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

Abstract

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.