Effect of Zr, Al Addition on Characteristics of MnS and Formation of Intragranular Ferrite in Non-Quenched and Tempered Steel

In this paper, the characteristics of inclusions, microstructures and mechanical properties in non-quenched and tempered steel with Zr and Al addition were investigated to compare the effect of ZrO2 and Al2O3 particles on the precipitation behavior of MnS and the formation of intragranular ferrite. The results show that oxides, sulfides and oxy-sulfides in Zr addition steel are all finer than those in Al addition steel. As a result, the volume fraction of intragranular polygonal ferrite (IPF) induced by tiny MnS + V(C, N) particles in Zr addition steel has increased to 14.9%, resulting in higher transverse plasticity. Low lattice mismatch between ZrO2 and MnS inclusions plays an important role in refinement of MnS inclusions. Besides, the single ZrO2 particle, which is not wrapped by MnS inclusions, would induce formation of IPF further due to the small mismatch with α-Fe.