Waiting between quenching and tempering

Hi Stu,

Good to meet you on this forum :biggrin: - only "moved"here a few days ago after the closing down of SA Blade forum...

predicting it is an effort in futility
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You know, I suspect it also has something to do with how the steel is treated - most "the knife will crack if not tempered immediately after quenching" advice is given by people who forge, and/or do their heat treatment in a forge or with a flame. I have hardened quite a number of knives made with O1, D2, 5160, 52100 and 1095 (old Nicholson files...), as well as many stainless steels, by "proper" controlled heating in an electric kiln, and as stated previously have only ever had one knife crack due to too rapid heating after cryo. I wonder if uneven heating, or perhaps not soaking for the correct time could have something to do with the problem of cracking knives?

Any thoughts on this?
 
Glad to be discussing this with you here, too!!!! :punk:

I think you're probably right over the target with "uneven" heating. Overheating can be an issue. A lack of proper normalizing/stress relief...especially on the forged blades. But untempered martensite is extremely "stress-filled"....even when everything is done right.
 
I agree with A-V what is the reason for waiting to temper, I thought that immediate tempering was best.
 
You shouldn't "wait" to temper. You do need to wait long enough for the steel to reach martensite finish temperature, tho. When speaking carbon steels, this is generally about 150F-200F. So once the steel has reached room temp.....there should be no delay in getting into the temper oven. Maybe 10 or 15 minutes after the quench, a carbon steel blade should be ready to temper.

If for some reason you can't do the tempering cycles all that day, just be sure to temper it at 300F for 30 minutes. This will relax stresses in the steel until you have the time to run the full cycles.
 
This isn't really the same question as the OP posted, but follows in the same vein.

Say I have a blade that I heat treated (stainless so some sort of sub zero exposure is part of the process), all done in a timely fashion from when the blade was initially quenched. Then, several weeks later, I decide I'd prefer to draw the hardness back a little more, say increase the final tempering temperature by 25 deg. Would I get different results than if I had done the same thing on the third of a back to back to back temper sequence?

Thanks

-Kurt
 
Would I get different results than if I had done the same thing on the third of a back to back to back temper sequence?
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I don't see any reason why you would get different results, but perhaps one of the experts could confirm this?
 
Ditto what HennieL said. I don't think there would be any change/problem....but perhaps someone else who knows more can chime in....
 
Don Robinson said:
Seriously, the drastic change in temperature due to the quench causes so much stress inside that the steel may crack across the weakest point. This may not show up until the knife is used.
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I read this post by Don right after he made it, and it didn't really sink in at the time. I think what Don is saying here is a VERY valid point, and perhaps the real reason tempering right after quench is desired. Not so much from a metallurgical aspect - perhaps that is the same if tempered right after quench or wait until next day. BUT - I think what Don is say here (and it make a lot of sense), is even if there are not visible cracks from delayed temper, with all the stresses formed during martensite formation in the 400ºF to 100ºF range there could well be tiny hidden cracks formed INSIDE the blade that are not visible. This would weaken the blade. So, to prevent this "possible" hidden stress crack, it's MUCH better to do a quench as soon as possible after quench.

Don, am I understanding your thinking here? Anyone else please do comment, especially on the metallurgical aspect.

Ken H>
 
Ken, I believe you are right over the target dropping bombs there. Dead on. What if with AEB-L (let's say we usually do three tempers), and we quenched, did one temper, then the second temper, but we didn't have time to do the third.....and we forgot and it's been a few days.

Would there be any significant problem or change if we waited days or even a couple weeks or more to perform that last temper? My gut tells me no problem at all. That the most important variables we are trying to deal with during tempering, namely stress relief, RA conversion, etc are taken care of during those first two tempers.
 
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