The "Ask Nathan a Question" Thread

Nathan the Machinist said:
I'm not sure is 3V has considerably less wear resistance than Cruwear.
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Perhaps the right word would be "noticeably".
Nathan the Machinist said:
CPM 3V with the industry standard heat treat (using the secondary hardening hump) will combine the carbon that leaks from the martensite with the free chrome, forming additional secondary chromium carbide. This carbide is not particularly hard (high 60's I think) but it would aid abrasive wear resistance in some applications and in some geometries, but I don't think it's going to pay much of a dividend in a knife application given the trade-offs needed in this material in our application.
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Agreed. I personally favor edge stability over wear resistance.
Nathan the Machinist said:
In my own extensive testing with regular 3V and Delta 3V in cutting cardboard I got better edge retention with Delta 3V, which is one of the primary reasons we went that way. The additional corrosion resistance was a happy side effect, not the goal.
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That is interesting. There could be some factors affecting the results which might be difficult to isolate (i.e. the dirt in the used cardboards?). But it seems the difference in wear resistance between industry standard 3V and delta 3V is not noticable. Additional corrosion resistance is always welcomed.
Nathan the Machinist said:
I think an important mechanism for better edge retention in Cruwear will be the higher working hardness. I expect we will give up some corrosion resistance and some toughness but gain some edge retention in Cruwear, which is why we're evaluating it as a steel offering.
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If memory serves right, CruWear carbide content (the fraction of carbides to the overall volume of the steel) is twice more in CruWear than 3V. 3V with industry standard heat treat would have 5% carbide, whilst Cruwear would have 10%. Of course the extra hardness of the matrix would also help with the wear resistance.
 
Nathan the Machinist said:
I think that 3V is not naturally a good candidate for hardness above 61 or 62 because the aust temp required to put that much carbon into solution will make a plate martensite which is inherently less tough than a lath mix and 3V isn't well designed for this. And the lower tempering temperatures to retain that hardness is going to be highly tetragonal martensite. Not tough. So higher hardness dictate a steel with a higher hardness sweetspot.
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That makes sense. It explains why 3V toughness nosedive once it passes 61.
Nathan the Machinist said:
I don't think the optimal hardness for MC is 63+. You might be thinking of 4V, which MC is not. For example, you will not see MC used as a competitive blade sports steel. It really is not the same as 4V.
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I was putting 4V and MC in roughly the same category even though I know there could be differences. When I think of MC I also think of AEBL. As I said I favor edge stability above all, wear resistance is secondary to me. The reason I think 62-64 or more specifically 63-63 would be the sweet spot for MC is, below that hardness I will take AEBL over MC due to the higher edge stability of AEBL at 60-62. But similarly to 3V, according to Larrin's work, AEBL toughness takes a nose dive after 62 and the toughness of MC becomes the same with AEBL at 63 and if memory serves me right, MC is tougher than AEBL once the hardness passes 63, making MC more stable than AEBL at those hardnesses. So, beyond 62, MC takes over AEBL both in edge stability and wear resistance.
Nathan the Machinist said:
Those three sample pieces were between HRC 60.25-61.0 which is low for 4V but I had a test piece from an earlier HT trial and I wanted to see what would happen.



The lesson to be learned from that particular trial is that 3V is (obviously) the better choice if you're looking for high toughness. Which isn't a revelation. What was a revelation (in the since that I did not know what to expect until I tried it) is the relative durability of the three steels at around 60.5. I didn't know what to expect. Now I do.
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Great you tested this. There are some makers making 4V around 60 for hard use knives which I would prefer them to use 3V. But many says 3V is pain to heat treat correctly, whereas 4V might be more straightforward to achieve reasonably good heat treat.
 
PD#1 aka Cruwear
30vPE9N.jpg

tested the f*ck!
impressive all around
 
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Brian77 said:
It was a lot less crowded back in those days. And I could just purchase a "Nathan knife".
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yoko said:
You guys gave CPK that ignition to get them going so us newer guys can have a chance


#thanksCPKOGs
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What yoko said👍🏼. It is an absolute honor to be accepted into this amazing community and to have access to so much knowledge, passion, and amazing craftsmanship. Thank you ! 🙏
 
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