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Abstract

This laboratory experiment dealt with the topic of heat treatment of metals. During the two week laboratory experiment, several samples were measured for their hardness, heated, quenched and then measured again. The experiment used water, air and oil to quench the metals that were heated to different temperatures. After the samples were quenched their hardness was once again measured. They were heated for a final time and remeasures.

Introduction

Heat treatment is a controlled process used to alter the micro structure of materials such as metals and alloys to impart properties which benefit the working life of a component, for example increased surface hardness, temperature resistance, ductility and strength. The heat treatment used in this experiment was quenching. Quenching is the cooling of a metal at a rapid rate. Non-ferrous alloys will become softer as a result of quenching, while ferrous alloys will be come much harder. Steel and cast iron are the two metals that are most commonly used in the quenching process. To harden a material, the sample must be heated above the critical temperature, and then quickly cooled. The surface of the material will cool more rapidly than the core, thus leading too a harder outside surface. After the metal is cooled, the austenite will transform into martensite. Martensite is a hard crystalline structure that is also brittle.

Although a highly effective method of hardening of a material, if steel is quenched too quickly, it can lead to cracking and fractures in the structure. Materials such as copper and aluminum will soften as they are quenched, but the quenching process for these materials renders them corrosion resistant.

Procedure

This laboratory experiment was performed in two parts. The first week a lesson on heat treatment was given on a power point. The power point showed the different charts for heat treatment of different metal samples and their different phases. Hardness was also discussed on the slide. After the presentation was finished, a Rockwell hardness machine was demonstrated and then used to determine the hardness of the samples to be heated. After all the values of hardness were obtained, the samples were set into a furnace and heated to different critical temperatures. In this first week all the samples were quenched in only water, and heated only once. After the quenching in water, the samples were then reevaluated for their hardness. The data was then recorded.

The second week of this experiment used a total of five samples. Three of the samples were quenched in water, one was quenched in air, and the last was quenched in oil. The samples that were quenched in water were also reheated to critical temperatures. The samples were all once again tested for their hardness values on the hardness tester. The five samples were placed in the oven and taken out to quench in their designated medium. After the oil quenched and air quenched samples were properly cooled and ready to handle, they were retested to determine the new hardness that the quenching process has given them. The same process was repeated for the water quenched samples, and after the hardness was reevaluated, they were once again put in the oven. After ample time to reach the desired temperatures, they were cooled in water. They were placed on the hardness machine to find the value of hardness.

Discussion

This laboratory experiment showed the complete process of the heat treatment by quenching. The fist week consisted of quenching only by water. The samples were measured to determine their initial hardness. The samples were then heated to three different temperatures, and were quenched in water. After the quenching the hardness was measured again to be reevaluated. The samples had developed martensite on the outer surface as a result of the heat treatment.

The second week consisted of using different mediums to quench the samples. They were again heated to different temperatures. The first sample was quenched in water. After the measurement of the hardness was taken, the sample was reheated. The second sample was quenched in oil, and then reheated. The last was quenched in air and also re measured. The samples that were quenched in water were reheated to different critical temperatures to determine the hardness.

This laboratory experiment also showed how to used a hardness machine to test a materials hardness. This skill is very important in the manufacturing and engineering industry . It is imperative to know the materials properties that are being used before it is used in production of a product. If the material does not have the desired properties that it was intended to have, the part o product that it is used in could fail.

Conclusion

In conclusion this was a successful experiment. The laboratory experiment demonstrated all the proper techniques of quenching in heat treatment. The experiment showed how materials can be strengthened to perform better and to withstand more pressures and perform better in the tasks they were intended to do. It is important to know how a metal will behave in the quenching process to obtain the properties that were intended. The phase chart is extremely useful in the manufacturing of materials and preparing them for everyday uses.

The techniques learned in this laboratory experiment will follow throughout the different aspects of manufacturing and engineering. Knowing how a material will behave in its intended purpose is essential to properly manufacture different products whether it be metal for engines, buildings or machines, they all need to properly work as they were intended.

Questions

Explain why the specimens of steel 1045, after being heated to 700o C and 960o C and then quenched from that temperature, have different hardness.

Because the surface of the material will cool faster, making the core still hotter and the hardness is not uniform throughout.

Explain why the specimens of steel 1025 and 1060, after being heated to 960o C and then quenched from that temperature, have different harnesses. Indicate the differences in the micro-structure of these steels after quenching.

They have different harnesses because of the different compositions of metals.

Is it possible to get the structure shown below by water quenching from an austenite state?

Yes

If the hardness of two metals were known, one by a Brinell number and the other by a Rockwell number, would converting one to the other system give a valid comparison of the hardness of the two metals?

Yes.

What is the average hardness of a pearlite structure?

240 Brinell

Is cementite harder than pearlite? If your answer is negative, give an explanation.

No, because of the strong adherence at the boundary between cementite and ferrite.

Is it true that the structure of hardened steel depends on the steel composition and hardening conditions? Yes

What does the casehardening process mean?

Define the following heat treatment processes:

a) normalizing; heat treatment process for making material softer but does not produce the uniform material properties of annealing

b) full annealing; results in the second most ductile state a metal can assume for metal

c) process annealing. is a heat treatment cycle that restores some of the ductility to a product during the process of cold working

What is martensite?

a hard and very brittle solid solution of carbon in iron that is the main constituent of hardened steel.

What is the purpose of tempering?

Tempering reduces the hardness in the martensite by transforming it into various forms of tempered martensite.

Table of Contents

Abstract............................................................................................................................1

Introduction.....................................................................................................................2

Procedure.........................................................................................................................3

Data.................................................................................................................................4

Discussion.......................................................................................................................5

Conclusion......................................................................................................................6

Questions …...................................................................................................................7