O1 Heat Treat Trouble

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Oct 11, 2019
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I was heat treating a couple O1 k-tip gyotus when I got distracted by something in the house.

I came out to the shop with my alarm going off signaling the cycle had ended.

Blades were at temp for about 30 minutes….
Oven had cooled to around 1,200f…..

I figured a long soak was not a problem with O1,
So I restarted the program,
Let them soak for another 10min.
Then quenched in Parks 50 as per normal.
Double temper at 400.

I just cleaned one blade up and did a test etch, and got a crazy pattern.
I think it looks cool….but even my amateur ass realizes it’s probably not good.

I’m assuming I should redo my heat treat….?

3YVlhXN.jpg
 
Grind it a little deeper and see if it goes away. If it goes away, finish the blade.
If it does not go away, you will have to put all the alloying back into solution at 1800-1900°F and then cycle the steel to refine the grain before a new HT.
 
Grind it a little deeper and see if it goes away. If it goes away, finish the blade.
If it does not go away, you will have to put all the alloying back into solution at 1800-1900°F and then cycle the steel to refine the grain before a new HT.
Out of curiosity…..
Do you think it was the long soak, or the slow drop to 1,200, then a return to critical that would cause that chaos?

I’d grind it further, (I’m sure I got the decarb off. I can tell pretty easily with O1.), but a bearing went on one of my platen idler wheels. 😤 Seems like the bearings are “built in” on the steel wheels of my KMG-TX platen.

While I was waiting, I just redid my heat treat on one of them to see what would happen.
As soon as I can knock the decarb off, I’ll give it a dunk.

As always, thanks for taking the time.
 
I would probably just go ahead an follow the normalization cycle, and redo the heat treat how stacy said to, even if you can grind past that. I think better safe than sorry.

Edit. I think I was the long soak. I'm not as knowledgeable as some people here about metallurgy, but I'm guessing that's banding from the formation of large carbides, and plate martensite. I could be way off. I could definitely be wrong though.
 
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Yeah that is carbide banding for sure. Could have come from the mill that way, but I highly doubt that. Most likely that extended time in the spheroidizing temperature range caused the banding. That is some intense banding. Reminds me of a knife a guy made from that batch of Blue 2 that came through NJSB. I had gotten pretty heavy banding with the steel I received, but nothing like the pattern on that one knife this guy had posted on British Blades.

You can try to get that alloying into solution with a high normalizing heat. Then thermal cycle a couple times.
 
Yeah that is carbide banding for sure. Could have come from the mill that way, but I highly doubt that. Most likely that extended time in the spheroidizing temperature range caused the banding. That is some intense banding. Reminds me of a knife a guy made from that batch of Blue 2 that came through NJSB. I had gotten pretty heavy banding with the steel I received, but nothing like the pattern on that one knife this guy had posted on British Blades.

You can try to get that alloying into solution with a high normalizing heat. Then thermal cycle a couple times.

Thanks
Next question (keeping in mind that I already did the sensible thing and followed the advice of better men)…..
I love that pattern.
What would be the functional drawback of just sending it …as is?
It tested at around 60 with my hardness files.
Stayed straight as an arrow.
And behaved like standard O1….other than that etch pattern.

Would it be more prone to fracture?
Less able to hold a sharp edge?

(I almost snapped one of them just to see what it looked like under a microscope, assuming it would have cracked at one of the “banding” lines. But I was more curious to see if I could bring them back. As of a quick post HT decarb removal grind (pre temper) and subsequent dunk, it seems as if they will be just fine.)

Thanks for indulging my unconventional curiosity.
(In this place, I often feel like a reckless adventurer, in a world of meticulous scientists.
(So unlike my “regular” life of being the guy who dots every i. It’s a kind of refreshing departure .))
 
If it's what I'm thinking it is. I'm thinking the toughness would be much lower than it would be with a properly heat treated knife. The carbide banding would definitely be areas that wre more likely to form fractures, and that extra long soak. Could potentially have lead to plate martensite (not sure, but I'm thinking it isn't out of the realm of possibilities) which is considerably more brittle than lath martensite.
 
I also prefer a more homogeneous structure. But hey, it looks great. I would be inclined to finish the knife and just give it some testing.

Extended soaks at spheroidizing temps won't result in plate martensite. Quite the opposite, actually. Plate martensite would be the result when too hot of an austenitizing temp is used, putting too much carbon in solution. If the austenitizing temp is kept in check around 1500°F, there shouldn't be much plate martensite at all, especially in a chromium steel. That's one of the reasons 52100 is so tough, that Cr keeps plate martensite in check. Same principle with O1, just not quite as strong of an affect due to 1.5% Cr in 52100 vs 0.5% Cr in O1

Side note, that Hitachi Blue 2 that I mentioned previously, I think the only reason it was sent to the states for sale was because of the banding problem. I could be totally wrong, but that batch of Blue 2 is the only Hitachi White or Blue steel I have seen available for sale in the states, other than bars you can get from Dictum, Schmeideglut in Germany, etc, or if you're a student of Murray Carter's school.
 
The soak at 1200 isn't what I was thinking would cause it. But how warm it was before that. Bringing it to the point of Austenizing, then keeping it in a temp that allowed it to remain austenite without transforming to anything else, then bringing it back up to 1500 again to soak. My thinking is even though o1 does have chromium and a few other alloying elements. It's still going to have more carbon in solution than a normal austenizing cycle.

I would need to actually need to see a ttt to say for sure. But without looking at one, I'm just saying that, its potentially going to have some amount of plate martensite.

Edit: so looking at the ttt on kevin cashens site. It doesn't have a lot of labels, but I'm guessing you dropped into the range where pearlite would have been forming, but you would still have had austenite as well. You having a partially austenitic structure still is what makes me think that going back up to the 1500 degrees would have the same effect as if it had been left in at that temperature for longer. Since it was going in with an already, somewhat austenitic structure.

but, again, I'm not a metallurgist, and I'm not 100% sure or anything, but that's just my theory on what's probably going on with the structure in that steel.

Edit 2: looking at it again, you may have even squeaked out hiting that point where you started forming pearlite, but I'm not sure.


 
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Well I had never even heard of martensite banding until your post. So I couldn't comment one way or another. You mentioned copper. O1 doesn't have a copper content. Maybe you meant chromium. As well I have never heard of manganese causing any banding whatsoever. Any steel that has a carbide structure can have carbide banding issues. Most of the time I see it in steels with a small vanadium content. But I also see it in 26C3, which does not technically have vanadium, but maybe present in very small amount. The cementite carbide causing the banding in 26c3.

And just to comment about "enough elements to form many carbides". O1 has PLENTY. Damascus steel (the real stuff. Wootz steel. Not pattern welded) has, from what I gather and for all intents and purposes, 2 elements. Carbon and vanadium. As I'm sure we all know, Damascus/Wootz is not really a steel that is constructed, but found in nature and then processed in a crucible. The carbon content is very high, 1.5% and above if memory serves, but the vanadium content is only in the sub 0.1% (again if memory serves). But what we get from just a minuscule amount of vanadium, with that super high carbon content, is amazing carbide banding.

Martensite banding, from the quick (VERY quick) reading I did, is martensite formations in a ferrite structure. I would think this would be caused by under austenitizing. IE.....not hot enough. Especially after an extended soak into the spheroidizing range, which makes it even harder to harden properly, unless dealt with accordingly.
 
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Well…..that went way over my head, quickly.

Thanks for the responses.
It’s interesting to listen to people that understand this stuff.

I should’ve just finished them as they were, but I thought I would get permabanned for it. 😂
I followed Stacy’s advice and they seem to be fine as of now.

I thought I noticed a faint pattern early on in one that I did a quick test etch on….but it came out fine after 60 seconds or so.
 
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