Effect of Heat Treatment on Properties of Laser Cladding Cobalt-Based Coating on 42CrMo Steel Surface

Herein, a Stellite-6 cobalt-based coating was prepared on a 12CrMo steel surface using laser cladding technology; heat treatment was then conducted on the coating at different temperatures. Moreover, the effects of heat treatment on the microstructure, hardness, corrosion resistance, and tribological properties of the coating were investigated. Results show that the heat treatment can effectively reduce the residual stress in the coating and eliminate defects, such as cracks and holes. After heat treatment at 900 degrees C, the faced centered cubic structure of cobalt evolves to hexagonal close-packed structure and metastable M7C3 carbide changes to stable M23C6 carbide. After 1 h of heat treatment at 900 degrees C, the near surface hardness of the coating is 1. 5 times that of the untreated coating, which is approximately 1300 HV. The friction coefficient of the untreated coating is 0.92, and its main wear mechanisms arc plastic deformation, furrowing, and brittle spalling. However, after heat treatment, the friction coefficient of the coating reduces to 0. 29, and its main wear mechanisms arc abrasive and adhesive wear. The stable M23C6 carbide produced after heat treatment can strengthen the alloy and improve the mechanical properties of the coating. The self-corrosion current density of the coating after heat treatment is approximately 3.3 X 10(-3) Lambda . cm(-2), the self-corrosion potential is approximately -0. 29 V, and the characteristics of the individual capacitive arcs nearly coincide. Further, the recrystallization and grain size variation during the heat treatment and martensitic transformation have no significant effect on the corrosion resistance of cobalt-based coatings.