tempering question

i appreciate your comments. I'll run that by bruce, but i see no flaw in your suggestions! thank you for your easy to understand wording. i am still quite a bit a newb and have a long way to go before i understand the nuances of how steel changes under heat.

heath
 
I'm not sure about the steels you use, but everything that I have ever read says that tempering twice at the same temperature, you gain practically nothing. What I have read is that you should back the 2nd tempering temperature down 25 degrees. This is pretty much a stress relief temper that aids further in the change of the austenite to martensite.

Everything also that I have read about tool steels says that you MUST temper after quench when the part drops down to 120-150 degrees. When you can hold the part in your hand, sort of - it will be major borderlining uncomfortable to hold in your hand, but you should be able to hold it. Have the tempering oven ready at temperature so the blade temperature goes up instead of dropping further down. The books I've read says that even if you can't visibly see damage done to the blade, it's been done if you wait till the blade falls to room temperature. After you temper the first time to relieve stress from the quench, you can wait either 1 hour up to 500+ hours to temper it the second time.

I say bring a small toaster oven when you go over to bruce bump's place and temper after the HT. Don't wait 10 minutes rushing over to whoevers place to temper. Buy a 30-40 dollar toaster oven and use a thermometer from say a barbeque grill to make sure you're at the correct temperature. You can even temper it low say 200 degrees so long as you get that first temper in after HT. When you do your final temper(s) or the highest your gonna temper, i'd suggest you do it in a kiln which a more accurate temperature holding wise than a toaster oven and then you can back in down again by 25 degrees on a 3rd temper to refine the grain even further.

I wouldn't just flat out jump into 400 degrees right off the bat with the first temper. you can always draw down, but you can't go up! :) hope I haven't confused you or just said a bunch of worthless crap.
 
Tempering has no effect on grain size, it cannot refine the grain !! Grain size is established by the austenite grain size and what happens at the Ms temperature.There's nothing wrong with going right to a 400 F temper.Reducing temperature by 25 F I don't think will have any significant effect. Don't confuse this with multiple hardening with reduced temperatures.
 
Sorry mete, perhaps i'm giving him tempering information regarding tool steels only. Atleast that's what I have read to drop it down 25 degrees for a stress relief temper. Perhaps all my terminology is all wrong. Oh well, I just know how to do it and not say or type it out. lol.
 
Leu Custom said:
Sorry mete, perhaps i'm giving him tempering information regarding tool steels only. Atleast that's what I have read to drop it down 25 degrees for a stress relief temper. Perhaps all my terminology is all wrong. Oh well, I just know how to do it and not say or type it out. lol.
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Hi,
The data sheets do have instructions for stress relieving heat treated parts, but it's optional. The purpose for it is if you do some post-heat treat machining or grinding, sometimes the part will warp, so you do the stress relief (after grinding) to help prevent/correct that.
 
Good thread. I think I saw something about Master Bruce offering his HT oven for two blades that are anywhere from 10 minutes to 3 hours drive away from tempering. Ten minutes away from temper may not (?) be too long. Three hours drive; forget it. Allow the steel, after quench, to cool to hand warm and place in PRE-HEATED temper IMMEDIATELY. You may be able to figure out a way to hold the steel at a high enough temperature long enough for the trip to tempering oven. That should be fine.

rlinger
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Take a cheap styrofoam cooler and fill it with warmed sand, after the quench stick the blades in the sand and away you go. Should keep you at around 150. Warmed kitty litter would probably be fine to and lighter. Just give the blades some accompanying mass and insulation. A large thermos full of hot coffee (or water) would do the same thing.
 
There you go. Good ideas there. Experiment prior with a blade boiled in water to bring up to 200+ F. before the real run to proof the idea(s).

rlinger
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You are dancing all around the obvious. Boil the blade for about 15-20 minutes and it will have a good snap temper. Another way is to bring the quench tank up to 200F by sticking in hot steel. Either method will not require any special ovens. Once it has a snap temper, you can safely take it home and do the tempering,cryo and all as usual.
Stacy
 
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