A novel Fe–Cr–Ni–Co–Mo maraging stainless steel with enhanced strength and cryogenic toughness: Role of austenite with core-shell structures

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 863; p. 144537
• Main Authors: Liu, Geng, Su, Jie, Wang, Ao, Yang, Zhuoyue, Ding, Yali, Ning, Jing, Gao, Qi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 26.01.2023
• Subjects: Austenite reversion; Chemical heterogeneity; Maraging stainless steel; Precipitation; Retained austenite; Retained austenite; Precipitation; Maraging stainless steel; Chemical heterogeneity; Austenite reversion
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.144537

Metastable austenite plays an important role in improving the cryogenic impact toughness of maraging steels by strain-induced martensitic transformations. However, a significant volume fraction of austenite decreases the yield strength of the material. In this study, to overcome the strength-toughness issue in maraging steels, austenite with a compositional core-shell structure and specific volume fraction are designed in Fe–Cr–Ni–Co–Mo maraging stainless steel. The core-shell compositional structure comprises retained austenite with bulk content in the core region and high Ni content reverted austenite layers in the shell region. During tensile testing, a step transformation of austenite with a continuous lattice is observed; herein, the shell regions are preserved. In contrast, the core regions transform to martensite. Close to the impact fracture, the thin austenite shell layers are retained from the martensitic transformation, which further contribute to the impact toughness. Under the combined influence of austenite and nanoprecipitates (Laves phase), the investigated alloy reaches a yield strength >1200 MPa at room temperature with good cryogenic impact toughness (77 K, >90 J), thereby outperforming conventional maraging steels and several high-entropy alloys. The current study demonstrates that the chemical heterogeneity within metastable austenite may create unique mechanical properties in structural materials. •A novel Fe–Cr–Ni–Co–Mo maraging stainless steel was designed with dual phase microstructure.•The steel reaches a yield strength >1200 MPa with good cryogenic impact toughness (77 K, >90 J).•Austenite with a compositional core-shell structure was designed in the steel.•A step transformation of austenite with a continuous lattice at deformation and impact test were characterized.•Austenite reversion process was simulated by DICTRA.