Have you ever seen the place where a piece of steel or iron has snapped? It looks as if the metal is made up of a bunch of small grains, doesn’t it? Actually, it is. Depending on the size of the grains, this area would look like sand, or sometimes more like a cream. In a blade, these grains are wanted as small as possible. For one reason, large grains take up more area than small ones, right? And so, if one grain breaks from another from stress, in a large grain steel, the other grains are more likely to follow suit because there are less grains around it holding on to each other than if they were all smaller and more numerous.
So, the knife would be much tougher and less brittle if the grains are smaller. How does the smith shrink these grains? The process is called normalizing.
The blade is evenly heated to critical temperature (where a magnet will not stick). You see, at this temperature, a lot of things are shaken up out of their original place, and if cooled, stay there, which makes the blade hard but brittle, or if cooled over several hours, extremely softens (anneals) the steel. However, for normalizing, the temperature is brought up an extra hundred degrees or so, probably to get a bit of extra heat beyond, to let the atoms move around a little more, as well as easier.
Then, all that is left is to let the blade air-cool. This lets the grains shrink as it is cooled, and also come closer together. Just hanging the blade on a rack in the air does this. After all this, if the metal is broken, the break will not look grainy, but rather smooth, and creamy.
Normalizing makes a much bigger effect than I would have thought. You know the block of steel on the back of a vise? I use one of those for an anvil, and it’s already cracking! I can see the grain structure inside, and it looks like this!
If I hammer on the corner, one hit dents the edge nearly half a centimeter!! And there is practically no mark at all on the hammer, which obviously must have been normalized.