Third temper

[Lo/Rez]

I heat treated some AEB-L (with dry ice and denatured alcohol after the plate quench) and because I have time today I'm doing a third 2 hour temper. Is there any advantage to doing a third temper, or am I just wasting electricity?

 

[Stacy E. Apelt - Bladesmith]

With AEB-L, not really. It won't hurt, but any gain would be undetectable.

On very high alloy and high carbon stainless steels, a third temper is a good thing. AEB-L is not much more than 1070 with 13% chrome.

 

[Lo/Rez]

Thanks. I appreciate it. On the high alloy or carbon stainless steels, what does the third temper accomplish?

 

[629hugo]

here's a decent paper on optimizing D2 and H13 heat treat for industrial knives. Triple temper is one of the parameters of the test.

https://tspace.library.utoronto.ca/bitstream/1807/13366/1/MQ45596.pdf

 

[idaho]

Thanks. I appreciate it. On the high alloy or carbon stainless steels, what does the third temper accomplish?

In high alloy steel (doesen't need to be stainless) you've got a secondary hardness effect with high temperature tempering. This effect is achieved by mechanisms, one of is martensite formations from retained austenite.

With freshly quenched high alloy steel you should get about 20% RA, during tempering you create conditions that allow this RA to be quenched when knife gets cold after tempering.
But you still have some RA, and you have now some fresh martinsite that requires tempering.
And you can do it 3 times with visible effects on some steels, depending on their composition and your Heat treatment proceres - Austeniting time and temp, quenching speed and final temperature