Microstructure and mechanical properties of a martensitic stainless steel (0.2%C–12%Cr) after quenching and partitioning (Q&P) process

Abstract

This paper investigates microstructure and mechanical properties of a commercial martensitic stainless steel (0.2%C–12%Cr) after the quenching and partitioning process. The characterization was performed by optical microscopy, SEM, XRD, EBSD, density, dilatometry, hardness, Charpy, and tensile tests. Different retained austenite fractions were obtained by varying the quenching temperature (Qt). The results showed a decrease in the yield and ultimate tensile strength because of the increase in the retained austenite fraction for Qt ranging from 90 °C up to 165 °C. The absorbed energy was increased by 79%, probably due to the increment of mechanically stabilized retained austenite fraction. The fracture surface showed ductile characteristics for Qt ranging from 90 °C to 165 °C after tensile and Charpy tests. The best balance of strength and ductile found was Qt = 190 °C with a total elongation of 22.9 ± 2.2% and an ultimate tensile strength of 1444 ± 20 MPa owing to the retained austenite to martensite transformation that postponed occurrence of necking (TRIP effect). On the other hand, a decrease in the impact toughness occurred due to the retained austenite presence with low mechanical stability in the microstructure. Different fracture mechanism behavior was observed for tensile tests (ductile fracture) and impact tests (quasi-cleavage). For Qt = 215 °C, the presence of fresh martensite and non-mechanical stabilized retained austenite promoted an increase in ultimate tensile strength and a decrease in the yield strength, area reduction, total elongation, and absorbed energy. Finally, fracture surfaces showed brittle characteristics after tensile and Charpy tests.