heat treating 440c stainless steel

[lapuser]

I have a customer who has ordered clamp feet made of 440c. What he wishes to achieve is to have a corrosion resistant but also hardenable clamp feet for mixer motors in a salad dressing mfg facility. What I need is exact info on how to heat treat 440c to a state that is both hard and also tough to resist some fairly serious compression and torque without deformation or cracking. The info I have found to date talks of things like soaking but gives no time frame for this step. I have yet to find out if this material needs to be wrapped in 321 foil prior to heating. In general what I have found to date is so incomplete that I cannot go forward with this project. Of course any he3lp at all would be greatly appreciated. Thanks, Dave Ault-

 

[TVP]

Soaking times employed in the hardening of martensitic stainless steels such as alloy 440C represent a compromise between achieving maximum solution of chromium-iron carbides for maximum strength and corrosion resistance, and avoiding decarburization, excessive grain growth, retained austenite, brittleness, and quench cracking.

For sections 13 mm and under, a soaking time of 30-60 minutes is recommended. For most parts, adding 30 minutes for each additional inch of thickness is adequate. Soaking times should be doubled if parts have previously been fully annealed or isothermally annealed.

You can find more information at the following websites:

http://www.timken.com/products/specialtysteel/engineering/tech_info/html/Knife Steels.htm

http://www.timken.com/products/specialtysteel/engineering/tech_info/html/T-T 102.htm

http://www.crucibleservice.com/eselector/prodbyapp/stainless/cru440cs.html

Strangely, Carpenter's website merely mentions soaking, with no associated time. Perhaps their information is what you have been seeing. Other than this omission, I highly recommend them, and their website for technical content:

http://www.cartech.com

(click on Technical Information)

 

[MattSac]

Heat treat and temper in a vacuum or inert atmosphere if possible. I'm no metallurgist, but the corrosion resistance of 440C can be seriously affected by heat treatment, and my experience has been that surface oxidation, crud & corruption or whatever, caused by exposure to air during heat treatment, doesn't help matters much. Of course this would negate the need for stainless steel foil wrap, too.