Effect of Heat Treatments on the Mechanical Properties of DIN 50Cr3 Spring Steel

Abstract

This experimental study was conducted to investigate the optimum combination of properties between ductility and toughness from one hand and strength and hardness from the other hand of a commercial grade of light duty spring steel DIN 50Cr3 having a chemical composition of (0.25 % C, 0.8%Cr , 0.79%Mn , 0.2% Si). A heat treatment process by quenching in both oil or water followed by tempering cycles at different temperatures for various tempering times was adopted. The proper austenitization temperature was found to be 870 C. The structure after quenching reveals the formation of martensite with limited amount of retained austenite. Tempering was performed at different temperatures from 250 to 550 C for prolonged times ranging from 1hr up to 3 hr. It was found that oil quenching provides sensibly higher elastic properties than water quenching particularly in the low tempering temperature range. More ever, by increasing the tempering temperature and time ultimate tensile strength, hardness were gradually decreased while ductility remarkably improved. The resultant microstructure after tempering was characterized by a tempered martensitic structure with simple and complex dispersed carbides. Optimum elastic properties were delivered out of this steel after tempering at 450 C for 1hr.