Blade Steel Rehardening

[dantzk8]

Despite my defense against Phil, am I the only one who finds it a little bit iffy/sketchy that cotdt is custom-formulating heat-treatment regimes?

Following industry protocols is one thing, but whipping up your own and then giving an assumed and untested resultant hardness strikes me as poor science.

Empiricism is science, experimentation is science. When behind empirical experimentation there are knowledges and skills, how can you speak about "poor science"?
Some people here are interested by this kind of stuff. Some people here share the results of their own researches. Some people here can't take the idea that their own knives are made for average users by manufacturers who don't want to disappoint their average customers.

Thanks to cotdt.

dantzk.

 

[Gator97]

Despite my defense against Phil, am I the only one who finds it a little bit iffy/sketchy that cotdt is custom-formulating heat-treatment regimes?

I think from the beginning it was conceived as an experiment. If it works, work, if it doesn't then it's ruined, irreversibly or not it's still an open question.
Besides, I guess you can ask specifically if you want your blade HTed according standard. If Cotdt refuses then you won't send in your blade.

Following industry protocols is one thing, but whipping up your own and then giving an assumed and untested resultant hardness strikes me as poor science.

Well, you have to remember that industry specs and recommendations are more conservative and not always knife optimized. Those CPMs I have from Phil Wilson, most of them are recommended in 61-62HRC, yet Phil took them to 64 and 65HRC easily.
The fact that a lot of factory knives are under even those conservative recommendations is another matter altogether.

In the end, nobody is infallible This is more like trail an and error thing than established rehardening service according to the specs. Otherwise it wouldn't be an experiment would it? And probably it wouldn't be free either.

 

[65535]

I think that Mnandi looks great with the HT scale in the finger groove. Looks amazing. I'll have to get that Izula refinished to remove rust then get it to you.

 

[Lucky Bob]

My particular complaint is not so much that he is treading uncharted water (although I personally wouldn't want any of my blades treated outside of established protocols) so much as claiming charting without any way to do so, ie claiming a hardness range without being able to test it.

I'm all in favor of people experiment (probably not on my blades, but to each their own), and even concede that there are significant data points, some even subjective/non-quantized, other than hardness, but I view non-trivial extrapolation (and notice that, syntacticly, that's the only thing I cited) as poor science.

I have no problem with people following Wilson's example of developing novel heat treatment methods (after all, that is science, even if I'd prefer to be the 100th blade rather than the 2nd) with the expectation that when they claim novel data, they have measured it, not just inferred it.

EDIT: also, because I'm a perfectionist and couldn't resist re-reading what I wrote after it was posted, I thought I'd point out that, despite most of the historical great advances in science coming from dilettantes/amateurs/polymaths, the modern understanding of metallurgy and related material science/engineering is sufficiently complicated that I at least would have more faith in/higher expectations for the experiments of someone with training and experience in the subject, as opposed to an enthusiastic amateur.

 

[Gator97]

ie claiming a hardness range without being able to test it.

???

the modern understanding of metallurgy and related material science/engineering is sufficiently complicated that I at least would have more faith in/higher expectations for the experiments of someone with training and experience in the subject, as opposed to an enthusiastic amateur.

I am with you, but the way things are there are very few metallurgist scientists working in the cutlery field. And the equipment is getting more and more expensive. So, this is where we are.

 

[cotdt]

This is amazing!
I was thinking about making a blade with HSS for this knife.
But this looks like much better!

To be added, the rebirth certificate looks also wonderful!

Really, really nice! Very mucho professionally done.

I think that Mnandi looks great with the HT scale in the finger groove. Looks amazing. I'll have to get that Izula refinished to remove rust then get it to you.

Thanks!

Despite my defense against Phil, am I the only one who finds it a little bit iffy/sketchy that cotdt is custom-formulating heat-treatment regimes?

Following industry protocols is one thing, but whipping up your own and then giving an assumed and untested resultant hardness strikes me as poor science.

It's a relatively standard HT for a high carbon stainless steel. The Crucible datasheet doesn't list the temperatures for some reason (it also doesn't list the full composition for S30V). Cryoquenching is based on the theory of how cryo works, and the 975F temper is used by Paul Bos on his S30V and 154CM knives. People have reported good results on them, despite not being done "by the book". Many of the knives you may own were not done "by the book" but by standard heat treating practices.

To Crucible's defense, they noted that the high temper had slightly worse corrosion resistance. In any case, Phil Wilson already tried 62 rc for S30V using the low temper, and according to him it was a little chippy. This may be why Crucible didn't list anything over 61 rc. However, I've found the 975F temper to work.

The story behind the development of S30V is very interesting. There's been some huge debates in the past between industry giants as to what is the best way to heat treat it. I'm not going to take sides here, just going by what has worked for me.

And of course, some people have specified how they wanted their knives to be heat treated.

 

[Lucky Bob]

???

My firm impression, and apologies if this is misplaced, is that cotdt didn't have access to rockwell testing equipment. If that is in fact the case, you can see my incredulity of assigning a specific value to it, no?

It's a relatively standard HT for a high carbon stainless steel. The Crucible datasheet doesn't list the temperatures for some reason (it also doesn't list the full composition for S30V). Cryoquenching is based on the theory of how cryo works, and the 975F temper is used by Paul Bos on his S30V and 154CM knives. People have reported good results on them, despite not being done "by the book". Many of the knives you may own were not done "by the book" but by standard heat treating practices.

It had been my impression that there was no "standard" heat treatment regime for cutlery stainless.

I have two specific issues with you M.O., the first of which is that you're using non (situation-specifically, according to you, which I'm somewhat willing to accept) proven heat treatments, which I freely accept is a personal bugaboo on my part and that others are free to partake as they wish to. As I addressed before, my bigger, less personal objection is that, based on what I recall from Shop Talk forums, you don't do hardness tests on the results, and yet extrapolate that data from other steels which may or may not produce identical hardness results. As I recall, part of the reason Bos tests every piece to come out of his ovens is that he can't guarantee going in exactly what hardness they will come out, and that's using tested and proven treatments on a per-steel basis.

 

[cotdt]

As I addressed before, my bigger, less personal objection is that, based on what I recall from Shop Talk forums, you don't do hardness tests on the results, and yet extrapolate that data from other steels which may or may not produce identical hardness results. As I recall, part of the reason Bos tests every piece to come out of his ovens is that he can't guarantee going in exactly what hardness they will come out, and that's using tested and proven treatments on a per-steel basis.

I already explained this earlier in the thread. I do do Rockwell testing by sending certain knives to be tested whenever a new formula is used. There is no need to test another knife using the same heat treat formula. I list the "aim hardness" and never made any claims as to tested hardnesses.

It is my belief based on metallurgical principles that the temperatures used are more important than final hardness. Hardness can be influenced by variations in each batch of steel, but in most cases I would still heat treat them the same way. The process used to make the steel also affects hardness. Consider 154CM vs. CPM154, which have similar composition, yet if you heat treat CPM154 the same way as 154CM, you'll end up with something 1-2 points harder. Would I still heat treat them the same way? Yes.

It had been my impression that there was no "standard" heat treatment regime for cutlery stainless.

The standard heat treat for the S30V/154CM/SG2 class of steels is 1900-2050F austenization for 20-30 minutes and 975F temper. The standard heat treat for low alloy carbon steels is 1500F 10 minutes and 340-450F temper. The standard heat treat for high speed steels is 2100-2200F and 1000-1025F temper. Many steels don't come with datasheets so heat treaters follow the standard procedure and they work just fine.

Paul Bos tests selected pieces of each batch, not every piece. Feel free to ask me for his contact info if you want to ask him yourself.

 

[sodak]

Me too. Do you know what kind of carbon steel the Opinel uses?

No, unfortunately. But Opinels are cheap enough that I'd send a couple and not worry about it.... Or a half dozen so that different heat treat regimes are tried, and then we can figure out what works and what doesn't.

 

[Lucky Bob]

I already explained this earlier in the thread. I do do Rockwell testing by sending certain knives to be tested whenever a new formula is used. There is no need to test another knife using the same heat treat formula. I list the "aim hardness" and never made any claims as to tested hardnesses.

It is my belief based on metallurgical principles that the temperatures used are more important than final hardness. Hardness can be influenced by variations in each batch of steel, but in most cases I would still heat treat them the same way. The process used to make the steel also affects hardness. Consider 154CM vs. CPM154, which have similar composition, yet if you heat treat CPM154 the same way as 154CM, you'll end up with something 1-2 points harder. Would I still heat treat them the same way? Yes.



The standard heat treat for the S30V/154CM/SG2 class of steels is 1900-2050F austenization for 20-30 minutes and 975F temper. The standard heat treat for low alloy carbon steels is 1500F 10 minutes and 340-450F temper. The standard heat treat for high speed steels is 2100-2200F and 1000-1025F temper. Many steels don't come with datasheets so heat treaters follow the standard procedure and they work just fine.

Paul Bos tests selected pieces of each batch, not every piece. Feel free to ask me for his contact info if you want to ask him yourself.

Well, I now consider myself mostly corrected and somewhat more educated (yeah, I'm a stubborn SOB, so sue me )

 

[fujita yuji]

Cryo is always better than cooled to room temperature in case of higher alloyed steel, but
is it worth doing in case of high temper applied three times ?

I have no experience with S30V that forgive me if I asked stupid thing.

 

[cotdt]

Opinels are cheap enough that I'd send a couple and not worry about it.... Or a half dozen so that different heat treat regimes are tried, and then we can figure out what works and what doesn't.

I'm curious about them myself. Send one over whenever you're ready.

Well, I now consider myself mostly corrected and somewhat more educated (yeah, I'm a stubborn SOB, so sue me )

Haha same here. You bring up reasonable points, and a little bit of controversy is a good thing. I could avoid it by keeping my heat treat formulas secret, but as a science person I'd rather share.

Cryo is always better than cooled to room temperature in case of higher alloyed steel, but is it worth doing in case of high temper applied three times ?

I have no experience with S30V that forgive me if I asked stupid thing.

Another good question, and I believe you are correct. The high temper raises the Mf each time the steel is quenched, so it might not be neccesary. Still, it wouldn't hurt since I have some LN2 around anyway.

 

[SteelSnob]

Well I got the knife back and there are some problems with the opening and lockup. I'm going to send it in to CRK and see what they say.

 

[Lucky Bob]

I had been wondering about that... assuming the piece was dimensionally constant throughout the heat treatment (not nearly as guaranteed as you might think, ask any diemaker), you still would have gotten decarb on the locking surface, which would (have to) get ground off, either in polishing or in usage. Grind off material and you change the locking geometry...

I hope it works out well, I have a ZDP folding blade which I think got kind of toasty at some point in its customization.

 

[Gator97]

Snob, is it stiff or loose? And what's with the lockup?

 

[SteelSnob]

There's side to side blade play. The slot on the tang that rests on the stop pin has been flattened so it's no longer a slot. It no longer glides open there's play in the pivot action making it more difficult to open.I was going to get on the waiting list for a damascus replacement blade from CRK anyway so it doesnt bother me that much. I figured it was worth a try. I could still use the knife but I'm a stickler for stufflike that.

 

[Gator97]

Sux... There's no way to adjust all that with pivot screw?

 

[fujita yuji]

Sorry to hear that..

Using some kind of protection during high temper is needed
as the pivot hole and the tang should keep their precision, which is
quite strict I suppose.

 

[midnight flyer]

Sorry to hear that..

Using some kind of protection during high temper is needed
as the pivot hole and the tang should keep their precision, which is
quite strict I suppose.

I would think in a CRK it would be very tight. That wouldn't have been my knife of choice for experimental lab work.

Robert

 

[ryan9977]

woohoo...my blades are almost on their way back...can't wait to see how they perform....thanks for tryin this out philip....ryan:thumbup: