Hand Tools

There's good merit to carbon steels...
Response To:
Re: large nicking... ()

David Weaver
..having the best fine edge strength. But I don't know what actually test that. The notch test breaks out a much larger portion of the blade edge.

I've heat treated or tried other steels that are same hardness, and nothing seems to do as well with a fine edge as finely grained carbon steel with fairly low toughness (though if you can get high enough hardness, the high toughness steels do OK).

What I've seen from actual makers and more experienced users is the same. Larrin Thomas does all kinds of things with knives and tests, and the tables generally appear by nominal values to support something other than his preference because the tests are standardized.

His actual preference for knives is AEB-L at very high hardness with the bevel thinned as its ability to work in that condition isn't shared by more highly alloyed knives (AEB-L and probably 3V are matrix steel characteristic steels - fairly low carbon compared to heavily pumped powder alloys with more carbide volume. I think 3V would be a better matrix steel if it was capable of higher hardness, but a typical snap temper at 400F leaves it around 59 hardness).

I'm not sure if the crumbling edge bill showed was 3V at 62 hardness, but if it was, I woudln't be surprised. I don't think CPM M4 would exhibit the same issues at 62 because it's tempered back a good bit to get there. O1 likely woudln't, and 26c3 and white steel definitely don't. They're supple at 62 and very pleasant - kind of in between, but 26c3 tolerates 64 hardness without much toughness loss in larrin's charts - that's the point of it, though. After quench, it's supposedly around 68 hardness.

We'll see what my samples are -I'm sure they're not 59 (if larrin dents my quenched samples along with the tempered coupons - 68 seems like a hard number to reach, but who knows - if you can start at 68 and aim for 64, you're likely to have better conversion to martensite and better tempering of it than starting at 63 and trying to get 62. I've not had luck with fine edge holding when trying to leave steel nearly untempered, but at some point, I'll try it with 52100 as the untempered samples are much harder to break than tempered O1.

Anyway, what I found from the knife folks in trying to find the temper schedule last night for 3V (I vaguely recall that it's not easy for inattentive heat treating to lead to 63 hardness, and the steel has two temper ranges - at the top end where most tempers are done, temper falls off very fast after only about 50 degrees of differential). I also found a comment from a maker talking about "through the carbide hardness" and the results in fine edge holding vs. toughness test, and more or less that no maker would state that same hardness and higher toughness for a high carbide steel leads to better fine edge holding or the ability to hold an edge at a more acute angle.

This is kind of advanced for people not interested in trying things, but the bottom line is that when an edge gets very fine, especially if it's going to be more acute, nothing really matches carbon steels. Even lower carbon carbon steels don't do it (80crv2 is a good toughness well regarded knife steel that will reach the hardnesses we use in tools, but its reputation for fine edge holding isn't as good as it is for toughness and "an edge that's OK if it's not that fine". Subjectively, 1084 irons that I've made are a little lacking, but they don't have to be driven past 60 and they do OK there - above that, they chip - steels in the 1%+ range with carbon don't).

Separately, white AEB-L is well regarded and will hold up at high hardness, I've made a couple of test irons with it and they're decent -but far better once the initial edge wears off (otherwise, it's hard to get them to hold that initial edge without small nicking). I think the knife users don't mind the minimal chipping of the bevel behind it is thin, and thought at first it may be because I can't normalize it (and I've pondered making a run of irons and having peters heat treat them to 62 to see if they come back chippy). In this case, AEB-L is around where 3V is for carbon (add chromium and vanadium and there is improvement in carbide hardness, so it's not totally true that 0.7% carbon steels are all the same.)

I see the same with japanese yxr7 chisels - it's another matrix steel left at high hardness in chisels. The initial crispness of the edge doesn't last, but the rest of the edge life lasts very long.

Posters on knife forums in "which steel disappoints you the most" (not meeting expectations) provide a lot of answers with 3v, AEB-L or 80crV because they're disappointed with the edge holding of a fine edge - all have fine grain, so I think they're expecting better - I would).

Crucible actually made a couple of batches of "improved 3V" that had more tungsten and had niobioum in it as well as some tungsten (niobium replaced vanadium - similar hardness, but double the number of carbides - finer). I don't know if they were looking to get a point or two more hardness out of it, but apparently, the rolled material (it's still rolled into bars before it's sold - as sintered, nothing would probably be that great) has a much better match in toughness longitudinal and transverse (the surprise in larrin's comments about 3V itself is that transverse toughness is only 25% of longitudinal.

"improved 3V" has closer to parity, but the hardness numbers are similar (60 after tempering), so it still may not solve the ability for good fine edge taking.

V11 does seem to hold a fine edge reasonably well, but with a little bit more small damage (at least in every picture I"ve taken), but it's got enormous amounts of carbon in it, so that's not that much of a surprise.

This is only interesting to me because the steels that seem to have a reputation in the knife world (and that are used for straight razors in the vast majority) also seem to take the least damage in routine work.

A2 is definitely not in that category - there's not much mention of it on knife forums, though.

Steels that we like for woodworking, that have the best fine edge holding, are often referred to as "good steel for a slicer", probably because they're low toughness and don't stand up well to being hammered on the spine. 3V has good longitudinal toughness (so does 52100), so it's not a surprise that they're well liked for abuse knives. CPM M4 has slightly lower toughness, but I'd bet its fine edge holding is probably decent (it's just expensive and expensive to get heat treated and ground post heat-treat).

Ever since starting to look at the toughness thing, though, the difference in fine edge holding vs. actual notch toughness results have baffled me. They are easy to discern in use testing side by side (notch toughness doesn't seem to mean much, but it does correlate a lot with how easily you can break untempered samples in the vise, as well as tampered. I can break 400F tempered O1 pretty easily, but I wouldn't attempt to temper 52100 to 60 hardness and then try to hammer it into a break in the vise - i'd be worried about breaking the vise - even untempered samples were uncomfortable to break, though I was also breaking them a couple of minutes after quench and some of that residual toughness may have left. )

How does this apply to the average boutique tool customer? I doubt it does. It's relevant for someone trying to make good tools that they like to use and that will be pleasing to someone with experience, though.

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