Effect of Spheroidizing Annealing on Microstructure and Mechanical Properties of High-Carbon Martensitic Stainless Steel 8Cr13MoV

The effects of holding time during both austenitizing and spheroidizing on microstructure and mechanical properties of high-carbon martensitic stainless steel 8Cr13MoV were experimentally studied. The results showed that the amount of carbides and the proportion of fine carbides decrease first and then increase with the increase in austenitizing time (t ₁) in the case of short spheroidizing time (t ₂), whereas the amount of the lamellar carbides increases. In the case of long t ₂, both the amount of carbides and the proportion of fine carbides decrease, and the amount of the lamellar carbides did not increase. The hardness of the steel decreases first and then increases with the increase of t ₁. Under the conditions of different t ₁, the change in the size of carbides and hardness of the steel show a same trend with the variation of t ₂. The size of spheroidized carbides increases, whereas the hardness of the steel decreases with increasing t ₂. The longer the holding time of austenitizing, the higher is the spheroidizing rate at the earlier stage. However, the spheroidizing rate shows an opposite trend with t ₁ at the later stage of spheroidizing. The effect of cooling rate on microstructure is similar with t ₂. With increasing cooling rate, the dimension of carbides became smaller, and the amount of lamellar carbides increased. The elongation of the sample fracture exhibits no corresponding relationship with holding time, whereas it is closely related to the precipitation of secondary carbides caused by the alloying elements segregation.