530 415 34@-30°C

X80 0.001 0.009 825 690 319@-30°C E81T8-Ni2 0.003 0.011 585 510 68@-30°C

X100 0.001 0.010 945 724 255@-60°C E11018 0.008 0.017 750 520 98@-20°C

X120 0.0004 0.004 1 128 1 087 250@-30°C 0.005 0.010 941 780 70@-30°Ca TS stands for tensile strength, b YS stands for yield strength, c AKV stands for impact absorbed energy

Fig. 2. Market demands for welding consumables.6)

Fig. 3. Effects of inclusion size on energy barrier to heterogeneous( ) and homogeneous ( ) nucleation of fer-rite.7,11,12)ΔG het( .)

* ΔG hom( .)*

Fig. 4. Crystallographic relationship at interface between car-bide.11) (a) (100) TiC; (b) (0001) WC and (100) δ -Fe.


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Δα value. Therefore, Mn-Al- or Al-silicates are effective forAF nucleation.

2.1.2. Effects of Alloying Elements on AF NucleationThe chemical composition of weld metals is a major fac-

tor for controlling fine structures and mechanical properties.According to different research results, the role of differentalloying elements on ferrites nucleation can be classifiedinto three kinds: first, to change the γ-α transformation tem-perature, including increase the austenite zone elementssuch as C, Mn, Ni, Cu or decrease the austenite zone ele-ments such as Al, Si, V, Cr, Mo, Ti; second, to reduce grainboundary energy for the segregation of solute elements suchas B, which can cause an increase of nucleation energy bar-rier and a decrease of the possibility for ferrite nucleation onan surface of grain boundary surface, and the probability forferrite nucleation reduces; third, to form a precipitation ofinclusion favorable for ferrite nucleation at inclusion surfaceduring the γ-α transformation.

Carbon can increase γ phase zone and delay transforma-tion temperature of austenite, and is also a strong hardeningelement. The typical range of carbon content in weld metalsis 0.05–0.15%. Ramirez14) studied the chemical composi-tion, microstructure and nonmetallic inclusions of highstrength steel weld metal, and concluded that when therange of carbon equivalent is 0.26–0.39, deposited metalsare mainly ferrites. The fraction of grain boundary ferrite(GBF) decreases with an increase in the fraction of ferrite

with second phase (FSP) and AF. The reheated zone of theweld metals transforms to equiaxed polygonal ferrite; witha carbon equivalent of 0.47 or higher, the fraction of lowertemperature transformation products including martensiteincrease in weld metal.

Kim et al.15) studied the effect of Ni on weld metal tough-ness and results showed that the weld metal impact tough-ness increased remarkably by an increase of Ni and thevalue was 118 J at –196°C when Ni content was 16.6%.However, Bhole et al.16) investigated the effect of Ni and Moadditions on weld metal toughness in a submerged arc weld-ing (SAW) of HSLA steel. 2.03–3.75% Ni can decrease theimpact toughness of weld metal and increase the fractureappearance transition temperature (FATT); the combinationof 2.03–2.91% Ni and 0.7–0.995% Mo may decrease thevolume fraction of GBF in weld metal to promote fine AFwith high toughness; 0.817–0.881% Mo may accelerate theformation of AF and granular bainite (GB). Weld metal with0.881% Mo obtains optimum impact toughness at –45°C.The microstructure is mainly comprised of 77% AF and20% GB.

Avazkonandeh-Gharavol et al.17,18) investigated the effectsof 0.14–0.94% Cu and 0.05–0.91% Cr on the microstructureand mechanical properties of Cr–Ni–Cu low alloy steel weldmetal. With the increases of Cu and Cr contents in weldmetal, AF increases and microstructures become finer in allweld zones while the amount of primary ferrite (PF) andFSP decreases in columnar zone and coarse-grained reheat-ed zone (CGRZ); the volume fraction and the size of non-metallic inclusions in weld metal cannot be affected by thechange in Cu and Cr contents, and the diameters of mostinclusions are in the range of 0.1–1.0 μm; tensile strengthof weld metal increase because of solid solution hardeningeffects of Cu and Cr; impact toughness decreases with theincrease of Cu content, but increases with the increase of Crcontent.

Beidokhti et al.19) studied the influences of Ti and Mn onHSLA submerged arc weld metal properties. Weld metal in1.92% Mn-0.02% Ti and 1.40% Mn–0.08% Ti has optimalmechanical properties. The AF in weld metals increaseswith an increase of Ti content in the range of 0.02–0.08%as shown in Fig. 7.19) Mn may refine and homogenize theweld microstructures. Further addition of Ti or Mn encour-ages grain boundary nucleation frequency of bainite withhigher than intragranular nucleation of AF and thus weldmetal hardness increases. Best combination of microstruc-ture and impact properties can be obtained in the range of0.02–0.05% Ti in weld metal. Further addition of Ti canaccelerate weld metal microstructure change from the mix-ture of AF, GBF, and Widmanstatten ferrite (WF) to a mix-ture of AF, GBF, bainite and ferrite with M/A.20)

By changing the Al/O ratio from 0.48 to 1.52, the inclu-sion nucleation core in a low alloy steel weld pool (mainreaction of deoxidation process) was observed by Terasakiet al.21) The results showed that with low aluminum con-tents, the glassy phase in Mn–Al–Si–O system dominatedthe inclusion core, while with middle aluminum contents,corundum alumina and some glassy phase serve as theinclusion core. Kojima et al.22) studied the case where theAl/O ratio is low (0.2 and 0.43) in weld metal. The experi-ment showed that when the Al/O ratio is lower than 0.45, a

Fig. 5. Effects of inclusion size in MDZ on activation energy ofheterogeneous nucleation of ferrite with different Mn con-tents in steels.11)

Fig. 6. The relationship between thermal expansion coefficient fordifferent inclusions and possibility of AF nucleation.11)

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reasonably high Al/O ratio is favorable for the toughnessmainly because there are more 0.2–0.8 μm inclusions andAF nucleation is accelerated.

Yamada et al.23) used an ion beam to make a layer of Ti-enriched film on inclusion surface with three Al/O ratios toinvestigate the relationship between the Ti-enriched layerand AF in low carbon Ti–B weld metals. (1) In samples withthe Al/O ratio of 0.48 and 0.73, inclusions near AF forma-tion are surrounded by narrow TiO layers with its thicknessin the range of 10–40 nm; (2) the TiO layer has a B–N ori-entation relationship with AF; (3) the TiO layer on the inclu-sion surface contributes to the heterogenous nucleation ofAF.

The influence of S on AF is reflected in sulfide inclusion.Liu8) studied the relationship between AF nucleation andsulfide inclusion without special alloying elements. (1)Complex Mn–Fe–S–O oxides and relatively pure SiO2 haveno effect on AF nucleation. But iron sulfide particles includ-ing a little concentration of Mn and Cu are effective for AFnucleation. (2) CuxS particles have no effect on AF nucle-ation. (3) Mn-depleted zone and P-rich zone around iron sul-fide inclusion in the iron matrix may be the two reasons thatiron sulfide can nucleate AF. It is concluded by Sarma et

al.11) that there is little difference in thermal expansion coef-ficients between austenite and MnS. The possibility of par-ticles covered by MnS as AF nucleation is lower than thatof Ti-oxide inclusions. Precipitated MnS layer on the sur-face of Ti-oxide inclusions may decrease the possibility ofAF nucleation on inclusions.

Terashima et al.24) studied the effect of oxygen concentra-tion of weld metals on toughness as shown in Fig. 8. Oxidesmay accelerate AF formation, the toughness of high strengthsteel weld metal is the highest at 20 ppmw O, and decreasedas an increase of O concentration in the range of 20–100 ppmw, and afterwards there is a peak value of thetoughness at 300 ppmw. Figure 9 shows effect of oxygenconcentration in high strength weld metal on continuouscooling transformation (CCT) diagrams.24) The increase ofoxygen concentration may enlarge bainite and ferrite areasbecause oxide may provide extra heterogeneous nucleationsites.

Lee et al.25) researched the effect of B on AF nucleationwith three experimental FCWs with B content of 32 ppmw,60 ppmw, 103 ppmw in weld metals. The volume fractionof AF decreases with an increase of B in the range of 32–

Fig. 7. Effect of Ti content on weld metal microconstituents.19)Fig. 8. Effect of oxygen concentration on absorbed energy of

HSLA weld metal.24)

Fig. 9. CCT diagrams for HSLA weld metal.24) (a) 20 ppmw O; (b) 140 ppmw O; (c) 270 ppmw O; (d) 350 ppmw O.


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103 ppmw. When B content is 103 ppmw, upper bainiteinstead of AF is formed. The impact energy of weld metalsslightly decreases with an increase of B content in the rangeof 32–60 ppmw, but significantly decreases with an increaseof B content in the range of 60–103 ppmw, duo to B causesa reduction of eutectoid temperature. Warren et al.26) studiedthe effect of lanthanum on toughness in ultra-high strengthsteels. Higher toughness can be obtained by the addition of0.015% lanthanum in MnS inclusions in AF1410 ultra-highstrength steels.

2.1.3. Effect of Inclusions on AF NucleationThe size, quantity, composition, metallurgy of inclusions

and other factors have great effects on AF nucleation inweld metals. AF nucleation occurs in weld cooling pro-cess.27) Energy barrier to heterogeneous nucleation of ferriteat inclusions decreases with an increase in the inclusiondiameter from 0 to 1 μm because of an increase in the inclu-sion particle surface area. When the inclusion diameter islarger than 1 μm, the energy barrier value slightly decreaseswith the further increase in inclusion size. Therefore, it isnot necessary to further increase the inclusion diameter topromote ferrite nucleation on an inclusion surface. The crit-ical value of an inclusion particle diameter for AF heteroge-neous nucleation is 1 μm.11) Grong28) also thought that inclu-sions of about 1 μm size could promote AF nucleationwithout harmful effect for mechanical properties duo to rel-atively small size.

Nevertheless, Ramirez14) proposed that the volume frac-tions of nonmetallic inclusions in weld metals are mostly inthe range of 0.2–0.6%, and rarely in the range of 0.8–1.1%.The inclusion density ranges from 1.2×108 to 5.4×108 mm–3,and the average and maximum value of the inclusion diam-eter are respectively in the ranges of 0.3–0.6 μm and 0.9–1.7 μm. Inclusion particle size distribution is related to fluxbasicity. Average inclusion size does not drastically changewith an increase in O and S content, but inclusion averagesize increases when O plus S content increases to above400 ppmw. Inclusions as AF nucleation are mostly within0.2–0.6 μm in diameter and are chemical heterogeneouscompounds containing various elements. Inclusions reducethe energy barrier as high energy inert substrates to promoteAF nucleation. When AF nucleates with inclusion as thecore, abundant interlaced AF nucleation may be caused.29)

Lee et al.13) found that it was easier to get nucleation in largesize inclusions than in small ones as shown in Fig. 10. It canbe seen that the nucleation probability is near to zero whenthe size of the inclusions is less than 200 nm; the probabilityfor AF nucleation increases markedly when inclusion diam-eter increases in the range of 0.4–0.8 μm, and the value is1.0 at 1.1 μm; inclusions with a diameter larger than 1 μmhave greater possibility for AF nucleation.

AF in weld metal is proportional to the number densityof inclusion with a diameter smaller than 2 μm.30) The den-sity of fine inclusions with their diameters in the range of0.2–0.6 μm may be increased by electromagnetic stirring inwelding and the number of AF increases.31) Figure 11shows the total size distribution of all inclusions and inclu-sions for AF nucleation.13) It can be seen that AF nucleationhas the largest quantity with an inclusion diameter in therange of 0.5–0.8 μm, which has large influence on the for-

mation of microstructure with a high ratio of AF.Al2O3 in oxide form is not effective for AF nucleation. On

the contrary, it may accelerate bainite formation. But MnO–Al2O3 is favorable for AF nucleation. Hidaka32) studied theinfluence of oxides on microstructure and impact toughnessof high strength steel weld metals and concluded that FATTof weld metals is related to the size of intragranular bainitenucleated by oxide inclusions. FATT is also influenced bythe density of dispersive oxide inclusions and the impacttoughness can be improved as the refined microstructurewith Ti–Mn oxide. Oxygen content in weld metals made byTiO2 type FCW may be reduced as a decrease of TiO2 activ-ity. Ti-oxide is the best particle for AF formation. There islow mismatch and a similar orientation relationship betweenTiO and α, so AF can be formed. Ti-enriched inclusions canaccelerate the kinetics of AF formation in weld metals.Inclusions have various shapes and textures in weld metalsincluding spherical, faceted and agglomerations. The inclu-sion core is mainly comprised of oxides like Ti, Mn, Si andAl in different proportions and performs as a complex deox-idation product.14)

In order to obtain more effective AF, it is necessary tostudy the inclusion metallurgy from the aspect of weldingmetallurgy. Andersson et al.33) proposed two points: one isto obtain microstructures with optimum mechanical proper-ties from the aspect of inclusion engineering; the other is toproduce cleanliness steel and then obtain AF microstructureby the addition of active inclusions separately. Zhang etal.34) studied the BaF2–Al–Mg slag system of high tough-

Fig. 10. Effect of inclusion size on the probability of ferrite nucle-ation.13)

Fig. 11. Inclusion distribution diagram in weld metal of mildsteel.13)

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ness all-position self-shielded FCW. By the addition of 10%Fe2O3 and 5% MnO2 in the flux, the Al content can bereduced to 0.84% and oxygen content be increased to 85 ×10–6 in deposited metal, avoiding the influence of δ-ferriteand aging effect. Circular inclusions of Al2O3 as its mainconstituent are produced in weld metals and intragranularheterogeneous nucleation particles are increased. Main weldmicrostructures with AF are formed and therefore the lowtemperature toughness of deposited metals is improved sig-nificantly.

It should be pointed out that it is difficult to decide whichmechanism that is most important for AF nucleation.Instead, it is believed that the four mechanisms often worktogether to promote the AF nucleation on inclusions. Forpromoting the AF formation, it is necessary to optimizealloying elements (see Table 3). Base on the influence onAF nucleation, inclusions can be classified into active andinert. The effect of two kinds of inclusions on AF nucleationis shown in Table 4.11) It can be seen that active inclusionsfor AF nucleation are mostly complex and multi-phaseinclusions. The critical value of an inclusion diameter forAF nucleation is 1 μm.

2.2. Impurity Control in Weld Metals and Cleanlinessof Weld Metals

The current recommended control level of S and P forcleanliness steel is less than 0.005% and 0.015% respective-ly. The actual content of S and P is mostly less than 0.003%

and 0.009%, and that of weld metals is usually in the rangeof 0.008–0.014% and 0.012–0.014% respectively. S and Pmainly influence the toughness and crack resistance of weldmetals. N and O contents in steels have been less than250 ppmw, while that in weld metals is usually in the rangeof 300–900 ppmw. Therefore, desulfuration, dephosphoriza-tion and denitrification are quite important for HSLA steelweld metals.

2.2.1. Dephosphorization of Weld MetalsP has no obvious effect on weld microstructures, but it

can increase the hardness and strength of weld metals andreduce impact toughness and crack resistance. When P con-tent in weld metals is less than 0.005%, further reduction ofits content has little influence on its properties. The mecha-nism of dephosphorization in weld metals is mainly to formphosphate. Dephosphorization can be done by the metallur-gical reaction and there is a limit which is related to basicityof flux and contents of P in the wire and base metal. Thelimit value of P in weld metal is about 0.010 ± 0.002% forhigh basicity fluxes of B1 ≥ 2.5.35)

Thermodynamic calculation and experiments in ferrousmetallurgy show that it is possible to adopt oxidativedephosphorization and reductive dephosphorization in weldmetal. But for most welding consumables, FeO in largequantities is not allowed in basic slag, and CaO in acid slagis not allowed to have greater activity. Therefore, dephos-phorization becomes a relatively difficult process.

Reductive dephosphorization must be realized by theaddition of a deoxidant that is better than Al, so that moltensteels can reach deep reduction. Table 5 shows the proper-ties of various phosphides.2) It can be seen that P and alkaliearth metals such as Ca, Mg, Ba can produce more stablechemical compounds with a lower density than Fe3P andFe2P, which proves that dephosphorization is possible underreductive conditions. In the study of oxidative dephosphori-zation, it is shown that the affinity of O and Si is greater thanthat of O and P.

By the addition of calcium dephosphorization flux inCaO–CaF2 slag, effect of precipitation dephosphorization inMn–Si–Fe alloy was investigated. The study concentrateson the influence of dephosphorization flux content andincrement of Si content in Mn–Si–Fe alloy on dephosphori-zation. When the dephosphorization flux quantity increasesfrom 2.5% to 7.5%, the dephosphorization effect increases5.56%. When the Si content in the alloy increases from 19%to 25%, the dephosphorization effect may increase by atleast 23.22%. This shows that an increase in Si content inMn–Si system has a much greater influence on the dephos-phorization effect than the addition of dephosphorization

Table 3. Influence of alloying elements on AF nucleation.

Element type Alloyingelements

Optimumrange/% Influence on AF Welding

process

Increaseaustenite zone

C 0.05–0.15 Small increase SMAW

Mn 1.40–1.92 Mild increase SAW

Ni 2.03–2.91 Moderate increase SAW

Cu 0.14–0.94 Moderate increase SMAW

Increaseferrite zone

Mo 0.7–0.995 Large increase SAW

Cr 0.05–0.91 Moderate increase SMAW

Ti 0.02–0.05 Moderate increase SAW

B 0.003–0.006 Small decrease FCAW

Table 4. Influence of chemical composition of inclusions on theirpotential to AF nucleation.11)

Compoundadded

Active inclusions forAF nucleation

Inert inclusions forAF nucleation

Simple oxides Ti-oxides (Ti2O3 and TiO) Al2O3, SiO2, Ti2O3

Complexoxides

(Ti, Mn)2O3,TiO2–(MnO–Al2O3)

MnO–SiO2,MnO–FeOx–SiO2,

MgO–Al2O3MnO–Al2O3Galaxite spinel MnO–Al2O3

Simple nitrides TiN, VN TiN

Simple sulfides MnS, CuS

Complexoxy-sulfides

andmulti-phaseinclusions

Al2O3–MnS, TiO2–Al2O3–MnSTi- and Ti-Ca-oxy-sulfides

Ti2O3–TiN–MnS,TiOx–TiN–MnS

FeS–(Mn,Cu)S, MnS–VC,MnS–V(C, N)

Table 5. Different phosphide characteristics.2)

Phosphide P2O5 Ca3P2 Mg3P2 Ba3P2 AlP Fe3P Fe2P Mn3P Na3P2

Valence +5 –3 –3 –3 –3 – – – –3

–Δ fHθm (298 K)/KJ mol–1 1 492 506 464 494 164.4 164 160 130 133.9

Density/g cm–3 2.39 2.51 2.06 3.18 2.42 6.80 – 6.77 1.74

Meltingpoint/°C 580 1 320 – 3 080 – 1 220 1 370 1 327 –


1479 © 2014 ISIJ

flux only. The increase in Si content can reduce oxygenpotential, and can also improve P activity so that Ca indephosphorization flux enters into the slag in the form ofCa2P3 rather than CaO.36)

It is shown that the addition of 3% Si–Ca alloy to ultra-low hydrogen high toughness stick electrodes can reduce themass fraction of P content in weld metals from 0.015% to0.008%, which proves that Si–Ca alloy does play a role inreducing dephosphorization. Rare earths, as good reducingagent in molten steel, have strong chemical activity. Theycan reduce P in molten steel to P3– to reduce dephosphori-zation of molten steel.2) O and S contents in molten steel arethe main factors that influence reducing dephosphorizationusing rare earths. In order to improve rare earth dephospho-rization efficiency, it is crucial to control O content in mol-ten steel to be in about 1% and 0.010% respectively duringreductive period.37)

BaO slag systems can improve the dephosphorization ratein an atmosphere of low oxygen. In recent years, BaOdephosphorization flux has been adopted in the hot metalextra furnace dephosphorization process, so that the dephos-phorization rate in low oxygen atmosphere has beenimproved. BaO can enter into slag by adding 10–20% bariumcarbonate to a CaO slag system after the high temperaturedecomposition of barium carbonate. This greatly reducesP2O5 activity in slag so that the dephosphorization effect isnotably improved. In electrodes with high strength andtoughness, replacing CaCO3 with BaCO3 not only reducesS and P content in weld metals, but also improves the oper-ative performance.2)

2.2.2. Desulfuration of Weld MetalsRecently, deep desulfuration for molten steel has proceed-

ed to improve the desulfuration effect in steel making. Oneway to accomplish this is to by using a Mg matrix, Ca andBa and its alloy desulfuration flux to perform deep desulfu-ration for molten steel. At the same time, O and P contentis reduced. Another way is using previously frequentlyadopted basic oxides like CaO, MgO and MnO during theprocess of basic slag desulfuration. But recent researchfocuses on the influence of the addition of Li2O and BaO inrefining slag on the desulfuration effect in the external refin-ing deep desulfuration treatment. When more than 7.5%Li2O is added, the desulfuration rate is higher than 90%, andwhen the addition reaches 20%, the desulfuration rate ishigher than 95% with the final S content in molten steelreducing to less than 0.002%. Another study shows that inthe CaO–Al2O3 refining slag system, when the ratio of CaOto Al2O3 is in the range of 2.5–3.0, optimum desulfurationcan be obtained by the addition of 10–13% BaO. S contentin molten steel reduces from 0.011% to 0.0028% after refin-ing.2) The above mentioned technological approaches forimproving the desulfuration effect can be adopted in thestudy of welding metallurgy and design of welding consum-able.

In addition, rare earth with a strong desulfuration capacitycan interact with S to form high melting sulfide. By additionof rare earths to high Mn steel, rare earth sulfides (RES,RE2S3) and rare earth sulfur oxides (RE2O2S) are formed,which are of 2 000°C melting point and dispersed in intrac-rystalline as fine particles. The addition of a rare earth

reduces the quantity of sulfide inclusions, and most impor-tantly the addition can improve shape (circular shape gran-ular), size (fine), distribution (change from segregation ingrain boundary and intragranular to dispersion in intragran-ular) and greatly reduce the deleterious effect of nonmetallicinclusions in high Mn steel. So, the influence of rare earthon the desulfuration effect is greatly related to reducing slag.When reducing slag dioxide is favorable, the desulfurationrate of rare earths is on average higher than 52%; whenreducing slag dioxide is not favorable, the desulfuration rateof rare earths is on average about 20%. S content in weldmetals can be controlled to 0.001% by Ba, Mg and a basicslag system. But the problem, that is an acid slag systemwith a good operative performance, has not yet achieved thislevel.37)

2.2.3. Denitrification of Weld MetalsWhen N content in weld metals is higher than 0.01%, the

impact absorbed energy of weld reduces sharply. Therefore,this is one of the important measures to improve weld metaltoughness by reducing N content. To reduce the deleteriouseffect of N, one way is by improving smelting technologyto a lower N content in welding materials; another way isby the addition of microalloy elements (e.g. Elementsformed by nitrides like Al, Ti) to produce nitrides and thento reduce the deleterious effect of free N.

Various new complex ferroalloys may play a part incomprehensive metallurgical processes such as deoxidation,denitrification, desulfuration and dephosphorization. Alkaline-earth metals such as Ca and Ba have a notable effect ondeoxidation, dephosphorization and desulfuration in themetallurgical process. From thermodynamic calculations,the deoxidizing capacity of Ca and Ba is much greater thanthat of Al. but in practical applications, the actual deoxidiz-ing capacity may barely reach the thermodynamic calcula-tion value because the solubility of Ca and Ba in moltensteel is affected by many factors and their vapour pressureis quite high. There has been much research and discussionon finding a solution to this problem. It has been found thataddition of Ba and Ca into molten steel through a complexferroalloy can reduce loss, increase the solubility of Ba andCa in molten steel, and improve their metallurgical capacity.In a multicomponent alloy containing Ba, the deoxidizingcapacity of Si may be equal to that of Al, the deoxidization,desulfuration and dephosphorization capacity of Ba may befully demonstrated and Al and Ti can play a part in denitri-fication and nitrogen fixation. So it is necessary to discussa way to further deoxidization and denitrification by theproper adoption of alkaline earth metals and multi-elementcomplex ferroalloys.

2.3. Crack Resistance of Weld Metal2.3.1. Cold Crack Resistance

As welding structural steel develops towards a low car-bon equivalent and high strength, hydrogen-induced coldcracking position in welding joint has transferred from HAZto weld metal. Cold crack resistance improvement is real-ized mainly through controlling the microstructure, impuritycontent, optimizing weld performance, reducing diffusiblehydrogen and so on.

Adding fluorides such as CaF2, Na3AlF6, K2SiF6, MnF3

© 2014 ISIJ 1480


and MgF2 to rutile-type FCWs at concentrations of 1.8–2.3% can reduce hydrogen content in weld metals. Theeffect of the fluoride content on diffusible hydrogen isshown in Table 6.38) It shows that all fluorides can reducediffusible hydrogen content in weld metals, but with a vary-ing reduction range. Wires with CaF2 have the lowest diffus-ible hydrogen content (6.32 mL (100 g)–1), while wires withMnF3 have the highest content (7.96 mL (100 g)–1). The dif-fusible hydrogen content in weld metals decreases with anincrease in the slag basicity. Wires with CaF2 and highestbasicity (0.27) have the lowest diffusible hydrogen content,while wires with MnF3 and the lowest basicity (0.01) havethe highest diffusible hydrogen content. Thus, diffusiblehydrogen content in the weld metals is influenced greatly byslag basicity rather than by fluorides.

Brown39) studied the reason for centerline cold cracking inweld metal caused by microsegregation of Mn, Ni, and Siwhen using flux cored wire to weld API 5L-X80 steel. Theresults show that the crack path is perpendicular to the ini-tially formed δ-ferrite cellular dendrite and growth directionof the intercellular-dendritic segregation formed in δ -ferritecellular dendrites. Micro-segregated regions are rich inhardening elements, which results in a higher hardness inthe segregation region. The increased hardness value isrelated to a reduction in toughness. Weld metal is sensitiveto cracks in micro-segregated regions. Beidokhti et al.40)

studied the effects of different Ti content on hydrogen-induced cracking, hydrogen sulfide stress cracking of thesubmerged arc welded API 5L-X70 steel weld metals.Increase of AF content in the weld metal can improvehydrogen-induced cracking resistance and hydrogen sulfidestress cracking capacity. More than 30% bainite and M/A inweld structures may cause testing failure of hydrogen-induced cracking resistance and hydrogen sulfide stresscracking capacity. The addition of Ti to welds may changethe nature of inclusions from Mn-based inclusions to Ti-based ones. The precipitated titanium carbonitrides maydelay cracking in H2S environments as beneficial hydrogentraps. Through further addition of Ti, bainite and M/A weldmetal structures appear and outweigh the beneficial effect oftitanium carbonitrides. As a result, weld metals with a highpercentage of AF and good distribution of titanium carboni-trides show the best performance in acid medium. Jin etal.41) studied the effect of nonmetallic inclusions on hydro-gen-induced cracking of API 5L-X100 steel. It is showedthat API 5L-X100 steel contains inclusions such as elongat-

ed MnS inclusions and spherical Al-, Si-, Ca-Al-O-S-enriched inclusions. Most inclusions in steels are Al-enriched. Cracking is mainly related to Al- and Si-inclusionsand has no relation with elongated MnS inclusion. The limitvalue of H content for hydrogen-induced cracking in API5L-X100 steel is 3.24 ppmw.

With improvements in the performance of steels andwelding consumable, many past testing methods for thecracking evaluation of base metal and weld metal are nowout of date. So it is important to improve the testing methodsfor cold cracking sensibility of weld metals. Using the orig-inal Y groove cracking test, the joint does not crack even at–10°C, which is not helpful for the estimation of the crackresistance of weld materials. Based on the Y groove typecracking test, Authors improved Y groove crack test bychanging the groove angle and enlarging the gap and testplate thickness. In this test, the welding current was 250 A, arcvoltage was 29 V, and the weld heat input was 1.6 KJ mm–1.The whole experiment was conducted at 0°C. The experi-mental design and results are shown in Table 7. The coldcrack resistance of an E71-T1 FCW welding joint was stud-ied. The cracking formation rate is the highest with thegroove angle being 120°. Cracking formation rate increaseswith an increase in groove angle. The cracking formationrate may increases by enlarging the gap and plate thickness.In addition, a crack can also form by further increase ofrestraint intensity and stress.

By using the G-BOP test, Zhang et al.42) studied theeffects of welding current, CO2 shielding gas flow and dif-fusible hydrogen content on the weld metal cold crack sen-sibility of three kinds of E71T-1 FCWs. With an increase inweld current and a reduction in CO2 shielding gas flow, thediffusible hydrogen content in the FCW weld increased. Atroom temperature of (25±3)°C, H content for the cold crack

Table 6. Effect of fluoride content on diffusible hydrogen in weld metals.38)

Wire TiO2 Mn Fe Ni FluorideHDM

a/mL (100 g)–1 HFMb/mL (100 g)–1

Discrete values Avg. Discrete values Avg.

A 37.0 10.5 4.5 9.5 CaF2 2.3 7.01, 6.31, 5.98, 5.97 6.32 3.55, 3.26, 3.27, 3.20 3.32

B 37.0 10.5 4.7 9.5 Na3AlF6 2.1 7.92, 7.59, 7.29, 6.80 7.40 4.31, 4.34, 4.20, 3.94 4.20

C 37.0 10.5 4.6 9.5 K2SiF6 2.2 8.29, 7.38, 7.07, 7.07 7.45 4.26, 4.26, 3.90, 4.28 4.18

D 37.0 10.5 4.6 9.5 MnF3 2.2 8.56, 8.56, 7.44, 7.28 7.96 4.52, 4.87, 4.15, 3.98 4.38

E 37.0 10.5 5.0 9.5 MgF2 1.8 7.74, 7.98, 6.37, 6.40 7.12 4.18, 4.31, 3.56, 3.61 3.92

F 37.0 10.5 6.8 9.5 0 10.68, 10.15, 9.94, 9.89 10.17 7.64, 7.30, 6.70, 6.86 7.13a HDM stands for diffusible hydrogen content in deposited metal, b HFM stands for diffusible hydrogen content infused metal

Table 7. Effects of groove angle, gap and plate thickness on crackformation rate.

Type Groove angle 60° 75° 90° 105° 120°

Gap

2 mm 33 35.5 41.3 52.5 64.3

3 mm 42.5 43.5 15.1 55.2 72.3

4 mm 63.3 72.3 100 100 100

Thickness

20 mm 33 35.5 41.3 52.5 64.3

25 mm 37.8 45.5 45.5 53.5 71.2

30 mm 39.2 55.5 51.5 55.5 77.7


1481 © 2014 ISIJ

appearing in the FCW in the G-BOP test was about 6 mL(100 g)–1. Authors also conducted the experiments to modifythe G-BOP test by enlarging welding restraint intensity. Thecold cracking rate can be as high as 63%. These improve-ments in the traditional testing methods are helpful for esti-mating modern welding consumable crack resistance.

By employing modern production procedure, the diffusiblehydrogen content in acid FCW is less than 5 mL (100 g)–1.But seeking a very low level of hydrogen should not be thegoal. Accurate and rapid detection of diffusible hydrogen inweld metals is very important. There are certain error in thechromatography, glycerol, hot extraction and mercury meth-od. When diffusible hydrogen content is in the range of 5–10 mL (100 g)–1, the measurement error can reach ±1.5 mL(100 g)–1. When the diffusible hydrogen content is less than5 mL (100 g)–1, the measurement error can reach ±1 mL(100 g)–1. The welding voltage, current, stick out, weld feed-ing speed, test temperature, test time, environment humidityand deposited metal quantity have great influence on thetesting result of diffusible hydrogen. Therefore it is difficultto meet the requirement of low hydrogen and super lowhydrogen for testing accuracy. Currently the nominal diffus-ible hydrogen content of seamless FCW has been less than3 mL (100 g)–1. The actual diffusible hydrogen of lowhydrogen stick electrodes for high strength steel has been1.8–2.2 mL (100 g)–1.

2.3.2. Hot Crack Resistance of Weld MetalsIto et al.43) developed a high quality FCW for shipbuild-

ing and bridge construction, and the FCW have excellent hotcrack resistance in small gap groove welding. Table 8shows the range of chemical composition of hot crack resis-tance and the chemical composition of the FCW.43) Figure12 shows the effect of P, Mn and C content change on a hotcrack resistance.43) It is clear that a reasonable control of Mnand C content, especially the reduction of P content canincrease the crack resistance. When P content is in the range

of 0.009–0.012%, Mn is 1.05–1.10% and C is 0.007–0.008%, the crack formation rate is the lowest. P can reducethe final solidification temperature of liquid residues in theinterdendritic area and thus increases the crack sensibility ofweld metals. S may intensify the deleterious effect of P.44)

By increasing the plate gap, slot of Paton cracking test, theeffects of different welding parameters and FCWs on hotcrack with a ceramic backing were investigated in differentrestraint intensity. The most important measure to prevent thebacking crack is that the welding current should be within 200A and the welding speed should be within 150 mm min–1. Anewly-developed FCW can increase the current from 200 Ato 260 A and the welding speed from 150 mm min–1 to200 mm min–1 in the backing weld. At the same time, whenwelding with ceramic backing, the side near the ceramicbacking would have different metallurgical reaction condi-tions from the side far from the ceramic backing. For theformer one, there is the problem of the reduction of the sil-icon oxide, which may increase oxygen and silicon in weldmetals. Therefore, the side near the ceramic backing hasmore silicon content than that distant to the ceramic back-ing. The decrease in Si content may cause a lower tough-ness.45)

Table 8. Chemical compositions against hot rack.43)

Element Optimumrange/wt.%

Experimental/wt.%

Conventional/wt.%

Metals

C 0.07–0.09 0.08 0.07

Si 0.40–0.50 0.50 0.60

Mn 1.25–1.60 1.35 1.10

ImpuritiesP Low 0.010 0.017

S Low 0.009 0.012

OthersAl – 0.020 0.010

Ti – 0.040 0.035

Fig. 12. Effects of P, Mn and C contents on hot crack resistance.43)

© 2014 ISIJ 1482


2.4. The Fumes and the Environmental-friendliness ofWelding Consumables

Currently the mechanisms of welding fumes and theireffects on the human body are key aspects of a new gener-ation of welding consumables. Thus, it is a key issue in theresearch of a new generation welding consumables.

Chu et al.46) centered on TiO2–CaO–SiO2–CaF2 slag sys-tems and studied on the effect of flux slag system and alloysystems on weld fume quantity and operative performance.It considers that based on the welding performance, anappropriate increase in TiO2 and iron content, a reduction inCaF2 content, and increase in calcium alloy can lower thequantity of electrode fume. The quantity of fume in thisnewly-developed electrode is 9.13 g Kg–1 and its weldingperformance is favorable. The influence of the addition ofthe iron powder content on the fume formation rate (FFR)is related to the slag system of FCW. Under the current slagsystem, FFR will reduce as the iron power content decreas-es. Li47) studied on the effect of the production process ofthe iron powder on FFR. The results show that FFR of thespherical atomization iron powder is slightly higher thanthat of the erose deoxidized iron powder. Different FFRs arecaused by different production processes of iron powder anddifferent amounts of iron oxide on the surface of iron pow-der. The quantity of iron oxide on the surface of sphericalatomization iron powder is greater than that of erose deox-idization iron powder. During the welding process, ironoxide evaporated very quickly so that the iron oxide in thefumes increased, and FFR also increased. Further, the formof the iron powder determined the conductivity and apparentdensity of the powder. The size of the electric conductionsection of the wires would be affected and thereby the arcdensity and arc temperature distribution would also beaffected. But this influence was limited. The effects of sizedistribution of atomization and deoxidization iron powderson FFR are shown in Fig. 13.47)

The effect of mineral powder content on FFR is shown inFig. 14.48) The FFR of FCWs increases with an increase insodium fluosilicate content. A favorable match of feldsparand alloy can reduce the FFR of FCWs. FFR decreases from8–12 g Kg–1 to 4–4.5 g Kg–1 with an increase in feldsparcontent. An additional amount of ilmenite has little influ-ence on the FFR of FCWs, while the stability (especially itshigh temperature stability) of mineral powder has a great

influence on the FFR. The effect of powder pretreatment onthe FFR differs: smelting powder can reduce the FFR, whilethe powder granulation influence is not obvious. A reason-able match of mineral powders can lower the FFR of FCWs.

The effects of shielding gas on the FFR and the fume par-ticles are shown in Tables 9 and 10.48,49) The FFR changessignificantly with an increase of CO2 in the shielding gas.Fume particle size becomes larger with an increase of O2

and CO2 in the shielding gas except the components of Ar-12% CO2-4% O2. This is due to O2 and CO2 increasing,which would make nucleation with a higher driving forceprompt particles to form nucleation at high temperaturesthat would be benefit the formation of coarse particles.When the diameter is less than 100 nm, the shielding gas

Fig. 13. Effect of iron powder’ granularity distribution on theFFR.47)

Fig. 14. Effect of mineral powder on the FFR of FCW.48)

Table 9. Influences of shielding gas mixtures on the FFR, O2

index and average particle composition.48,49)

Gas composition FFR/g min–1

O2index/%

O/wt.%

Si/wt.%

Mn/wt.%

Fe/wt.%

Mn/Fe

Ar-5%O2 0.274 5 27.5 0.9 8.7 62.8 0.14

Ar-5%CO2 0.246 2.5 27.5 0.7 7.0 64.8 0.11

Ar-10%CO2 0.298 5 27.4 0.3 5.9 66.4 0.09

Ar-18%CO2 0.396 9 28.1 1.3 4.2 66.3 0.06

Ar-5%CO2-2%O2 0.242 4.5 27.5 0.6 7.4 64.5 0.12

Ar-12%CO2-2%O2 0.312 8 27.8 1.0 5.8 65.3 0.09

Ar-18%CO2-2%O2 0.392 11 28.4 2.3 7.0 62.3 0.12

Ar-5%CO2-5%O2 0.352 7.5 28.1 1.6 6.1 64.2 0.10

Ar-12%CO2-4%O2 0.318 10 28.1 1.6 6.1 64.2 0.10

Ar-20%He-12%CO2 0.279 – 28.1 1.3 4.0 66.6 0.06

Ar-30%He-6%CO2 0.273 – 27.7 0.8 6.1 65.4 0.10

Ar-30%He-10%CO2 0.277 – 27.7 0.8 4.8 66.8 0.07

Table 10. Particle composition as a function of particle size rangefor the Ar–CO2 and Ar–CO2–O2 shielding gas groups.49)

Particle size range O/wt.% Si/wt.% Mn/wt.% Fe/wt.% Mn/Fe

< 20 nm 28.4 2.1 6.8 62.8 0.11

21–40 nm 28.3 2.1 6.7 62.9 0.11

41–60 nm 27.8 1.2 7.0 64.1 0.11

61–80 nm 27.6 0.7 6.4 65.3 0.10

> 81 nm 27.5 0.4 5.4 66.8 0.08


1483 © 2014 ISIJ

composition has little effect on the form of fume particles;binary Ar–CO2 that adds 2% O2 has no effect on the FFR.When oxygen is added into the binary mixed gas, the FFRis only larger when 5% CO2 is added. Increasing He or CO2

into a ternary Ar–He–CO2 mixtures has little effect on theFFR or particle size distribution. The majority of fume par-ticles are spherical single crystals whose mainly composi-tion is (Fe, Mn)3O4. In the Ar-based shielding gas, anincreasing in the FFR is closely related to increases in CO2

which can be attributed to the CO2 affecting metal transferand arc characteristics. Increasing CO2 content will formdroplets with a larger size, longer separation time, higher arctemperature, which in turn will increase the production offume.48,49)

Welding technology, including welding conditions andpolarity, exerts an effect on the diffusion rate of the weldingconsumables. Increasing hot input also makes FFRincrease.50) The energy input influences not only the FFR,but also the composition and structure of the smoke and thegas. The FFR of FCW is influenced by factors includingdroplet transfer mode, arc stability, shielding gas composi-tion and welding spatter and so on. Granular transfer causeshigh FFR, and spraying transfer can somehow decrease theFFR. The FFR increases as the shield gas oxidation propertyincreases; the increase in shield gas oxidation property willincrease spatter which will also heighten the FFR.51) The lat-est research proves that in the welding fume of the FCW,slight spatter takes 30% of the entire fume, which also cor-responds to respirable particulate matter.52) A mathematicalmodel of FFR on the base of welding current, feeding speedand component of weld wire was established.53)

Currently most of the welding material is developedunder traditional systems, which focus on the maximizationof material performance rather than considering any adverseimpact to the environment. Environment-performance coor-dinated welding consumable overall considers both perfor-mance and possible harm caused to the environment. Thisincludes productivity and operating advantages, as well asenvironmental compatibility (including production processenvironmental compatibility and operating process compat-ibility). Research into welding consumable’s environmentalload and the environmental impact of the welding productlife cycle has just started under the development of new gen-eration low toxicity and low fume welding consumables.The emission standard of welding will likely become strict-er. Because of this, the evaluation of the environment loadof the main ingredients and supplementary materials willhave important significance for development of environ-ment coordinated welding consumables. The environmentalload of the core wire and four supplementary consumablesincluding marble, mica plate, feldspar and fluorite are eval-uated as shown in Table 11.54) The core wire has the largestenvironmental load. The factor is 68.62. The correspondingfactor for marble, feldspar and fluorite during the productionprocess is 0.39. Compared with these three materials, thefactor for mica production is 2.80, larger than the total sumfor the above three materials, which is related to the produc-tion process for mica. However, the environmental impactof these four materials is still less than that for the core wire.This is because their production processes and productionwaste are simple. A life cycle assessment (LCA) to the core

wire using a fuzzy assessment method. This included steelstrip and supplement production and transportation, the pro-duction of the core wire, and the impact of the welding fumeon the welder was made as shown in Table 12.55) It can beseen that the production of steel strip constitutes the largestenvironmental load. Among the supplements, iron powderand mineral powder have little impacts on the environment.Ferrosilicon, ferromanganese and ferrotitanium have mod-erate impact, among which ferromanganese has the largestimpact, followed by ferrosilicon, and the impact of ferroti-tanium in last place.

3. Future Trends in the Development of Welding Con-sumables for HSLA Steel

(1) From stick electrode to solid welding wire to copper-free solid welding wire, flux-cored developed into metal-coredwire, and seamless copper FCW developed into seamlesscopper-free metal-cored wire. Slag and gas alloy protectionhave developed into reduced slag protection and increasedalloy and gas production, with gas and alloy protectionbeing especially prominent. In different regions, the protec-tion gas can be pure CO2 or Ar+CO2 or ternary, quaternarymulti-component gas. All these developments have includedautomation, high efficiency, environment protection, andlow cost.

Table 11. Environmental load assessment of production flow ofmineral substance.54)

Mineralsubstance Type Crushing Screening Granding Wet

cleaning

Totalinfluence

factor

MarbleDust 1(0.14) 1(0.12) 1(0.13) – 0.39

Processinfluence 0.14 0.12 0.13 – 0.39

FeldsparDust 1(0.14) 1(0.12) 1(0.13) – 0.39


FluoriteDust 1(0.14) 1(0.12) 1(0.13) – 0.39


MicaDust 4(0.24) 4(0.12) 4(0.13) 4(0.21) 2.80

Processinfluence 0.96 0.48 0.52 0.48 2.80

a Integer is influence amplitude, and value in bracket is correspondingweight coefficient. Environmental factor is influenced by influence ampli-tude multiplied by weight coefficient.

Table 12. Main normalized date of FCW steel strip and accesso-ries.55)

Item Steelbelt

Ferro-silicon

Ferro-manganese

Titaniumwhite

powder

Ironpowder

Mineralpowder

Consumptionof resources 0.96 0.01 0.01 0.02 0 0

Energyconsumption 0.80 0.02 0.04 0.03 0.08 0.03

Emission ofthree wastes 6.143 0.614 0.106 0.051 0.025 0.051

© 2014 ISIJ 1484


(2) Further research in welding metallurgy has controlledimpurities such as N, H, O, S and P. The values of P, N andH can be decreased, and the appropriate value of O can begot. The weld becomes deeply purified. By reducing the dif-fusible hydrogen content in weld metals and combiningmicrostructure and welding technology, crack resistance canbe improved. By oxide metallurgy, the solidification pro-cesses and phase transformations of weld metals can beaccurately controlled in arc welding, and finer AF can beobtained. The optimization of lower bainite (LB), lath mar-tensite (ML) and residual austenite further toughen the weld,to match higher strength steel.

(3) Through further research on welding slag, problemssuch as deoxidation can be controlled, and the oxygen con-tent in the arc weld can be reduced or controlled to meet thedemand of weld oxide metallurgy. Deoxidation in the acidslag system and overcoming the problem of poor weldingoperability in the basic slag system, have improved the tech-nology and cleanliness of arc welding consumables.

(4) It is a requirement of sustainable development toreduce the quantity of weld fume and its harm to welders.A new type of friendly-environment welding consumableswith lower fume and spatter and better operability perfor-mance should be developed. LCA evaluation of productionprocedure of welding consumables should be emphasized torealize eco-material, eco-process and eco-solution gradually.

(5) Figure 15 shows trend of the ratio of sales andresearch expenditure and expenditure of R&D per regularresearcher of general industries together with the Japaneseiron and steel industry.3) The insufficiency in R&D of weld-ing consumable can be found. So, more investment in R&Dof welding consumable is expected.

REFERENCES

1) S. K. Yin, X. J. Pei and X. Y. Qing: Weld. Join., 9 (2007), 26.2) B. G. Tang: Weld. Join., 12 (2009), 20.3) The Technical Society, The Iron and Steel Institute of Japan: ISIJ Int.,

50 (2010), 777.4) Z. X. Li: MW Met. Form., 14 (2010), 4.5) D. Q. Zhang: PhD dissertation, Tianjin University, Tianjin, China,

(2000).6) K. Ito and T. Hidaka: Kobe Steel Eng. Rep., 59 (2009), 98.7) S. S. Babu: Curr. Opin. Solid State Mater. Sci., 8 (2004), 267.8) Z. Z. Liu, Y. Kobayashi, F. X. Yin, M. Kuwabara and K. Nagai: ISIJ

Int., 47 (2007), 1781.9) S. P. Song, Z. X. Li and G. D. Li: China Mech. Eng., 21 (2010), 1752.

10) P. Yu: PhD dissertation, Xi’an Jiaotong University, Xi’an, China,(2005).

11) D. S. Sarma, A. V. Karasev and P. G. Jonsson: ISIJ Int., 49 (2009),1063.

12) L. Q. Xiong and H. W. Li: J. Iron Steel Res., 22 (2010), 53.13) T. K. Lee, H. J. Kim, B. Y. Kang and S. K. Hwang: ISIJ Int., 40

(2000), 1260.14) J. E. Ramirez: Weld. J., 87 (2008), 65s.15) S. H. Kim, C. Y. Kang and K. S. Bang: Mater. Sci., 36 (2001), 1197.16) S. D. Bhole, J. B. Nemade, L. Collins and C. Liu: J. Mater. Process.

Technol., 173 (2006), 92.17) M. H. Avazkonandeh-Gharavol, M. Haddad-Sabzevar and A. Haerian:

Mater. Des., 30 (2009), 1902.18) M. H. Avazkonandeh-Gharavol, M. Haddad-Sabzevar and A. Haerian:

J. Mater. Sci., 44 (2009), 186.19) B. Beidokhti, A. H. Koukabi and A. Dolati: Mater. Charact., 60

(2009), 225.20) B. Beidokhti, A. H. Koukabi and A. Dolati: J. Mater. Process. Technol.,

209 (2009), 4027.21) H. Terasaki, T. Yamada and Y. Komizo: ISIJ Int., 48 (2008), 1752.22) K. Kojima, T. Hasegawa, M. Minagawa, J. Octani and K. Ishida: Q.

J. JWS, 38 (2009), 138.23) T. Yamada, H. Terasaki and Y. Komizo: ISIJ Int., 49 (2009), 1059.24) S. Terashima and H. K. D. H. Bhadeshia: Sci. Technol. Weld. Join.,

11 (2006), 509.25) H. W. Lee, Y. H. Kim, S. H. Lee, S. K. Lee, K. H. Lee, J. U. Park

and J. H. Sung: J. Mech. Sci. Technol., 21 (2007), 771.26) M. Warren, J. Garrison and L. James: Mater. Sci. Eng. A, 403 (2005),

299.27) T. Koseki and G. Thewlis: Mater. Sci. Technol., 21 (2005), 867.28) O. Grong, L. Kolbeinsen, C. V. D. Eijk and G. Tranell: ISIJ Int., 46

(2006), 824.29) X. M. Guo, B. N. Qian and Y. Wang: Trans. China Weld. Inst., 28

(2007), 5.30) B. J. Kim, S. H. Uhm, C. H. Lee, J. B. Lee and Y. H. An: J. Eng.

Mate. Technol., 127 (2005), 204.31) X. M. Guo, B. N. Qian, Y. Zhang, J. L. Li and P. Zhu: Trans. China

Weld. Inst., 22 (2001), 27.32) T. Hidaka, K. Suenaga, Y. Okazaki and H. Ishida: Q. J. JWS, 27

(2009), 154s.33) M. Andersson, J. Appelberg, A. Tilliander, K. Nakajima, H. Shibata,

S. Kitamura, L. Jonsson and P. Jönsson: ISIJ Int., 46 (2006), 814.34) Z. W. Zhang, W. S. Li, Z. K. Xue and S. W. Bai: J. Tianjin Univ.,

43 (2010), 186.35) S. B. Xue, D. L. Ye, H. M. Hao and H. L. Wang: China Weld., 5

(1996), 22.36) S. L. Zeng, S. J. Chu, H. F. Yu and Z. L. Liang: Ferro-alloy, 6 (2009),

1.37) F. Yang: MW Met. Form., 19 (2010), 73.38) K. S. Bang, H. C. Jung and I. W. Han: Met. Mater. Int., 16 (2010),

489.39) I. H. Brown: Scr. Mater., 54 (2006), 489.40) B. Beidokhti, A. Dolati and A. H. Koukabi: Mater. Sci. Technol. A,

507 (2009), 167.41) T. Y. Jin, Z. Y. Liu and Y. F. Cheng: Int. J. Hydrogen Energ., 35

(2010), 8014.42) Z. Zhang, Y. K. Li, L. H. Peng, T. Liu and F. Q. Liu: MW Met. Form.,

14 (2010), 25.43) K. Ito, S. Nagaoka and T. Hashimoto: Kobe Steel Eng. Rep., 54

(2004), 15.44) K. Tamaki, K. Nakajima, H. Shibata, S. Kitamura, L. Jonsson and P.

Jönsson: Q. J. JWS, 20 (2002), 266.45) Z. Zhang, B. G. Chen and L. H. Jin: MW Met. Form., 6 (2009), 30.46) J. J. Chu, M. Chen and J. Liu: Weld. Join., 6 (2006), 46.47) X. B. Li: Master dissertation, Beijing University Technology,

Beijing, China, (2006).48) K. R. Carpenter, B. J. Monaghan and J. Norrish: ISIJ Int., 49 (2009),

416.49) K. R. Carpenter, B. J. Monaghan and J. Norrish: ISIJ Int., 48 (2008),

1570.50) Z. X. Li, J. M. Jiang, X. B. Li and W. Jiang: Electr. Weld. Mach., 35

(2005), 6.51) F. Saenger: Svetsaren, 58 (2003), 18.52) N. T. Jenkins, W. M. G. Pierce and T. W. Eagar: Weld. J., 84 (2005),

156s.53) J. H. Dennis, P. J. Hewwitt, C. A. J. Redding and A. D. Workman:

Ann. Occup. Hyg., 45 (2001), 105.54) Z. Z. Wang, J. M. Jiang, H. W. He, X. B. Li and Y. Jiang: Electr.

Weld. Mach., 35 (2005), 69.55) Z. H. Wang, Q. Li, J. M. Jiang, D. Y. He and Z. X. Li: J. Beijing

Univ. Technol., 33 (2007), 1212.

Fig. 15. Trend of the ratio of sales and research expenditure andexpenditure of R&D per regular researcher.3)

review global progress on welding consumables for hsla steel

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