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In order to compare the hot deformation behavior and microstructure evolution of the rack steels with and without segregation, hot compression tests are carried out in the temperature range of 1173–1423 K and the strain rate range of 0.01–10 s−1 on a DIL805A/D quenching and deformation dilatometer. The flow stress, constitutive relation, processing map, and microstructure characterization are investigated. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The calculated activation energy (Q) and stress exponent (n) for the segregated samples are 395.245 kJ mol−1 and 6.046, which are higher than segregated samples, showing 376.815 kJ mol−1 and 5.930. The processing maps show that the workability of the nonsegregated steel is significantly more excellent than segregated steel. The segregated steel shows a higher kernel average misorientation angle and local strain. Complete dynamic recrystallization occurs at a high strain rate, and high deformation temperature can refine the grains. [ABSTRACT FROM AUTHOR]

A multistep quench−lamellarization−tempering treatment (QLT) is designed for a low‐carbon high‐Ni martensitic steel to obtain extra high strength, low yield‐to‐tensile ratio, and extra high cryogenic toughness. A mixed microstructure composed of intercritical ferrite, tempered martensite, and Ni‐rich retained austenite (RA) is obtained under the QLT treatment process. The volume fraction of Ni‐rich RA is 13.6% in the QL655T sample. The QL655T sample has a yield strength of 915 MPa and tensile strength of 1080 MPa, leading to a lower yield‐to‐tensile ratio of 0.85. In addition, a total elongation to failure of 19.9% and Charpy impact toughness of 190 J at −196 °C are encouraging in comparison with the conventional counterparts. During tensile deforming, the blocky RA grains can transform easily with increasing strain, while the strain leads to rotations of the film‐like RA grains before the transformation. The RA grains with high thermal stability are attributed to the enrichment of Ni and the effect of size, which makes the ≈11.6% RA grains remain at −196 °C in the QL655T sample. During impact, the transformation‐induced plasticity (TRIP) effect of RA leads to the excellent cryogenic toughness of the QL655T sample. [ABSTRACT FROM AUTHOR]