Effect of Ti on microstructure and mechanical properties of CrNiMo low alloy cast steel

To improve the comprehensive mechanical properties of CrNiMo low alloy cast steel, the effects of micro-alloying element titanium and quenching temperature on its microstructure and performance were investigated. Utilizing various characterization methods such as scanning electron microscopy （SEM）, electron backscatter diffraction （EBSD）, transmission electron microscopy （TEM）, and optical microscopy （OM）, the influence of titanium content and quenching temperature on austenite grain growth behavior was analyzed, and the mechanism by which titanium affects the morphology of tempered sorbite and the final mechanical properties was explored. The results indicate that during quenching at 900-950 ℃, titanium content has no significant effect on the average austenite grain size but noticeably affects the uniformity of grain size distribution. When the quenching temperature exceeds 1 000 ℃, titanium plays a more pronounced role in inhibiting grain coarsening, and higher quenching temperatures lead to larger grain sizes. At quenching temperature of 950 ℃ and titanium mass fraction of 0.035%, the austenite grains are the finest and most uniform, with an average size of 11.13 μm. Mechanistic analysis reveals that at lower quenching temperatures, Ti（C,N） does not fully dissolve, and the quenching temperature dominates grain size evolution. If the titanium content is too low, the number of precipitates is insufficient, while excessive titanium content can lead to titanium atom segregation. Both scenarios weaken the pinning effect on grain boundaries and compromise microstructural uniformity. After tempering at 550 ℃, the test steel corresponding to the above process parameters shows the best mechanical properties, the tensile strength is 1 134.95 MPa, the yield strength is 1 101.59 MPa, and the impact energy at room temperature is 43.74 J. By regulating the quantity and size of Ti（C,N） precipitates, titanium enhances strength of steel while maintaining good toughness, achieving a comprehensive optimization of strength-toughness balance.