The following provides a very brief overview of steel treatment and properties:
By definition, steel is a combination of iron and no more that 2% carbon. Steel is alloyed with various other elements that combine to produce special properties. Once a particular alloy combination (or steel type) is selected, specific procedures are used to maximize the unique qualities required for that steel to perform. Generally speaking, the process for converting a steel alloy into a premium knife steel is heat treating.
Heat treatment is the most important stage in the evolution of an alloy into a performance knife steel. The first step in the heat treatment process is to reach a critical temperature. This temperature is held for a specific amount of time (depending on the steel being hardened) and causes the steel to become austenetized. Heat treatment is one of the many factors that determines the grain size of the steel (a fine grain structure is more desireable for knife blades because it improves edge retention and enhances blade finish).
Next, the steel is quenched to achieve its maximum level of hardness. At this point, the steel is too hard and brittle for practical use and thus tempering is of key importance in bringing the steel to its ideal hardness level (different knife steels perform best at different levels of hardness). Tempering also increases wear resistance and toughness properties. When tempering, it is important to understand the interaction between hardness and toughness. An increase in yield strength and tensile strength and a decrease in impact strength and ductility. An increase in toughness is usually accompanied by the opposite effect (i.e. an increase in toughness and ductility and a decrease in yield strength and tensile strength). Therefore, high-impact knifes such as swords and machetes would benefit from a softer blade (to avoid blade breakage), while low-impact knifes such as pocket knifes may benefit from a harder blade (to improve wear resistance). Once tempering is complete, the final hardness of the steel can be determined using a Rockwell Test.
For more detailed information of the above processes and properties, we recommend the following references that were used to compile this information: Metallurgy Fundamentals by D.A. Brandt (published by Goodheart-Wilcox) and Heat Treaters Guide by P.M. Unterweiser (published by ASM).