Influence of Heat Treatment on the Microstructure and Corrosion Resistance of 13 Wt Pct Cr-Type Martensitic Stainless Steel

The effect of heat treatment on the microstructure and the electrochemical properties of a typical corrosion-resistant plastic mold steel in Cl − -containing solution were studied in this research. Through X-ray diffraction patterns, SEM and TEM analysis, it was found that the sequence of the precipitates in the steels tempered at 573 K, 773 K, and 923 K (300 °C, 500 °C, and 650 °C) was θ -M 3 C carbides, nano-sized Cr-rich M 23 C 6 carbides, and micro/submicron-sized Cr-rich M 23 C 6 carbides, respectively. The results of the electrochemical experiments showed that the pitting potential of the as-quenched martensitic stainless steels increased with the austenitizing temperature. However, the corrosion resistance of the steels would decreased after tempering, especially when tempered at 773 K (500 °C), no passivation regime could be found in the polarization curve of the MSSs and no effective passive film could be formed on the steels in Cl − -containing environments. The present results suggested that the temperature around 773 K (500 °C) should be avoided for tempering process of MSS used as plastic molds.