I have a set of Sorby chisels that have the dimple from the hardness tester, but the hardness is not uniform throughout the tool. The cutting edge had to be ground down before the actual hard metal was reached. Whether that was from initial grinding or burnout at the edges during heat treat is the question. The hardness tester only tests one point, is the point here, I think.
Decarb frpm the heat treat most likely.
Originally Posted by SpikeC
Wilsons analog or digital (mine is analog about 20 years old) if well calibrated, will get you pretty accurate readings - +/- .25 or less. Helps to have test blocks to check on accuracy periodically and to have replacement indenters, should the one in the tester wear out, as that will throw off your reading. I typically take 5 readings and average.
Originally Posted by ajhuff