CPM3V vs CPM4V

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I have no way of measuring it, but my guess is the modified heat treat does not increase impact strength as defined by energy absorbed in a break. In fact I have no way of visualizing the structures involves, but my best guess is the modified heat treat does what it does by reducing "areas of stuff" (precipitated carbides, retained austenite, structures formed from the conversion of RA and other gunk) that act like the perforations in a postage stamp, weakening a fine edge. Also, I expect the harder stronger tetragonal martensite supports the primary carbides better than weaker carbon lean martensite. I don't know *shrug* there is no SEM or x ray diffractometer in my shop. But I don't think there's in increase in impact strength or lateral strength as industry would define it. I think it boils down to the structures formed and their behavior in a thin section. There are idiosyncrasies with this alloy.

The SHH would probably have somewhat higher abrasion resistance but it would not be much. Some alloys, D2 for example, develop a lot of their abrasion resistance from the formation of secondary carbides and even on that material the difference is small. 3V has a significant amount of vanadium primary carbides that are not greatly effected by the temper used and these carbides provide the majority of the abrasion resistance. Making a little more carbide is not going to make a huge difference. But the ability of the matrix to support those carbide makes a really big difference in real world edge retention.

These tweaks were never about making the steel tougher, it has always been about addressing the chippy mushy edge that so many people have come to accept as normal in today's steels. What good is abrasion resistance in a chippy mushy edge? It's all about edge durability, edge stability.

Therein lies the problem with edge retention testing that apply a careful applied light force against abrasive media, it will tell you all sorts of weird things like S30V having great edge retention etc. Most folks don't sit and lightly saw at abrasive card stock. Real edge retention testing requires a different approach.

 

Nathan, just caught your signature logo. Awesome. Sign me up!

This thread is funny, btw.

 

Hey Nathan, tell me what your take is on 3v vs 4v. To me it seems one gains a little in abrasion resistance only to loose a lot in toughness...

 

That chart says that D2 has the same toughness and wear resistance as A2. That's silly. It also says 3V has twice the wear resistance as D2, which is also silly. So I wouldn't put too much weight in that graph.

I actually hate charts like this because they're misleading. People think that wear resistance equates to edge holding and it doesn't. Or that toughness equates to a durable blade and it doesn't. There are correlations that can be drawn, but a chart like this, even if it were accurate, doesn't tell you the whole story.

 

In my experience in the non-knife world impact strength was never an exact thing but only a guide. Just like the "Equilibrium Diagram" . I'll look through the thread and see ifI can provide some logic !!

I've suggested 400 F temper often . The 1000 F was developed for dies ,especially precision dies , for dimensional stability with some added wear from secondary hardening.

Nathan , do you have any connections for the use of an SEM ? Would be nice to see exactly what's in the edge.

I would assume in the good stuff you'd see lot's of strained matrix, lots of dislocations [martensite is full of that ] etc --little stuff can mean a lot !!


[ never "save " poorly HT'ed steel , do it right the first time !! ]

 

Quick question, does the 400f temper require full cryogenic, or is sub zero enough?

 

I don't. I wish I did.

I think you could get good results without full cryo if your quench and austemp were right and you could hit -100. I'm not sure where that line is, but I'm pretty sure 3V is actually not that sensitive to RA.

 

Nathan , with LN [-300 F]you also get eta carbides .It may add the edge stuff you want . Cryo is more than just RA. Go right to LN from room temperature ,hold 4-6 hours . Most apparently get 1-2 HRc points higher.

 

So what would give better performance, industry standard, or sub-zero, but no access to cryo with 400f temper? I didn't think the eta carbides were that important, but if they are, I need to upgrade.

 

Nathan is looking for special blade properties which really have to be tried, it's not in the books. While sub-zero will reduce RA some more the eta carbides should do something for strengthening the matrix with added cohesion.That's why we need experimenters !!

 

as with any steel you dont want to over heat it then "fix" it with some other processes (in this case gettign rid of extra RA with cryo). the extra alloys help keep grain size pinned but if you push too hot grains will grow and knife makers have no need for that
look at the data sheets and see about where the max RC from quench happens then shoot for that or juat a hair more then cryo to max RA reduction & pick up eta carbides. this give you the full temp range to temper at so you can play around

 

I'll be doing some experiments when the steel arrives.

 

Well... steel....experiments....results....

Sent from my SM-G900R4 using Tapatalk

 

Great data - thanks! And thanks to Nate and Dan as well!

 

I'd like to dust off this turd of an old thread. It turned into a discussion about the validity of heat treat tweaks and deviated from the original topic of 3V vs 4V. I didn't have much of an opinion at the time but have formed one over this winter as we've done much more testing and optimization of 4V.

In a nut shell: Optimized 4V is more durable than optimized 3V at high hardness where you're looking at edge damage. That's not to say it is tougher than 3V. It is not as ductile and can more easily break and failure mode tends to be chipping rather than denting, but it has higher gross edge durability, which was surprising to me.

However this is only true when using a heat treat for it that is optimized for cutlery. When given the heat treat in the data sheet it has a crumbly edge that turns to dust in impact with hard wood knots etc. This is also true for variations of that HT given cryo tweaks. The SHH doesn't do it for 4V in a knife edge we tried. BUT! Fortunately for you knife nuts the low temp tweaks for tool steels are well understood and work well with 4V and are offered by Peters HT and have tested very well here. So those of you wanting to use 4V can look forward to a relatively durable steel with good edge retention and good edge stability at hardness from 62-65.

Comparing 3V to 4V, optimized 3V has much greater total toughness and corrosion resistance, similar edge stability, lower wear resistance and a lower hardness range sweet spot of 60-62. I'd choose 4V for applications needing wear resistance and edge durability at high hardness. The chemistry is used on winning competition cutters (has replaced CPM M4 as king) and I think it's a good alloy for some high performance choppers and certainly smaller knives as well. Though it isn't 3V it is still plenty tough for most uses. Down sides is reduced corrosion resistance, more difficult to sharpen, and a real bear to grind hard.

^ these opinions are formed after evaluating and testing to destruction many blades and looking at many variations in tightly controlled experiments. The conclusions I've drawn are probably not very surprising, but they are based upon a lot of observation at this point and are pretty solid. 4V is a good high performance steel. :thumbup:

 

I apologize, what is shh, or did you mean sht?

*edit, secondary hardening hump, got it.

Hoss

 

Sorry, I was being lazy. I should have said "secondary hardening hump".

 

4V is a copy of vanadis 4 extra. V4E is nearly impossible to get so we are lucky to have 4V available.

My experience with V4E shows that it is a very good steel with high toughness and wear resistance. I find that it has a wider band of hardening temperatures than 3V.

Uddeholm has come out with a steel that is based on the V4E technology, Vanadus 8. I got my hands on ~12# of 2 inch round stock. It's supposed to have higher toughness than A11/10V and almost the same wear resistance. I'll report my findings after I try it out.

Hoss

 

Can someone show me where Roman Landus talks about LTT of these steels?

Hoss