The quenching temperature is usually 800-9009C, and the tempering temperature is controlled at 350-650 1C according to the characteristics of steel. If the tempering temperature is well controlled, its influence on delayed fracture strength can be reduced, and the tensile strength of core-pulling rivet products can meet the design requirements. In order to ensure the uniformity of heat treatment, it is necessary to choose steel grades with little reduction in intermediate hardness after heat treatment.
It is necessary to accurately adjust the dew point in the furnace during heat treatment, because decarburization on the surface of heat-treated products is the main factor causing the deviation of riveting torque coefficient, and increasing carbon will increase the sensitivity of delayed fracture.