Its simple metallurgy not a” Black Art”?
Because 440C has the feature of secondary hardening, maximum hardness is achieved in a very narrow tempering temperature range. This temperature is dependent upon the actual chemistry of the material. It’s usually 875 df. The hardness increases with tempering up to 875 then hardness decreases quickly with tempering temperatures above 875 df. Stainless steels conduct heat more slowly than alloy steels so a practical way to “hit “the maximum hardness tempering temperature without overshooting is to pre-heat. Hold the parts at a slightly lower temperature for sufficient time and then set up the temperature to the desired temperature and hold for sufficient time. Pre-heating will also insure uniform tempering throughout the thick/thin sections of the part. 440C has very low ductility at its maximum hardness and ductility would be further reduced by cold operating temperatures.
Originally Posted by Smithy
On the edge of performance? A few degrees. No more than 10, I'd prefer 5, with correct soak times and timing on the change in temps. That's the really hard part - can you get the entire body of the knife (not just the outer skin) from hot to cold fast enough to get the right matrix across the blade? For most carbon steels, this is straightforward if not trivial, but stainless is a whole 'nuther ball of wax.
96 XR650L, 96 Guzzi Sport, 07 BMW K1200GT,
86 Husky 400 XCE, 00 Husky Te 610 e, 1999 Husky TC610 SM, 2000 Cagiva GC; Google: TX7
fritzcoinc screwed with this post 12-06-2012 at 06:39 AM