Manufacturing High Strength-Toughness High-Nitrogen Stainless Bearing Steel 30Cr15Mo1VN by Pressurized Duplex Process

Abstract

The high-nitrogen stainless bearing steel 30Cr15Mo1VN, possessing excellent tensile strength (~ 2466 MPa) and impact toughness (~ 130.3 J), was manufactured by pressurized induction melting and pressurized electroslag remelting (PIM + PESR) duplex process. Herein, the inclusion characteristics and element segregation of as-cast ingots, as well as the precipitate characteristics, retained austenite (RA) distribution were systematically investigated to clarify the effect of PESR on tensile and impact properties. Compared with PIM ingot, the lower quantity and larger spacing of inclusions in PIM + PESR ingot were beneficial to improving toughness. Besides, the dendrite segregation originating from solidification inherited to tempered steels and changed the multiphase structure and toughening mechanism. First, the lighter segregation (C, N, Cr, etc.) was induced by the high cooling rate, directional solidification, and short-time homogenization during PESR process, obtaining the higher contents of precipitates and RA in the PIM + PESR ingot. Second, the smaller precipitates and more RA were uniformly distributed in tempered PIM + PESR steel by alleviating segregation, obtaining better interface and matrix plasticity. Third, the dislocation densities of martensite and RA were increased by the greater precipitation pinning effect after PESR, and the uniform area ratios of close-packed and Bain groups were obtained, effectively inhibiting the propagation of secondary crack. Finally, the smaller strength difference between RA and martensite owing to lighter segregation after PESR, alleviated strain localization at phase interfaces and accommodated plastic deformation of matrix, thus, significantly enhancing the strength and toughness of the PIM+PESR steel.