Determination and Analysis of Continuous Cooling Transformation Curves of New Low-Activation Ferritic-Martensitic Steels

The critical transformation points of a novel Y-containing low-activation steel were identified, and continuous cooling transformation (CCT) experiments were conducted over a cooling rate range of 0.05–40 °C/s using the expansion technique on a DIL805A quenching dilatometer. Static CCT diagrams were generated, and the microstructure along with room-temperature micro-Vickers hardness were evaluated. The influence of varying cooling rates on the microstructure and hardness of the steel, austenitized at 1150 °C, was comprehensively investigated. The findings indicate that the Ac1 and Ac3 temperatures for this steel are 837 °C and 903 °C, respectively. During continuous cooling, the steel exhibits dual-phase transformations into ferrite and martensite at cooling rates of 0.05 °C/s and 0.1 °C/s, producing blocky ferrite and lath martensite structures. With increasing cooling rates, the transformation is dominated solely by martensite. As the cooling rate rises and the steel undergoes complete martensitic transformation, its microhardness peaks at 400 HV.