Influence of Mg addition on inclusions and mechanical properties of Cr12Mo1V1 steel under high pressure

Abstract

Conventional methods that involve an increase in pressure are used to improve the solubility and yield of Mg in the steelmaking. Under high pressure, the effect of Mg addition on the number, morphological characteristics, composition, size, and density of inclusions in Cr12Mo1V1 steel (C: 1.40–1.60 wt%, Si: ≤0.60 wt%, Mn: ≤0.60 wt%, S: ≤0.03 wt%, P: ≤0.03 wt%, Cr: 11.00–13.00 wt%, V: ≤1.00 wt%, and Mo: 0.70–1.20 wt%) is studied. The experiments are made under three contents of Mg: 0, 0.0012 wt% and 0.0041 wt%. Results show that Al2O3 and MnS inclusions transform into approximately spherical MgO·Al2O3 spinel and spherical MgO·MgS inclusions, respectively. At ~0.07 wt% dissolved aluminum content, the micro content of Mg in molten steel leads to the formation of MgO·Al2O3 spinel inclusions. The MgO·Al2O3 inclusions disappear completely when the mass fraction of Mg is larger than 39.734 × 10−6. Further, as the Mg content increases, the number of inclusions <1 μm increases, whereas the number of inclusions >2 μm decreases. Meanwhile, during molten steel solidification, MnS and MnS–MgS precipitate around MgO·Al2O3 and MgO inclusions, respectively. The densities of MgO·Al2O3 spinel inclusions are lower than those of alumina inclusions. As the Mg content in Mg-containing inclusions increases, the density of inclusions decreases, leading to an improvement in inclusion removal efficiency. The role of Mg in the mechanical properties, tensile fracture morphology, and inclusions of quenched and tempered Cr12Mo1V1 steel is also investigated. As the Mg content increases from 0 wt% to 0.0041 wt%, at the tensile fracture, the area of shear lip goes through a process from small to large, the dimples go through a process from generation to deepening, and the strength and plasticity correspondingly increase.