Improvement of solidification structure and stress distribution of large section Fe-6.5% Si alloy ingot using weak cooling method

Direct rolling for high-silicon ingots simplifies the forming process, but quality control limits their weight. This paper presents the casing of Fe-6.5 wt.% Si alloy ingot with a weight of 200 kg. The air-cooling casting experiment revealed coarse grains and transgranular and surface cracks. A weak cooling method after demoulding is proposed to address these issues. A physical model was established and validated. The evolution of thermal, solidification structure and stress distribution are simulated under air cooling and weak cooling condition. Comparative studies show that applying weak cooling reduces the temperature gradient from the centre to the one-sixteen length position from 1.54 K/mm to 0.3 K/mm, achieving an equiaxed crystal ratio of 81.73%. The maximum stress during solidification decreased from 132.35 MPa to 33.81 MPa. Then, weak cooling casting and rolling experiment produces defect-free ingots and plates, confirming the feasibility of the optimisation.