Choice of quenching temperature and quenching time for 35CrMo4 steel

Good mechanical properties of 35CrMo4 steel can be obtained by quenching below 500℃. When quenching temperature is low, the tensile strength and yield ratio increase faster. At high quenching temperature, due to the degree of surface decarburization is more serious, the surface hardness is relatively low, so the quenching time of 35CrMo4 steel should not be too long, so as to avoid the deterioration of the organization and produce brittleness and temper brittleness.

In addition, rapid quenching process is not suitable for some 35CrMo4 steel workpiece which needs to be heated to 950~1100℃ and held for 2~3h for rapid cooling during quenching. In order to obtain the best machining performance and surface quality, multi-layer and multi-pass (3~4 passes) high-speed cutting method can be used.

35CrMo4 steel will appear obvious martensitic structure after high temperature quenching. At this time, the high temperature tempering treatment can make the structure into tempered sotensite or obtain martensitic phase without transformation. This is called "isothermal strengthening" : martensitic tissue is obtained by rapid cooling after a period of time at a high temperature of around 1000℃. In practical applications, the temperature is generally heated to 800℃~1000℃ for quenching and then cooling quickly.