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Couple of Questions About Japanese Kitchen Knives...

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-Kiku-

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Do you consider yourself to be fairly knowledgeable in cutlery, particularly in metallurgical aspects of Japanese cutlery? If so, then the following questions are for you:

1. Why are all kitchen knives made of SRS13 or SRS15 alloys clad in much softer stainless steel? For a couple of weeks, I've been hunting around for cutlery in either SRS13 or SRS15. Every such knives were found to be clad in much softer stainless steel. Whatever the reason, it can't be for scratch resistance because cladding in a much softer material will only make it more scratch-prone. So then is it for corrosion resistance? If the cutting core was made of corrosion-prone alloys such as YXR7, Shirogami, Aogami, or some other form of high-carbon steel, then I can understand the reason behind the cladding. But both SRS13 and SRS15 are considered to be corrosion resistant stainless steels, much more so than its brittle counterparts such as ZDP189. So why the clad?

2. What exactly is the difference, if any, between SUS405 vs ANSI405? Google search didn't provide much of an answer. Are they both same stainless steel but made by the same/different manufacturers under different standards/conditions? Whatever they are, they appear to be popular cladding material for many of Japanese kitchen knives.
 

lemeneid

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Soft cladding let’s the knives be more malleable. So it’s easier to make adjustments and straighten them after forging. All blades will bend and warp to some degree after forging, but it’s much easier to straighten a san-mai without snapping it than a fully hard monosteel or honyaki.
 

M1k3

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Soft cladding also makes it easier to thin when you've worn down a knife enough.
 

Barmoley

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The 405 steels are equivalent. 405 grade steel was developed for welding so is probably easier to weld to other steels and that’s probably why it is used a lot for cladding. It can’t really be hardened by heat treatment. In general when san mai is heat treated the goal is to heat treat the core not the cladding, so cladding needs to be compatible with the core material.
 

Barmoley

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The question is about soft stainless cladding on stainless steel. Mike is right that soft, 405 type, unhardened stainless is easier to thin than srs15 at 64 hrc.
 

4wa1l

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Does it also have anything to do with keeping the price down? Is a good PM steel more expensive than a steel commonly used for cladding?
 

Barmoley

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Does it also have anything to do with keeping the price down? Is a good PM steel more expensive than a steel commonly used for cladding?
Steel in general is a tiny cost of the overall knife cost. There are exotics such as damasteel or expensive nitrogen steels, etc. In general the price of the material is not a major portion of the knife cost. Some steels are much harder to work with though especially once they are heat treated and so that labor is what will cause high alloyed steels to contribute to the price. Such steels are usually also more costly to heat treat requiring extra equipment or cryo, or other stuff. So even though mono srs15 vs San Mai of same would probably cost close enough, once hardened mono would be more costly, I suspect due to labor cost of final shaping and finishing.
 

M1k3

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There's also sanding belt/grinding wheel wear. Cost of those. Plus the time to switch them out.

I think I remember a maker saying with high alloyed steels, the sanding belts would have 15-30 seconds of usefulness. Then have to change it.
 

josemartinlopez

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Based on your previous post, you are better off browsing the Knife Steel Nerds blog by @Larrin first, or buying his book. That's a much more organized introduction to metallurgy for kitchen knives. It will also avoid the random photos of someone's Toyama gyuto.
 

-Kiku-

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Soft cladding also makes it easier to thin when you've worn down a knife enough.
This answer makes sense. For a given blade thickness, very acute bevel angle equates to wide bevel width. So if the entire blade is made of single alloy of high hardness (e.g. ZDP189), then it'd be awful lot of wear and tear on the grinding belt or whatever tools are used to sharpen the blade. Cladding the hard core with a much softer stainless steel makes the knife easier to sharpen.

Thanks, everyone.
 

M1k3

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This answer makes sense. For a given blade thickness, very acute bevel angle equates to wide bevel width. So if the entire blade is made of single alloy of high hardness (e.g. ZDP189), then it'd be awful lot of wear and tear on the grinding belt or whatever tools are used to sharpen the blade. Cladding the hard core with a much softer stainless steel makes the knife easier to sharpen.

Thanks, everyone.
Not so much sharpen. Initial geometry cutting and maintenance of the geometry are easier. Actual sharpening, in this hypothetical case, would still be dealing with ZDP-189.
 

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