There are many different types of steels that are good to use for a knife, depending on the function and purpose intended for a particular knife will determine the type of steel you will want to use to make the knife. The most important part of the definition of steel is how much carbon has been added to iron to make it a certain grade of steel. The addition of carbon makes it much harder and the more carbon you add the harder the steel will be. But there is a point where the steel is so hard that it is brittle. And we don't want a brittle knife.There are certain basic ingredients of steel and uses of each when added to make up a certain type or grade of steel.