What is grain, and what role does it play in steel knife blades?
The word "grain" in steel refers to the particles of the crystalline lattice, and how the word is interpreted and in what context it is used changes the definition of grain. For instance, a grain may mean the singular crystalline lattice of a microscopic particle of carbide, or it may mean the group of bonded lattices that are surrounded by another material. Grain may mean the visual appearance of finished steel or freshly broken steel, or it may mean the finest particles visible under an electron microscope.
Literally, the word
grain is defined as the discrete particle or crystal determinable in the matrix. So you can see that the type of particle, the size of the particle, and even the viewing apparatus used to see the particle identifies the type of grain being described. Grain study and structure is common in steels, it can determine the material, size, shape, and bonding structure of the crystalline particles, and thus their percentage in determining the effects of various thermal treatments. There are studies about grain size, grain shape, and grain boundaries. There are studies and procedures for lapping the surface, etching the metal, and examining and counting grains under a microscope. From this, you can see that grain complexity is a science into itself, and belongs, in our case, in the realm of the metallurgist and materials scientist.
When knifemakers talk about grain, you should probably take what you read with a grain of salt. Sorry for the bad pun, but in all seriousness, grain manipulation, grain bonding, grain sizing, shape, and structure is beyond the realm of the knifemaker, no matter what forum or venue he is posting on.
This strange fascination with grain probably hearkens back to the blacksmithing or hand-forging days, when you could heat treat a piece of metal and then break it in half, and visually examine the grain. A large crystalline grain would mean it wasn't at it's best hardness, a small, fine grain meant you were close to the mark. But this is far and away from scientific grain testing and study, something I will flatly claim is out of the realm of knifemaking.
The reason this is not the knifemaker's realm is that knifemakers only control the shape of the steel blade, its geometry, and the process of heat treating and finishing of the steel, and do not control grain structure. Mistreatment and bad practices on the part of the knifemaker will result in an inferior blade performance, and some of these defects may be visible in the grain structure. Understand that no knifemaker is working under an electron microscope, and no knifemaker imparts some special magic in his process to manipulate grain changes in the steel that are improvements on standard process and cryogenic processes.
https://www.jayfisher.com/Heat_Treating_Cryogenic_Processing_of_Knife_Blade_Steels.htm
