Fundamentals and the present state of thermomechanical treatment

Abstract

Methods and conditions for the thermomechanical treatment of steels under which optimal structures and properties can be attained are described. They include lowered temperature of the end of deformation at the concluding stage of rolling; rational control of deformation at continuously dropping temperature in the process of rolling; increase of the degree of deformation on finishing stands at lowered temperatures of the end of rolling; fixing the structural and substructural state produced by hot deformation; and regulated cooling with self-tempering. The dependence of thermomechanical treatment effectiveness on impurity content was determined by mechanical testing and by Auger spectroscopic analysis of samples of steel 40KhSG2NMKF melted from both an ordinary and a primal charge. It was found that the required level of mechanical properties can be attained in ordinary steel by subjecting it to thermomechanical treatment for dynamic polygonization. The favorable effect of thermomechanical treatment was attributed to the increased uniformity of the steel structure resulting from the formation of the substructure, the more uniform distribution of impurities, carbide and other inclusions, and the reduced effect of the grain boundaries.