Extended Tempering Times

[J. Hoover]

Has anyone Tempered blades longer than the usual 2 hour recommended time for most steels. I was just wondering what 4 hour tempering cycles would do to a blade. Harm or help???

 

[Bill DeShivs]

Nothing.

 

[J. Hoover]

Thanks Bill, I was kinda figuring that, but wasn't sure. Just a waste of time and energy huh.

 

[Gabaski]

there is a good read in the forum about tempering the steel for more then 5 hour . - and if your heat control is right . doing it for 5 hour is not going to make it a better knife ..

ok i found it , her ethe great thread

Analysis of the 5 hour O-1

http://www.bladeforums.com/forums/showthread.php?t=398842


------------------------------------------

 

[Nathan the Machinist]

The tempering time and tempering temperature dictate the temper the steel will receive. In theory you could do a very short temper (only a few minutes) at a slighter higher temperature, or a very long temper (a day) at a somewhat lower temperature and get the same results. We use 2 hour tempers because it removes time related heat gradient issues and doesn't take all day.

A knife left in temper overnight (because you forgot) will probably be a point or two softer. A knife left in an extra hour won't be measurably different.

I'm not aware of any advantage of a cooler slower temper. However, I am aware that a water "quench" out of temper isn't generally harmful, and can reduce the nano precipitation of certain carbides that can cause cold brittleness in certain steels.

 

[Kevin R. Cashen]

there is a good read in the forum about tempering the steel for more then 5 hour . - and if your heat control is right . doing it for 5 hour is not going to make it a better knife ..

ok i found it , her ethe great thread

Analysis of the 5 hour O-1

http://www.bladeforums.com/forums/showthread.php?t=398842


------------------------------------------

It is very important never to fall victim to the old, but very large, error of using "tempering" and "hardening" interchangeably. Many older texts that do not cover heat treating in depth refer to all the operations from heating and quenching to tempering as "tempering". The thread linked to above concerned soaking before the quench, and not tempering. It is also worth noting again that while there was no real grain growth, there are plenty of reasons NOT to soak a steel for 5 hours, beneficial primary carbides will be poor little cripples and what they gave up will not doubt give you endless retained austenite issues.

On the topic of extended times in actual tempering, there was a thread just two weeks ago or so here that we discussed this in answering the question of whether it is wise to try to shorten the time with higher temperatures. Without retyping it all again I will refer to to that thread, if you can find it, and the explanation of the possible benefits of lower temperatures with extended times, as well as the referenced texts.

 

[J. Hoover]

Thanks guys, good information, I am especially intrigue by the water quench out of the tempering oven. I always stick to the recommended hardening and quenching guidelines from Crucible and other sources for my blades with the exception that I usually do three tempering cycles.