engineering materials lab3
DESCRIPTION
lab for engineering materialsTRANSCRIPT
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)
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)