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Mono steel knives like Masamoto KS or others is considered much easier to make with much more Profit, they do not need any forging or special heat tread to make them stay straight.
Unlike Honyakis witch is forged and hardened with different hardening is way more expensive to make then San Mai !
Couple of points to address:
Honyaki and monosteel blades are essentially the same with the exception that one is forged to shape and requires annealing before heat treating and the other is cut from a sheet of steel and requires profilign. After a forged blank is annealed, they are heat treated the same - quenched in water or oil. In US most makers quench carbon steels in medium to fast oil to to minimize warpage, but many still quench in water for more active hamon (W2 and 1095, etc). Rarely blades are coming out of a quenching medium perfectly straight, almost always some straightening required during the process of making a knife.
Hamon on nonyaki is not for decoration but for make the steel to absorb shock better and to make it easier to
straighten the edge. Removing scratches (as you know yourself) from hardened monosteel is no fun, and that is where a whole lot of work is. Monosteel blades hardened to 62-63RC, with steels that have some chromium, vanadium and other alloys that are harder than iron, are often
much more difficult to finish than a typical honyaki at 64RC or so, let alone san mai with a soft cladding. I can refinish san mai in 30 minutes, while a monosteel blade can take me 2-3 hours or more.
To straighten the edge on a san mai, all you need to do is to bent the spine in the spot where you see warpage on the edge. If you know of an easy way of straightening monosteel blade, I would like to know it, as I haven't found one (easy) yet.
Steels like 52100 is a deep hardening steel because of presence of chromium, so hamon method straightening the edge would not work.
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