Air Quenching Question

[CDS]

Hello Everyone,
I have done a little searching on this subject, but have not come up with much in the way of a direct answer. I am getting ready to start my first heat treating attempts. I have a Paragon Knife makers kiln and will be starting out with 440C. These are primary going to be small(2.5"-3.5") folder blades. I plan on using a rack inside the kiln for standing the knives on and also pulling this rack out for quenching. My main question is, do I need to get a fan to quench with or should the steel just be allowed to cool with ambient air? Also, I have been told by a couple of people to remove the steel from the foil wrap as soon as it is removed from the oven. Any particular suggestions, thoughts, or recipes on this subject are greatly appreciated.
Chris S.

[Jerry Hossom]

Faster quenching is better. If you use a fan, make sure it is pointed at the tangs or points so both sides of each blade cool at the same rate. The best way to cool them is with quench plates, basically any large plates of metal that will serve as heat sinks to draw off the heat. Most people I know use 1/2" or thicker aluminum plates and sandwich the blades between them while still in the foil after they come out of the oven. This is almost a must with CPM-3V or S30V to get full hardening.

[SteveS]

I'm doing what Jerry says (quench plates). Works fine. Some guys insist I take them out of the packet first, but I get the rated hardness while in the packet.

I know one guy that uses a fan and in the packet. He could not get full hardness without a wind tunnel (read coffee can with both ends cut off). He also does one blade at a time.

So, if you are going to use a fan (based on my buddy's tests - and he does a lot of that) either take them out of the packet or put them in a tunnel with the fan putting all its air thru it.

Steve

[rlinger]

That's about it. I do not believe in taking time to remove from foil. Faster to quench the better. Regardless of quench preference get the steel there quickly.

For 440C, I austenitize at about 1850 or 10 to 15 degrees higher. Rapid air quench and snap temper at 280 to 300 F / 1 hr, deep cryo and temper @400 F followed by a 375 F temper. Target hardness is 58 HRc. The 440C I just finished HT'ing last evening tested 59 HRc. It was done the same as decribed above except that the snap temper was 280 F.

Be sure to get your steel (stainless or otherwise) in snap temper or temper before falling below hand warm.

RL

[R. D. Finch]

rlinger

What do you mean by snap temper?

[rlinger]

I do not think I know all the machanics about it but:

It is a temper performed at a lower temperature and for less duration than a 'temper' is. It transforms enough austenite for safe handling before tempering and can be used to post pone tempering for a little later, even after the steel has fallen below hand warm. I use it for the main purpose of deep cryogenic treatment before temper. It helps insure against micro-cracking from the extreme thermodynamics while getting the steel to such low temperatures.

RL