Another question about heat treating...

H

Hesparus

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Oct 31, 2004
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Hopefully this will be my last question(s) about heat treating for a while.
I've got four blades that are ready or almost ready for heat treating, and, after a few unsatisfactory results, I want to get a few things straight before I turn my hard work into crappy knives again — although maybe the crappiness is inevitable ;).
I'm using Admiral steel 1075/1080, forging 95% to shape (~1mm edge at quench). I'm not using a calibrated quenchant. I did my first couple of blades in canola oil: the first one didn't really harden, and the second hardened but poorly. I rehardened the first blade using an interrupted quench in warm water for a fast count of three, then into canola oil. It got pretty hard, but cracked. After reading some more and thinking about it a lot, my feeling is that the edge was probably too thin to harden safely in water (right?). Being so thin, though, should canola oil work well enough?
I've been heating my canola oil to around 110º-120º (my quench tub is plastic and I'm worried about it melting. I guess I should just get a better one). I've heard two different recommendations about oil heat: (1) the oil must be around 160º and no hotter than 180º, or (2) that 120º is fine. How big a difference is it going to make if my oil is 120º vs 160º?
Finally, I've heard two different things about normalizing. One method of normalizing says to let the steel cool to room temperature, and the other says to let it cool to 600º. What's up with that?
I'm starting to wish I had gone with 5160 instead of 1075.
Thanks,
Chris
 
" I'm starting to wish I had gone with 5160 instead of 1075.
Thanks,"
Chris "
No you're not. Your oil temp is OK. I go 130° 135°, but no hotter. Any temp beyond 140° is BS. That should not melt plastic, even with the increased temp of the hot blade. You can go either way with normalizing 1075. Try this. Forget the magnet if you are using one. In very dim light, bring the blade to a bright red-orange. I know, everyone sees light different, but try it. Let it soak at BRIGHT red-orange at least 30 seconds to a minute, then quickly plunge into the canola oil moving the blade fore and aft. Not sideways at all. Keep moving it while in the oil. 45 seconds to a minute and it will be hard. Remove, adjust for warp if you have any. You have maybe five minutes to hand straighten any warp. Then check the edge for hardness. If it ain't hard, it ain't 1075. You can take the edge down to around .040 beforehand. I take my edges to almost their finished thickness, although I use 01, an oven, and Parks AAA oil. Try a sample piece if possible, but if it is 1075, it will be hard. Try a sample piece.
 
I had a batch of 1075 from Admiral that I never managed to get a fully hardened blade from. They consitently turned out with soft spots and showed a good deal of alloy banding in the unhardened areas when etched. I was quenching in Tough Quench which should have been fast enough. I eventually gave up on it and went to a different steel.
I can only suggest that you try higher austenizing temps than what is spec'd, and a faster oil would likely help also. Soak time never seemed to help for me.
 
LRB: Thanks for the advice, I'll give that a go. At the risk of sounding dumb, how do I soak a blade at temperature in a charcoal forge without it overheating? Relatedly, I have always heard that 1075 doesn't need to soak?
Justin King: That's discouraging. I have tried quenching at a higher temp than is recommended, and it worked but gave poor results.
Thanks again.

- Chris
 
I should add that I was HT'ing in a gas forge without temp. control, so there are lots of possible variables.
 
LRB said:
" I'm starting to wish I had gone with 5160 instead of 1075.
Thanks,"
Chris "
No you're not. Your oil temp is OK. I go 130° 135°, but no hotter. Any temp beyond 140° is BS. That should not melt plastic, even with the increased temp of the hot blade. You can go either way with normalizing 1075. Try this. Forget the magnet if you are using one. In very dim light, bring the blade to a bright red-orange. I know, everyone sees light different, but try it. Let it soak at BRIGHT red-orange at least 30 seconds to a minute, then quickly plunge into the canola oil moving the blade fore and aft. Not sideways at all. Keep moving it while in the oil. 45 seconds to a minute and it will be hard. Remove, adjust for warp if you have any. You have maybe five minutes to hand straighten any warp. Then check the edge for hardness. If it ain't hard, it ain't 1075. You can take the edge down to around .040 beforehand. I take my edges to almost their finished thickness, although I use 01, an oven, and Parks AAA oil. Try a sample piece if possible, but if it is 1075, it will be hard. Try a sample piece.
Click to expand...

This has been my experience also, almost to the letter. I used to do some blades (1080) in canola oil and they hardened just fine using the above method.

Justin- I wasn't very happy with 1075 steel from admiral either, though I had different issues than uneven hardening.

To the OP, you may want to try steel from another supplier but 1075 is good steel.
 
I have stopped buying steel from Admiral because their steel and their service are both crap, but I think in this case it is more likely your technique. First, how are you determining your steel temperature in the forge? How are you measuring your hardness? Are you grinding through your decarb layer before trying to test your hardness?

have you read the stickies?

-Page
 
I get my 1075/1080 (from Admiral) from Rob at Ranger Originals in Cremona. I haven't had any problems with the steel not hardening properly in plain canola oil. I actually really like this steel. LRB has good advice.
 
1) I've been determining temperature by color (I've been going to full orange. Non-magnetic starts for me at dull red). I've been thinking about doing my quenching at night to standardize this.
2) After quenching, I test hardness with a chainsaw file. My real problem has been with the edge-quality, though. After putting an edge on with my lansky, my blades either don't shave or barely shave. The time I quenched in water yielded a clearly harder edge and cut pretty well, but the edge cracked. I've been tempering twice for an hour each at 400º. I'm going to try a cooler temper, and if that solves my problem, boy will my face be red. It occurs to me now that I haven't checked the accuracy of my toaster oven, but it did work for the water quench, and I can't imagine it'd be so far off as to really mess up the temper (or can it?).
3) I have read the stickies, but I must confess I had a hard time understanding a lot of the information.
4) I guess I have no way of knowing whether there is hardened steel underneath. I don't have a grinder (and nowhere to put one if I did), so I need to forge everything pretty much to the end. On one knife, though, I ground it down with my dremmel and there was no sufficiently hard steel in there at all.
5) I've always heard people speak highly of Admiral steel until now. Is the overall quality low or does it vary by batch? I've got another 7' of this stuff, so I really hope I can get it to work.
Thanks,
Chris
 
You mentioned this but I want to stress it. You MUST check your toaster oven temp. Those things can be off by as much as 75 degrees going by the dial. Spend the few bucks and get an oven thermometer and know for sure.

My dial on the oven was WAY off. But it holds an even heat almost to the degree for three hours without spiking at all. I even checked mine with two oven thermometers to make sure the heat was even and both thermometers were right.:)
 
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