Effect of In Situ Nano-Particles on the Microstructure and Mechanical Properties of Ferritic Steel

Transmission electron microscopy (TEM), optic microscopy (OM), and small‐angle‐ X‐ray‐scattering(SAXS)are combined to comprehensively characterize the effect of endogenous nano‐particles obtained by a new method, on microstructure and mechanical properties of the ferritic steel. Morphology of nano‐particles, the change of microstructure, and the performance of steel are systematically studied. Results indicate that the endogenous nano‐particles are titanium oxide which not only has a positive effect on refining the structure of ferrite steel, but also can significantly improve its strength without much losing its plasticity. Tensile tests reveal that tensile strength and yield strength of the investigated steel are increased from the original 392 and 247 MPa to 524 and 430 MPa, respectively. However, the value of the elongation‐to‐failure is only decreased by 3%, reached to 25% ultimately. Effect of in situ nano‐particles produced in melt directly is investigated here. On the one hand, these in situ nano‐particles present coherent or semi‐coherent relationship with the matrix, which allow of a substantial improvement of the strength while without sacrificing its plasticity and toughness too much. On the other hand, the as‐cast structure is obviously optimized due to the heterogeneous nucleation effect of these in situ nano‐particles.