Lab # 8
To perform hardness test on a given steel specimens using Rockwell hardness testing machine:
Purpose:
- To check the hardness of materials
- Indirect strength test of materials
- Quality control in industries
Apparatus:
- Shimadzu Rockwell hardness testing machine
- Indenters steel balls and diamond cone
Related theory:
Hardness:
Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting.
If there is more hardness, the material will be more brittle.
Hardness Test Methods:
- Rockwell Hardness Test
- Rockwell Superficial Hardness Test
- Brinell Hardness Test
- Vickers Hardness Test
- Microhardness Test
- Moh’s Hardness Test
- Scleroscope hardness test
Indenters:
- 1/16” dia steel ball for mild C steel sample
- Diamond cone for high carbon steel sample
Procedure:
Rockwell Hardness Test (BS-891)
The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load usually 10 kg. When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration. When equilibrium has again been reached, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration. The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell hardness number.
Observations and calculations
| Sr no. | Specimen | Type of indenter | Scale | Load (kg) | Hardness no. | Mean hardness | |
| Minor | Major | ||||||
| 1 | Mild C steel | 1/16” dia steel ball | B | 10 | 90 | HR 92.5 B | |
| 2 | 1/16” dia steel ball | B | 10 | 90 | HR 93 B | HR 93 B | |
| 3 | 1/16” dia steel ball | B | 10 | 90 | HR 93.5 B | ||
| 1 | High C steel | Diamond cone | C | 10 | 140 | HR 88 C | |
| 2 | Diamond cone | C | 10 | 140 | HR 89 C | HR 88.33C | |
| 3 | Diamond cone | C | 10 | 140 | HR 89.5 C | ||