Stainless heat treat

J

John L

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Oct 28, 2004
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I have a heat treat oven but no cryo treating capabilities. What stainless material is the easiest to heat treat?
 
416, but it isn't good for blades.;) All the blade types are a bit more involved, and require higher temperatures. Cryo lets you, AND your customer realize the best the steel has to offer.
 
John L said:
I have a heat treat oven but no cryo treating capabilities. What stainless material is the easiest to heat treat?
Click to expand...

ATS-34, CM-154, and S30V are all I can comment on. And, well, in terms of hard to do, they're all the same. Easy or hard. The important part is to practice on a few pieces.

As far as the hardening process, I use the same thing for all three. The only difference is I used about 25 degrees hotter for S30V.

If you have an oven with a digital control, stainless is more fool proof than using a torch or forge with carbon steels. To me that borders on art and requires much practice.

Steve
 
Chris - I don't think so. Thanks for mentioning, but it my book its a requirement for those 3 in a high quality knife.

I do believe the dry ice/acetone cryo method is acceptable (that's the temp listed on the Crucible data sheets). But I haven't tested that myself. John, that's one use can use without any special equipment.

Steve
 
You can do without cryo for those steels but you would loose 2 points of hardness. Using top of the line steels and not getting the maximum properties from them seems a waste.
 
I really don't understand how the cryo works, so please be patient with my quesions...

If the cryo gives you two points of extra hardness, are you not going to loose that when you temper or draw the blade back to your desired final hardness?
 
Chris,

I'll see if I can get the cryo story straight myself - without getting too much detail.

When quenching high-alloy steels not all the austenite gets converted to martensite. This results in a lower hardness, but also some other undesirable properties (brittleness?) Definately less edge retention. In any case it's not as good as it could be.

Turns out if you soak steel in this condition in sub-sub-zero temps that austenite will finish converting. So now your blade is all martensite. This rasies the hardness and improves the performance.

Yes tempering will bring those 2 points back down, but this steel at 59 is better than non-cryo at 59.

Steve

PS Boy I hope the information helps.
 
I see... So it's more about refining the grain of the steel than it is about achieving a specific hardness. Is that right?
 
No Steve. Cryo'd and tempered - martensite [61Rc] , uncryo'd and tempered -martensite +retained austenite[59Rc]. Without cryo you still have austenite which is softer [not brittle].
 
It has been my limited experience on these high alloys I get about a two point increase after deep cryo compared to no cryo. As expected to follow, I have realized about a two point increase after tempering a deep cryo'd compared to one with no cryo. This is because of the lack of retained austenite after quench that has been transformed by cryogenic aging.

RL
 
OK Maybe I'm wrong - or didn't express myself well.

Let's use a pretend steel and do this process:

2 blades, both as quenched at 61. One I cryo'd and now it's at 63.

The first blade I temper 2 times at 400 and get 59.
The second blade I temper 2 times at 600 and get 59.

Both are measured at the same hardness (it took a higher temper temperature to do the second one, but it happened). But the second blade is in better shape.

Or can't that be done.

Steve

I do understand that if the tempering was identical the results would be different.
 
If you can't cryo it is best to temper at the highest temperature below the sensitizing range. I recommend 700-750 F. This will help to convert retained austenite and maximize the hardness. Also keep in mind that austenite retains when the material is soaked too long at high (hardening) temperatures. All the stainlesses above in knife thicknesses need around 30 minutes of soak time to dissolve the proper alloy amounts. Then quench as fast as possible and this will also keep the retained austenite down. A little retained austenite is not a bad thing. It actually helps ductility in small concentrations.
 
Uncryoed steel is has untempered austenite left in the mix.The cryo converts it to martensite.The next temper them tempers the martensite,which is much better than the martensite/austenite mixture.At the same Rockwell an all martensite is much more durable than the mixture of martensite/austenite.The end result after cryo is a higher Rockwell by about two points,due to the fact that martensite is inherently harder than austenite.
All of this metallurgy is not necessary to understand,since the trolls do all the work inside the steel.They are born with the knowledge of how it works.Trolls are funny creatures,They like it very hot and very cold.Give them both and they will reward you with superb steel.
SA
 
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