There are two basic forms of martensite, one is lath martensite, which is composed of groups of laths under the crystal phase microscope, and the other is lamellar martensite, which is bamboo leaf like under the crystal phase microscope. In terms of properties, lath martensite not only has high hardness, but also has good toughness; while lath martensite has high hardness, poor toughness, typical hard and brittle, which needs tempering, sacrificing hardness to improve toughness. Therefore, we hope to get more lath martensite after quenching. In practical production, lath martensite is produced in all steels with carbon content less than 0.2% after quenching. Lath martensite and sheet martensite are formed in steels with carbon content between 0.2% and 1.0% after quenching. Sheet martensite is formed in almost all steels with carbon content more than 1.0% after quenching.