Snap tempering for hardness testing...

[Mike Krall]

I pulled this... Martensite goes through a few changes as you heat it, the first begins well below 365F when carbon atoms move enough to allow the stressed body centered tetragonal to relax into the body centered cubic formation, but there will be no visible changes in martensite at all from this except that we can avoid a blade going "ping" just setting on the bench.... out of the end of post #8 (K.Cashen) in this... http://www.knifenetwork.com/forum/sh...ad.php?t=50189.

I've got access to a Rockwell tester but I have to travel to get to it. I can't test for hardness as a blade reaches martensite finish. I was thinking I could snap temper blades then test them for hardness later. As I understand it, a snap temper will reduce stress enough to avoid "the dreaded 'tink' ". I'm looking for discussion and/or reference to the process.

What I think I know is this... bring hand warm blade to 300F - 325F and hold one hour.

Is there a rule of thumb for percentage hardness loss from as-quenched to snap-tempered?

Mike

[AcridSaint]

Hi Mike - you may want to temper lower to relieve some of that stress and maintain hardness.

My specs show that 440C and 154CM should retain as quenched hardness to 212F. I also see that you'll pick up two points over as quenched with 212 and cryo, at least with 154CM.

O-1 should retain as quenched hardness to 300F.

Hope that helps.

[mete]

There were some makers who ran tests for stabilizing retained austenite with 154CM over on BF. We found 300 F did not effect RA while 350 F did. From that I recommend 300 F for a snap temper. That temperature shouldn't change as quenched hardness.

[Mike Krall]

Thank you both... Does the time at temp (300F) have a minimum?

Mike

[mete]

1-2 hours should do fine .

[Mike Krall]

Thanks, Mete... I'm in 'bidness' now...

Mike