Measured: Blade hardness is quoted on the Rockwell C scale as HRC, from about 54 on a soft European blade to 64 on a hard Japanese one.
The basics
What to know about blade material
A knife blade is judged on one trade: how long it stays sharp against how easily you can make it sharp again. Every blade material sits somewhere on that line, and no material wins both ends of it.
Hardness is the number behind the trade. Steel is measured on the Rockwell C scale, usually written as HRC, and kitchen knives run from about 54 to 64. A harder blade keeps a fine edge far longer, but hardness and brittleness rise together. The same blade chips if you twist it in a squash or scrape it sideways across a board. A softer blade dulls sooner and forgives all of that, and a few passes on a steel bring it straight back.
Rust is the second question, and it is decided by chromium. Enough chromium in the mix and the blade is stainless, so it survives a wet sink and an acidic tomato. Little or none and the blade is carbon steel, which takes a keener edge and stains, spots and rusts unless you dry it the moment you finish.
Judge the blade before the block. A knife you will actually sharpen beats a harder one you will not.
