Effect of Deep Cryogenic Treatment on Microstructural Evolution and Mechanical Behavior of a Low‐Carbon Martensitic Stainless Bearing Steel

Deep cryogenic treatment (DCT) is a key influencing factor in the heat treatment of CSS‐42L bearing steel. The microstructural evolution and mechanical characteristics of CSS‐42 L samples subjected to different cryogenic temperatures (room temperature, −154 °C, and −196 °C) and subsequent tempering are systematically investigated, and correlations between phase constituents (residual austenite (RA), martensitic matrix, and carbides) and the resultant mechanical properties are established. DCT reduced austenite content by 10.9%, decreased average martensite grain size (Gm) from 3.74 μm to 2.39 μm, increased yield strength (YS) by 54.1%, and lowered impact toughness (IT) by 55.7%. After tempering, DCT‐treated samples showed a 172% rise in YS and a 58.2% drop in IT, whereas non‐DCT samples experienced a 4.6% decrease in tensile strength, nearly unchanged YS, and a 43.7% improvement in IT. Tempering further reduced Gm in DCT samples to 1.81 μm but increased it to 6.68 μm in non‐DCT samples. Furthermore, DCT is identified as a critical determinant for subsequent carbide precipitation during the tempering cycle. The −154 °C treatment produced the optimal phase configuration, with the least residual austenite, finest martensite laths, and highest carbide density, resulting in a superior ultimate tensile strength of 2003 MPa.