Enhanced strength and toughness of high nitrogen stainless bearing steel by controlling interstitial partitioning via V-microalloying

High-nitrogen stainless bearing steel (HNSBS) with ultra-high tensile strength (∼ 2403 MPa) and good toughness (∼80.0 J) was obtained by V-microalloying, overcoming the strength-toughness trade-off of conventional V-free HNSBS. In this work, since V-microalloying facilitated the enrichment of interstitial atoms (C and N) in precipitates, the content of interstitial atoms in the matrix was reduced accordingly (i.e., interstitial partitioning). On the one hand, V-microalloying reduced the substantial intergranular precipitates and transformed the precipitates from M23C6 + M2N into V-containing M23C6 + M2N + MN with multi-scale particle sizes, causing a coupling strengthening effect, which contributed to the toughness and additional strength increase. On the other hand, V-microalloying controlled interstitial partitioning, effectively refined coarse retained austenite (RA), increased the fraction of dislocation martensite, and reduced the fraction of twin martensite. The more film-like RA and dislocation martensite with high dislocation density coordinated plastic deformation and prevented crack propagation, thus obviously enhancing the strength and toughness of 0.2 V steel. This study provides a new route to develop high-performance HNSBS for aerospace applications.