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Engineering Materials Lab MATLENG 201 Section 811 Cold Working and Annealing Performed on October 16-23, 2014 by Tyler Doro 991-21-1781

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Engineering Materials Lab

MATLENG 201

Section 811

Cold Working and Annealing

Performed on

October 16-23, 2014

by

Tyler Doro

991-21-1781

Objective

The main objective of this lab was to see how the processes of cold working (which is working on the material at less than half the temperature required to melt that material) and annealing can affect the hardness of a material. A secondary objective was also to see the difference in grain structure of an annealed material and a cold worked material. Knowing how the grains are different can help us understand the hardness properties.

Materials & Equipment

Free cutting brass

62% Cu, 35% Zn, and 3% Pb

Rolling Mill

Furnace

Rockwell Instrument

Brale diamond cone indenter, 60 kg load

Grinding Machine

Various grit sandpapers

Polishing Machine

Alumina Suspensions

Microscope

Procedure

Measure- measure the samples and record length width and height

Cold work- cold work the samples by placing them through the rolling mill (which is an example of a strength hardening mechanism) until they achieve appropriate amounts of cold work

Hardness test- record 5 measurements for each sample using the Rockwell hardness test

Anneal- heat samples in furnace for 20 min at 650oC

Hardness test- record 5 measurements for each annealed sample using the Rockwell hardness test

Grinding- grind two samples one 40% CW and the other annealed

Polishing- polish the two ground samples to prepare for etching

Etch- Etch the two samples in f 1 g Fe (NO3)3 in 100 ml H2O for 8-10 seconds

Observation- samples were inspected under microscope

Results & Analysis

The data from this lab was tabulated in three different tables. The first being a table about the theoretical percentage cold worked the actual cold worked percentage.

Cold working %

Initial Thickness (in)

Theoretical Final Thickness (in)

Theoretical Number of Passes

Actual Final Thickness

Actual Cold Working %

0

.375

.375

0

.375

0

10

.375

.3375

7.5

.336

10.4

20

.375

.300

15

.299

20.27

30

.375

.2625

22.5

.2635

29.73

40

.375

.225

30

.225

40

60

.375

.15

45

.14

62.67

From this table we can see that there is a slight error in our cold work process that could possibly be attributed to human error.

The next data table is the hardness values of samples after cold working.

From this data table we can see that the harness goes up as the percentage cold worked goes up.

The next data table is the hardness values of samples after annealing.

These hardness values are more consistent after the annealing process.

Here is a plot of the two hardness values from cold work and annealing

The picture on the left is the grian structure of a sample that has been annealed. The picture on the right is that of a sample that has undergone a cold working of 40%. As you can see in the picture on the right the grains are flattened by this cold work process. The cold work proces increases the dislocation density of a material. Dislocation density is the amount of dislocations in a certain area of a sample. This is what inevitably gives the sample more hardness vs when it was just annealed. When a sample is annealed then the dislocations disolve and the sample reverts back to a more ductile state. That is why the process of annealing is used to bring samples maechenical properties back to where they will not frocture due to further cold work.(The black dots in the pictures are just parts of lead in the sample.)

Conclusion

From all of this data we can come to some very clear conclusions. The biggest conclusion we come to is that if you are taking a material and performing cold work on that material it will in turn become harder due to an elevation in its dislocation density. Also if you take that same material and wish to revert those properties back to their original state. You must anneal the sample effectively dissolving dislocations in the sample restoring it to a more ductile state. This is important for engineers to know, for when you are designing a part or a system and need something to be harder you can cheaply and affectively make it harder with cold work. In the opposite situation an engineer should also know that in order to make a piece that has been cold worked more ductile again annealing will do just that.

Hardness for Cold Worked and Annealed conditions

Cold Worked0102030406025.83999999999999637.6442.946.3849.0452.08Annealed0102030406024.08000000000000221.3818.4821.08000000000000224.43999999999999822.360000000000003

Cold Working (%)

Hardness (HRa)

Hardeness Values After Cold Working

12345

025.525.726.226.125.725.80.297

1038.338.537.237.636.637.60.783

2041.841.842.544.144.342.91.223

3046.545.946.945.746.946.40.559

4048.748.448.349.85049.00.802

6051.752.751.952.251.952.10.390

Cold

Working

HRa Rockwell A HardnessAverage

(HRa)

STDev

(HRa)

Sheet1Hardeness Values After Cold WorkingCold Working (%) HRa Rockwell A HardnessAverage (HRa) STDev (HRa)12345025.525.726.226.125.725.80.2971038.338.537.237.636.637.60.7832041.841.842.544.144.342.91.2233046.545.946.945.746.946.40.5594048.748.448.349.85049.00.8026051.752.751.952.251.952.10.390

Hardeness Values After Annealing

12345

024.224.224.023.924.124.10.130

1022.121.921.620.32121.40.733

201918.218.218.818.218.50.390

302022.321.621.120.421.10.920

4024.424.724.424.324.424.40.152

6022.622.821.722.322.422.40.416

Cold

Working

HRa Rockwell A HardnessAverage

(HRa)

STDev

(HRa)

Sheet1Hardeness Values After AnnealingCold Working (%) HRa Rockwell A HardnessAverage (HRa) STDev (HRa)12345024.224.224.023.924.124.10.1301022.121.921.620.32121.40.733201918.218.218.818.218.50.390302022.321.621.120.421.10.9204024.424.724.424.324.424.40.1526022.622.821.722.322.422.40.416