What is Near-surface hardness?
What is Near-surface hardness?
(OP)
I just received a test report from a lab we ask to do a surface hardness and core hardness test of a part. They reported the surface & core hardness test results using the Vickers Low Load test. They also reported the "near-surface" test results using the Rockwell test. The part drawing specified a Rockwell C hardness in a certain range. I expected surface & core hardness done with a Rockwell test (in addition to the HV0.3) but I am confused by the "near-surface" moniker. Can someone help explain?
Thanks,
Jeff
Thanks,
Jeff





RE: What is Near-surface hardness?
The hardness usually defined as the "surface" hardness is exactly as you describe which is a test performed directly on the surface using an approriate load depending on the case depth.
RE: What is Near-surface hardness?
A star for you. Such an elegant answer. I cannot imagine anyone argueing with this explanation but I have been wrong before.
RE: What is Near-surface hardness?
Thanks,
Jeff
RE: What is Near-surface hardness?
" The effective case depth is measured normal to the finished gear surface to a location where the hardness number is 50HRC ( 542 HK 500 or 515 HV 500 min) by conversion from a microhardness test result."
The microhardness test provides the necessary accuracy for these determinations particularly for effective case depths of thin cases.
RE: What is Near-surface hardness?
As you state conversion isn't always the best approach but has to be used at times. Generally with good equipment and competent technicians there isn't any problem.
RE: What is Near-surface hardness?
The lab wasn't asked to determine case hardening depth (the part should have through hardened, by my limited heat treating understanding), but Rockwell hardness values.
RE: What is Near-surface hardness?
RE: What is Near-surface hardness?
RE: What is Near-surface hardness?
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: What is Near-surface hardness?
While this is generally a true statement: "There is no general process for accurately converting Rockwell hardness into other scales or hardness into tensile strength." when the discussion is limited to quenched and tempered low alloy steels, then the conversions given in ASTM E140 are pretty good. In my experience, they usually fall within +/- 1 HRC value which is the generally accepted accuracy of the Rockwell test. It needs to be remembered that any such conversions are only apporximations. To demonstrate compliance to a specfied requirement, the test really should be performed by the test method specified.