Temper question.

B

Brainburn

Member
O-1
Would it be better to temper three times at approx two hrs each or two tempers for three hours each?

If I heat up the blade during the final sharpening (after HT) will re tempering take care of the brittle spots?


Thanks all,

Mike P
 
how thick is the blade? for thinner stock, 1/8" or less, 2 one hour tempers with water quench in between should be all you need. if you are OCD about tempering, then 2 two hour tempers with water quench in between. with O1, do not temper over 400F. one reason is you are entering the temperature zone where hydrogen embrittlement can happen. second, temper at 350F to 400F will give you your best hardness and toughness https://www.crucible.com/eselector/prodbyapp/tooldie/ketos.html
if you heat the blade during sharpening, you will end up with 'Soft' spots, where small areas of the blade were heated above your tempering temperature.
 
I second what Scott said. Small heat increments of even 25° can make a difference when it comes to tempering and there's no way you can tell the difference while sharpening. I assume you are sharpening on a belt. Hold your knife with bare hands so that you can feel the heat build up and when it gets hot to the touch cool in water. You may have to wipe your blade dry if your belts don't like water.

Doug
 
As the concept of multiple tempering has caught on (everybody use to just heat for two hours and call it good) I have seen some misunderstanding leading to some really extreme tempering times. Two hours is really all you need and so multiple tempering cycles were intended to fall within the two hour allotment, i.e., two 1 hour tempers equals two hours, rather than four or six hour temper schedules which are rather extreme, unless ones backs off the temperature to compensate.


Final sharpening should involve no heat; that is why it is best not to use a belt if you cannot incorporate coolant. Should it overheat it will lose hardness and strength and tempering will do not thing for it but further that process.
 
I totally agree with Kevin's input! He and I both have been doing this for a LOT of years, and I always find myself amazed at some of the strange time/temp "recipes" that people seem to be coming up with these days. :)
 
Hey thanks guys...

Forgot to mention thickness. Sorry..
Either 1/8th or 5/32 for the most part.

I have been over doing it then.

Tempering =
1/8th O-1 500 F for a total of 6 hrs (3 X 2 hr temps)
5/32 O-1 = Same as above.


Kevin,

Final sharpening should involve no heat; that is why it is best not to use a belt if you cannot incorporate coolant. Should it overheat it will lose hardness and strength and tempering will do not thing for it but further that process.
Click to expand...

Well, if what I am hearing is that I basically burned a blade and it cant be salvaged. I am really anal about everything and I would never feel comfortable with it now... Crap!

[EDIT]
Can I re-heat treat to correct it? (maybe?)
 
Last edited:
Yes, you can simply re-heat-treat and re-temper. On a side note- I hope 500F was a typo. 500F is way too hot for O-1 in in any cutlery application. O-1 has a strength to toughness ratio sweet spot for edge stability up around 62HRC, making 400F for 2 hours about the highest you would want to go with this alloy. If you need greater toughness it is much better to switch to another alloy that can hold a better toughness for the given Rockwell, then you will not have to overcook the steel in the temper.
 
No, it was accurate. 500 is what I was tempering at.
I got the info from this chart:

Tempering Temperature Rockwell
Hardness
[SUP]o[/SUP]C[SUP]o[/SUP]FHRC
14930065
17735064-65
20440062-63
23245060-61
26050059-60
28855057-58
31660055-57
34365054-55


I want to get the most out of my blades but, I do understand mistakes will be made. There is an ENORMOUS amount of information out there and a great deal of it can be conflicting.

Hey Kevin, sincerely, thanks man.
I would love to run my recipe by you at some point. I have a great deal to learn and my skin is pretty thick. I could use the wisdom...

Take care man,
Mike P
 
All I can add is DO NOT rely on any chart(s) as absolutes...... the problem with any chart is they assume too much. Use them ONLY as a starting point. When it comes to tempering, time and experience has taught me that the best avenue when using a "new" steel is to always temper on the low side, test, and if necessary, bump up the tempering temps in 25 degree increments, until you achieve the desired results. One thing that most fail to recognize/understand is the geometry factor when it comes to blades...... different grinds require different tempering temps for optimal results....which is a major reason that charts should only be a STARTING POINT.

Simply stated, you have to spend the time, and do the experimenting to achieve specific results YOU desire, otherwise it's nothing more then guessing/hoping.
 
Brainburn said:
No, it was accurate. 500 is what I was tempering at.
I got the info from this chart:

Tempering Temperature Rockwell
Hardness
[SUP]o[/SUP]C[SUP]o[/SUP]FHRC
14930065
17735064-65
20440062-63
23245060-61
26050059-60
28855057-58
31660055-57
34365054-55


I want to get the most out of my blades but, I do understand mistakes will be made. There is an ENORMOUS amount of information out there and a great deal of it can be conflicting.

Hey Kevin, sincerely, thanks man.
I would love to run my recipe by you at some point. I have a great deal to learn and my skin is pretty thick. I could use the wisdom...

Take care man,
Mike P
Click to expand...


Yes that looks familiar, tempering charts are a tricky thing and are one of those specs that Ed refers to when he says they are just a starting point. Austenitizing and quenching specs are much more relevant and I have found them to be highly reliable. But here is the problem- each thermal treatment the steel sees effects the subsequent ones; your annealed condition will heavily determine austenitizing soak times and even temperatures. Tempering is the final thermal event in a long sequence and so it has the most previously introduced variables to deal with. Through years of testing and observation I have found that if everything was done by the book (literally) the more the specs. in that book will more accurately reflect reality, this is why industrial heat treatment recommendations so often frustrate folks who use forges, torches etc. as a heat source. By the time one gets to tempering, in the average bladesmiths shop, so many variables have been introduced into the thermal history that a given HRC for tempering temperature is guesswork at best.

This is why I am very hesitant to recommend exact tempering temperatures for a precise HRC value, heck I still walk each and every one of my blades in to the exact HRC I want with several increasing tempering heats and I can hold austentizing temp within four degrees F. timed to the exact second… and still. Thus, you will notice, that any charts or advice I ever provide about HRC for tempering temperature will have a range and not a specific HRC number, and once again, that is still presuming everything up to that point was to the letter.
 
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