Double tempering of 01 steel

DiverTexas

DiverTexas

Well-Known Member
I could have sworn I saw some info here on the benefits of double tempering 01 steel, but my searches have come up empty.
I have been tempering my blades twice at 450 degrees for 1 1/2 hours each time with an hour cool down in between cycles.

I had someone on another board tell me it was a waste of time doing the second temper. Is this true?
 
IMHO, the second temper is a good idea. After the first one some of the retained
austentite in the blade will convert to untempered martinsite. The second
temper fixes that problem.
 
I temper twice too

2x 1.15 h

I have heard it´s best to cool it in cold water between cycles to give it more durability and don´t let it cool down for too long

That can mess up the hardness...

I think 450F is too high ... all the steel experts told me that I shouldn´t go over 400F

Don´t know if it´s true but hardly anyone over here tempers O1 over 400F

AL
 
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Regarding tempers, yes for O1 I do two tempers. For some high alloy stainless steels, I do three.

You can quench in cool water to room temperature after each temper without effecting the steel. I just let mine cool in room air. There shouldn't be any real difference as far as anything I've ever read or heard. As for what temperature? That depends on your indended use. 350 will often get you a little chippiness if the knife is used hard (around 61-63RC depending on your austenitizing temperature), 400 is better for a slicer at around 60RC, and 450 might be good for a hard user at 58-59RC.

--nathan
 
I do three two hour cycles on all my steels, except when I austemper when I do two one hour cycles at about the same temp that the oil bath was at. I have just started doing that proceedure so that process my change in time.

Doug Lester
 
Heat Treaters Guide doesn't recommend a double temper for O1. Martensite finish is about 150F (99%) so there shouldn't be retained austenite when putting in tempering oven at recommended "hand warm" (125F -150F).

"Mete" has always recommended two, two hour tempers and Kevin Cashen does two or three tempers but he is creeping up on desired finish hardness by taking Rockwell readings after a temper.

Me, I always seem to be doing multiple blades of differing steel requiring differing quench temps so the oven is tied up when I want to temper. I dump the hand warm blades into a toaster oven at 300F - 320F for 1/2 hour, then air cool, and do a single temper later when the oven has cooled.

Mike
 
Mf is really 150F? Interesting, in that case 1 temper is probably enough. My book lists the sister steel 1095's Mf as -50F when all the carbon is dissolved. I wonder about the discrepency.

I've tempered O-1 as low as 350F and it's performed well. Note that my toaster oven read 400F, but the actual temperature as measured from a probe was 350F. And the temperature is different depending on where in the oven you place your knife, by as much as 50 degrees, so it's hard to give recommendations.
 
In any case, a second temper could do no harm. Just consider it as insurance.
 
cotdt said:
Mf is really 150F?
Click to expand...

No, not really... I haven't read the diagram right and I'm sorry... not 150F but 100F for O1 @ 99% martensite.

The two references I have show W1 of 0.95% C and 1.14% C at 0F and 100F for 100% martensite, respectively. That seems odd to me given the austenitizing temps were both the same (5F difference... 1450 and 1455). The 0.95% C W1 is very similar to 1095... very slightly less Mn is the difference.

Mike
 
Mike Ms or Mf (now mostly referred to as M90%) are not set in stone, nor in any exact place on the chart. It is determined by the amount of carbon in solution, in conjunction with other alloying elements. If you look around you can find I-T diagrams that can show over 100F difference for the same steel :eek: Then if you look closer the charts will list different austenitizing temps for the samples used. Soak times and temps determine the amount of carbon in the austenite, the greater the temp, the more carbon, the more carbon the lower Ms/Mf. Overheating hypereutectoid steel results in M90% reaching room temp or below, and thus retained austenite. Under soaking results in lower hardness as well, but it also raises Ms/Mf significantly. So the good news in under soaking is that one can get it to where you can temper while still quite warm without stabilizing even more austenite, but the bad news is that you won't notice the advantage because your hardness levels will suffer anyhow. That is why there is a narrow window, or certain time to nail the proper austenitizing for a steel, and it is so bad to overheat steels with more than .8% carbon.

This is just one more illustration as to how important it is to have reliable temperature and time controls on austenitizing heat. Get that heat right and a lot of the other factors get much smaller, get that heat wrong and most of the other factors won't save you anyhow:(.
 
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In this discussion of double temper - would a "snap temper" at 100 deg less be considered as a "temper cycle" or just a stabilization?
Also, we've all seen charts on 0-1 saying 1450-1500 for quench temps- does this range relate to final tempering temps in any way? Say if I am going to go for a lower hardness, then use higher quench, lower temper etc.?
 
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