Cold Working of Brass
Kevin Louie
MatE 25
October 20, 2014

| Marine Research Corporation | To: | Irene Huang | From: | Kevin Louie | Date: | September 29, 2014 | Re: | Determination on whether brass ingot can be used instead of plate form for a motor bracket application. | | |
In response to the assigned investigation for Equipment used in the Oceanographic Research Platforms in the Arctic region, the following observation and test were performed. The scenario is having Research equipment installed on the Research Platforms that can survive harsh marine environments while operating for long periods of time with little or no maintenance. The material used for these equipment are to be made of brass plate because it is good corrosion resistance, easy machining tough. The question seeking for an answer of the investigation is “Can buying brass ingot and roll it flat to get a 60 percent reduction in thickness and hardness of 45 without it cracking?” For this experiment, there was two test that was conducted, Cold Working test and the Heat Treatment Test, on a sample of 260 Brass in ingot form. For the Cold Working Test, the first done was putting the sample through a Stanat Rolling Mill to reduce the thickness of the ingot. Part two of the Cold Working Test was to use the Rockwell Hardness Tester to measure the hardness of Brass. Do this test ten times at increments of -0.75 from 10.5mm to 3mm. At each targeted thickness, measure the width and length. The result of the test is on Table 1. After doing the Cold working Test, Heat treatment test is done. For this test, take the 3mm brass plate and cut it into 5 equal pieces and place each piece into the5 furnaces at 100°C, 260°C, 350°C, 450°C, and 565°C. Test the Hardness of each piece on the Rockwell Hardness Tester and the results are on Table 2. After conducting this experiment, the answer to “Can buying brass ingot and roll it flat to get a 60 percent reduction in thickness and hardness of 45 without it cracking?” is proven yes. The Stanat Rolling Mill was able to flatten the 260 brass ingot from 10.5mm to 3mm without it cracking. According to the Heat treatment test results on Table 2, 260 Brass can get a hardness of 45 if treated with heat of 350°C to 450°C.

Introduction The scenario of this experiment is that the Marine Research Corporation have many research platforms with equipment used for oceanographic studies. The equipment used must survive harsh marine environment and operate for long periods of time with little or no maintenance. The material used for the equipment is made of brass plate due good corrosion resistance, easy machining, and sturdy. The Corporation wanted to buy Brass in ingot form instead of buying it in plate form because cost will be dropped by 50%. The purpose for this experiment is to determine whether the brass ingot can be reduced by 60% in thickness and still have a HRB (hardness) of 45 without it cracking. For this experiment, the equipment used are: Stanat Rolling Mill, Rockwell hardness tester, and furnaces. The material for this experiment is 260 Brass (70% Cu and 30% Zn).
The first process used in the experiment was Cold Working. Cold working, also known as Strain Hardening, is the process of strengthening a material by plastic deformation. Cold Working on metal causes the “metal to increase in strength but there is a chance that it could decrease in toughness, ductility and corrosion resistance.” This means it will “increase the dislocation and decrease in grain size.”(MatE25 Lab Notes, 5-2)The increase of dislocations will make dislocation push against each other causing limited movement. A limited movement of dislocation decrease the amount of movements in the slip plane, hence, causing the metal to increase in strength but decrease in toughness and ductility. Some advantages to cold working are: it requires no heat, improved strength, dimensional control and improvement. Some disadvantages are: requiring more force for deformation, Stanat rolling mill is required, less ductile and might induce undesired stress.
The second process used in the experiment was Heat Treatment. Heat treatment is a combination of temperature and time. “Temperature determines the amount of stored energy released and Time is how long it will be to release the X amount of energy. Energy is released in stages: Recovery, Recrystallization and sometimes Grain-Growth.
During Recovery, “internal strain energy is relieved by dislocation motion.” (Callister, 219) At a certain, temperature, Recovery is a movement of dislocations that orient themselves. After Recovery, “Recrystallization is the formation of new set of strain-free and equiaxed grains that have low dislocation densities.” (Callister, 219) Recrystallization is the process of new grains forming that have small dislocation density and consume cold-worked grains. And after recrystallization, “strain-free grain if left at elevated temperature.” (Callister, 224) At long periods of time, larger grains consume smaller ones.
Procedure
For this experiment, there will be sample of 260 Brass ingot. There will be two Test called the Cold Working Test and Heat Treatment Test. For the first part test of the Cold Working Test, the sample will be fed through the Stanat Rolling Mill. There should be 4 students handling this part of the test.

Fig.1 260 Bronze ingot form(left) and plate form(right) Step to use Stanat Rolling Mill 1. Rotate the wheel to 0 2. Student 1 rotate wheel slowly to estimated measurement 3. Verify there is sufficient space for the sample to pass between roller 4. Student 2 feed the sample into the hole on the left side of wheel with wooden wedge slowly 5. Let the sample roll to the other side 6. Do not stick finger in rolling part and Student 3 carefully take the sample out from right side of wheel | Fig.2 Stanat Rolling Mill
After feeding the sample into the Rolling Mill, Student 4 measure the thickness of sample and count the number of time that the sample has passed the Rolling Mill. If the sample doesn’t meet required, redo Rolling Mills starting from Step 2. When it has reach the required thickness, measure the width and length and pass it to the Students doing the second part of the Cold Working Test. The second part of the test is the Hardness test, and there is a machine called the Rockwell Hardness Tester. This machine measures the Hardness of sample. Steps to using the Rockwell Hardness Tester 1. Place sample on the center of the Anvil 2. Turn wheel until digital bar reach the Square box on the frame of the Tester 3. Release wheel 4. Press test 5. Do test of sample three times at three different areas of the sample and record the Hardness | Fig. 3 Hardness Tester with Sample on Anvil
After recording the hardness, pass it back to the Stanat Rolling Mill group and repeat the process until the sample has reached the thickness of 3mm from 10.5 of equal increments of 0.75mm reduction in thickness.
The Second test is the Heat Treatment Test that requires 5 furnaces at temperatures of 100°C, 260°C, 350°C, 450°C, and 565°C. Cut a 3mm thick bar of 260 Brass into 5 equal pieces. Place each piece into one furnace for 45 minutes. After 45 minutes take out the pieces and measure hardness on Rockwell Hardness Tester 3 time each.

Fig. 3 Furnace
Data
Stage | Target Thickness(mm) | No. of passes | Actual thickness(mm) | Width(mm) | Length(mm) | %CW(area) | %CW(thick) | HRB1 | HRB2 | HRB3 | Ave HRB | 0 | 10.5 | 0 | 10.5 | 13.8 | 69 | 0 | 0 | 37 | 37.9 | 40.3 | 38.4 | 1 | 9.75 | 5 | 9.75 | 14 | 70 | 5.9 | 7.1 | 66.6 | 67.8 | 67.4 | 67.3 | 2 | 9 | 4 | 9.09 | 14.39 | 75 | 9.8 | 13.4 | 73.8 | 73.5 | 73.9 | 73.7 | 3 | 8.25 | 6 | 8.29 | 14.73 | 80 | 15.8 | 21 | 78.8 | 80.2 | 81.9 | 80.3 | 4 | 7.5 | 5 | 7.49 | 15.1 | 88 | 22 | 28.7 | 83.1 | 83.3 | 82.9 | 83.1 | 5 | 6.75 | 1 | 6.73 | 14.97 | 94 | 30.5 | 35.9 | 85.4 | 84.7 | 84.5 | 84.9 | 6 | 6 | 3 | 5.83 | 15.09 | 108 | 39.3 | 44.5 | 84.5 | 85.8 | 85.3 | 85.2 | 7 | 5.25 | 3 | 5.08 | 15.34 | 125 | 46.3 | 51.9 | 89.3 | 90.1 | 90 | 89.8 | 8 | 4.5 | 3 | 4.45 | 16.35 | 137 | 50 | 57.4 | 88.5 | 90.1 | 90 | 89.5 | 9 | 3.75 | 3 | 3.68 | 15.53 | 165 | 60.6 | 65 | 92 | 92.2 | 92.4 | 92.2 | 10 | 3 | 2 | 2.97 | 16.05 | 206 | 67.1 | 71.7 | 92.8 | 93.4 | 93.8 | 93.1 |
Table 1 Hardness Vs Cold Work
Some error were not zeroing the micrometer and recording the width and lengths incorrectly. Some errors were due to putting the sample through the rollers too fast. The equation used to calculate %CW of Area and thickness are:
%CW=Tinitial-TfinalTinitial×100 (1) %CW=Ainitial-AfinalAinitial ×100 (2)

Heat Treatment(℃) | HRB1 | HRB2 | HRB3 | AveHRB | 22 | 99 | 98.7 | 99.3 | 99 | 100 | 96.2 | 96.4 | 95.1 | 95.9 | 260 | 87.1 | 95.6 | 89.6 | 90.8 | 350 | 65.9 | 67.5 | 67.7 | 67 | 450 | 35.4 | 40.4 | 38.1 | 38 | 565 | 8.2 | 4.2 | 9 | 7.1 |
Table 2 hardness Vs Heat Treatment Temperature

Conclusion/ Recommendation
After doing this experiment, the result of the Cold working test does make sense because Cold Working is a process that strengthens the hardness of metal by limiting movement of the slip plane. Looking at Table 1, as the 260 Brass’ thickness become thinner, the hardness of the brass increases. But the Heat treatment Test result does not make sense because Heat treatment is also a treatment that strengthen metals. By looking at Table 2, the results are not doing that. As the Temperatures increases, the hardness of the Brass decreases.
The answer to “Can buying brass ingot and roll it flat to get a 60 percent reduction in thickness and
Hardness of 45 without it cracking?” is yes. According to Table 1, the metal thickness went from
10.5mm to 3mm without cracking and 7.5/10.5 is greater than 60%. According to Table 2 at 450℃, it passed HRB of 45. And if I were to predict the correct heat temperature it would probably be 430℃.
The labor required to do rolling mill would be high since it is requiring five people to do it. One to turn the wheel, One to put in the metal, One to take it out, one to measure the correct length and one person to measure the hardness on the Rockwell Hardness tester. It could be cut down to four, because the one taking it out can also measure. Heat Treatment process can just be one person putting in as many piece of metal the furnace can handle to save time.

Work Cited https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Structure/strengthening.htm http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=266
http://www.midweststeelsupply.com/store/360BrassFlatBar