View Full Version : Heat Treating questions (moved from the old board)


ChrisChatelain
04-24-2003, 09:41 PM
today I signed up and posted a message at the old board, and it wasnt until after posting that the message at the top of the screen registered in my brain. so here I am. my message I just pasted below:

Every knife I make seems to be getting better and better...I'm hooked. I love this hobby.

anyway, my last knife attempt I tried hardening myself. Ran over to my dad's machine shop, used the oxy-acetelene torch, heated it up to the color said on the chart they got there, and quenched. a file test showed it was hard. but I dont think I tempered it very well, as it broke a few days later while I was making a handle...

the new incarnation of the knife is very small, blade length being 2", with a flat grind, from 1095 using the stock removal method. This time I'm gonna try using this big magnet I have under the workbench.

I picked up a propane torch the other day and heated up a small peice of 1095 until it glowed a bit, but it took a while. is it realistic to think that I can heat up the first 1/2" of the edge to the non-magnetic state with a propane torch and enough time? Would plain distilled water be a good choice to quench in? (my understanding is that plain water is less "harsh" than brine...is it?)

Now for tempering:
Last time I tried this, I brought the edge to a light straw color....would it be easier for me, having done very little heat treating, to just use my household oven to temper it? If so, how long should I leave it in there for? Do I need to quench the knife right out of the oven?

My last knife broke halfway down the blade when I had it clamped in a vise, and was filing away at a piece of pvc clamped to the handle....I'm guessing from my experiance that either that tempering job sucked, or that working on the handle of a tempered knife is a no no....anyh thoughts

Thanks for all your help people, even though I've just been lurking until now, your discussions have really helped.

Terry Primos
04-25-2003, 01:03 AM
Hey Chris, and welcome to the forums. I moved your thread to the Newbies forum so that you can get more action.

I'm tied up on some other things right now but I'll quickly touch on a couple of things for you. These will be my personal opinion.

You probably did reach critcal temperature and did get a hard edge. I think the fact that the blade later broke is because of the tempering.

I don't care for the idea of drawing back (tempering) a blade with a torch. The transformations that need to occur in the tempering phase, occur slowly. I'd use the oven. A common method is to temper three times at two hours each.

The first pass will convert the un-tempered Martensite (fully hardened) to tempered Martensite. This slow controlled tempering will also convert retained Austenite into Martensite. This newly formed Martensite will of course be un-tempered and hence unstable. The second pass will resolve that. Most of us go for a third temper just to make sure.

You will probably get different opinions on the temps. On the 10xx series steels I like to take the blade up to somewhere in the range of 435-450 degrees F. This will be well beoynd the light straw you mentioned. I just feel that light straw is still to brittle for these steels.

Definitely buy an oven thermometer. Kitchen oven are not precise. Mine is off by 25 degrees F. when set at 375 F. Another fellow I know said his is off by 50 degrees F. I have heard of them being even worse.

I'll let someone else chime in now.

Sethhoward
04-25-2003, 08:28 AM
Terry hit on most of it but I would like to stress somthing you mentioned in your post. DO use the magnet to tell if you are at critical temp. It doesn't lie. Colors vary according to the amount of light around at the time. My questions may not show it : ) but I have been making knives on and off for several years and there has been many a time when a blade got to critical way before I thought the color was right.

Some really like tempering with a torch or touching the blade to a heat source. I think most everyone that uses this method heats the spine and watches the colors move to the edge. I prefer the oven myself but either way do temper multiple times as Terry has said.

Seth

Ray Rogers
04-25-2003, 08:30 AM
You might be able to get that little 2" blade hot enough with a propane torch but generally propane is not hot enough. Try MAPP gas if you can't get acetylene.

The magnet is a good idea.

Quench in used motor oil. Warm the oil a little first by putting a piece of hot scrap steel in it. Water works fine for 10xx steels but there is a much higher chance that the blade will crack during the quench.

Temper in the oven like Terry said. The process is: heat with the torch, quench in the oil, then temper in the oven. DO NOT quench after the temper, just remove the blade from the oven and let it air cool. Multiple quench cycles like Terry said are the best way, but if you are in a hurry - or your wife wants the oven - tempering even one time for one hour will work .....

whv
04-25-2003, 05:58 PM
they got you covered, chris. welcome to ckdf!

ChrisChatelain
04-25-2003, 09:50 PM
wow guys, thanks for the help...

does MAPP come in a bottle that fits my propane torch or am I gonna have to buy more equipment for it?

Terry Primos
04-25-2003, 11:00 PM
It will fit your current propane torch.