On Tuesday, September 24, 2019 at 1:52:28 PM UTC-4, wrote:
On Sunday, September 22, 2019 at 9:42:41 PM UTC-4, Ignoramus9254 wrote:
I sharpen knives on my bench grinder. I have a relatively fine hard
wheel on one end and a polishing style non-vowen wheel on the other.

Most stainless kitchen knives that are of whitish color are relatively
easy to sharpen and then cut well.

I noticed that some knives with greyer stainless steel blades are
difficult to sharpen and somehow they do not like to stay sharp.

I spent a while today sharpening those two grey knives, first cutting
a sharp vee on the grinding wheel, and then polishing, it finally
seems acceptable. But somehow they are clearly worse than other
knives. What gives? Ayn idea what steels they are?

Hi Iggy! I don't have time to get much into this, but as Joe said, sharpening good knives on a bench grinder is a good way to wreck them. (Joe -- real India stones (a Norton trademark for aluminum oxide) are yellow-brown, not red, unless Norton has licensed out the trademark to someone who makes them red)

All stainless can be "bright," but it's the austenitic, 18-8 types (302, more or less) that won't hold an edge. However, if you sharpen them aggressively -- like with a bench grinder -- they will *take* an edge, and a bench grinder typically leaves a microscopic serration that gives the illusion of making the knife cut well. In vegetables, it really *does* cut well, for a while. And it's good for meat, too. In fact, that microscopic serration actually improves performance for most *slicing* operations, but not for *chiseling* operations, where you push the edge into whatever you're cutting. For that, you want ultrafine edges, and very sharp ones.

Good kitchen cutlery and quality pocket knives today are made from 400 Series (410, 440, 441) stainless. It is heat-treated and MUCH harder, and much harder to sharpen. (410 doesn't have much carbon, but it has enough manganese and chromium to multiply the effect of the carbon in conversion to martensite upon heat treatment). But it holds a good edge. It is rough on aluminum oxide stones -- I only use them for finishing. For hard stainless, a silicon carbide stone, which typically is blue-gray, is much better.

Hard wheels are the worst for heat build up and wrecking a good knife or other cutting edge. Soft ones, often white, are used commercially, and VERY carefully to avoid drawing out the temper.

If you have a microscope, you can learn a lot by examining the edges after you sharpen them. You'll see that some stones will not produce a really fine edge on hard stainless. The edge chips if you use too much pressure, and it doesn't do much at all if you use too little.

I learned a lot of this from Norton folks when I was writing about it, and from 60 years of screwing up good edges. d8-)

--
Ed Huntress

Whoops, I said "blue-gray" for SiC. Good ones often are green.