The effects of a ferritic or martensitic matrix on the tensile behavior of a nano-precipitation strengthened ultra-low carbon Ti–Mo–Nb steel

This work investigates the correlation between microstructure and mechanical properties of a nano-precipitation strengthened ultra-low carbon (NPS- ULC) Ti–Mo–Nb steel. Two types of matrix microstructures (ferrite and martensite) with nano-precipitates were obtained through hot rolling and isothermal transformation in the case of ferrite, or by quenching and tempering, for martensite. The martensitic microstructure showed increases in both YS and UTS by ~110 and ~100 MPa, respectively, over the ferritic microstructure without sacrificing tensile ductility. All ferritic and martensitic specimens exhibited a two-stage work hardening behavior with different work hardening rates at high strain levels. Quantitative analysis of the strengthening contributions confirms that the increase in yield stress of the NPS-ULC specimens with a martensitic matrix was a result of the fine martensitic laths as well as the higher dislocation density and nano-precipitates.