Determining the Optimum Conditions for Heat Treatment of Cold Rolling Mill Rolls by Studying Their Influence on the Microstructure and Properties of the Billet

Abstract

Quality, reliability, and service durability of mill rolls are critical factors determining the quality of finished products and efficiency of rolling mills. The main problem that arises in the course of production of steel forged mill rolls is selection of reasonable conditions of heat treatment. As far as the size of the grain with an original structure and the pattern of distribution of separate structural components within the billet play a significant role in formation of final properties of the article, the objectives of this work are studying the heat treatment influence on the microstructure and hardness of steel mill rolls and development of reasonable process conditions on the basis of obtained data, in particular: determining the optimum conditions of primary heat treating the cold rolling mill rolls after their forging to reach the homogeneous structure and reduce the carbide grid score and carbide liquation; determining the optimum conditions of secondary thermal treatment of cold rolling mill rolls to provide the hardness within the range of about 300 HB, favorable structure for industrial frequency current hardening and reduction of carbide network score and carbide liquation; determining the hardening temperature, holding time and cooling rate to obtain the optimum structure and hardness within the range of 650-700 HB. Optimization of heat treatment conditions and analysis of steel microstructure have been performed with the application of cylindrical items (diameter 30 mm, height 20 mm) cut from the sample and template. Based on the study findings some microscopic images of steel microstructure after application of certain heat treatment conditions have been made and data on carbide network and current grain evaluation have been obtained