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Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by gsx-rboy750, Oct 7, 2014.
Is the thread you are referring to:
http://www.hypefreeblades.com/forum/viewtopic.php?f=3&t=77 Here, if I selected the right stuff (I'm in my phone).
That was a good read. Thanks for the link guys.
Thanks, good stuff.
From what I gather, pre heating allows faster heating and shorter austenitizing time which causes finer grain. Cryo reduces RA to low levels, flash tempering, low temp tempering and water quenching between tempers reduces or eliminates the preciptation of nano sized carbides. Nano carbides cause brittleness at the edge and less stain resistance. The process works for high alloy steels but is not necessary for high speed steels.
I think the RA in HSS stabilizes so fast that the only way to remove it is with high temper. Vanadis 4 extra is like a HSS optimized for cold work, so I wonder if Landes heat treatment is still valid and able to eliminate RA. Some that I respect A LOT in this industry uses high temper in Vanadis 4 extra and no cryo so I don't know what to think anymore!
For whatever it's worth, when I was having some blades made out of ZTuff from Zapp (a steel similar to 3v, erring more on the side of toughness and wear resistance), I contacted Mr. Landes about using the lower temper, and while he said I could give it shot, he wasn't enthusiastic about it. I'd have to dig out the conversations for the specifics, but he didn't seem to understand why I would pick a steel designed to be high tempered and try to force it into low temper protocols. I got the impression, the just thought I should pick a steel with naturally more toughness if that was what I was after.
Along those lines I think it's an interesting question...if the low temper protocol essentially reduces carbide formation (lowering it's abrasion resistance) and produces a finer grain, why not just choose a steel that naturally does that, like 80CrV2, and not worry about having to go through a complicated heat treat in order to produce fine grain, minimal carbide formation, low RA and high RC? (One of the reasons that does occur to me is the stain resistance, but that's not a particularly desirable attribute for me personally).
I think a metallurgist thinks exactly like that! For work in cold conditions, if you need toughness just choose a medium/low alloy steel, simply to heat treat. Batoning? Chopping? Choose a shock resistant steel. I think they don't see a point in using steels optimized to hot work or with high alloy in knife tasks, other than cutting soft materials. But we insist on that!
Low temper prevents the formation of the secondary carbides. The primary carbides are set during the heat treat protocol. Low temper is an advantage when using geometries and hardnesses that are outside the spec the steel was engineered for. With 3v, we can run higher hardness with better edge stability with low temper. I'm experimenting with low temper on z-wear with promising results. I can run Rc64 and thin (0.003") edges and they are holding up. With a steel like z-tuff, rather than trying to run higher harness, go with 3v, eliminating the need for low temper in z-tuff. It's plenty tough to start with, so there is little advantage to going tougher yet, trading off wear resistance. Even with high temper on z-wear, I'm finding the edge stability is the best I've found on any steel I've used so far.
I agreed with Nathan's assessment above. As for LTT (low temperature temper) vs HTT (high temp temper) - there are quite a few major variables involved. I think 'Bend Strength' and 'Dimensional' are key variable for edge tools. Pic below is my reluctant mini-blah about it. With some staring + simple deduction in physical world (+ whatever published data out there), you might find reason why LTT (with Cryo) might has advantage over HTT in edge tools. As for extra wear resistance - I would just use steels with higher carbide volume than getting it via HTT.
*dimensional changes: think of a huge packed cube of lego blocks/grains of different sizes and shapes. Increase size = increase stressed (dislocation). Fair to ask - at working dimension of LTT & HTT, which one has lower dislocation? Oh sorry, I blah :foot: