Can you temper a blade to long??

I am going to temper a couple of blades. one is 01 and the other is 1095. If they are left in the oven at 375dagrees for more than 3 hours will it affect the blades performenc?

Thanks for your advice

Dan Keffeler

According to most metallurgists, the short answer is "no". It's the minimum time that's critical (2 hours). As long as the temp remains stable at the desired level, you can leave them in all day.

Don's right! I would much rather see a blade tempered all day than only tempered for 1 hour. As long as the oven your using is fairly consistent at holding temp, your going to be OK. If your using a kitchen type oven, I strongly recommend that you get a good oven thermometer and check the oven before you begin. Some kitchen type ovens will have a wide range when the dial is set on certain temps. For example, a friend of mine was tempering with the dial set on 375F, and could not understand why his blades were chipping. To make a long stroy short, we found that his oven was 100F OFF! (on the low side), so his blade were only being tempered at 275F! NOT GOOD!

Thanks Don and ED
I have 2 other ?s
Some Makers pull the blades out of the oven and let them air cool from the tempering cayle and others leave the blades in and let them cool slowly with the oven. I s there a difrenc in what happens to the steel?

#2 Is there any diffrenc between a 3 three hour tempering cycles, and one long 9 hour dempering one.

Thanks again

Dan Keffeler

I think it's all a matter of what works best for you. I personally take the blades out and let them cool down in still air, then put them in for the next tempering cycle.

On #2, I have found that the cooling cycles between temperings does have a positive effect on converting the matrix. Steel that has experienced one long tempering cycle versus 3 shorter ones, will not show as fine a grain, and will have less of the matrix converted. Although in some cases it is only a slight difference...that is often the difference between a good blade and a great one.

I love discussions like this. I learn so much.

I might be able to add something here (it feels nice to contribute after asking so many questions).

First, just a simple comment about the temperature, not the time. 1095, for me, seems to want something in the low 400 range. I have tried 375 but get a pretty brittle edge. Of course this all depends on intended use, etc., but I just thought I'd comment.

Second, as one fairly new to all this, about four years now, I might be able to clarify Ed's comments on "the matrix." Now Ed's a master smith and when he writes "the matrix" he knows exactly what he means. Problem is, some of us others are left thinking about Kianu Reaves movies . The way I finally "got" this triple tempering with cooling between cycles was when someone explained it as follows: Bringing a blade to the critical temperature transforms the steel into austenite. Quenching transfoms that austenite into martensite (please forgive my ommission of the several other possibilities here--I am trying to be as simple as possible). In a perfect world, all of this would happen perfectly. In the real world, however, there is some retained austenite in the blade. Anyway, untempered martensite is very brittle. During tempering, the purpose of which is to produce tempered martensite, some of that retained austenite forms new, untempered martensite. So you remove the blade from the oven or other heat source and let it cool. Now, back in to temper the newly formed martensite, and to assure the complete tempering of the original martensite. Well, there is still a bit of retained austenite, which again forms new, untempered martensite. Thus a third cycle. Don't ask me why but three seems to be the magic number in thermal treatments. More may not hurt, but they don't seem to help much either (and I guess in some cases can hurt). Ed has born this out in experiments, as have Ed Fowler, Don Fogg and Howard Clark (though all for slightly different operations and different steels, they all come up with the number three). Now I'm not saying these men have all the answers, but they have enough to keep me busy for the forseeable future.

I hope this helps. I hope even more that this will start a fun discussion on various thermal treatments.

John