Grain refinement of A517 steel by inoculation with Al–5Ti–B master alloy

The edge-to-edge matching model was used to identify TiB 2 as a potential grain refiner to refine the high temperature δ-ferrite in low carbon steels. To effectively introduce the grain refiner, Al–5Ti–B master alloy (MA) was used to add TiB 2 particles into an A517 steel. However, there was no grain refinement in the as-cast A517 steel, attributed to the decomposition of TiB 2 particles in the molten A517 steel, into Ti and B. As a result, BN particles formed on the pre-existing Al 2 O 3 particles were detected within prior austenite grains. Nevertheless, there was significant grain refinement after reheating the A517 ingots to 1150 °C, isothermally holding for 2 h and air cooling. The austenite grain size of the reheated A517 steel was decreased from 318 ± 70 μm to 38 ± 4 μm using 0.1 wt% Al–5Ti–B MA. Grain refinement was caused by Ti-containing nanometre-sized precipitates along prior austenite grain boundaries inhibiting the grain growth. The grain refinement improved the strength and ductility of ingots after reheating and improved workability for the production of hot worked products.