Thermal Fatigue Behavior of Nitrocarburized and Low Pressure Nitrided Modified JIS SKD61 Hot Work Mold Steel

Abstract

A novel method using induction heating equipment was employed to investigate the thermal fatigue behaviors of two hot-work steels, JIS SKD61 and modified JIS SKD61, vacuum hardened treated to 45 HRC. Selected specimens, austenitized at 1298 K for 25 min, gas quenched to room temperature and tempered at 873 K, were salt bath nitrocarburized at 843 K for 80 min and low pressure nitrided at 813 K for 6 h, respectively. Microstructure, microhardness, X-ray diffraction and thermal fatigue tests were conducted. The results show that the thermal fatigue properties of the 898 K tempered specimen were better than those of other treated specimens. The reason is that the hardened processes would give high tensile strength, which improved the tool material thermal fatigue resistance. The thermal fatigue properties of modified JIS SKD61 specimen, including mean crack length and crack distribution density, were better than those of JIS SKD61 specimen. Low pressure nitriding treatment with a homogeneous nitrided layer could better maintain thermal fatigue resistance than the nitrocarburized steel.