**4.1 Categorization of alloy steel and their heat treatments**

Alloy steels are categorized into low- and high-alloy steels. High-alloy steels would be more than 10 wt% of alloying elements in steel groups [1, 5, 8, 9]. The majority of alloy steels lie under the group of low alloy. The most common alloy elements include chromium, manganese, nickel, molybdenum, vanadium, tungsten, cobalt, boron, and copper.
