Hardening brittleness refers to the phenomenon of significant toughness reduction during tempering in certain temperature ranges after the workpiece has been quenched. There are two types of hardening brittleness: hardening brittleness that appears within the temperature range of 250℃ to 350℃ is known as the *th type of hardening brittleness, also referred to as "low-temperature hardening brittleness" or "irreversible hardening brittleness." This type of brittleness should be avoided in both carbon steel and alloy steel. After quenching, alloy steel containing elements such as chromium, nickel, and manganese, when tempered within the temperature range of 450℃ to 650℃ and then slowly cooled, is prone to the *th type of hardening brittleness, also known as "high-temperature hardening brittleness" or "reversible hardening brittleness." To prevent the occurrence of the *th type of hardening brittleness, small parts can be rapidly cooled during tempering, while larger parts can be made from alloy steel containing tungsten or molybdenum. Many mechanical parts, such as gears, shafts, cams, etc., operate under conditions of friction, impact loads, and alternating loads, requiringDuctile iron pipeThe surface must possess high hardness and wear resistance, while the core needs adequate strength and toughness. Whole heat treatment methods are insufficient to meet these requirements. In production, surface heat treatment or carburization, nitriding, and other chemical heat treatments are widely used.