Surface heat treatment of steel

⑴ Surface quenching: It is the process of rapidly heating the surface of a steel component above the critical temperature, but cooling it quickly before the heat can reach the core. This allows the surface layer to be quenched into a martensitic structure without undergoing phase transformation in the core, achieving the goal of surface hardening while keeping the core unchanged. Suitable for medium carbon steel. ⑵ Chemical heat treatment: refers to a heat treatment process that uses the ability of atomic diffusion at high temperatures to infiltrate the surface layer of a workpiece, thereby changing the chemical composition and structure of the surface layer of the workpiece, and achieving specific requirements for the structure and properties of the surface layer of steel. According to the different types of infiltrating elements, chemical heat treatment can be divided into four methods: carburizing, nitriding, cyaniding, and metalizing. Carbonization: Carbonization is the process of allowing carbon atoms to penetrate into the surface layer of steel. It is also to give low-carbon steel workpieces a surface layer of high carbon steel, which is then quenched and tempered at low temperatures to give the surface layer of the workpiece high hardness and wear resistance, while the middle part of the workpiece still maintains the toughness and plasticity of low-carbon steel. Nitriding, also known as nitriding, refers to the process of infiltrating nitrogen atoms into the surface layer of steel. Its purpose is to improve the hardness and wear resistance of the surface layer, as well as enhance fatigue strength, corrosion resistance, and so on. At present, gas nitriding method is commonly used in production. Cyanation, also known as carbonitriding, refers to the process of simultaneously infiltrating carbon and nitrogen atoms into steel. It gives the steel surface the characteristics of carburizing and nitriding.