Abstract
Relevance and Objectives: Both crop top ingots of normal length and elongated crop top ingots as well as elongated ingots without crop tops are used for the fabrication of hollow forgings. Chilled top ingots provide the best efficiency both in terms of final product quality and performance indicators. Materials and Methods Applied: The object of research is a 1.53 ton chilled top ingot of ‘38ХН3МФА’ steel teemed with a 10.8% cooling top extension. 2D ingot models with transparent walls were used for the physical modeling of crystallization and structure formation in the ingot under study. Etching was applied when examining the macrostructure of the cast ingot metal. The process of crystallization was studied with the help of the Crystal simulation software. Findings: Based on the physical modeling results obtained for model ingots with cooling top extensions of various volumes, we were able to identify the solidification patterns typical of both the whole ingot and its parts. With the help of mathematical modeling, a relationship was obtained which correlates the ingot geometry (H/D ratio) with the relative depth of the shrinkage cavity. For quantitative assessment of the vertical solidification efficiency supported by the mold cooling top extension, calculations were done to determine the thermal performance of a chilling top extension and a warmth-keeping top extension. It was established that the axial porosity zone in chilled top ingots is twice smaller in diameter and in length compared with that in conventional ingots. While conventional ingots have a significant chemical heterogeneity, in chilled top ingots these elements are more evenly distributed. The location of the shrinkage cavity along the chilled top ingot centerline ensures the cavity can be easily eliminated when the ingot is used for a hollow forging provided the shrinkage cavity is only minor. Chilled top ingots require only minimum preparation cost and have minimum top scrap. This technology provides a more homogeneous distribution of segregates along the height of the ingot and improved structure and quality.
Keywords
Chilled top ingot, solidification, chemical and structural heterogeneity, shrinkage, segregation, physical and mathematical modeling.
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