This is a continuation of part 3, which can be found here.

Effective Case

The effective case is the depth from the surface to 513 Vickers (or approximately 50 HRC).

 

Total Case

Total case is the depth to core hardness plus 50 Vickers (or approximately 5 HRC scale) on the real core-hardness value.

 

Test Method

The method of testing is usually applied to a sample that has been cut from either a test coupon or the part being tested. The hardness test loading is usually microhardness that can be varied from 10- up to 1,000-gram load mass. The thickness of the diffused case will determine the load that is to be selected. It is usually a 200- to 300-gram load that is used to determine a total case depth. A microhardness load mass can be as low as 10 grams, but one may have difficulty in measuring the diamond indentation with such a light load.

The application of the test is performed on the test coupon across the formed case through to the core hardness. Another hardness testing method for microhardness (and some macro) is to use the Knoop hardness test unit. This will give the operator the tested values in Knoop hardness units. Unlike the Vickers test (which makes a “pyramidal” square diamond impression and the measurement is made across the two axis), the Knoop impression is an elongated diamond impression. The hardness value is ascertained by measuring the longitudinal axis. 

 

Conclusion

Whichever test procedure is used for hardness testing, it is necessary that the test method is chosen carefully. The test must be conducted in an accurate and meaningful manner. It is this test that will determine the effectiveness of the heat-treatment process. It is also very important that the quality-assurance technician/heat-treatment associate has a good understanding of the test methods, the load/indenter selection and the interpretation of the results to produce accurate hardness values.