Evolution of Dendrite Structure and Shrinkage Porosity in 30Cr15Mo1N Ingot with Pouring Rate

In this study, to clarify the evolution mechanism of dendrite structure and shrinkage porosity in 30Cr15Mo1N ingots under varying pouring rates, the changes in cooling rate, temperature gradient, secondary dendrite arm spacing (SDAS), columnar to equiaxed transition (CET), and area of shrinkage porosity with pouring rate are investigated. The cooling rate and temperature gradient calculated by using the ProCAST software increase with the pouring rate, leading to a great solidification rate. As a result, the SDAS decreases and the position of CET moves toward the center of 30Cr15Mo1N ingot. Additionally, the area proportion of shrinkage porosity increases with the increase in pouring rate. This phenomenon can be mainly due to the less overlap between columnar dendrite and higher permeability with the larger SDAS, which are conducive to the feeding of the molten steel. In addition, the delayed formation of semi-solidified shell at the top of the ingot at low pouring rate minimizes the impact of solid contraction on the surface sink, which results in a flatter top surface of the ingot at low pouring rate. Increasing pouring rate increases the cooling rate and temperature gradient, which promote the position of columanr to equiaxed transition moves toward the center. Meanwhile, the area proportion of shrinkage porosity increases with the increase in pouring rate. The top surface is more flat at lower pouring rate due to the delayed formation of semi-solidified shell at the top.image (c) 2024 WILEY-VCH GmbH