Hi Larrin. I'd love to see a video about DLC coating and Rockwell hardness. I have a hard time wrapping my mind around how applying a very thin coating of something harder than the blade steel, actually reduces HRC. It's kind of counter intuitive, and I think a video on it might be very interesting.
When the coating is applied it has to be "baked" on to the steel and if that temperature is higher than the original tempering temperature the hardness of the steel is reduced. In other words, applying the coating means the steel is tempered hotter. The coating is not on the edge so there is a potential reduction in strength and cutting performance at the edge.
@@KnifeSteelNerds A video on this would be super interesting. The influence of the coating on the corrosion resistance is also hard to understand, because the VPD coating are *in theory* so thin that they allow corrosion to build underneath. In reality you can rarely get all the important info from the manufacturing process, because a lot of companies outsource both the coating and the HT. Speaking about HT processes with marketing department of knife companies fails with 100% reliability.
Thank you Dr. Thomas, l am a knife maker in Taiwan and got a lot of help from your articles. May l ask a question? I am curious about that will there be some difference in wear resistance between tempered martensite and bainite(especially for Carbon steel)? Because there will be rare or very small size carbides after carbon steel got quenched, but in bainite carbides form completely.
Carbides are also found throughout tempered martensite. That is what happens during tempering is that carbon goes out of solution as small temper carbides. There are some studies that have shown a small advantage for bainite vs tempered martensite at the same hardness. This is due to either more carbide, larger carbides, or retained austenite. Retained austenite is undesirable for knives, and the type of wear resistance tests that show an advantage from that are when high pressure leads to retained austenite being converted to untempered martensite, which we don't want. Furthermore, selecting a steel with higher carbide volume would lead to a much greater difference than a tiny difference in carbide volume of tempered martensite vs bainite. I have a discussion of this subject and references at the end of this old article: knifesteelnerds.com/2018/07/09/bainite-vs-martensite/
I never thought I'd pop a chub during a lecture on bainite formation in knife steels, but then again, when you start talking about tough, resilient structures under pressure, it's hard not to feel a little heat treat in the air! 😂
Nice clip. There are metalrecipes with tin and bismut that go around 400°C you can long quench then the steel in a metalbath. Looks fancy too 😅 Just never drop a blade or whatsoever with oil or grease on into such a high temp liquid or it will EXPLODE into your face. Why? Because the stuff will like to evaporate in the 400°C bath. The blades are very tuff indeed, we made some a few years ago.
Extremely interesting. I will definitely utilize this as I don't need the absurd hardness of 60+. I wonder what would happen if you did indeed austemper something like high speed steel for 48hrs lol.
You could compare the 1095 result (24:00) to a hitachi white paper #2, or Takefu V2c (V2 has a touch more nickle and Cr), which should both have tighter control of P and S impurities than 1095.
Makes me wonder how much tougher zdp could be in tempered this way, whilst keeping the insanely high hrc. I've never really understood bainite processing, this video helps me make some sense of it, but it also gives me the impression that my favourite steel, zdp, would have to be held for days to get toughness up to small load batoning levels
minutes, seconds and hrc, ok. but Fahrenheit? i have learned english in school but the temperature unit is like listening to greek 😂 very interesting information. Thanks for sharing.
Hello Larrin, amazing video/study as usual. I'll definitely read the article too. I most likely didn't understand everything and will need to read the article, but from this study, should I be able to understand how Howard Clark achieved bainite on the spine and martensite on the edge for its L6 sword?
I believe the rumor is that Howard does an austemper on the entire blade and then heats the edge with a torch and quenches in oil. If Howard has given more specific details somewhere hopefully someone can post a link. I believe his bainite spine is somewhat lower in hardness than what I was trying to achieve here.
@@KnifeSteelNerds Thanks a lot for replying. Many years ago, like a dozen or even more, I read on a forum that he had never given details about his process and said something like: " I didn't invent anything, the information is out there, find it out for yourself ". Not literally from Howard Clark himself, just what I remember. In other words, he wasn't going to reveal his process, but he was humble and said there is really nothing "magical" about it. Maybe he has finally revealed his process after that though...
I found some discussion online of Narex austempering but they don’t seem to claim it anywhere on their website. The 59 Rc claimed for many of the chisels could feasibly be achieved with austempering though.
@@KnifeSteelNerds as I recall I heard about it from some behind the scenes manufacturing videos they produced for marketing purposes. not sure if those are still online anywhere
Increasing toughness using martempering will also increase other strenghts like shear strenght and shear modulus? Whats the common property to specify the toughness of a steel? The UTS or something else?
Hey Larrin, do the S series tool steels have significantly higher toughness than the 8670 sold on alphasupply? And does this method work on those types of lower alloy "already tough" steels?
S5 has 0.6% carbon and S7 is a high alloy steel with 0.5% carbon. So they have less to benefit from austempering than higher carbon steels. With less carbon than 8670 they also have the potential for better toughness but I haven’t tested them.
S5 (martensite/quenched +tempered) at 58-59 HRC in particular has crazy high toughness, even tougher than S7 at 56-57 HRC where it peaks. However, after 59 HRC, S5's toughness drops drastically and at 60 HRC, it has about the toughness of CPM-1V which is still pretty high but much less tough than at 58-59 HRC. S5 has its best Toughness-Hardness balance right at 58-59 HRC and I doubt there is a tougher steel out there at this hardness. If ones doesn't have the equipment to austemper and want maximum toughness at slightly below 60 HRC hardness, quenched + tempered S5 is probably the way to go. Difficult to find steel in thin bar stock thought. Forging probably necessary. These toughness numbers are from a graph in an article titled " Silicon Additions for Improving Steel Toughness " written by Larrin Thomas on KSN. Any mistake, if any, in this very comment is from me, not Larrin.
Those two steels are very different but probably with both I would say no. I would prefer to take the 60-61 Rc and very high toughness with Q&T of 15N20. And 154CM being a high alloy stainless wouldn’t be a good pick for austempering.
Most oils have a flash point that is too low, there are marquenching oils that can be used for lower austempering temperatures. I don’t know where to buy them though.
Hay what happens when you have a really strong magnate surounding a quenching bin, while the steel cools down it would regain its magnetic pull, would that mess things up or could you control processes during the quenching if you diled it in a really well? I know nothing about metalergy, but i always wonder if anything wh change about it, could you align grains or eliminate gaps in the steel
Intuitively you'd get oriented crystal structure. What that would do to strength I wouldn't know, but could be anisotropic strength. Could be a PhD thesis in testing this.
@@KnifeSteelNerds Oops! I only can Celsius. So Bainite forms in 400 F? My fault. However, low temperature metal alloys like Woods metal might be suitable though. Does the high heat transfer have a negative impact on forming Bainite?
