The effect of temperature and strain rate on the mechanical properties and microstructure of super Cr13 martensitic stainless steel

In this study, the formability of super Cr13 martensitic stainless steel (MSS) is examined by means of hot tensile tests at different temperatures (900oC–1100 °C) and t strain rates (0.01s−1-10s−1). The potential effect of strain rates and temperatures on the mechanical properties, microstructure and fracture surface of super Cr13 MSS were examined. The post-test analysis, which includes hardness measurements, X-ray diffraction (XRD), fracture analysis by scanning electron microscope (SEM), and Energy-dispersive X-ray spectroscopy (EDS), was carried out. Results show that ultimate tensile stress (UTS) decreases with temperature, this way, the highest UTS was obtained at 900oC-10s−1 (187 MPa), while the lowest UTS (38 MPa) was obtained in the 1100oC-0.01s−1 sample. By contrast the elongation of the material increases with strain rate, since the elongation of the sample at 900oC-10s−1 was near 16% and the elongation of the sample at 1100oC-0.01s−1 was 57%. The XRD and EDS analysis indicated that Cr23C6 and Cr2N are formed inside the microstructure of samples tested between 900 °C and 1000 °C, and these carbides are dissolved above 1000 °C. Temperature affects also retained austenite which increases with temperature. Fractography analysis indicated that the δ-ferrite phase has a primary role in high-temperature rapture. Fracture surface evaluation of samples revealed semi-ductile fracture behaviour below 1000 °C and low strain rates, while ductile fracture was detected on the tensile samples at temperatures higher than 1000 °C and high strain rates. Furthermore, the ductility of super Cr13 MSS was increased by increasing strain rate.