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topic 6690

Hardness testing of hot steel


Q. I was wondering if a micro Brinell hardness machine can be used on test samples that are at high temperature (steel, say at around 500° C?) I am concerned if the indenting ball will deform because of the high temp of the test sample, any deformation in the sample is acceptable.

Prashanth Ravi
- Madison, Wisconsin, USA


I cannot give you specific info on testing hot steel, but do know it can be done in real time, too. The equipment is of specific design, not the indentors, etc. that would be OK at room temperature, for example. Recommend you contact one of the several companies that sell such equipment for advice. I would also inquire if one of the Brinell impact pin types would work on hot materials, and the impression then measured after object had cooled, using a conventional microscope, but factoring in the expected change in size due to this. While not in real time, it could be acceptable if there was sufficient co-relation performed, and probably less costly.

W. Carl Erickson
- Rome, New York


Hardness testing at elevated temperature is relatively uncommon, but not unheard of. Hardness at elevated temperature is often given for tool steel alloys. The test method is usually Rockwell C hardness testing. As indicated in the previous response, specialized testers (read expensive) are used for this testing. The Wilson company, now owned by Instron, used to sell a hot hardness tester. There are a few test labs around with elevated temperature Rockwell testers.

There are also a few Vickers microindentation hardness testers around for use at elevated temperature - mostly at universities I would guess. These are mostly "home built". I don't know of a commercial unit.

I like the idea of using the impact Brinell tester. Perhaps one of these equipped with a carbide ball would work. The regular steel balls would probably soften too quickly at 500C. Carbide balls are readily available as intended for room temperature testing of very hard steels, but the carbide will hold its shape at high temperature if it doesn't crack from thermal shock.

Good luck.

larry hanke
Larry Hanke
materials testing laboratory
Minneapolis, Minnesota

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