Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Abstract

The macro-scale segregation of alloying elements during the casting continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still commonplace, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today's steel ingots are as chemically homogeneous as possible.This article briefly reviews the development of our current understanding of macrosegregation phenomena during the 20 th century, before going on to assess the latest developments in the field of macrosegregation modelling. The aim of the text is to highlight the shortcomings of applying contemporary macromodels to steel-ingot casting, and to suggest practical alternatives. In addition, the experimental characterisation of macrosegregation is explored, and a review of the various techniques currently available is presented.

Acceleration of Macrosegregation Simulation Based on Lattice Boltzmann Method

“…However, there is a longstanding problem in practical use of these models, i.e., high computational cost. 4) It restricts the computational system to a small size and/or it forces one to use coarse mesh size, often hampering accurate description of macrosegregation behavior. 4) Hence, it is important to develop a simulation model with high computational efficiency.…”

“…4) It restricts the computational system to a small size and/or it forces one to use coarse mesh size, often hampering accurate description of macrosegregation behavior. 4) Hence, it is important to develop a simulation model with high computational efficiency. The simulation models for macrosegregation consist of a set of momentum, mass, energy and solute conservation equations 2) and the momentum conservation is described by the Navier-Stokes (hereafter abbreviated as NS) equation for fluid flows.…”

“…Computational approaches have played an important role in this field as well as experimental and theoretical approaches. [1][2][3][4] Several models have been developed for numerical simulations of formation processes of macrosegregation, for instance, so-called single domain models based on a mixture theory 5) or volume averaging, [6][7][8] two-phase model which accounts for relative movement of solid and liquid, and multi-phase models [9][10][11] where mesoscopic details such as the interdendritic liquid, the columnar and equiaxed dendrites are separately modelled. The simulation models have been gradually sophisticated and have been widely applied to a variety of complicated and realistic processes.…”

“…[1][2][3][4] Macrosegregation is non-uniform distribution of alloying elements over spatial scales ranging to ingot scales. It is caused by long-range advections of alloying elements due to flows of segregated liquid and motion of solid.…”

Detection of macrosegregation in a large metallic specimen using XRF

“…1) This segregation is that which occurs over distances similar to the dimensions of the casting, and arises during solidification due to the movement of microsegregated solid and liquid. [1][2][3] In the case of large ingots and sand castings, the distances involved may be of the order of centimetres or metres.…”