Cold Work

Objective: To study the effect of cold working on the hardness and microstructure of brass.

Introduction: Cold working promotes rapid change in the mechanical properties and in the appearance of copper alloys. The most rapid method of accomplishing it is by cold rolling as in rolling sheet and bar.

Equipment:

 Rockwell Hardness Tester

 Rolling Mill

 Micrometer

 Hacksaw

 Belt Sander

 Polishing and Etching Equipment

 Metallograph

Material: One piece annealed cartridge brass 3/4 " x 4" x 1/8" thick.

Procedure:
    1. Using the hacksaw, cut the annealed cartridge brass into 7 pieces of about 1/2 " length and mark them as 0, 10, 20, 30, 40, 50,60.
    2. Measure the RB or RF (Rockwell B or Rockwell F Scale) of the piece marked "0". This means that sample "0" has no cold work. Take three readings and average them.
    3. Using the rolling mill reduce the thickness of sample "10" by 10%. This means that the sample "10" represents 10% cold work. Measure the hardness and record.
    4. Continue rolling and measuring the hardness numbers of samples 20, 30, 40 ,50 and 60 and record.
    5. Examine the microstucture of the cold worked specimens, parallel to the rolling direction.

Experimental Data: Construct the table shown below and include your experimental results. If the % reduction you obtained in the laboratory varies from the nominal value, indicate what the actual % reduction is. For example, if you obtained 11% reduction (Actual value of cold work) instead of 10 % ( nominal value of cold work), use 11 % in the second column. If you measured the hardness in Rockwell B scale (RB), convert each reading to Rockwell F scale (RF) and include them in the last two columns of the table.

% Reduction Nominal

% Reduction Actual

Thickness After Rolling (in.)

Hardness

(RB)

Hardness

(RF)

0

 

 

 

 

10

 

 

 

 

20

 

 

 

 

30

 

 

 

 

40

 

 

 

 

50

 

 

 

 

60

 

 

 

 

Table 1

After the construction of the table plot a graph that shows the effect of cold work on the hardness of the material as shown below:

Figure 1

Report:

 Prepare a report with the following format:

 Objective

 Equipment

 Experimental Procedure

 Laboratory Data

 Discussion of Results

 Present your experimental data as shown in Table 1.

 Plot Hardness vs. % Cold Work as shown in Figure 1.

 Label the microstructure photographs of the selected specimens. Discuss the structure differences and their relationship to hardness of the specimen and explain what has happened to the structure after 60 % cold working .

 Answer the following questions:

 What is the effect of cold working on the hardness of annealed brass? (Plot the graph before answering this question)

 What is the effect of cold working on the microstructure of annealed brass? (Use the microstructure photographs to answer this question)

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Last Update: March 5, 2000

By: Serdar Z. Elgun