Influence of solution treatment on the strength-toughness balance of 00Cr12Ni10MoTi steel: Comparative analysis of room-temperature and 77 K mechanical behavior

To obtain strength-toughness balance of 00Cr12Ni10MoTi steel, a varying solution-treatment temperatures (750–900 °C) before aging treatment at 500 °C were designed. The microstructure evolution was analyzed during heat treatment, and the mechanical behaviors and strengthening-toughening mechanisms at room-temperature and 77 K were researched. Results revealed that lower-temperature (750 °C) solution treatment promotes higher austenite content ($\mathrm{RA}\approx 16\%$) and a more refined martensitic hierarchical structure ($D_{\text{block}}=5.23\mathrm{\mu m}$), with many nanoscale Ni₃Ti precipitates in the martensitic matrix. Mechanical testing results indicate that the steel after lower-temperature solution treatment demonstrates a high combination of strength and toughness at both room temperature and low temperature (77 K). The yield strength reaches as high as 1025.50 MPa at room temperature and 1276.00 MPa at low temperature. The impact toughness achieves approximately 165.00 J at room temperature and 75.20 J at low temperature. The study elucidates that the cryogenic toughness preservation in lower-temperature solution-treated 00Cr12Ni10MoTi steel is governed by two interlinked mechanisms:(1) high-angle grain boundaries (HAGBs) forming a three-dimensional obstruction network that effectively deflects and bifurcates propagating cracks through boundary pinning effects; (2) metastable retained austenite (RA) exhibiting phase-transformation-mediated toughening via both stress-induced martensitic transformation (TRIP effect) and intrinsic ductility contribution at 77 K. By analyzing the strength contributions, the origin of ultra-high strength of steels mainly includes the contribution of different strengthening effects due to dislocations, grain boundaries, precipitation, and frictional stresses. The reason for the increase in yield strength at low temperatures compared to room temperature is mainly due to the pronounced temperature dependence due to frictional stresses.