Effect of austenitization on martensite transformation in Co–Cr–Mo alloys by in situ observation

The martensite transformation of Co–Cr–Mo alloys during cooling after holding at different austenitization temperatures ( T a ), was investigated via high-temperature confocal laser scanning microscopy (HT-CLSM). The martensite starting temperature ( M s ) increases with increasing T a . Martensite area fraction ( f M ) firstly decreases, then increases, and finally decreases with increasing T a . Additionally, inverse martensite transformation, grain growth, and σ phase decomposition were examined during heating via differential scanning calorimetry and HT-CLSM. The effects of T a on martensite transformation and phase composition of the alloys were analyzed. M s and f M were influenced by both grain size and pre-existing martensite at T a of 900–950 °C, grain size alone at 950–1100 °C, and both grain size and elemental diffusion at 1100–1200 °C. This study will provide basic theoretical guidance for regulating the microstructure and enhancing the mechanical properties of Co–Cr–Mo alloys.