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Hi guys,

well I had some S-7 tool steel dumped on to me a while back and its been laying around. I haven't done anything with it yet because its an air hardening steel and I don't know how to go about treating it. My curiosity's been getting to me and I've been tempted to try forging some but I don't wanna screw it up and waste material, due to having limited amounts of it. Any advise for treating the steel?

S7 is a tricky one because it has plenty of alloying that is “needy” when it comes to carbon but it doesn’t have enough carbon to go around for the properties desired in most knives. Heat treating it “properly” may yield a knife capable of chopping or cleaving cuts that can take a bit of a pounding. Intentionally skewing the heat treatment in unconventional directions may produce a tough/ductile blade with hard suspended particles that could make a rough edge capable of aggressive draw cuts, but not necessarily a true fine cutting edge. The problem here is that with over 3% Cr and only .5% carbon to go around, something’s gotta give. This is one of those steels that was designed with applications in mind that are quite a bit divergent from knives. The real key component is the added molybdenum; this steels real talent is in resisting weakening from heat during use, something one doesn’t normally associate with knives right off the bat.

If you want to try it out for a tough chopper, industry recommends that you heat it to a range from 1700F to 1750F. You may get more out of it for a knife if you use the upper half of the range, a good 10 to 15 minute soak if you prefer the lower side but at least some soak time at any temp. You can quench in air or oil. The higher temp will facilitate the air while the lower will accommodate the oil.

If all goes well you can expect to see as-quenched hardness not much harder than 61HRC. But for tempering be ready for the real adventure to begin- remember that molybdenum? Expect to go very high to see appreciable drops in hardness (think of adding as much as 100F to normal tempering temperatures). I cannot venture a guess as hardness vs tempering and it will be a bit of trial and error for you probably.

Thank you for the very informative reply. I know it's not the best steel for knives but its laying around so I figured I could experiment with it. I will be making a camp knife with it tomorrow and I'll post the results when I'm done.