440c cryo benefits?

[teejay1980]

Ok so I've got four knives ready to go to Texas knifemakers for HT and I was wondering what the benefits of cryo were. I searched and could only find info saying it would increase hardness a point or two will this inversely affect toughness I'm using 440c and two of the knives are skinners so ill have them cryo them but the other ones are a camp knife and a big chopper and I don't want to cryo them if it decreases toughness to a large degree.

[WBE]

Cryo will increase the strength. They will be tempered after the cryo treatment, so you may want a softer temper for the camp knife.

[Doug Lester]

One of the problems with complex steels like 440C stainless is that it can form retained austinite on quenching due to it's high carbon content and other alloys. This reduces the Mf point, the point at which to conversion to martensite is complete, to below normal room temperatures. Cryotreatment will essentially lower the quench to below this reduced Mf point and convert more of the austinite to untempered martensite.

When using something like a 440C for something like a chopper you are going to have to do something to off set the higher brittleness of the alloy. As WBE mentioned, you may want to temper the blade a little softer. You will give up some hardness, strength, and wear resistance for an increase in toughness. Thicker stock will also off set this loss of strength and increased brittleness of the steel. A convex edge will add some strength there.

Stainless steels and high carbon air quenching tool steels are not the best choice for making big choppers.

Doug

[teejay1980]

Thanks guys that's what I wanted to know. I know the 440c is not the best for a chopper but its what I have right now and I thought id give it a go. The chopper is 1/8" thick by 1.5" wide with a full convex grind I will ask them if they can temper it a little softer for me and hopefully it will work out ok. If not I guess that's what experimenting is for and ill have fun destroying it!

[Doug Lester]

It's all about learning and I have a drawer full of lessons that didn't come out the way I wanted. Have fun.

Doug

[Larry Peterson]

Teejay

I would like to add my 2 cents if I may. Years ago I purchased a liquid nitrogen bottle like the A.I cattlemen use, to treat my knives. I use more 440-C than anything else. I made a thin leather skiving knife which I have used for about 6 years now. My old skiving knife had the same thickness and profile. Both tempored to 58 R. c.

I could observe "0" difference in the ecge holding ability between the two knives. If there is any gain, I can't observe it in the actual use of the knife. The bottle is out in the knife shop. I would like to find someone else who is excited about -320 degree Cyro. I would recoup my $250.00.

In my opinion, the Cyro has not proved out to be enough benefit to hire it done nor worth the bother and expense to do it myself.

I didn't mean to "crumble your cooky" or "rain on your parade." This is just my opinion and I have no problem for those who like to use the cyro.

Best wishes, Larry Peterson

[Ray Rogers]

OK, I'll throw in my two, or even 3, cents. I too use a lot of 440C and I also cryo all of it. One difference between my set up and Larry's is that I paid $1000 for my dewar and that was about 14 years ago when a dollar still had a marginal value. Anyway, I find that it adds considerable toughness to the blades. It will not, however, make the edge last any longer - just as Larry said - if you temper exactly the same way. The key is to temper for a higher hardness because the extra toughness will allow you to do that. So, instead of 58 temper for 59. That may not sound like much difference but it really does make a difference. I'm not saying the knife suddenly becomes twice as good, it doesn't, but you can get 20% improvement give or take.

Since you plan to send your blade to TX Knifemakers the added cryo doesn't cost much. If you can send two blades, cryo one of them and compare the results for yourself. As the saying goes, "your mileage may vary". That's the cheapest way I can think of for you to be able to decide for yourself whether cryo is worth it to you .....

[Doug Lester]

To piggy back on Larry's comment, I think that many of the people who do cryoquenching do so to reduce the amount of retained austinite and reduce the embrittlement that it can cause. This may be because that they are aware that they are starting with an alloy that is already more subject to brittleness than some of the simpler steels and want to take steps to reduce this problem and still use a stainless or other air quenching steels. The benefit to them may well be more on the theoretical side than a benefit actually seen in the performance of the blade but they feel it is worth it.

Doug

[teejay1980]

Ok so if I'm reading this right the cryo doesn't add any hardness it just allows you keep it harder so if I had them cryo the bigger blades and just temper to normal 440c hardness like 58rc they should be tougher than non cryo blades tempered to 58rc. Well I think I'm just gonna have them cryo one small and one bigger blade and then test the heck out of em all lol guess I won't be using any of that pretty wood I got on these, micarta it is!

[teejay1980]

Oh and thanks everybody on this site a couple of months ago I thought I knew a lot about knives because I bought spyderco and benchmades and I watched the cold steel videos haha man was I wrong you guys have been very helpful and encouraging and I wouldnt even be halfway as far along as I am if not for you and your recommended reading!

[Doug Lester]

Teejay, we all started out from ground zero. When I started out I didn't know the difference between tool steel and the stuff that Lowes carried. However, I did know there was a difference at least. I knew nothing of austinite, pearlite, martensite. I had a rough idea about quench hardening and tempering, an extremely rough idea. A lot of people were very patient with me and were willing to work with me when I displayed my willingness to learn. If you are willing to work at it, we are willing to help you.

Doug