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What is the purpose of quenching and tempering steel

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Reference no: EM131023481

EXPERIMENT 1: HEAT TREATMENT OF STEEL

Purpose

The purposes of this experiment are to:

- Investigate the processes of heat treating of steel
- Study hardness testing and its limits
- Examine microstructures of steel in relation to hardness

Procedure

You are provided with 6 specimens of SAE 1045 steel for your study. Measure the hardness of all specimens using the RA scale.

1. Heat four specimens in one furnace at 1600 ± 25ºF (870 ± 15ºC) for 1/2 hour.

2. Put the other 2 specimens in a separate furnace at the same temperature for 1/2 hour.

3. Remove one specimen from the furnace with 2 specimens and cool it in air on a brick.

4. Turn off the furnace with the one remaining specimen. Allow the sample to remain in the furnace for one hour. The air-cooled and furnace-cooled specimens can be cooled in water after one hour. Why? (Answer this in your write up).

5. Remove the four specimens and quickly drop them into water; the transfer should take less than one second. A little rehearsal could help.

Be careful not to touch the specimens before they are cooled in water.

6. Measure Rockwell hardness of the quenched specimens before the next step.

7. Temper 1 each of the quenched specimens for 30 minutes at 600ºF (315ºC), 800ºF (430ºC), and 1000ºF (540ºC). After tempering, the specimens can be cooled in water.

8. Measure hardness of all 6 samples using the Brinell (3000 kg) and Rockwell A or C scales.

Data Analysis

1. If more than one impression is made per sample, average the Brinell diameters for each specimen.

2. Compute the Brinell hardness numbers and compare with the numbers read from a conversion chart for Rockwell A or C to Brinell.

3. Graph BHN (x-axis) versus Rockwell Hardness numbers (y-axis).

4. Graph Rockwell A or C hardness vs. tempering temperature (oC).

5. Compute the ultimate tensile strength (psi) of all specimens from the average BHN for each specimen using:

σult= 500 x B.H.N.

Write Up

Prepare a single memo report in conjunction with experiment #2 (Hardenability of Steels). The report should combine both experiments in one report. Do not write this up as a two part report. (The hardness and hardenability concepts from the experiments are related). Within this report you should discuss the data referenced in the "Data Analysis" as well as the following:

1. What is the purpose of quenching and tempering steel?

2. Discuss the sources of error for the various hardness testers, the relative ease with which they may be used, and the comparative consistency of test results.

3. What factors probably contributed to the scatter in the hardness data?

4. Which hardness test appears to be most accurate?

5. Using the inverse lever law, estimate the amount of carbide (Fe3C) present at 1338oF (just below the eutectoid temperature) for SAE 1045.

6. What are (or should be) the differences in the microstructure for each heat treatment process and how do these differences correlate with hardness?

7. Discuss errors in this experiment and their sources.

EXPERIMENT 2: HARDENABILITY OF STEELS

Purpose

This experiment is aimed at understanding the effect of cooling rate on the hardness of two steels. The experiment also shows why adding alloying elements other than carbon enables a part to be heat-treated more uniformly and to a greater depth.

Procedure

You will be given two steels: (type 1045) and a low-alloy steel (type 4143). Before heating the specimens, practice mounting the specimens in the rack and adjusting the water flow to spray the end of the specimens.

Stamp each specimen for identification and measure the hardness on the Rockwell A scale. Check to make sure the fork is secure and put the specimen in the furnace at 1600 ± 25oF (870 ± 45oC) for 45 minutes. While you are waiting for the specimens, examine the microstructure of the alloy steel and carbon steel specimens provided by your instructor. At the end of the austenitizing treatment above remove one specimen and carefully, but rapidly, place the specimen in the holder with the water turned on.

Write Up

Prepare a memo report, in conjunction with Experiment #1 (Heat treatment of steels). Plot the hardness as a function of distance from the quenched end with plots for both samples on the same graph. Discuss the effects of alloying on hardenability. Discuss the shift in the TTT curve due to alloying.

Attachment:- Report.rar

Reference no: EM131023481

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