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New micrographs of 42 knife steels

A lot of us have been thoroughly enjoying the IG posts leading up to the article. Very cool, interactive way to draw people in.

I think it may also be illustrative and interesting to see images of same composition, with ht process blown in a couple ways, to highlight the effects of the structure when the ht isn’t done with care.

Excellent article, per usual.
 
Super article, Larrin. Much appreciated.

Can you explain this statement:
I am not aware of any PM stainless steels with less than about 13% carbide volume. This is why there aren’t any high toughness Z-Tuff, 3V, 4V, or CPM CruWear type stainless PM steels, because the carbide volume is not low enough.​

I thought 3V is a CPM powder steel. The last sentence confuses me.


In the graph near the bottom, showing the toughness of stainless steels and D2, Vanax seems too low, even below CPM 154 and M390 (when hardness is taken into account). Elmax looks too low, too.


And I remember that CPM D2 steel fell out of favor a while ago, purportedly because there wasn't enough difference between ingot D2 and powder D2. But your carbide photos seem to show that there would be a big increase in going to powder on D2.
 
Twindog said:
Super article, Larrin. Much appreciated.

Can you explain this statement:
I am not aware of any PM stainless steels with less than about 13% carbide volume. This is why there aren’t any high toughness Z-Tuff, 3V, 4V, or CPM CruWear type stainless PM steels, because the carbide volume is not low enough.​

I thought 3V is a CPM powder steel. The last sentence confuses me.
Click to expand...
That sentence says stainless PM steels. 3V isn’t stainless.

In the graph near the bottom, showing the toughness of stainless steels and D2, Vanax seems too low, even below CPM 154 and M390 (when hardness is taken into account). Elmax looks too low, too.
Click to expand...
Elmax and Vanax are about where they should be I think, there is a similar difference between them and V4E as in Uddeholm’s datasheets. The Bohler-Uddeholm toughness report showing Elmax having much higher toughness than other stainless steels I can’t explain. That wasn’t done by the normal Bohler or Uddeholm people in Europe. What is unexpected is how much better CPM-154 than those others. I’m hoping to do some more CPM-154 in the future to give more confidence in that result.
And I remember that CPM D2 steel fell out of favor a while ago, purportedly because there wasn't enough difference between ingot D2 and powder D2. But your carbide photos seem to show that there would be a big increase in going to powder on D2.
Click to expand...
I don’t know why CPM-D2 is disliked, some say it isn’t as aggressive as the larger carbide version. Maybe people prefer to use a stainless if they are getting a high carbide PM steel. Maybe it just hasn’t been promoted by the right people.
 
Twindog said:
Super article, Larrin. Much appreciated.

Can you explain this statement:
I am not aware of any PM stainless steels with less than about 13% carbide volume. This is why there aren’t any high toughness Z-Tuff, 3V, 4V, or CPM CruWear type stainless PM steels, because the carbide volume is not low enough.​

I thought 3V is a CPM powder steel. The last sentence confuses me.


In the graph near the bottom, showing the toughness of stainless steels and D2, Vanax seems too low, even below CPM 154 and M390 (when hardness is taken into account). Elmax looks too low, too.


And I remember that CPM D2 steel fell out of favor a while ago, purportedly because there wasn't enough difference between ingot D2 and powder D2. But your carbide photos seem to show that there would be a big increase in going to powder on D2.
Click to expand...

“PM stainless steel” — 3V is 7.5% chromium. Non-stainless, tool steel.

Edited to add: beat to the punch. My bad.
 
so, the way I read it, it's time for some machete's in 8670 - in fact, all of them should switch from 1070 or 1075 (like ontario)
looks like the most tough/lowest cost (and very old) non-stainless steel
5160 is good also, but I don't expect it will be as super-easy to home-heat treat it

a quick search on kc shows only southern grind has a machete in 8670 ; ) --- but they wrecked it with a giant rectangle cut out like a spdy hole, makes me sad because it looks nice otherwise
 
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How much higher would 1095 score in thoughness in the hardness range Esee uses? Just seems like there would be other steels more suitable for the use they promote, steels that can take a higher hardness and still be thoughe?
 
Pr3inar said:
How much higher would 1095 score in thoughness in the hardness range Esee uses? Just seems like there would be other steels more suitable for the use they promote, steels that can take a higher hardness and still be thoughe?
Click to expand...
I don't know what hardness Esee uses. I cut off the lowest hardness specimens that were tested from the chart. Going softer marginally increases the toughness following the same line as the other tests.
 
A pleasingly visual and relatively brief article. Much appreciated. I was surprised by the intense uniformity of CPM154 - something that has been described to me, sure, but seeing it next to other particle metallurgy steels speaks volumes.

As someone whose interest nearly matches their ignorance regarding the finer points of metallurgy, this was an excellent read.
 
Larrin Larrin , please put up some numbers for 80crv2 if possible? I was sure some testing has been done on the test thread, but can't find it...

80crv2 benefits over 8670 with 0.2% vanadium, but the nickel amount drops quite a bit (down to around 0.25% from 0.7-1% in 8670)
 
Thank you so much for your amazing work Larrin, and for sharing it with us. These pictures are just incredible, and so is your ability to explain all of this in an instructive, easy to understand article.
 
another great article Sir. enjoyed this one immensely. thank you.
 
Larrin said:
I don't know what hardness Esee uses. I cut off the lowest hardness specimens that were tested from the chart. Going softer marginally increases the toughness following the same line as the other tests.
Click to expand...
Ok, thank you. They use 55-57, and if it follows the same line I can «see» it myself :)
 
Had a conversation with Larrin Larrin and we geeked out on the micrographs.


It's very powerful being able to SEE what these steels look like with the same magnification and etching procedure versus the patch work of pictures there were previously available.

-I think the important take away from these micrographs is the Non PM steels can be finer, just depends on the steel composition.
(AEBL for example)

- PM steels will have finer Carbides than the same high alloy chemistry that is not PM.

- Carbide volumes and fine size isn't everything, carbide hardness also plays a huge role Hench why AEBL is not very wear resistant but has other merits, everything has trade offs.

-in PM steels with high volume, Vanadium makes the finest hardest carbides next to Niobium than Tungsten/Molybdenum than the larger carbides are Chromium if present in large volume. (52100 and AEBL have fine chromium Carbides smaller than PM steels thanks to low volume, TRADE OFFS)


- I was surprised at the size of M2 steel, the clusters of moly/tungsten rich M6C Carbides for not being a PM steel were pretty fine, just shows that chemistry volume can change the sizes.

-Not all performance factors can be discernable with these micrographs alone. It will be fun to fill everything out with more testing over the next decade.

The biggest take away...

3rd gen Bohler-Uddeholm PM process doesn't make finer Carbides than 1st gen Crucible PM.

So M390 and 20cv can be thought of as the same for all intents and purposes and other variables such as melt to melt chemistry variations, rolling, HT, grinding, geometry and sharpening are the bigger factors.


It was a lot of fun discussing the finer nuances and caveats in the video.

I feel at a certain point that is the only way to share such detailed information.
 
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Other strong notes:

- D2, PSF27, CPM-D2 vs AEB-L provides a “can’t miss” model for why certain compositions benefit from PM process, while others do not.

- seeing the big effects that small amounts of certain carbide forming elements can have on carbide size, even in chromium carbide dominated steels. XHP is a great example. This shows that compositions may differ substantially more in practice than they appear to on a data sheet.

- the piece about nitrides should be educational for even the more familiar viewers. That was gold.
 
Banter 247 said:
Other strong notes:

- D2, PSF27, CPM-D2 vs AEB-L provides a “can’t miss” model for why certain compositions benefit from PM process, while others do not.

- seeing the big effects that small amounts of certain carbide forming elements can have on carbide size, even in chromium carbide dominated steels. XHP is a great example. This shows that compositions may differ substantially more in practice than they appear to on a data sheet.

- the piece about nitrides should be educational for even the more familiar viewers. That was gold.
Click to expand...
Yea that was interesting to see that the PM process for CPM D2 didn't shrink those Carbides as fine as we would have thought due chromium and carbon volume and no Vanadium presence to keep fine. The M2 looked like it could give it a run for the money and has harder carbides too.
 
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What's wild is pinned abrasive rubber wheel testing in materials science shows that large Carbides may be more wear resistant in some cases which means that some of these large carbide steels may have more synergy to explore with coarse edges.

"Mastiff" Joe had gifted me some non PM steels to explore this

such as A7 Mod which is close to a type of non PM A11/10v class with reduced alloy which should help with segregation/clumping/size issues versus a NON PM 10v, much like how M2 looks vs NON PM M4

A7 MOD may show promise with very aggressive 400 grit edges more than some PM grades at a cost to raw tougheness.

In fact that is why some other edge freeks were curious about spray form A11/10v

Which as seen in PSF27 is in between sizes of cast ingot and PM.

That would be very curious to see on an edge.

I'm curious to see what A7 MOD looks like and I'll have to send some I HT to Larrin to check out along with some M3-1, another curious non PM steel.
 
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