CPM-S90V Weirdness

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
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Jun 11, 2006
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So this is a first out of the thousands of blades I have heat treated. This is cpm-S90V from jantz and I fallowed crucibles HT schedule to a T. We don’t get a ton of the more exotic alloys in for HT so when we do we default to the manufactures schedules unless it’s a steel that’s proven to benefit from low tempers and cryo.

these blades where 309 foil wrapped and soaked for 20min at 2125° (crucible calls for 2100-2200 for 10-30 min). Thy where then both pulled out and put between quench plates and slowed to cool. When I cut open the foil I noticed one had cracked and opened up quite a bit. I looked it over and the crack has a slight discoloring that’s conducive to steel that’s heated inside a foil with very little oxygen. This points to the crack forming in the oven. If it happened during the plate quench I don't think it would of discolored as the steel would bee under that color forming temp by the time it started to harden up.

I then cryo treated both blades and gave them a temper cycle. We have tempered up to 600° so far and the blades are still at 61-62+. From looking over the charts it looks like it should hit around 58-59 at 500°. I then ran a circle of tests around the hole in the tang where the crack is and found more weirdness. The bottom side of the hole that’s not cracked is really soft at 56-58 and the other upper area is 61-62. I tested along the length of the tang and it all measured 61-62.

This has got me scratching my head as to what caused this to happen. My first thought was it’s not S90V but then how does that explain the soft patch. Also am I correct in assuming that softer steel is smaller on the molecular scale. I know in blades that I have clay coated thy have a tendency for the point to rise.

Here are the pictures, what’s your thoughts?

Photo%20May%2011%2C%207%2001%2011%20PM.jpg


Photo%20May%2011%2C%207%2002%2053%20PM.jpg


Photo%20May%2011%2C%207%2003%2022%20PM.jpg
 
That’s from decarb, it will cause some strain in the steel. It came from the mill that way. That’s why the mill rolls it oversize, so you can get under that layer. The decarb area moves less and the decarb free area moves more causing it to crack.

There is a chance the crack was there before heat treating and showed up after the quench. Surprisingly, high alloy pm steels are not very tough in the annealed condition. They cannot be sheared for example.

Hoss
 
Interesting!
Hoss, do you think the de carb also caused the hardness differences?
 
Larrin said:
The recommended austenitizing temperatures are too high for S90V, that steel gets hard. I used 2050F for the CATRA study.
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Thats what I was starting to think.
 
Larrin said:
The recommended austenitizing temperatures are too high for S90V, that steel gets hard. I used 2050F for the CATRA study.
Click to expand...

It seems several of these high carbide steels like a11, S90v, and k390 are best heat treated lower than the datasheets suggest. Is that because plate quench, cryo, and the thin cross sections we use are more efficient than industrial heat treat, or other reasons I am not considering?
 
Willie71 said:
It seems several of these high carbide steels like a11, S90v, and k390 are best heat treated lower than the datasheets suggest. Is that because plate quench, cryo, and the thin cross sections we use are more efficient than industrial heat treat, or other reasons I am not considering?
Click to expand...
A11 and K390 it’s because of differences between low and high temperature tempering. S90V is a bit harder to answer. I think the composition may have been slightly modified to promote higher hardness than when the datasheet was developed.
 
Larrin said:
A11 and K390 it’s because of differences between low and high temperature tempering. S90V is a bit harder to answer. I think the composition may have been slightly modified to promote higher hardness than when the datasheet was developed.
Click to expand...

Thanks, there is still so much to learn.
 
The S90V says (if my memory is correct) oil quench with freeze treatment. I always hate “freeze” I want to see numbers lol. But this brings up another topic I have been meaning to start for the last few days. I hope we can hash some things out on it.
 
JTknives said:
The S90V says (if my memory is correct) oil quench with freeze treatment. I always hate “freeze” I want to see numbers lol. But this brings up another topic I have been meaning to start for the last few days. I hope we can hash some things out on it.
Click to expand...

The terms really should be standardized. We seem to have sub zero and cryo sorted on this forum, but freeze means what, exactly? I agree with you.
 
Usually, means -75C/-85C or something around it. The value where RA is almost fully transformed to Martensite. Haakonsen and Landes always (that I remember) talk about sub zero treatment. Cryo is probably not needed, in their opinion. But it doesn’t hurt.
 
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I think it’s time to start that other topic I have been putting off starting lol
 
Larrin said:
A11 and K390 it’s because of differences between low and high temperature tempering. S90V is a bit harder to answer. I think the composition may have been slightly modified to promote higher hardness than when the datasheet was developed.
Click to expand...

But some people always insist the company datasheet HT is the best... :D:thumbsup:
 
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