Tempering question

P

Pete Allan

Joined
Oct 29, 2003
Messages
220
I read that some of you use a number of tempering cycles like 2 hr at 400f and then another 2 hr at 400f. My question is -- do you get a different result than I would if I did 4 hr at 400f ?

Thanks guys
Nice to have the forum up and running again.
 
What steel are you using Pete. If you are talking about steel like 5160 then yes, no and maybe. The two cycles just make sure the first cycle worked right. Other steels require very precise cycles, soak times, Etc.

I'm sure Mete or someone will chime in and give you the atomic count before and after the second cycle. ;)
 
Tempering is a complex process. As you heat the steel up the atoms start moving around and stuff starts changing. In general those changes seem to peter out at about 2 hours at the given temperature and little change takes place without restarting the cyle by cooling them off and heating them up again. Least thats how it was explained to me and it seems to make sense.

So in theory, a 4 hour temper won't be much if any better than a 2 hour temper cylce, and not as good as 2 -2 hour cycles.
 
Hi again I use 1080 and 1084 which I think are just simple carbon steels.
With the few knives I get to make I don't think I will move to any of the more complex steels
Thanks
 
I believe I understand your question as "why do two at 2 hours instead of just one at 4 hours". I am anxiuos to wait for Mete to expalin this but I think it may have alot to do with retained austenite that should be transformed after the first tempering. I think Matt may have nailed it in his above posting.

RL
 
Roger ,that's right. The first temper transforms retained austenite to martensite . This new martensite is untempered so it must be , therefore the second temper.Steels with lower carbon levels don't see retained austenite so the second temper wouldn't be necessary with something like 5160.
 
mete said:
Roger ,that's right. The first temper transforms retained austenite to martensite . This new martensite is untempered so it must be , therefore the second temper.Steels with lower carbon levels don't see retained austenite so the second temper wouldn't be necessary with something like 5160.
Click to expand...
Yeah,What Mete said. Especially important for stainless steels due to their high (as high as 3% ) carbon content.
 
Matt and Roger figured my question better than I did so at least I can tell you what brought the question in the first place.
I have a small HT oven that I bought about 30 yrs ago but I can't set a temp setting as it is the kind that I have to watch the gauge and keep adjusting the setting -- just like a kitchen oven. :grumpy:

Any one know where I could get a controller with a thermo couple that can be set to hold a temperature (at a reasonable price) I have lots of koa wool board so an oven would be easy to make.
Thanks again
 
You must log in or register to reply here.
Back
Top