Rockwell Testing

Chris Railey

Chris Railey

Well-Known Member
I have recently gained access to a hardness testing apparatus and I want to do some testing on my HT results. I know that it is good to grind the coupon down some before testing but my question is how much? I do not have precision capabilities to remove .003 at a time so are we talking about enough to remove the scale from HT or scale plus a little more? Most of what I will be testing will be .100 to .125 starting thickness. Thanks
 
Chris, a lot depends on what type of steel - SS that was HT'd in a foil packet? That doesn't take much at all, just a short clean up with 320 grit belt on the flat platen should be good. Carbon steel that was HT'd without protection - that's going to take more grinding to clean up.

I do all HT'ing of that thickness as profiled only and grind bevels post HT. Remember, you do want parallel sides, not on the bevels for Rc testing.
 
Chris, I used to work at a heat treating facility, and we would surface grind about .020 off our testing surfaces. You do want a fairly decent finish, if you try to test on too coarse of a finish it will throw your results off.
 
With carbon steels that have some decarb after heat treating, you can grind some off and test etch them to make sure the decarb is gone. Also, if I get a reading that I think is lower than it should be, I will grind a little more and retest. If it stays the same, I adjust my heat treat process. If it reads higher, I probably didn't have all the decarb ground off.
 
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