Effects of Tempering AISI 4140 Steel in Double-

Angle Connections

A Major Qualifying Project Submitted to

the Faculty of Worcester Polytechnic Institute in partial fulfillment of the requirements for the

Degree in Bachelor of Science in Civil Engineering

______________________________________

Kelly Soto

Note: This project is part of a much broader researcher in which two goals were involved throughout the process. The first goal is to investigate the effects of single versus double tempering on the mechanical properties and microstructure of 4140 steel described on the “Metallurgical Investigation of the Effects of Double Tempering on the Hardness, Impact Toughness and Microstructure of AISI 4140 Steel”. The second goal of this project is to incorporate the given results from single and double tempering in the design of a double-angle connections in frame structure to be further develop in this paper.

Date: 4/26/18

Project Advisors:

__________________________________ Professor Leonard D. Albano

1. Introduction

Steel in construction can be utilized in different ways such as building frames, suspension

cables, bridge deck plates, security fencing, and reinforced concrete. Most of the infrastructures

created today are mainly built of concrete and steel. Due to a better reaction of compressive forces

present in concrete, the reinforcement of steel bars embedded in concrete provide a tensile

contrasting force. This combination makes a building able to withstand higher loads and also other

environmental external forces.

Based on AISC standards, new constructions require reinforced steel bars to be more

ductile. This mechanical property shows a crucial turning point when constructing anti-seismic

structures. So far in industry there are two types of steels; hot rolled and heat-treated steels. Heat-

treated steel has been used since 1990, due to its lower cost production cost compared to that of

hot-rolled steel. By making the steel undergo heat treatment, it improves the strength of the steel

which is a very desired material property during construction. Yet, with such an advantage, heat-

treating steel might show some disadvantages such as the loss of some ductility, a non-uniform

part/structure, or even the failure of passing certain flexural strength tests, in some cases.

However, further heat-treating processes can fix the undesirable outcomes of other heating

methods. For example, if a part after heat treatment does not cool evenly, and the part is rendered

non-uniform, this can be fixed by a heat treatment process called annealing, where the part is held

in a furnace of suitable temperature, then furnace cooled into a part suitable for machining.

Tempering also contributes to the acquisition of the desired mechanical properties, and the

temperature at which the tempering is performed is directly related to the outcome in terms of

mechanical properties.

Based on the beneficial effects of tempering after other heat treatment procedures, a design

of a steel frame structure will be proposed using tempered steel. Within this building frame,

components such as beams, girders, columns and angles connections will be design. Furthermore,

design requirements such as occupancy and purpose of the building will be taken into account

throughout the process. All these regulations will comply with the capstone design needed for the

completion of this project.

Along with satisfying building and design requirements, professional ethical practices will

be taken into consideration. Specifically, for the revision of the structure design, Canons 1 and 6

from American Society of Civil Engineers (ASCE) will be followed. These applicable canons are

described as the following:

Canon 1: Engineers shall recognize that the lives, safety, health and welfare of the general

public are dependent upon engineering judgments, decisions and practices incorporated

into structures, machines, products, processes and devices.

• This cannon will ensure good practice of the implementation of heat-treated 4140

Steel. Safety factors will be revised and adapted to comply with canon1 as well.

Canon 6: Engineers shall be scrupulously honest in their control and spending of monies,

and promote effective use of resources through open, honest and impartial service with

fidelity to the public, employers, associates and clients.

• Canon 6 will allow a better judgement of the money spend on the project. This way

no extra expenditures that will result in exceeding the stablished budget will be

allowed.

By following these two canons, engineering calculations and spending will be well

structured. Furthermore, it will set boundaries or reasonable limits by which certain decisions can

be made.

For constructability practices, standard sizes used in the construction industry of W-shape

beams, girders and columns will be maintained. Also, traditional sizes for double angle

connections will be kept. No required additional machining or manufacturable processes would

have to be essential or mandatory for the construction. Thus only, external heat-treatment

procedure would be taken under consideration.

2. Methodology

For the purpose of this project, a design and analysis of the WPI Park Ave Parking garage/

athletic field will be conducted. This design procedure will involve comparing the effects between

the un-tempered and tempered steel connections.

Factors taken into account for comparison are economical, ethical, structural/safety, and

constructability. The required structural calculations corresponding to the beams, girders, columns

and double angle connections within the structure will be carried out. Also, the necessary safety

factors, which can withstand all the loads, will be found. In this section, the AISC building code

will be used as a reference. In the economical aspect, a budget plan will be created, in order to

evaluate the costs of the materials involved in the project. This budget study will be mainly focused

on the incorporation of heat treatment on the desired improved member. In compliance with the

previous assessments, the practice as a civil engineer in performing this project would be

evaluated. As a guide, this part of the project will refer to the ASCE Code of Ethics. Once obtained

the given cost and structural analysis, the manufacturability will be determined following the

required dimensions of heat treated steel employ in the construction of the Parking Garage.

Furthermore, it would be discussed how the adaptation of this resource can potentially be used as

a more sustainable material.

Therefore, in order to accomplish the design comprehension of tempered 4140 Steel in

double angle connections, the following objectives have been established:

• Obtain heat treated steel data regarding surface hardness, impact toughness and

microstructure.

• Create a design of beams, columns, girders and double angle connections of frame

structure.

• Asses and compare connection designs based on structural, economical, ethical,

manufacturability and sustainability factors.

• Provide further suggestion for the implementation of heat-treated steel in construction.

2.1. Obtain 4140 Steel heat treated data

Tested results will be gathered from single and double tempered analysis. Based on the

results from tempered research, a tempering method would be chosen. The most effective tempered

cycle will be considered under study for design purposes. Furthermore, this previous research will

be integrated in order to accommodate required building analysis design.

The Hardness test, Charpy V-notch test, and SEM microstructure will be revised and

evaluated. These three different types of tests will be explored due to their relevance and relation

to physical properties for building design.

2.2. Create a design of steel components within frame structure

An understanding of loads associated with occupancy, external seasonal factors and other

materials will be taken under consideration. The governing combination load would be determined

in order to size the beams, girders and columns. The 2016 AISC Specification for Structural Steel

will be used to determine the size of each of these building components.

For the design of double angle connections, the capacity at each angle would be identified.

This would determine if the connecting member would be able to withstand all the transferred

load. Also, it would contribute to the number of bolts used in the connection. Based on the required

bolt spacing and the number of bolts, the plate length and height would be determined. The

connection will be check under the following conditions: bolt bearing and tear-out, angle shear

rupture, and angle shear yield. The governing thickness will then be specified.

All the calculations involved in the design of beams, girders, columns and double angle

connections, would be performed under the same principles using 4140 Steel. With the previous

incorporated data and the iterative method in finding these steel frame components, an

approximation of the design behavior of 4140 Steel would be conducted.

2.3. Assess and compare double angle connections

Based on the design requirements, structural, economical, ethical and manufactural

modules will undergo study. The main comparison will be focused on the different types of steel

used for double-angle connections.

For the structural comparison, it will be taken into account the required thickness. This

governing factor will be determined by previously described limiting states. Double-angle

connections will be design for the same required capacity and same region within the building

frame. When studying the economic effects, the cost of steel components like beams, columns and

girders will remain the same. The varying cost of the double-angle connections would depend on

the time and type of cycle used for the tempering purpose. For the intension of this study, a single

temper for four hours will be considered. Additionally, a manufactural approach will be reviewed

in order to find out the integration efficiency in the world on construction.

3. Experimental Results

For the purpose of this chapter the results of hardness, impact toughness and microstructure

will be revisited. Each test result was recorded for single and double tempering cycles for the

purpose of the previous research. Based on the results of indicating no significant difference

between both methods, this chapter will focus on the impact of single tempering.

3.1 Hardness

Hardness testing was completed in order to observe the impact of different tempering

temperatures on the material. As observed in the table below hardness will decrease as the

temperature increases for the set amount of time. Hardness is usually associated with ductility,

based on its definition of resisting localized plastic deformation. Thus, a decrease in hardness will

indicate a more ductile transition in the material properties.

Temperature & Time

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average

300 C 4hrs 51.04 50.92 51.16 51.62 51.28 51.204 400 C 4hrs 44.2 43.62 45.24 43.28 43.5 43.968 500 C 4hrs 38.64 37.98 37.46 37.58 38.4 38.012 600 C 4hrs

31.9

32.68

32.52

32.82

31.44

32.272

3.2 Impact Energy and Impact Toughness

A Charpy V-Notch test was carried out in order to experimentally determine how much

energy would be needed to fracture a sample. This test can correlate to the fracture toughness of

the material, since both are based on the same principle. As can be appreciated from the graph

below, as tempering temperature increases more energy is needed in order to break the sample.

Thus, this would also indicate an increase in the fracture toughness of the material.

Figure 1: Impact energy vs Time (of single and double tempering methods)

In order to find the relation between the results from the impact energy testing and the

fracture toughness of the material, a yield strength versus temperature graph was obtained from

previous tempering testing. The graph shown below depicts the previously mentioned relation. It

also shows how the yield strength of the material decreases as the tempering temperature increases

Figure 2: Yield Strength vs Time

Once yield strength and impact energy were obtained, the Rolfe-Novak-Barsom correlation

was used to combined both data sets and numerically determine the fracture toughness at each

tempering temperature. The Rolfe-Novak-Barsom relation can be expressed mathematically with

the following equation:

{K𝐼𝐶y } = 5 ∗ {𝐶𝑉𝑁

y − .05}

In which y is the yield strength in ksi, CVN is the Charpy impact energy in ft-lbs, and

KIC is the fracture toughness in ksiin .

The fracture toughness was obtained and graphed to observe the trend due to tempering. It

is possible to notice that for lower tempering temperatures, the fracture toughness does not have a

significant change. Also, a small deviation can be seen between the 450 C and 500 C temperatures;

this abnormality is due to the temper embrittlement region. Later in the graph a significant increase

in the fracture toughness of the material can be appreciated. This relation is important for the

design purpose, in which the ultimate strength of the material in necessary and essential to satisfy

some required load-capacity conditions.

Figure 3: Fracture Toughness vs Temperature

3.3 SEM Microstructure

As an additional check point, the microstructure of the tempered steel was taken under

consideration. The following set of pictures were taken using a scanning electron microscope,

which allowed the view of the different phases within the structure. It is possible to observe the

increase in size of carbides from low to high temperatures. In the picture, the carbides are

represented by the white specks. This transition also agrees with the change in mechanical

properties. Thus, the 4140 Steel becomes more ductile as temperature increases.

Figure 4: Scan Electron Microscopy at X1500 resolution

4. Design Results

The existing precast Park Ave parking garage/athletic field was taken as a main model for

the design investigation. Floor plans were obtained from the Facilities Department at WPI. Beam-

girder sections were resized in order to accommodate and create a more symmetric layout. This

process facilitated a more standard size for beams and girders. The new equivalent structure, had

no major changes, due to the fact of its serviceability purpose as a parking garage on the main

level.

Existing Size (ft)

Redesigned Size (ft)

Number of Members

Beam 61.33 61 30

58 56 180 57 57 30

Girder 43 42 12 36 36 60 42 42 12

Column not given 15 96

Beams, girders and columns were sized based on occupancy and weight capacity of the

building. Each beam, girder and column were sized using AISC Specifications for Structural Steel.

For constructability purposes the larger beam was picked in certain areas of the building.

Also, the required shear capacities at each connection were determined in order to facilitate the

design of double-angle connections.

Beam Span connection capacity (kips)

W30X132 61' 100.91 W30X132 56' 92.64 W30X132 57' 94.29 W30X116 61' 86.6 W30X116 56' 79.5 W30X116 57' 80.92

For the design of each double-angle connection, the following limit states were taken into

account: bolt bearing and tear-out, angle shear rupture, and angle shear yield. Each of these

conditions was a necessary consideration to determine the required thickness of the angle

connections. The table below summarizes the required thickness found under each limit state.

Furthermore, it is possible to observe a decrease in thickness due to the change in material used

for the double-angle connection.

Girder Span

connection capacity (kips)

Exterior girder W30X173 42' 100.91 W33X291 42' 201.81 Exterior girder W30X148 36' 86.6 W30X235 36' 173.19

Beam – Girder connection 1

Steel Type of

Connection Beam Span

Required Capacity (kips)

Shear Rupture (in)

Gross Shear Yield (in)

Bolt Bearing and Tear-out (in)

A36 W30X132 61' 100.910 0.201 0.334 0.773 W30X173 42' Tempered 4140

W30X132 61' 100.910 0.080 0.095 0.306 W30X173 42' Beam – Girder connection 2

Steel Type of

Connection Beam Span

Required Capacity (kips)

Shear Rupture (in)

Gross Shear Yield (in)

Bolt Bearing and Tear-out (in)

A36 W30X132 61' 193.550 0.184 0.153 0.709 W33X291 42' Tempered 4140

W30X132 61' 193.550 0.080 0.095 0.306 W33X291 42'

Girder – Column connection 1

Steel Type of

Connection Beam Span

Required Capacity (kips)

Shear Rupture (in)

Gross Shear Yield (in)

Bolt Bearing and Tear-out (in)

A36 W30X173 42’ 151.365 .301 0.250 1.159 W14X74 15’ Tempered 4140

W30X173 42’ 151.365 0.119 0.072 0.461 W14X74 15’

Girder – Column connection 2

Steel Type of

Connection Beam Span

Required Capacity (kips)

Shear Rupture (in)

Gross Shear Yield (in)

Bolt Bearing and Tear-out (in)

A36 W30X173 61' 281.265 .259 0.215 .995 W14X132 42' Tempered 4140

W30X173 61' 281.265 0.119 0.072 0..461 W14X132 42'

In order to determine the cost per square foot, the floor plan was divided into 6 main

sections. Each section contains a different beam-girder combination used throughout the design of

the frame. It is possible to observe that for these sections the price found was consistent with the

amount of steel used in the construction. An average of 51 dollars per square foot would be

required in order to create the main structure of the building.

Member Member Weight Span Number of

Members Weight of Members

W30X132 132 61 10 80520 132 56 90 665280 132 57 10 75240

W30X116 116 61 25 176900 116 56 225 1461600 116 57 25 165300

W33X291 291 42 24 293328 W30X235 235 36 60 507600

Total

Weight 3425768 Weight/

Area 20.862 Price/(ft^2) 51.113

Another price calculation was made, in order to find out how much more money would be

spent if heat-treatment of double-angle connections were required. As observed in the table below,

an additional 26, 880.00 dollars would be spent if the metallurgical process were part of the

construction necessity. This drastic price difference will be the turning point on whether or not,

processes like tempering would be desirable. Furthermore, the price given in the table is aside of

the regular cost of purchasing un-tempered double-angle connections.

Number of

Double-Angle

Connections

Price/unit Total Price

with Heat Treatment

840 32 $ 26,880.00

Not Heat-Treated

840 N/A 0

5. Conclusions

Based on the testing results and the design applications of tempered 4140 Steel, it can be

concluded that there exists a potential field development in construction as well as design.

Compared to the current usage of A36 Structural Steel, tempered 4140 Steel was able to withhold

greater loads. Due to the increase in fracture toughness, the design of double-angle connections

required a smaller thickness and thus less material. Yet, the cost of heat-treating a large number of

double-angle connections, could possibly exceed the planed budget stablished at the beginning of

the project.

Further research can involve exploring the effects of increases in tempering temperatures

and increases in tempering times and expanding on tensile testing. Another direction that could

possibly be taken is the tempering of bolts in order to study the effect on the dimensions of the

double-angle connection.

6. References

[1] Code of Ethics. (n.d.). Retrieved from https://www.asce.org/code-of-ethics/

[2] Structural Steel Shapes and Plates. (July 06). Retrieved from

http://www.civilengineeringx.com/construction/heat-treated-constructional-alloy-steels/

[3] Chang, S., Chen, M., & Lin, J. (2015, August 26). Study of Heat-Treated Steel and Related

Applications [PDF]. Taoyuan City, Taiwan: American Journal of Engineering and Applied

Sciences. Retrieved from http://thescipub.com/PDF/ajeassp.2015.611.619.pdf

[4] The Iron Carbon Phase Diagram. (n.d.). Retrieved from https://www.tf.uni-

kiel.de/matwis/amat/iss/kap_6/illustr/s6_1_2.html

[5] State Board of Building Regulations and Standards [PDF]. (n.d.). Retrieved from http://www.mass.gov/eopss/docs/dps/inf/780-cmr-53-01-24wind-and5snow-tables-8-8-08-correction.pdf [6] PCI Design Handbook - interaction curves, load tables, and section properties. (n.d.). Retrieved from https://www.pci.org/PCI/Resources/Guides_and_Manuals/Design_Tables_and_Charts/PCI/Design_Resources/Guides_and_Manuals/Design_Tables_Charts.aspx?hkey=620e1421-c5bb-4f7a-8129-1138dfc38ea4. [7] Minimum Design Loads for Buildings and Other Structures [PDF]. (n.d.). Reston, Virginia: American Society of Civil Engineers. Retrieved from https://law.resource.org/pub/us/cfr/ibr/003/asce.7.2002.pdf [8] WSDOT Highway Construction Costs[PDF]. (n.d.). WSDOT. Retrieved from https://www.wsdot.wa.gov/NR/rdonlyres/A8EE6CB0-46F6-4EE8-95A3-62E9B793F31C/0/CostIndexData.pdf

Appendix