Effects and mechanism of titanium modification on structures of cast steel ZG270-500

Abstract

The influences of titanium modification on the solidification behavior, shrinkage characteristic and primary austenite refinement of cast steel ZG270-500 smelted in intermediate frequency induction furnace were studied. 0.15wt% titanium modification increased the fluidity of the steel liquid, enhanced the feeding capacity of cast steel, changed the dispersed shrinkage porosity to concentrated shrinkage cavity, turned the coarse dendrites into fine equiaxed grain structures and greatly reduced the primary austenite grain size. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that titanium combined with carbon to be solid phase particles TiC, with high melting point, to promote the primary austenite nucleation authentically by non-spontaneous nucleating. The crystal lattice match growing model between γ-Fe and TiC was established. The mechanism of TiC heterogeneous nucleating existed in that the primary austenite grew up by {111}γ-Fe parallel to the closest packed plane {111}TiC in the crystal orientation 〈110〉γ-Fe//〈211〉TiC. The crystal planes mismatch \( \delta _{\{ 111\} _{\gamma - Fe} }^{\{ 111\} _{TiC} } \) and the lowest orientation mismatch \( \delta _{\{ 110\} _{\gamma - Fe} }^{\{ 110\} _{TiC} } \) were 8.18%. and 2.25% respectively, almost achieving complete coherent lattice match growing of austenite on TiC.