Consideration on the Formation Mechanisms of Macroscopic Segregation in Large Steel Ingot or Casting

Abstract

The cause for macroscopic segregation in large steel ingot and casting is reviewed. The formation mechanisms of macroscopic segregations, which have not yet been solved, are as follows.
1. A-segregation and speckle-segregation.
2. V-segregation (positive V-segregation and negative V-segregation).
3. Pock mark segregation and negative V-shape segregation accompanied with electric arc heating in feeder head or upper part of ingot or casting.
4. Negative segregation in lower part of ingot or casting.
In order to solve the cause for above-mentioned macroscopic segregations, the authors investigated. metallographically the macro-segregations of large ingots or castings sectioned longitudinally or transversely, and furthermore carried out model experiments with water-oil, etc. to elucidate the floatation mode of lighter segregated metal in bulk liquid metal.
Based on the results obtained and microscopic feature of dendrite structure, the authors made clear that the macroscopic segregation of steel was induced by difference of specific gravity between segregated liquid metal in the dendritic region and bulk liquid metal and also by interfacial tension between them.