differentially hardening stainless

[ChrisChatelain]

I know you cant differentially heat treat stainless, but why? is it because you bring it up to temp and hold it for a while, then the heat "leaks" to the other parts of the blade?

[Jason Cutter]

There are more ways than just forge or oven to bring it up to temperature. I understand that it can also be done with electrical induction to selectively harden parts of say, saw blades, but I'm not sure if thats just carbon steels anyway.

Stainless steels CAN be differentially tempered, though (as opposed to differential hardening). So you can technically temper the spine of a blade softer at a higher temperature.

BUT you have to remember that high-alloy steels do NOT behave necessarily in the same way as plain carbon steels. Softer is not necessarily tougher.

An example is D-2. When properly HT-ed with a quench, cryogenic treatment and triple tempering, it can achieve a hardness of 60-61Rockwell. Another piece of D-2 might eg.- be hardened and tempered to 58Rockwell. From what I understand, the 61Rockwell D-2 is actually both harder AND TOUGHER than the 58Rockwell one.

This has to do with the way the HT arranges the elements and carbides within the steel. There are optimum ranges for these things. This borne in mind, there should be no reason to need a differntially tempered blade, if at 61Rockwell the D-2 is not only more wear resistant, but also tougher.

The bottom line is that it can be done, but it may not be worth the trouble. Thats the simplest way I can explain it. Its not something I understand well myself and I'm hoping that others who understand the science behind it can explain it further. Hope that makes sense. Jason.

[ChrisChatelain]

yeah that helps tons jason, thanks

[whv]

The bottom line is that it can be done, but it may not be worth the trouble.

like so many things in this business of knife making! in the current issue of blade, wayne goddard explains why he doesn't waste his time forging d2, especially out of large pieces. it can be done, but why? it doesn't yield a better knife, and by the time you're done you end up with a piece of steel that cost you many times more to make than you would have spent if you reduced a piece of bar by stock removal.
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thanx, kwong!