Effect of the Final Rolling Temperature on the Precipitation Behavior and Toughening Mechanism of Nanoparticles in Ferritic Steel.

We have analyzed the effect of the final rolling temperature on the morphology, mechanical properties, carbide nanoparticle size, and dislocation density of Ti-Mo ferritic steel. The microstructure was mainly composed of equiaxed ferrite, ultrafine ferrite, and polygonal deformed ferrite, whose three proportions were affected significantly by the final rolling temperature. The change trend of the mechanical strength was in line with the dislocation density under different finishing rolling temperatures, whereas the ferrite grain size change trend was the opposite. There were various types of nanoparticle precipitation in the test steels: interphase precipitation, dispersion, dislocation precipitation, and deformation-induced precipitation. The optimum mechanical properties were obtained at a final rolling temperature of 900 °C. Quantitative analysis showed that the effect of the final rolling temperature on the yield strength was mainly because of dislocation and precipitation strengthening. The toughening mechanism is attributed to the fine grain strengthening of nanoparticles in austenite stage and the precipitation strengthening of ferrite stage. [ABSTRACT FROM AUTHOR]