Knife Steel Nerds

Seems like a thread where people might be interested in https://knifesteelnerds.com/, which has made the front page on HN on a couple of occasions. I have no relationship of any kind, beyond finding it interesting.

That is a great origin story, and his writing is awesome[1]. I have always been interested in knives and swords but not to the extent to go full on nerd on them! [1] https://knifesteelnerds.com/2018/03/26/cru-forge-v-toughness-testing-p…

> Damascus steel requires much more time to hone. It holds an edge longer, but I'm not sure it is worth the frustration involved in getting an edge. I don't think there is any truth to this. It's one of the myths listed here, and goes into detail: https://knifesteelnerds.com/2018/07/30/five-myths-about-damascus-steel…

https://knifesteelnerds.com/ Sounds cool, I'll check it out. Thanks.

I'm not at all convinced that the highly corrosion resistant knife/tool steels you mention are actually especially high on the corrosion resistance scale -- I think they may just be excellent for a tool steel. If you look at the knifesteelnerds article on H1 (https://knifesteelnerds.com/2019/06/24/h1-steel-how-it-works/), you'll find that it's an austentitic alloy (which is highly unusual for any sort of tool steel), and that it seems like it's likely a somewhat less corrosion resistant than usual variant on steels like 301 or 304. And the rather common stainless alloy used for non-tool applications where high levels of corrosion resistance is 316, which is more corrosion resistant than 304. In any case, this new alloy is weird -- it seems like it specifically has excellent resistance to electrochemical corrosion when it is used as an anode, which is not what people usually use stainless steel for :)

Steel is almost magic. Stainless steel is beyond magic. I had a specialization in Chemistry in High School. For some analysis, the fist step is to dissolve everything in boiling Nitric Acid. But stainless steel has Chrome is like a spell of protection, so you must use boiling Hydrochloric Acid instead. I have no idea why. It's just like magic. It may have Nickel, Molybdenum, and other metals, that give it more magical properties. A few years ago there was a nice post about copying a normal steel alloy for knives to get an equivalent made of stainless steel. You need to reduce the the Carbon content to make it less brittle. And they had to add Vanadium so it keeps the sharpness of the knives. I have no idea why. It's just like magic. If you have half an hour, it's worth reading, but beware that it has too many technical details that are close to magical https://knifesteelnerds.com/2021/03/25/cpm-magnacut/ (HN discussion https://news.ycombinator.com/item?id=29696120 | 375 points | Dec 2021 | 108 comments)

Kershaw has a US-made product line and a China-made product line, which typically use different steels. The steel used in most US-made Kershaws is Sandvik 14C28N. This is very likely the steel you're thinking of, and the owner of knifesteelnerds.com rated it as his favorite budget steel[0]. It has extremely high toughness (resistance to chipping/breaking) and a fine grain structure that allows it to take a very sharp edge without microscopic rolling/chipping. Some other steels are used, including 420HC on low-end models, CPM154 on automatics, and several steels commonly found on more expensive knives in special editions. Chinese Kershaws usually use 8Cr13MoV, and don't put much effort into heat treatment. Some use D2, which is semi-stainless, somewhat hard to sharpen, and low-toughness (it chips easily), but high in wear resistance. Some low-end models use even cheaper steels. [0] https://knifesteelnerds.com/2020/06/15/what-is-the-best-budget-knife-s…

Looking at some of the comparisons, the data appears to be (I could be wrong) scraped from this article by Dr Larrin Thomas based on his personal research and testing, possibly also including some of the other articles on his website: https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallu…

"Stainless (e.g. AEB-L) is up to four times tougher than simple low-alloy carbon steel (e.g. 1095). See https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by... for example." I'll guarantee my UHC 1080 cleaver will slam a good distance through your stainless steel knife edge-on. Your chosen steel has toughness but it lacks in actual strength.

That's just not true, though. Stainless (e.g. AEB-L) is up to four times tougher than simple low-alloy carbon steel (e.g. 1095). See https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallu… for example. High hardness simple carbon steels do have their place in knives, but what you're saying is factually incorrect.

This will be interesting. I wonder what will happen to Dr Larrin Thomas (https://knifesteelnerds.com/about-me/) he's been able to bring some new knife steels to market while working for US Steel by day. Wonder if Nippon allows side gigs.

I believe it was this post? If not I'm curious about it if you remember. The link and discussion here was a fascinating look into another world for me. https://news.ycombinator.com/item?id=29696120 https://knifesteelnerds.com/2021/03/25/cpm-magnacut/

This study should be considered along with that from metallurgist John Verhoeven, who thought the main cause of chipping is corrosion. (https://knifesteelnerds.com/2021/01/11/what-causes-razor-blades-to-dul… What both these studies reveal is an absence of bending of the sharp edge, indicating that the tradition of razor stropping has no real effect.

There are plenty of things to control for when designing and producing steel. An important consideration for some applications is the brittle to ductile transition temperature. Some steels have a DBTT around 0­°C, which means that they loose most of their impact resistance below that temp. By adjusting the chemistry, processing methods, and post-processing methods, you can adjust the DBTT of steel down below -70°C. My guess is that they were being paid to supply steel with a DBTT below -70°C, and that the contract included proof testing. The standard testing method would be a Charpy impact test at various temperatures. It sounds like they were making complex castings, so they probably had some non-standard testing requirements. More info: https://www.punchlistzero.com/dbtt-ductile-brittle-transition-temperat… https://knifesteelnerds.com/2018/12/21/why-cold-steel-is-brittle/

There are different grades of steel, doped with all sorts of additives, depending on the desired traits. The most corrosion-resistant variant today used in knives would be one of the nitrogen steels, like Nitro-V. https://knifesteelnerds.com/2019/09/23/nitro-v-its-properties-and-how-… But they all corrode, eventually. If you want a true corrosion-resistant metal that stays (kinda) sharp, look at one of the cobalt alloys like Stellite.

Thats a good point the knives he was familiar with were probably case hardened! So you would get to mild steel just like you said if you kept removing steel. Nowadays though, knives are generally homogenous or some other composition like san-mai which will have the good steel in the center all the way through so even if you grind it down to a toothpick most modern knives will still have the good steel on the edge. Modern metallurgy means we can have high hardness, high toughness, high wear resistance and high corrosion resistance all in one composition. See Magnacut and other modern powder metallurgy knife steels: https://knifesteelnerds.com/2021/03/25/cpm-magnacut/ I am sure there are still some case hardened knives but for the most part case hardening is a historical technique. Same goes for the type of laminated construction you describe above. All told the metaphor makes sense historically and in context but taken in the context of modern knives it makes less sense. This is interesting in and of itself because the meaning of metaphors and sayings can change drastically across time and social context.