Heat treatment of 35CrMo
35CrMo steel is a Chinese alloy structural steel which is widely used in the manufacture of important parts of automobiles, tractors and other engineering and engineering machinery, as well as in the manufacture of parts for aircraft, ships, petrochemical industry, metallurgy, boiler industry, and nuclear industry. In order to meet the needs of such applications, after being molded, the 35CrMo steel should be subjected to heat treatment such as annealing, normalizing and quenching.
The annealing process of 35CrMo steel is divided into two stages, namely low temperature annealing and high temperature annealing. Low-temperature annealing can eliminate or reduce the stress on the surface of the steel, reduce or change the hard structure at the surface, and eliminate the cold-working strain of the steel. The annealing temperature of the low temperature annealing is relatively low, usually between 550-650℃, and the annealing time is relatively long, usually 8-12h. The high temperature annealing is aimed at eliminating and reducing the residual stress of the steel, making the structure of the 35CrMo steel uniform and stable, and improving the toughness of the 35CrMo steel. The high-temperature annealing temperature is between 650-850℃, and the holding time is about 0.5-3h.
The normalizing of 35CrMo steel includes two parts, semi-normalizing and complete normalizing. The purpose of semi-normalizing is to refine the grain of the steel body. Generally speaking, the temperature of semi-normalizing is lower than that of high-temperature annealing. The temperature of semi-normalizing is usually between 700-800℃, and the time of medium-term holding time is usually 3-5h. The purpose of complete normalizing is to make the structure of the steel body uniform and stable. The complete normalizing temperature is usually between 850-960℃. The time of medium-term holding time is usually 2-3h.
35CrMo steel quenching is divided into water quenching, oil quenching and air cooling three methods. Water quenching refers to rapid cooling of the heated metal material after quenching in water or other cooling medium. The quenching temperature of 35CrMo steel is usually 820-860℃, and the water quenching time is 0.5-2h. The amount of deformation of 35CrMo steel is relatively small and the strength is relatively high after water quenching. Oil quenching refers to rapid cooling of a metal material after quenching in oil or other cooling medium. The quenching temperature of 35Crmo steel is generally 1000-1050℃, and the time of oil quenching is 1.5-2.5h. Air cooling means that the heated metal material is not put into the cooling medium, but only the natural cooling method is used, and it is cooled in the open air until it is cooled to room temperature.
In conclusion, in order to meet the needs of different applications, the 35CrMo steel needs to be subjected to heat treatment including annealing, normalizing and quenching. It is necessary to strictly grasp the temperature and time of heating and cooling in the process of transforming 35CrMo steel, and it is not allowed to misoperate to ensure the best performance of 35CrMo steel parts.
