Effects of Gradient Temperature Field on the Internal Quality of Casting Ingot

The high temperature reduction pretreatment (HTRP) technique effectively control internal defects in the ingot. To assess the effects of gradient temperature fields on the HTRP processes and internal defect healing, this study prepared various ingots using a one-pass HTRP process with identical reduction amounts but different surface temperatures. Ultrasonic non-destructive microscopy and macrostructure analysis were employed to evaluate the size, morphology, and distribution of internal defects. Heat transfer and rolling finite element simulations provided the temperature field and strain distributions. Molecular dynamics simulations investigated the defect healing under varying temperatures and grain sizes. The findings reveal that higher surface temperatures during reduction result in larger austenite grain sizes, reduced defect counts, increased average defect sizes, and higher average relative densities. The sample treated at 950 °C by HTRP showed superior internal quality, with a 50 pct reduction in defects smaller than 500 μm compared to the 850 °C sample, and better average defect size and distribution than the 1050 °C sample. Elevated temperatures accelerate defect healing, with smaller initial grain sizes also promoting faster recovery. Effective control of internal defects necessitates considering the combined influences of equivalent strain penetration, healing temperature, and initial grain size.