proper speed of air quench

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In reading various posts it seems that many guys are trying to get the temp down asap. How fast should an air quench actually be?
Does it differ for different steels? Can you differentially harden by blowing compressed air on the blade edge? Can you cool it too fast? Will it still harden if you just let it slowly cool in room temp air?

Got my HT furnace wired and want to do some testing with air hardening steel.
 
I admit I am still a little confused by the idea of air quenching. Every other type of quenching is about putting the blade into some medium like oil but is air quenching as simple as pulling the blade out of the furnace?
 
Well, the idea of air quench works for those steels, typically Stainless Steels that will cool fast enough in air to fully harden. Sandvik's steels are an example - they only require to drop from soak temp (1950ºF range) to 1200ºF in 2 minutes to fully harden. In small blade sections this will happen with only air cooling, but best is to use plate quench. Clamping the blade between two plates help prevent warping of blade.

I like using these steels so messy oils are not require with all the oil vapors given off in the room.

Good luck and have fun,

Ken H>
 
What if you get it to room temp in 15 seconds? Reason I ask is if you were doing multiple blades and didn't want to over soak them. So, you clamp one in the quench plates, blast it with air, take it out of the vise, pulle the next blade out of the furnace, lather rinse repeat.....
 
if you can get to 15 seconds everytime, you could do O2. haven't seen any comments about cooling air hardening too fast. several manufacturers sites have oil quench as an option for 440C. would be great to have two sets of quench plates and 2 vises.
 
There is no need to blow air between the plates or freeze them as some people claim. These steels will harden in still air but the plates give it a boost and keeps everything nice and straight like Ken said. If you have a handheld infrared thermometer, you can shoot the surface of the plate until the temp. stops rising and take the blade/blades out. Once the temp. max's out, the plates have done all they can/will do. I just use my hand and when they stop getting hotter I remove the top plate, cut the blade out of the foil, check for straightness, & make corrections if necessary.
There really is no need for more than one set of plates because they will cool back to room temp. while the next blade is coming up to temp. and soaking. It only takes a few minutes. I hope that answered the questions. If not let me know.
 
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I've done quite a few blade is the CPM S30 and S35 vn steels. I use quench plates also.
I remove from the oven and cut the end off of the wrapper , place between the plates , put my knee on top of the plates and blow compressed air inside the wrapper and around the blades. I've never( in the past 7-8 years) had a warped blade and they are always harder than the hounds of hell afterwards.
If the blade is ground evenly , they usually wont warp.
I think the plates just help speed up the process.

Dwane
 
Thanks guys. Another way of asking would be if you wanted to heat treat three blades and have the soak time of all three within a minute of each other, would cooling the blade quickly with plates and air damage the blade any? Or, Is there a reason to not want a blade to cool in 10-15 seconds?
 
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