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View Full Version : Reheat treating a blade?



Ernie Swanson
04-23-2011, 09:58 PM
Last weekend I heat treated and tempered my first knife, I sent it out to get tested and only got 55rc.

What would I have to do to reheat treat this blade?

It is 1095.

scherar
04-23-2011, 10:35 PM
Hi Ernie,

Is that the blade you had Clint test? If so, I'm impressed that you were that high in rockwell with the oil you were using; just going off all the time I spent with 1095 and canola oil. To answer your question, I think some would say to just restart your recipe and I think others would say it would be a good idea to do a quick normalizing cycle (probably two times at around 1450 and air cool) beforehand to eliminat any possible warpage.

My suggestion would be to order some faster oil if you are set on using 1095. If not, I would go to another steel (I think you said before that you have used O-1). I am pretty certain with a HT oven and the canola, you will be able to put some knives together. That is what I told myself a while back. Find a steel you are getting good HT results with and go with it. I am not the type of person to use a different steel for every day of the week. It is different when you are doing the HT yourself. I think you'll find yourself devoting a lot of time to "perfecting" a recipe!

Good luck.

Ernie Swanson
04-23-2011, 10:42 PM
I think I know why its so low. When I was tempering I noticed my oven hit 500 for about ten minutes before I turned it down. I tempered twice at 475

murphda2
04-23-2011, 11:27 PM
I think I would start at a lower temp. for tempering. I'd try 400 for two cycles and then test the blade. If it seems to still be too hard on a file test, I would bump it to 425 and go for another hour and test again and so on.

scherar
04-23-2011, 11:41 PM
Another thought is HT'ing another piece and not tempering it. This way you know what is going on during the quench. Quenching and then tempering before testing leaves you little in the dark since you don't know if you got good results to begin with. I would say at least do this until you are confident with your quench recipe/technique.

UncleBillyKnives
04-24-2011, 09:51 AM
I think I would start at a lower temp. for tempering. I'd try 400 for two cycles and then test the blade. If it seems to still be too hard on a file test, I would bump it to 425 and go for another hour and test again and so on.

I agree with Murph. i did my quench in used motor oil and did a triple temp at 400. my hardness was at 60RC.

scherar
04-24-2011, 10:31 AM
That is interesting. I tried all the different "home recipe" oils and just couldn't get good results, but maybe the actual cutting edge got harder due to its thinner section. I tried motor oil, tranny fluid, veg oil and then finally tried water. Water was the only thing that got me up there, but I didn't want to risk using it on blades. I bought the McMaster 11 second and it was definitely better, but I only use it for my Damascus.

ARCustomKnives
04-25-2011, 08:15 AM
I'd recommend along with the others to lower your tempering temperature to around 400F and see if you get closer to the results you're looking for. 475-500F is the absolute highest I would ever want to take a 1095 blade.

Kevin R. Cashen
04-25-2011, 09:23 AM
Another thought is HT'ing another piece and not tempering it. This way you know what is going on during the quench. Quenching and then tempering before testing leaves you little in the dark since you don't know if you got good results to begin with. I would say at least do this until you are confident with your quench recipe/technique.

This is very good advice for anybody attempting to evaluate their hardening operation. I very often see folks claiming their quenchant is good because they got a 60HRC after tempering:31: A Rockwell reading after the temper with nothing as a baseline for the initial hardness can't really tell you anything about the hardening or the tempering. If your initial hardness was 61 HRC on a high carbon steel and you get 60 HRC after tempering, your quench isn't working very well at all. And your temper isn't all that great either if all it is doing is shaving off 1 point in that particular range, should you eventually nail the quench that temper will probably result in brittle blades.

Also since Rockwell can only accurately be taken on a flat and true surface edge bevels cant really be measured. This leaves the thicker portions without an edge as your only test areas. I have only found one oil that is capable of fully hardening 1095 in thickness greater than 3/16" reliably. So don't let readings in the 50's on the ricasso or tang get you too down.

Doug Lester
04-25-2011, 01:28 PM
In reference to your comment that the edge might have gotten harder than the spine during quenching. That is something that can happen with a shallow harding steel in thin cross sections as found in knife blades. The steel will only harden to twice the depth of hardening. Thicker than that the steel will form pearlite.

One thing need for this to occure is a fine grain in the steel. Course grain will promote a deeper depth of harding and might allow a knife blade to harden all the way through. That, however, would also result in the loss of toughness. If you keep the grain fine the higher carbon content 10XX series of steel will have a soft back and a hard edge. There will also be a hard edge to the corners of of the spine. I'm assuming, possibly wrongly, that those edges could be eliminated by rounding the the spine instead of leaving sharp corners.

Doug

Ernie Swanson
04-25-2011, 04:41 PM
Thanks all!! I am going to heat treat a bunch of samples. Some tempered some not, Then I can see the variations.


Thanks again for all the help!

Keith Willis
05-04-2011, 05:10 AM
Hey Ernie,did you get a chance to try your samples?
Just courious as to what you came up with.

God bless,Keith

Ernie Swanson
05-05-2011, 09:25 PM
I have not gotten a chance to make any sample, crazy busy right now, I am hoping next weekend.