The Hazards of Hardness Testing

[Kevin R. Cashen]

Unfortunately a post temper Rc reading alone lacks any reference point from which to evaluate your heat treatment. As was touched on earlier, if your as-tempered blade reads 59Rc but your as-quenched blade was only 62Rc when it should have been 65HRC, you will never know that your hardening operation needs some adjusting. Tempered martensite makes a great knif,e a tempered pearlite/martensite mix is not going to quite cut it in comparison (pun intended). But if you have the numbers to show you have a 59-60HRC post temper and that is after a 65HRC as-quenched, you have all the information to be confident that you are at least nailing the hardness aspects.

I say ?at least the hardness aspects? in order to emphasis that no one test will tell you everything you need to know and the more stand-alone the test is the less it tells you. Enlarged grain will harden more deeply so even great Rc numbers can still occur in a overheat situation, but if you know your grain size is good, you as-quenched numbers are good, and your post temper numbers are where you want them, then you are on a pretty good heading. Also the more HRC tests you do the more accurate they are as the number should always be an average. I always do at least five readings and average it for the final number, if there is a range the average helps, if there is no deviation in the five you give yourself a pat on the back and proceed with a good feeling about the whole process.

Edited to add- oops there were two more posts in the time I was writing mine and the quality of both of them was such that it tells me I am not really bringing much more this conversation as you folks got it pretty well figured out, and I am just being redundant.