Effect of Heat Treatment Processes on the Microstructure and Mechanical Properties of Spray-Formed 440C Martensitic Stainless Steel

Herein, 440C martensitic stainless steel (440C MSS) is manufactured by spray forming (SF) technology. Microstructural and mechanical properties such as strength, ductility, and toughness are evaluated after quenching and tempering-partitioning (Q-T-P) and quenching-intercritical-quenching-tempering (Q-IQ-T) heat treatments. The microstructural features that control the deformation and fracture behavior of the heat-treated specimens are discussed. The experimental results show that after austenitizing at 1050 degrees C, the material exhibits no apparent plastic deformation before fracture. However, specimens austenitized above 1050 degrees C and the specimen subjected to Q-IQ-T exhibit an improvement in the tensile properties by showing an elastic-plastic transition that is related to the strain-induced martensitic transformation of retained austenite formed during the Q-T-P process and to a decrease in the volume fraction of martensite with increasing austenitizing temperature. Also, it is observed that the strain hardening rate decreases with increasing austenitizing temperature. Furthermore, the stress-strain data suggest that the Q-IQ-T heat treatment effectively improves the toughness and ductility of the steel without compromising strength. The results indicate that the mechanical response of the SF-440C MSS can be tailored by adjusting the heat treatment parameters to enable better design for industrial applications.