METHOD FOR IMPROVING SPHEROIDIZING STRUCTURE OF HOT WORKING TOOL STEEL BY PERFORMING SPHEROIDIZING ANNEALING AFTER PERFORMING NORMALIZING

摘要

PURPOSE: To provide a method for improving forming property of products and mechanical properties after heat treatment by conducting normalizing before performing spheroidizing, thereby improving non-uniformity of microstructure and hardness. CONSTITUTION: The spheroidization heat treatment method of hot working tool steel comprises a normalizing step of heating a work for hot working tool steel to a temperature of 920 to 950 deg.C, holding the work at the temperature of 920 to 950 deg.C for 1 hour/50 mm, and air cooling the heated work to a temperature of 300 to 350 deg.C; and an annealing step of heating the normalized work to a temperature of 830 to 850 deg.C, holding the work at the temperature of 830 to 850 deg.C for U+30 min/25 mm, cooling the heated work to 400 deg.C in a maximum cooling rate of 25 deg.C/hr, and further furnace cooling the work to a temperature of 200 deg.C or less.