STD11강의 열처리 조건에 따른 모상 안정화 및 내마모 특성

Abstract

Abstract

Effect of Heat Treatment Conditions on the Stabilization and Wear Resistance in STD 11 Steel

By Choi Won Il Advisor: Prof. Jang Woo-Yang Ph. D. Dept. of Advanced Parts & Materials Engineering Graduate School of Chosun University

Effect of austenitization and cryogenic treatment conditions on the the stabilization of parent phase and mechanical property has been studied in the STD11 steel for cold-work tool and dies. When austenitizing temperature is low or holding time is short, not only the mixture of α' martensite and M7C3), but α-ferrite is revealed. However, When austenitizing temperature is high or holding time increases, austenite is retained as well the mixture of α' martensite and M7C3. The optimal austenitizing conditions, which absent α-ferrite or retained austenite in matrix, are 1,000 ℃×20min or 1,040 ℃×10min in this study. The retained austenite shown at improper austenitizing conditions is contributed to the lowering martensitic transformation temperature(Ms ~ Mf) by the stabilizayion of parent phase. The retained austenite is transformed to martensite by cryogenic treatment i.e., by immersing into liquid nitrogen. The mechnical properties such as hardness and wear resistance are closely allied to resulting micrstructure after heat treatment; The retained austenite as well α-ferrite revealed at improper austenitizing conditions abruptly decreased hardness or wear resistance. The cryogenic treatment is necessity to decrease the volume fraction of the retained austenite revealed after quenching because the retained austenite exerts a harmful influence on the mechanical properties of the STD 11 steel.