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Ugh - Carbon steel is not easy to sharpen because it is soft. It is because it contains fewer carbides. Typical stainless steel alloys used in production knives
by abakker 10y ago
Ugh - Carbon steel is not easy to sharpen because it is soft. It is because it contains fewer carbides. Typical stainless steel alloys used in production knives are hyper-eutectoid, and the excess carbon (anything > .77%) ends up forming carbides with the alloying elements. These carbides - Tungsten, Chromium, and Vandium carbides, are harder than the surrounding matrix of hardened and tempered steel, and can only really be "cut" with a diamond stone. If you only have a water stone, the high proportion of carbide in stainless knives makes it difficult to sharpen because the exposed bits of carbide in the matrix are harder than the stone and don't get removed.
Another issue with commercial knives altogether is that frequently the mass market ones are soft by design (<58 HRC). This saves costs in the post-heat treatment grinding into final form. (knife blanks are oversized when heat treated so that any slight warpage during quench/temper can be ground away). handmade knives are usually not done this way, and so many hand makers are comfortable going much harder since they are less worried about the economics of hard material removal at mass scale.
(Source: Have spent several years learning to make knives)
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- abtinf 10y agoPardon me if I use the wrong nomenclature or if this question is wrong in some fundamental way: Would the higher hardness of the carbides mean a high-carbide knife needs less frequent honing/sharpening when used in regular cooking tasks?
- abakker 10y agoCarbides are a double edge sword. On the one hand they impart "wear resistance" but only if the heat treatment is done right (read: very precisely). Frequently, that is not how commercial stainless is done, though. On the other hand, they can make it harder to sharpen. Usually, good heat treatment can lead to fine grain carbides, while bad heat treatment does not get the carbides into solution very well prior to quenching and they get too large. (This is not the same thing as grain growth). When they are big, they impart roughness to the edge and difficulty of sharpening with no benefits in wear resistance as the steel matrix around them wears away. If you are interested in this, I can't recommend John Verhoeven's "metallurgy for bladesmiths" enough. It is a free PDF if you search for it. (If you like open source things, I recommend reading the foreword especially).