Heat Treatment Lab Report

0

Heat Treatment Lab

by Karl Andersen Carl Behlmer Andrew Block Jacob Carlson

University of Wisconsin-Stout MFGT150 – 006 Introduction to Engineering Materials October 27, 2014

1

ABSTRACT The purpose of this lab was to determine how different types of heat treating would affect a metal. The various steel samples were water quenched, oil quenched, and air cooled, along with certain steels being tempered and requenched. Each team had three different types of metal (1020, 1045, and 4140 Steel) that would be heated to 1550 F. Then each team applied the heat treating process that they were assigned. For the teams that had to temper their steel, the steel samples would then be placed back into an 800 F furnace. We found out that the water quench and temper heat treatment process was the best and increased the hardness of the steel the most.

2

Table of Contents ABSTRACT....................................................................................................................................1 INTRODUCTION...........................................................................................................................3 OBJECTIVES..................................................................................................................................3 BACKGROUND RESEARCH.......................................................................................................3 Definition of Terms, Symbols, Abbreviations, and Acronyms....................................................4 MATERIALS...................................................................................................................................4 PROCEDURE..................................................................................................................................5 Material Selection and Description.............................................................................................6 Methods.......................................................................................................................................6 Assumptions................................................................................................................................7 Procedures....................................................................................................................................7 Summary......................................................................................................................................8 RESULTS........................................................................................................................................8 Item Analysis...............................................................................................................................8 CONCLUSION................................................................................................................................9 APPENDIX....................................................................................................................................10 REFERENCES AND BIBLIOGRAPHY......................................................................................11

3

INTRODUCTION This lab involves the process of heat treating three different kinds of steel and performing various different cooling methods on these steel samples. The purpose of this lab is to see how said cooling methods will affect the hardness of our heat-treated steel samples. With this information, we will learn how to apply heat treatment to materials that we will potentially use when designing parts, and what cooling methods will provide the hardest material. OBJECTIVES This lab will primarily help us better understand the concept and application of heat treatment as well as cooling methods used after heat treatment. As future engineers that will be dealing with many different kinds of metal, we will need to know whether or not a certain material is suited for its intended purpose, as well as how to increase the hardness of said material provided its hardness is not sufficient. By actively heating three different kinds of steel and cooling them in various different ways, we will know which cooling method provides the hardest heat-treated steel. Through this experiment we will also be able to see which cooling method is the easiest and most efficient to apply to a heat-treated steel. BACKGROUND RESEARCH In our previous labs we have worked with hardness by using the Brinell and Rockwell testers. However, this lab has a twist to it; we quench the hot metal in different liquids which affects the hardness. So even though we have tested these specimens in our previous labs it doesn’t matter because after we heat these metals and cool them down at different rates they change completely. Knowledge from our previous labs will allow us to make assumptions for how the metals’ hardness will compare. Also, Chapter 11, Section 8 of our textbook discusses heat treatment of

4 steel, especially how steel is ‘hardenable’ through the formation of martensite as a result of a given heat treatment. Definitions and Terms Hardness- The quality or condition of an object being hard. Resistance to being scratched/deformed. Brinell hardness- testing the hardness using the Brinell hardness tester Rockwell hardness- hardness of a specimen using the Rockwell testing machine Quench- to rapidly cool specimen in a liquid Heat treated- heating a material to change hardness Tempering- increasing strength of a material by introducing an appropriate heat treatment Annealing- generic term to denote a heat treatment within the microstructure MATERIALS 

8 1020 Steel Samples



8 1045 Steel Samples



8 4140 Steel Samples



Heating Oven



Tempering Oven



Industrial Tongs



Digital Rockwell Hardness Tester



Brinell Hardness Tester



Millimeter Microscope



Face Shields



Industrial Oven Mitts

5 

Bucket of Water



Oil Tank

PROCEDURE The purpose of this experiment was to evaluate how heat treatment and cooling methods affect the hardness of a steel sample, as well as seeing how a higher carbon content and alloy presence will affect the hardness after heat treatment. In order to accomplish this, we measured the hardness of three different steel samples (one with low carbon content, one with medium carbon content, and one with a high carbon content as well as chrome alloy), using different cooling methods as well as tempering in order to see how this would affect the hardness. Obtain eight samples of three different steels, 1020 Steel, 1045 Steel, and 4140 Steel. For one set of steel samples, perform a Rockwell and Brinell Hardness Test for each different type of steel without performing any heat treatment. Measure the indentation created by the Brinell machine and convert this length to a Brinell hardness number. Record the hardness values obtained from these tests and make sure to label scale for the Rockwell test. Heat the seven sets of steel samples in a furnace which is set to a hardening temperature of 1550 degrees Fahrenheit. Set a second furnace to a tempering temperature of 800 degrees Fahrenheit. After the steel samples have been heated so that they are the same color as the oven, remove one set of the steel samples (1 of each steel) and allow it to air cool. For the next two sets of steel samples, cool them in oil, wipe them clean, and place them in the tempering oven for half an hour. Do the same for the following two sets of steel samples, except cool them in water rather than oil, followed by being placed in the tempering oven. After 30 minutes have passed, remove these samples from the tempering oven and cool them in their respective cooling method, either oil or water,

6 depending on how they were previously cooled. For the last two sets of steel still in the heating furnace, cool one of the sets in water and one of the sets in oil. Do not place them in the tempering furnace. After all seven sets of steel have been cooled, perform Rockwell and Brinell hardness tests for all 21 steel samples, again making sure to record scale for the Rockwell test. Material Selection and Description For this lab we were dealing with only three different kinds of steel, 1020 Steel, 1045 Steel, and 4140 Steel. 1020 is a simple carbon steel with the lowest carbon content of all of the steels we used. 1045 Steel is also a simple carbon steel, although it has a much higher carbon content that 1020 Steel. 4140 Steel is a complex carbon steel with a high carbon content. The reason we used such varying steels is to see how carbon content would affect the hardness before and after heat treatment. Our cooling methods were air cooling, water cooling, and oil cooling. We did this to see how cooling methods would affect the steel’s hardness following the heat treatment.

Methods We used Rockwell and Brinell tests to measure the hardness of our steel samples following the heat treatment and cooling. The Rockwell test is ASTM E18, while the Brinell test is ASTM E10. These tests, especially the Rockwell test, are very accurate as much of the operation is digital. The Brinell test is markedly less accurate due to the fact that the indentation must be measured using a device which can yield human error. This could lead to a Brinell Hardness number which is slightly off from what the Rockwell test would indicate.

7

Assumptions Before performing this experiment, we assumed that the 4140 Steel would have the highest hardness, followed by 1045 Steel, followed by 1020 Steel. The reason for this is that in our previous experiments, we found that steel with a higher carbon content would have a higher hardness, especially if it was a complex carbon steel in the case of 4140 Steel. Likewise, due to our lessons in Intro to Engineering Materials, we assumed that the air cooled samples would cool the slowest, followed by oil, followed by water.

Procedures After measuring the Brinell Hardness numbers for our three steel samples after heat treatment, we converted this number to a Rockwell Hardness number using a conversion chart. We converted our Brinell Hardness number to tensile strength by multiplying our Brinell Hardness number by 3.45. In order to cool our samples more quickly when cooling in water, we moved the samples in a figure-eight pattern using tongs. For the oil cooled samples, we moved the samples up and down using a tray similar to a French Fry frying device. The air cooled samples were placed on a brick that would help absorb heat more quickly. Summary This experiment was performed in order to analyze how heat treatment and cooling methods would affect the hardness of three different steel samples of varying carbon content. The experiment was performed near identically to the process described above, save for the fact

8 that we divided the workload between eight different groups, with our group performing the water cooled sample test (no tempering). RESULTS Our group’s conclusion was that the water quenched steel that was tempered created the hardest steel, making it the best heat treating process. However, sometimes there is an application for steel that does not need the hardest possible metal. If we would just heat the metal to 1550F and water quenched it without tempering it, it would save time and money and it would still give you a quality product. In addition to the Rockwell hardness testing we could also give it a stress rest to see if the heat treating significantly enhances the strength of the metal Item Analysis Lab Questions Answer the questions below using the information from all groups that you compiled in Table 3 above. Q.1 Examine the heat treated specimens; do any of them have visible surface cracks? If yes, then what could be the cause of cracks? Our samples did not seem that they had any cracks. However, the creaks could be from dropping the sample into the bucket of water too hard. Q.2 Compared to untreated samples, what effect does oil quenching have on hardness of (a) 1020 Steel, (b) 1045 Steel, and (c) 4140 alloy steel? According to our data the oil quenching gave the 1020 and 1045 steel a harder reading but for the 4140 metal the hardness was greater when air cooled. Q.3 Compared to untreated samples, what effect does water quenching have on hardness of (a) 1020 Steel, (b) 1045 Steel, (c) 4140 alloy steel? According to our data the oil quenching gave the 1020 and 1045 steel a harder reading but for the 4140 metal the hardness was greater when air cooled. Q.4 For a specific type of steel, do you see a difference in hardness of water quenched and oil quenched samples? If you see a difference, can you think of reasons that cause the difference in the hardness?

9 There is a difference between the WQ and the OQ, the reasoning behind this is the oil will cause the metal to cool at a slower rate the then water. Q.5 Compared to quenched samples, what effect does tempering have on hardness for (a) 1020 Steel, (b) 1045 Steel, (c) 4140 alloy steel? The short period of time that the metal was in the tempering oven the hardness increased with all of the metals. Q.6 Compared to untreated samples, what effect does air cooling have on hardness for (a) 1020 Steel, (b) 1045 Steel, (c) 4140 alloy steel? The metal was not as hard when the sample was air cooled. Q.7 How do hardness values of 1020 Steel and 1045 Steel compare to each other before heat treatment? For the 1020 steel the hardness decreased then heated to 1550F. then air cooled. For the 1045 steel the hardness increased after heating. Q.8 How do the hardness values of 1020 Steel and 1045 Steel compare to each other after water quenching? The water quenching made the steel increase for both of the metals. Q.9 What are some possible sources of error in this lab? If the metal is dropped too hard in the bucket of water it could cause cracking. Cracking could potentially affect the hardness. For the Brinell hardness test, if the indentation is not measured correctly, the Brinell hardness number would not be accurate. Also, if all of the carbon is not removed it could cause some error. CONCLUSION The purpose of this experiment was to find which cooling method would provide the hardest heat-treated steel. By cooling eight different sets of three kinds of steel using various cooling methods, we found that heat-treated steel was hardest when it was cooled in water, tempered, and cooled in water again. This agrees with what we have learned previous to this lab, as water cools the steel samples the quickest of all of the tested cooling methods. The faster the sample is cooled, the harder it will be. By tempering the steel after cooling it, we were providing another form of heat treatment to the sample which made it even harder. Likewise, our

10 assumptions were largely correct; 4140 Steel was the hardest steel before and after heat treatment. APPENDIX

11

Test Material

Hardness before treatment

Heat Treatment Applied

Rockwell (C)

1020 Steel 1045 Steel 4140 Steel

59.1 57.8 63.0

WQ WQ WQ

Reading 1 33.2 56.6 60.1

Reading 2 33.9 54.2 60.7

Reading 3 34.3 55.3 64.0

Average 33.8 55.4 61.6

Test Material

Hardness Before Treatment 207 229 277

Heat treatment applied WQ WQ WQ

Diameter of Indentation 3.4 mm 2.7 mm 2.2 mm

Brinell Hardness Number 321 514 745

Tensile Strength, MPa 1107.45 1773.3 2570.25

Rockwell Hardness and scale 34.3 C 52.1 C 65.3 C

1020 Steel 1045 4140 Steel

REFERENCES AND BIBLIOGRAPHY Callister, William D., Jr. "Section 11.8." Manufacturing Science and Engineering: An Introduction. 7th ed. N.p.: Wiley, n.d. 390-401. Print.