rephrase the mothed

Procedure: To start off this lab, obtain a piece of the aluminum that you used in the tensile test from last lab. Use this piece to practice with the hardness tester machine.

Recognize that aluminum is a fairly soft metal and so the hardness scale you use with this material may not be appropriate for testing harder metals.

Next you will be testing carbon steels. Each lab group will be given one sample each of the following four types of steels:

1

018,

4

1

40

, 10

4

5

, and 1090. Your first task is to mark these samples (make some permanent cut mark) so that you can identify them as belonging to your lab group and so that you can recognize which one is which. Next, run a metal file along the side of the sample to get a feel for how hard the material is. Record your observations.

After you have marked the samples and used the file on them, now use the hardness tester to obtain the hardness value for that sample. When you do your test you should test it multiple times (three works well for these samples) and take an average. Make sure that you do each test far enough away from the previous indentation so that you do not measure the effects of cold working that occurred when you used the hardness tester on the sample for a previous test. Also, do your testing away from the edge so that you don’t obtain data that is distorted by edge effects. Be sure to record all three test values and then take an average. Do this for each of the different types of steel. Once again, be careful. Have a system that allows you to keep track of which sample is which.

Procedure: For this lab we will place the four samples (one of four different kinds of steel) in an oven. Before placing the samples in the oven, make some permanent mark on the samples for identifications. This is important. The oven will be heated up to approximately 1,

60

0oF. It will take approximately 4 hours to reach this temperature. Then the samples need to be held at this temperature for approximately 1 hour. This will allow sufficient time for the materials to transition into the “Austenite” range on the Equilibrium Phase Diagram. Then we will take two samples, remove it from the oven and quickly cool it to room temperature (quench) in a bucket of water. The other two samples of steel will be left in the oven, the oven will be turned off and the pieces will be allowed to cool slowly overnight. This will allow these samples to cool in equilibrium. That will finish up the lab for this week. Then we will check the hardness of the quenched samples. We will check the hardness of the annealed samples next week.

Procedure: There is a table provided below to record your hardness test results on. An Important Note is to continue to take your hardness readings from the same side of the sample that you used before. That keeps all of the ‘dimples’ on one side of the sample. This will make it easier when we mount the samples in Bakelite and start polishing them. Having a side without dimples will make it quicker to polish since you won’t have to grind away as much material.

Procedure: Turning the Bakelite® powder into a solid involves high temperature and pressure. There is a potential for injury whenever you work around high temperatures and pressures. Follow all of the instructions given to you in the lab.

IMPORTANT: Be sure that you know which of your samples you are putting into Bakelite®. Once that sample is set in the plastic you won’t be able to read the markings on the side, so you will need to create a new mark on the plastic.

Procedure: Follow instructions, ask questions, have fun. Important information for performing the polishing is given in the following table (ref: LECO manual):

300

45

30

300

45

Time
(sec)

Wheel Speed (RPM)

Pressure (psi)

60

30

Grinding Steps:	SiC Grit Size		Time (sec)		Wheel Speed (RPM)		Pressure (psi)
1	180		60			3 0 0			45
2	320			30
3	600
Polishing Steps:	Polishing media
4	6 micron diamond compound/red felt cloth/microid extender	250	40
5	Al2O3/Lecloth™/water	15 0	15