Optimizing microstructure of medium Ni-bearing steel to ensure high resistance to corrosion and corrosion-assisted mechanical degradation

This study aims to investigate the effects of microstructural modifications through quenching and tempering (QT) and quenching and partitioning (Q&P) processes on the corrosion behavior and corrosion-assisted mechanical degradation of medium Ni-bearing steel. The primary objective is to identify strategies for enhancing the long-term lifespan and reliability of these alloys in neutral aqueous environments. Various electrochemical evaluations as well as microstructural characterizations were conducted to elucidate the relationship between heat treatment processes and corrosion behavior. The findings revealed that the conventional Q&P process formed partitioned austenite with a coarse size within the martensitic matrix, leading to an uneven distribution of Ni and higher kernel average misorientation, resulting in increased susceptibility to corrosion and corrosion-induced mechanical degradation. In addition, preferential attacks around cementite clusters due to selective dissolution appeared in the corroded QT sample. On the other hand, a slightly higher partitioning temperature, just above the martensite transformation start temperature, providing finely distributed austenite within bainite in the microstructure, which exhibited lower corrosion kinetics and reduced susceptibility to mechanical degradation in corrosive environment. This study highlights the potential of optimizing the microstructure through the Q&P process with a higher partitioning temperature as an effective technical strategy for achieving superior durability and reliability in medium Ni-bearing steel alloys in neutral aqueous environments.