ON THE CONTROL OF THE CRYSTALLIZATION PROCESS DURING TOP POURING OF STEEL INTO AN INGOT MOLD

Abstract

The relevance of this study stems from a fundamental contradiction between the mass character of metallurgical production and the growing demands of heavy machinery engineering for unique monolithic ingots weighing 50–300 tonnes, intended for critical components in power generation and shipbuilding equipment. During the crystallization of large melt volumes, liquation inhomogeneities, shrinkage porosity, and a coarse-grained dendritic structure inevitably form due to slow cooling rates and significant temperature gradients between the ingot surface and its central axis, thereby degrading the operational properties of finished products. Existing methods for mitigating crystallization defects–such as directional solidification and electroslag remelting–suffer from systemic drawbacks, including 15–25% metal yield loss and relatively low productivity. This work aims to investigate the possibility of controlling the crystallization process in top pouring of steel by introducing melt along the inner wall of a mold rotating uniformly about a vertical axis. The article presents results of preliminary cold physical modeling using glycerin as a model fluid and mathematical modeling based on a self-similar solution of the Stefan problem with a moving phase boundary. Experimental data confirm a 6.9% increase in heat extraction intensity at a rotation speed of 30 rpm compared to static pouring, indicating more uniform heat flux distribution and an enlarged effective contact area between the melt and mold wall. The mathematical modeling demonstrates the feasibility of forming a layered microstructure with impurity concentration oscillation amplitudes up to 15%, provided that each added layer solidifies within a time not exceeding 20% of the total pouring period. The findings confirm that the proposed method reduces liquation defects without significantly complicating the technological process, increasing metal cropping, and reducing pouring productivity. The study opens prospects for enhancing the quality of large-scale ingots for critical applications with moderate capital expenditures for equipment modernization.