Heat treating 01 tool steel..... help

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Lynn Westfall said:
I use a salt pot to soak my O1 at 1500 F for 20 minutes and then quench into 400 F low temp salt, when cooled to room temp, I put them in cryo (liquid nitrogen for at least 4 hours). Since changing to this setup, I've found that my blades tempered at 400F are not passing the brass rod test. I've gone to 450F and still had chipping issues. (Note, I'm using some pretty thin edges.)
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Lynn, are you tempering again after the cryo? Someone please correct me if I'm wrong, but my understanding is that you use the cryo to remove retained Austenite. The retained Austenite changes to Martensite, but then you have untempered Martensite left in your blade. You need to temper again after the cryo to get rid of the untempered Martensite. If you are not doing so, that may be a reason for the brittleness you are encountering.

By the way, the Heat Treater's Guide says that O1 should be soaked at 450 to 500 degrees F for 10 to 30 minutes. You are right at the upper temperature limit with your salts. Unless you are very sure of your temperature measurements, perhaps it might help to hedge a little and shoot for 1475 for the soak. Just a thought...
 
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I think that in Lynn's case with the salts and cryo, he is probably squeezing every last bit of martensite he can get out of the steel. That could then well demand a higher tempering temp, based on this HTG chart I abstracted. (Thanks, again, to the one who gave it to me originally!:)) I lowballed the original figure I gave to the OP assuming (perhaps incorrectly) that there would not be complete conversion with canola oil.

Another thing that occurred to me thinking about this was an excellent article that Steve Hayden has cited several times. The article was an investigation of the effects of cryo on A2. It concluded that cryo'd pieces had lower toughness at a given HRc than non-cryo'd samples. Perhaps it is applicable to this case with O-1, also.

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Chris, I go straight to cryo after quenching in 400 F low temp salt. (after cooling to room temp - I no longer utilize a 300F snap temper prior to cryo). After cryo I temper in a carefully regulated kitchen oven for at least two and usually three sessions. I've found that a 400F temper leaves a blade that does not pass the brass rod test. I've bumped my tempering temperature up to 450F and still have had blades fail. They are usually good at 475F but I've had to go to 500F with some batches.

I'm still playing with the variable with my O-1. I get my steel on-line and don't know the manufaturer. I've seen various heat treating formulas calling for different tempering temperatures to hit 59-60 RC, which is what I am shooting for. A Rockwell tester is moving up on my list of equipment to acquire next.
 
Oh well, it was worth a shot. I should have know that if you were using salts you would know enough to temper after cryoing.

As for your source for O1, maybe you should try some Starrett or other name brand for a comparison test. I buy most of my Starrett from KBC Tool. They often have it on sale at a good price, but don't list the brand during the sales. Every time I've bought some it's been good old Starrett O1.

I just grind my O1, since I haven't set up my kiln yet and can't return it the sheroidized annealed state it comes in yet. Each piece of steal comes with hardening and tempering instructions on the label. Interestingly, their numbers seem to differ slightly from the Heat Treater's Guide on the tempering temps, but perhaps that just the way I eyeball the curve on the HTG's chart...

Here's an image of the label.
Starrett-O1.jpg
 
Thanks for the info. I'll have to give KBC a try. I haven't had any Starret in a long time. There are tons of variables with this process. Sometimes figuring them out is a big part of the fun and at other times it is frustrating.
 
I have a 1/4 x 2 1/2 x 18 inch blade of 01 to heat treat. Only have a makeshift charcoal forge to do it. Anyone have 2 cents to put in on the how to do it? I am a newbe, first timer.
 
Carbon steel does not get wrapped in foil as it will interfere with the quench. you would also probably get more answers if you had started your own thread rather than digging up one that is 7 years old. many people see the old date and just skip them. Never worked with O1 so i wont volunteer any other info on that subject.
 
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