This week I overdid it when profiling a blade and ended up with an edge much thinner than usual when I came to the edge quench step. Since the blade was good in other respects I decided to go ahead and finish it. The tip of the blade was probably .040, maybe a bit thicker. I looked at the edge after the 2nd quench and it seemed thinner. I examined it more closely and was convince the width of the edge had shrunk noticibly. I assume I was looking at the physical effects of "grain reduction" and never noticed it before because I usually leave a lot more material on the edge and the relative shrinkage would not have been as evident. The edge after the 2nd quench appeared half as thick as it was before quenching. I didn't mike anything so I'm not certain what the difference was, but it was there. I'd be interested in comment on this from somebody with more forging experience and background in metallurgy.

Very common thing with oil quench steels. Anytime you heat metal it will expand, and when it is cooled it will contract. I'm sure that's nothing new to anyone, but the reason it was noticable in this case was the beginning thickness of the material. When something is that small (thin), and it contracts during the quench, it's just much more noticable than with a thicker cross section. there are formulas for determining the shrinkage in a piece of heat treated steel versus a non-heat treated one, but the differences are measured in the thousandths and microns. Not many of us concern ourselves with it, since we will be grinding on is anyway...................I'll bet if you test that blade against one of the same material that had a thicker edge before quenching, you'll see a big difference in performance.

Ed,
Which blade would perform better?
Mike

Dollars to doughnuts says that the blade that is left thicker at the edge before heat treat will be a better performer. I truely believe in the sacraficial material protecting what lies beneath!