Heat treat question

[SpikeC]

The knife that I just made is in O1, and when I was heat treating it the oven slipped up to 1600º for a few minutes after I put the blade in.
What are the consequences of this? I lowered the temp promptly, but it stayed around 1550º for a few more minutes. :devilburn:

 

[Michael Rader]

Hi Spike. You might have a little grain growth, but I doubt it. Since you lowered your temp back down to 1550 and I assume you quenched from that temp, you should be fine. However, you should definitely do quite a bit of testing, etc... And do you have a hardness tester? You might find this blade is a point higher than normal, but might not hold an edge as long. Strange things can happen here, so keep notes on your testing and you might have discovered a little technique here worth repeating... or not.
-M

 

[SpikeC]

Thanks, Michael! I do not have a hardness tester, butt I just put an edge on the blade a couple of hours ago and it felt good on the stones. I didn't heat soak very long, so that should help, I think. I quenched in a fast quench oil and tempered at 350 for an hour.

 

[Michael Rader]

So, just curious, why 350 on the temper? As Bill Burke might say, "just enough to take the curse off." (Paraphrasing. He told me that once regarding how he tempers his 52100 kitchen knife blades.) Does the edge flex under the brass rod or chip out? Cutting some rope - do the little micro teeth break off? Might be too hard still. Or not. Soak times make a huge difference too. If you have some chip-out, try the same tempering temps, but do it for two more hours and then test again. Lots happening there with the second and third temperings.
-M

 

[SpikeC]

I'm finding that tempering at 350-355 is not resulting in any chippy behavior at all. If I whack the blade on a piece of brass brazing rod I get a dimple, not a chip. I've coated my blades with a firescale preventer from Brownells and the steel comes out of the quench quite clean. These 2 blades seem to behave pretty much the same.