I sharpen alot of knives freehand on stones, belts , etc
From experience,
I've observed non-stainless high carbon knives form very nice edges quickly and de burr better the high carbon (greater then 0.8%) stainless knives.
I have a few idea about why but I honestly don't know.
I know the chromium has an affinity for carbon.
I also know that grain size and hardness are a factor
And that Chromium carbides are larger and softer then some of the other alloying carbides.
My thrist for knowledge has become a consuming obsession.
My question is (all other variables being equal)
How does the chromium affect the micro structure and why is it more difficult to form an apex and deburr.
For example CPM 10v versus CPM S90v
Thanks guys, I've been learning a ton about steel from all of your responses.
Shawn
Chromium affects the microstructure in a lot of ways. The most pertinent to knives is it makes carbide formation easier, it makes hardening easier, and it makes removing retained austenite more difficult.
Chromium does have an affinity for carbon, and if enough is present, it will form carbides in preference to iron carbides. 52100 is known for containing more carbides than say 1095. These are mostly not really chromium carbides. They are iron carbides with some chromium dissolved into them. (Fe,Cr)3C for instance is cementite with some chromium dissolved into it. As the Cr, C, or both, goes up, the tendency is to form more and more unique carbides to chromium, Cr7C3 and Cr23C6. Another thing about the carbide formation is the usual composition of the eutectoid point (0.8ish %C) goes down. This means that steels like 420HC are actually hypereutectoid, though they contain only about 0.4%-0.6% carbon, but considerable chromium. Chromium carbides are not inherently larger than other carbides, unless one solely considers the molecular size carbides with only 4 to 30 individual atoms. Carbide size is controlled mostly by processing, whether it be use of the CPM process or similar, or by heat treatment of regular ingot steels.
Cr makes hardening much easier, reducing the speed required in quenching to achieve full hardness, thus moving something like 1095 from a water quench to an oil quench when considering 52100, or even plate quenching in 440 series, 12C27, etc. Were I making a chopping knife and could choose from 1055 or 5160, the hardenability difference alone would play a very large role in my choice.
The presence of large amounts of chromium reduces the temperature when the conversion to hardened steel is complete, which means that, if additional steps aren't taken, the amount of retained austenite will be considerable. There aren't many gummier structures to try to sharpen than austenite. Try putting an edge on 304 or 316 stainless to see what I mean.
IMHO, the difficulty often observed in sharpening the less expensive stainless steels is indirectly related to chromium. These difficulties arise from the stabilization of Retained Austenite (RA), the greater difficulty in getting rid of it, and the generally less expensive and involved heat treating procedures. The larger primary carbides may not be properly dissolved, RA may be stabilized and the amount may be excessive.
A word about grain size. The grain size of stainless steels CAN generally be larger than plain carbon or low alloy steels due to the higher temperatures needed in hardening. However, these stainless steels are generally more resistant to grain growth, so grain size depends almost entirely on processing.
