Microstructure, crystallographic aspects and mechanical properties of AISI 420 martensitic stainless steel after different thermomechanical process routes

In this study the microstructure, crystallographic aspects and mechanical properties of AISI 420 martensitic stainless steel were analyzed after different thermomechanical process routes. In general, the quenching process of martensitic stainless steel can be carried out from deformed or annealed condition (ferritic microstructure) in the manufacturing process. In this context, samples were strained 50% cold-rolled followed by recrystallizing during soaking time of 30 s and 5 h at 770 °C. Then, the samples were austenitized at 1050 °C for 5 min and quenched. The results showed that the microstructure was composed of sub-block boundaries (V1/V4 variant pair) and high misoriented variants. In addition, the formation of a specific misorientation between a variant pair was not observed. The intervariant boundary fractions, the packet and Bain group sizes, and block width of martensite were significantly close, indicating that no interaction of metallurgical phenomena occurred during the austenite fomation. Therefore, the morphology, crystallographic aspects and mechanical properties were not susceptible to change with cold rolled or recrystallized initial conditions. The findings herein demonstrate that the Bain group size can be used to evaluate the refinement of martensite microstructure in AISI 420 martensitic stainless steel due its orientation relationship. •Bain group size can be used to determine the refinement of martensite which shows the same morphology.•Morphology and crystallographic aspects of martensite were not affected by the initial ferrite microstructure.•The mechanical strength after quenching was not influenced by the initial ferrite microstructure.