Effect of Heat Treatment Processes on the Microstructure and Mechanical Properties of 00cr13ni5mo Super Martensitic Stainless Steel (Smss)

The effects of quenching and tempering temperatures on microstructure and properties of super martensitic stainless steel (SMSS) 00Cr13Ni5Mo were investigated. The heat-treated SMSS steel consisted of tempering martensite (δ-phase) and a small amount of austenite. When the quenching temperature was 930 °C, with tempering temperature increasing from 530 °C to 630 °C, the enrichment of Ni in martensite leads to in the formation of reverse austenite, so the martensite phase content decreased from 84.9% to 80.0%. The δ phase transformed from a granular to a strip morphology, ultimately appearing as continuous strips with an increased grain size from 23.23 µm to 27.07 µm. The hardness and yield strength of SMSS initially decreased and then increased with increasing tempering temperature (hardness: 275.18 HV → 240.99 HV → 241.65 HV; yield strength: 873.10 MPa → 797.95 MPa → 823.51 MPa). While the plasticity first increased and then decreased (elongation: 19.80% → 22.87% → 20.67%; shrinkage of section: 68.79% → 71.41% → 69.60%). At a tempering temperature of 580°C, the phase content of martensite decreased from 80.0% to 83.7% as the quenching temperature increased from 880 °C to 1030 °C. Additionally, the grain size increased from 25.23µm to 35.01µm. The hardness and yield strength of SMSS initially increased and then decreased (hardness: 239.16 HV→240.99 HV→237.52 HV→238.22 HV; yield strength: 792.91 MPa→797.95 MPa→779.52 MPa→786.81 MPa). Similarly, the plasticity initially decreased and then increased (elongation: 22.87%→22.87%→21.73%→22.53%; shrinkage of section: 71.87%→71.41%→70.66%→69.31%). These changes in mechanical properties were mainly associated with the content of reverse austenite in the microstructure. Moreover, a comparison of the product of tensile strength and elongation under different processes revealed that SMSS 00Cr13Ni5Mo exhibits the best overall performance with a value of 18700 MPa*% when the quenching temperature is 930°C and the tempering temperature is 580°C. This value is higher than that of forgings by 31%. Finally, the formation mechanism of reverse austenite was discussed and a strengthening model for SMSS 00Cr13Ni5Mo was established.