Alloy banding in A2?

[aarongough]

By all means, do not throw your existing A2 blades away Clearly, you've shown that it works pretty dang well for knife blades, as have many, many other makers.

I'm really looking forward to your comparison testing between A2/CPM-154/CPM-3V and whatever else you decide to try out. :thumbup:

Haha, clearly the discovery of a new (to me) trait in my favourite steel drove me slightly batty and I over-reacted in all kinds of ways! That said it's good that I've learnt something new about the steel, have to keep learning on that front! In the future I'll just have to learn to damp out my reactions a bit and do further testing/research before I wig out.

I've been putting together some ideas for proper testing rigs that would test the steels in a hopefully repeatable way. The testing I did last time was not exactly scientific. I'd like to come up with something a bit more thought-out this time... I actually have an idea for a poor-mans CATRA-style edge-retention test rig that I think could work pretty damn well.

We'll see, I don't want to over-do it too much In the meantime I'll be putting together some CPM154 blades to see how I like them, I'm still pumped at the idea of getting to use a stainless.

 

[james terrio]

Cool thread mate! It's cool that 3V is so rust/stain resistant.

A couple more years' experience and study leads me wonder if maybe a lot of the chrome in 3V is actually "free" and not tied up in carbides. I think the vanadium in it forms carbides more readily than chromium does and uses up the moderate amount of carbon, so that may account for the wear-resistance, fine grain, and leaving the chrome free to help with stain-resistance. I don't know for certain, I'm just thinking out loud...

Any of you guys have tips for getting 3V to high hardness in heat-treat?

I do not do my own HT, I let Brad at Peters' worry about that. So my advice is, give him a call and pick his brain. I can tell you that both he and Hossom and Harner and others have been nudging me to have my 3V knives (large and small) tempered to 60 or 61Rc... they're pretty adamant that the toughness in that range is still excellent and the extra hardness really does help with strength at the edge. Those are guys I respect a lot, so I'm gonna have my current batch run at 60-61 and see what happens.

As for higher Rc values, there are some tricky things going on regarding austenizing temps, avoiding certain tempering temps, and cryo (or perhaps just dry-ice quenching?) is really important to address retained austenite.

 

[james terrio]

Haha, clearly the discovery of a new (to me) trait in my favourite steel drove me slightly batty and I over-reacted in all kinds of ways!

That's not over-reacting, it's just paying attention to details and wanting to figure out what's going on, and seeking the very best. That's our job as professional knifemakers. That's why we stay up late obsessing over this stuff, and hopefully get paid more than a robot in a factory. That's why guys like Nathan and Dozier and Hanson and Cashen tweak and re-tweak their HT procedures. "Good enough" is not good enough.

It may turn out that the banding in A2 really isn't a measurable factor in terms of real-world performance. But it looks like hell, and that counts too. If there are steels that demonstrably perform better (which I'm convinced is a fact), and happen to look prettier while doing it, why not use them instead?

The steel industry didn't spend millions of dollars to develop this "new" CPM/powder stuff (or A2 or O1 or D2 for that matter) just on a whim.

 

[aarongough]

That's not over-reacting, it's just paying attention to details and wanting to figure out what's going on, and seeking the very best. That's our job as professional knifemakers. That's why we stay up late obsessing over this stuff, and hopefully get paid more than a robot in a factory. That's why guys like Nathan and Dozier and Hanson and Cashen tweak and re-tweak their HT procedures. "Good enough" is not good enough.

It may turn out that the banding in A2 really isn't a measurable factor in terms of real-world performance. But it looks like hell, and that counts too. If there are steels that demonstrably perform better (which I'm convinced is a fact), and happen to look prettier while doing it, why not use them instead?

The steel industry didn't spend millions of dollars to develop this "new" CPM/powder stuff (or A2 or O1 or D2 for that matter) just on a whim.

Thanks for the words of encouragement there James!

I'll be very interested to see how CPM3V goes in my second round of testing. I feel like I'm a lot more experienced with heat-treating now, so I'll be curious to find out if I simply missed a trick last time.

 

[aarongough]

I'm also quite curious now about CPM4V. It's much less tough than 3V is at lower hardnesses, but at high hardness the toughness is almost equal and it has a higher level of wear resistance.

It also seems that the maximum attainable hardness for 4V is much higher than for 3V. Crucible's datasheet shows a max hardness of about 64.5HRC after tempering, whereas CPM3V seems to top out at about 61HRC.

Seems like it would be less corrosion resistant than 3V, but probably slightly more than A2. Will probably grab a bar of this for testing at the same time as the others.

Thanks to Matthew Gregory for the recommendation on that front!

 

[Nathan the Machinist]

leads me wonder if maybe a lot of the chrome in 3V is actually "free" and not tied up in carbides. I think the vanadium in it forms carbides more readily than chromium does and uses up the moderate amount of carbon, so that may account for the wear-resistance, fine grain, and leaving the chrome free to help with stain-resistance. I don't know for certain, I'm just thinking out loud... .

I'm pretty sure you're right. And, if you avoid the secondary hardening hump you'll avoid the secondary carbides that consume free chrome, but you must quench to Mf to avoid RA if you do that.

he and Hossom and Harner and others have been nudging me to have my 3V knives (large and small) tempered to 60 or 61Rc...

.

3V is a lath martensite, it's very tough, and tends to roll. It needs the extra hardness to maximize strength. This improves the edge retention and you still can't break it.

When evaluating some tweaks to 3V I did some destructive testing for my own comparison. This is a "rough use" 3V knife at HRC 60, it was .025" before sharpening and 20 deg per side : http://youtu.be/IcovoTyGiRg The tweaked HT improves edge stability, it goes through 4" concrete containing granite aggregate and a 16 D nail with reduced roll and chipping. Going softer would reduce edge retention and I really don't see where it would need to be any tougher.

 

[Kloepper Knife Works]

I'm also quite curious now about CPM4V. It's much less tough than 3V is at lower hardnesses, but at high hardness the toughness is almost equal and it has a higher level of wear resistance.

It also seems that the maximum attainable hardness for 4V is much higher than for 3V. Crucible's datasheet shows a max hardness of about 64.5HRC after tempering, whereas CPM3V seems to top out at about 61HRC.

Seems like it would be less corrosion resistant than 3V, but probably slightly more than A2. Will probably grab a bar of this for testing at the same time as the others.

Thanks to Matthew Gregory for the recommendation on that front!

You hit the nail on the head. 3V is limited to around 61-62Rc, thus the creation of 4V with the higher attainable hardness and associated increase in wear resistance.

With the lower chromium content (5% vs 7.5%) and higher carbon, I'd expect 4V to be noticeably less corrosion resistant. But that's based on guessing based on the chemistry and others experiences not my own, so take that with a grain of salt.

 

[james terrio]

I'm pretty sure you're right. And, if you avoid the secondary hardening hump you'll avoid the secondary carbides that consume free chrome, but you must quench to Mf to avoid RA if you do that.

That's exactly what I'm trying to wrap my head around. :thumbup: I'm gonna find out pretty soon if my next batch of "hard-use" 60Rc 3V blades out-perform my previous batches of 58Rc 3V blades... frankly I'm really looking forward to it, and I'm reasonably certain that they will. Next batch after that will be run at 62Rc, and we'll see what happens. Again, I suspect I know what will occur in testing (I think that will over-shoot the sweet-spot for a tough "survival/combat" blade, but may be just right for a thin kitchen knife or skinner), but there's only one way to find out for sure

If I understand all this half-way-correctly, the "lath" structure as opposed to "plate" structure of the martensite is a major factor in toughness. I think that's largely dependent on chemistry (carbon content), and isn't really going to change much in an alloy like 3V, so that gives us some wiggle-room to play with hardness without giving up much toughness.

Nathan's test video, embedded here just because I know how...

[video=youtube;IcovoTyGiRg]https://www.youtube.com/watch?v=IcovoTyGiRg&feature=youtu.be[/video]

 

[Nathan the Machinist]

That one is not really a "test" video so much as a demonstration video. I put that on the sales threads. It's one thing to say "hey, this particular knife is intended to tolerate very rough use" but another to actually show it so people don't have to simply take one's word on it.

^ Lath vs plate is a function of carbon in solution during quench. You could get lath in 1095 if you left the carbon in carbides.

There is enough carbon in 3V to get plate, and there can be advantages to plate, but a standard HT for 3V is going to be mostly lath because of the low carbon and high vanadium content and moderate austenitizing temperatures used.

 

[james terrio]

Lath vs plate is a function of carbon in solution during quench.

Clearly, I still have a great deal of homework to do.

 

[aarongough]

Clearly, I still have a great deal of homework to do.

I think anyone not saying that has already lost the battle!

 

[mete]

Nathan it's rarely lathe vs plate at those carbon contents. It's usually a mix.

Dry ice vs cryo -- While both reduce retained austenite [cryo more so ] cryo [liquid nitrogen. ] Permits the formation of fine eta carbides on tempering !! That's gives the best prformance !

 

[aarongough]

Hey all!
Thought you guys might like to hear the latest development in my search for good steel sources... Just been chatting with Niagara Specialty Metals, the prices on their website are really not that great for small pieces, apparently they price to guarantee that they don't undercut their distributors which seems reasonable to me. The problem comes when you want to order a grade that none of their distributors carry..

A 0.186x6x36" piece of CPM4V will cost $467 direct from NSM. If you bought it from one of their distributors it would be something like $280 for the same piece.

When I was chatting to them though they mentioned that their first real price break when buying from them is when you start buying full sheets. I asked for pricing on this assuming that it would be too rich for my blood but I wanted to check. Turns out I was wrong!

A full sheet (24x36") of .186" thick CPM4V is around $600. CPM3V, CPM154, etc are all LESS than that for a full sheet! So if you're using a bunch of this steel then it seems that it really makes a *lot* of sense to simply buy full sheets from NSM.

Additionally they do waterjet on-site, and if you ask them to cut a full sheet by waterjet then you won't be paying for scrap, or for postage of scrap. They said they're likely a bit more expensive per inch than a dedicated waterjet shop would be, but I would bet that the cost difference is easily made up by not paying for the excess material and so on.

This may be old news to some, but I was pretty impressed by the pricing for an array of really nice steels. Given that I only make a few different models ordering waterjet-cut blanks from NSM likely makes a lot of sense!

 

[Nathan the Machinist]

I was asked to etch some Latrobe A2 for comparison. This was still wearing color from heat treat except the grind on the bevel.

Those black stripe things on the bottom right that look like scratches are, in fact, scratches. I was cutting cinderblocks with it.

This was etched in hot vinegar, I don't have ferric chloride.

It appears to me that this particular batch of Latrobe A2 might have less alloy banding than the OP.

 

[aarongough]

Thanks for taking the time to do that Nathan, greatly appreciated!

The banding I see in the photo you posted looks similar to what I saw in the Uddeholm A2, the banding in the Starret A2 was longer, like lines as opposed to dots.

I have made my peace for the moment with the banding in A2. I've shown satin-finished blades to several other craftspeople whose opinions and work I respect, and none of them were able to spot the banding. To be able to see it you definitely have to know exactly what you're looking for, and have exactly the right light.

For the moment I'll be continuing to use A2 as I've been very happy with it's performance to date. The blades that have gone out to past customers have all been 62HRC or even 63HRC. Those knives have been getting used hard and I've seen zero issues. My personal A2 blade is 63HRC and the only time I've been able to mar the edge was when I batoned it into, and then twisted it out of, a knot in dried hardwood, and even then that was a tiny chip that sharpened out in a few minutes.

I'm aiming to finish up my backorder list by the end of this year, at that point I will be looking at doing another round of steel evaluations (I'm already buying up samples for testing: CPM154, CPM3V, CPM4V and more) at that point I may end up changing steels, we'll see.