Effect of Cryo on Toughness

Unfortunately my Norwegian grandparents came here to become Americans so they never spoke Norwegian to their grand children !
I haven't been using translations recently but certainly in the past technical dictionaries were really needed for technical translations !
Northern and southern Norwegian are very different ! ! Some Norwegians speak English to avoid that problem ! o_O
 
Willie71 said:
I also question the carbide volume as a contributor to the difference. Ra is not good for fine edge stability, but does help toughness. If low temper has improved fine edge stability, I suspect carbide volume is at play too.

I also suspect there is a level of alloying that will not do a full conversion to martensite so cryo will no longer work. At the extreme end I have some rex121 for testing. It’s ridiculous in its alloy content.
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I think I’ve read somewhere that PM high speed steels need high temper, no matter what. Seems that RA stabilizes so fast that only high temper converts most of that RA to Martensite.
 
hugofeynman said:
I think I’ve read somewhere that PM high speed steels need high temper, no matter what. Seems that RA stabilizes so fast that only high temper converts most of that RA to Martensite.
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Yes, I heard that too, but I’ve heard reports that M4 can respond well to cryo/low temper. Time to test it out.
 
I don’t understand why PM would lead to more rapid RA stabilization.
 
Larrin said:
I don’t understand why PM would lead to more rapid RA stabilization.
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Just clarifying, just because I heard it in the past does not mean I think it’s true. :cool:

I think this is something that needs to be tested.
 
Willie71 said:
Just clarifying, just because I heard it in the past does not mean I think it’s true. :cool:

I think this is something that needs to be tested.
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Same here. I’m searching and searching and can’t find the damn article. But I’m almost 100% sure I read somewhere that high speed steel (or PM high speed steel, can’t remember) RA stabilizes so fast that only high temper treatment can remove it.
 
hugofeynman said:
Same here. I’m searching and searching and can’t find the damn article. But I’m almost 100% sure I read somewhere that high speed steel (or PM high speed steel, can’t remember) RA stabilizes so fast that only high temper treatment can remove it.
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I recall it’s the volume of alloys that prevent full conversion, but regardless, testing is needed. Some alloys, such as nickel stabilize retained austenite, so specific alloys play a roll.
 
Well if regular high speed steel is your concern, a bunch of the data in Part 1 is with T1. I can’t think of a reason why PM versions would stabilize any faster. Easier to dissolve carbides maybe, but you can always adjust austenitizing temperatures and times.
 
There is a point where LN2 temps aren't cold enough to convert all of the retained austenite. Where that point is would interesting to know, but quickly doing online research I can't find any clues.

But when you look at the heat treatment data given by Crucible for CPM T15 (and other heat treat data for T15), there is no reference whatsoever to any cold treatments or cryo treatments. They even specify "Do not temper below 1000°F". I take that to mean that the only way to get rid of the majority of retained austenite in T15 (or CPM T15) is with the upper tempers. That is a steel with a LOT of alloy!
 
One side note on PM High speed steel: cobalt raises martensite start temperature. Perhaps that is part of why Rex 121 can achieve 71 Rc as-quenched. I've never seen anything else with that level of as-quenched hardness.
 
samuraistuart said:
There is a point where LN2 temps aren't cold enough to convert all of the retained austenite. Where that point is would interesting to know, but quickly doing online research I can't find any clues.

But when you look at the heat treatment data given by Crucible for CPM T15 (and other heat treat data for T15), there is no reference whatsoever to any cold treatments or cryo treatments. They even specify "Do not temper below 1000°F". I take that to mean that the only way to get rid of the majority of retained austenite in T15 (or CPM T15) is with the upper tempers. That is a steel with a LOT of alloy!
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This is why I did my testing in z-wear. The datasheets warned not to temper below 1000f, but it works very well with cryo/low temper.

I’ll keep doing samples in the alloys I have with both high and low temper. At some point, I’m sure there will be too much alloy to get the full conversion.
 
My question that keeps coming to mind is that on some steels the low temper eliminates a "mushy" edge but there is a threshold where the low temper no longer works. Why does that change how the edge behaves? I would think that there would still be mushy edge problems but that doesn't seem to be the case. Does anyone know if spyderco uses high temper on their M4? That has fantastic edge stability. I don't have the experience myself so its going to be a interesting rabbit hole.
 
skillgannon said:
My question that keeps coming to mind is that on some steels the low temper eliminates a "mushy" edge but there is a threshold where the low temper no longer works. Why does that change how the edge behaves? I would think that there would still be mushy edge problems but that doesn't seem to be the case. Does anyone know if spyderco uses high temper on their M4? That has fantastic edge stability. I don't have the experience myself so its going to be a interesting rabbit hole.
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I’m with you on cpmM4 from Spyderco having a great edge (great edge stability?). I’m sure they use high temper, it’s the industry’s standard. Fredrik Haakonsen also uses high temper in his Vanadis 4 extra knives and I’ve never noticed a “mushy” edge in the knife he made me (hardened to 63 hrc, so it can withstand some punishment (he can harden this steel until 66 hrc))!
 
My M4 blades are done with cryo and then low tempers, the apex stability is excellent. Very impressed! But I don’t have apples of the same exact geometry with cryo/low tempers to compare with apples of exact geometry and high tempers!
 
samuraistuart said:
My M4 blades are done with cryo and then low tempers, the apex stability is excellent. Very impressed! But I don’t have apples of the same exact geometry with cryo/low tempers to compare with apples of exact geometry and high tempers!
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Do you have any advice for M4 low temper? I could try a test blade in each with a spare coupon for the toughness test. If people are interested I can do a pass around. I'm doing a bunch of tests with M2 just because its cheaper and easier to come by. I do have some M4 and could try to find some more.
 
skillgannon said:
Do you have any advice for M4 low temper? I could try a test blade in each with a spare coupon for the toughness test. If people are interested I can do a pass around. I'm doing a bunch of tests with M2 just because its cheaper and easier to come by. I do have some M4 and could try to find some more.
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I have M4 that chuck donated for testing. Do you want me to throw a chunk in the box I’m sending you? I’ll list the protocols I was going to try.
 
Willie71 said:
I have M4 that chuck donated for testing. Do you want me to throw a chunk in the box I’m sending you? I’ll list the protocols I was going to try.
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It's up to you. I have 3 pieces of 2x11.5x.100 that I will use for chef knives and I have another 3x36x.140/156 that I am willing to use about half for research. I. Already doing the testing for M2 I would just do M4 if there is intrest in trying to find something specific that others would be interested in. I don't have Rc tester yet so I would have to get some help on that end. The other option is that I send you more steel. Is there something that we could try to discover with test blades?
 
skillgannon said:
It's up to you. I have 3 pieces of 2x11.5x.100 that I will use for chef knives and I have another 3x36x.140/156 that I am willing to use about half for research. I. Already doing the testing for M2 I would just do M4 if there is intrest in trying to find something specific that others would be interested in. I don't have Rc tester yet so I would have to get some help on that end. The other option is that I send you more steel. Is there something that we could try to discover with test blades?
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I’ll think about what we need to test. We’ll chat on the phone and make sure we aren’t duplicating samples.
 
skillgannon said:
Do you have any advice for M4 low temper? I could try a test blade in each with a spare coupon for the toughness test. If people are interested I can do a pass around. I'm doing a bunch of tests with M2 just because its cheaper and easier to come by. I do have some M4 and could try to find some more.
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No advice really. Just go direct from quench to cryo, no snap tempers. And I have also heard that a faster quench on these air quench steels is said to help minimize RA as well. So a medium speed oil for the initial quench, then into plates for straightening, then into a 24-36 hour cryo hold, then triple tempers 2 hours each ~400f. To get fancy, prequench the M4 and then respheroidize it. I haven’t tried that approach with M4 tho. There is a tech paper available online about CPMM4 heat treating. I forget the name of it, but a google or Bladeforums search will bring it up. It’s a good read.
 
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