Abstract
A dual phase structure mainly consisting of martensite and reversed austenite has been achieved in Ti-Mo martensitic stainless steels, which were austenitized, cryogenically frozen, and further aged at various temperatures to investigate the effects of microalloying elements and aging treatment on the microstructural evolution and mechanical properties. Interestingly, the results indicated that the Vickers hardness increased with isothermal aging time after aging at a relatively low temperature, i.e. 480 °C, but it decreased with aging time after aging at a temperature higher than 520 °C. For example, the Vickers hardness (HV0.1) values of specimens aged at 480 °C were 645 ± 37 (1 h), 657 ± 31 (4 h), and 673 ± 29 (8 h). In contrast, specimens aged at 640 °C had Vickers hardness (HV0.1) values of 389 ± 15 (1 h), 383 ± 16 (4 h), and 375 ± 16 (8 h). The greatest ultimate tensile strength (UTS), 1730 MPa, was that of the Ti-Mo martensitic stainless steel aged at 480 °C for 4 h. The strengthening of Ti-Mo martensitic stainless steel can be primarily ascribed to the numerous nano-sized intermetallic particles, i.e., η-Ni3Ti, that precipitated within the martensite matrix upon aging treatment. Furthermore, more reversed austenite with various shapes, namely, film-like, granular, and blocky, formed when the aging temperature was the relatively low temperature of 520 °C and effectively enhanced the ductility of the martensitic stainless steel.
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