Effect of different grain structures on centerline macrosegregation during direct-chill casting

Abstract

Duplex grain structure consisting of coarse-cell and fine-cell dendritic grains is frequently found in the central portion of direct-chill cast billets and ingots. Coarse-cell grains are usually considered as free-floating grains settled to the bottom of the billet sump. These grains are assumed to be solute-lean and contribute to the negative centerline segregation. In this paper the contribution of coarse-cell and fine-cell grains to macrosegregation is for the first time studied experimentally by direct measurements of their composition. It is shown that the coarse-cell, floating grains are depleted of solute and the areas of their accumulation contribute to the negative macrosegregation. The areas of fine-cell grains can be either enriched in solute or be close to the nominal composition. It is argued that their composition results from the interplay between thermo-solutal and shrinkage-induced flows. The roles of casting speed and grain refining are also under scrutiny in this paper.

Simulation of 3D-Microstructure in Free-cutting Steel 9SMn28 under Water Cooling Condition with Convection and Porosity

“…Jinlong WANG, 1) Fuming WANG, 1) Changrong LI 2) and Jiongming ZHANG The 3D-microstructure in 9SMn28 free-cutting steel under water cooling condition was simulated based on the finite element-cellular automaton method with convection and porosity, and the simulated results are consistent with that of the experiment. The casting of 9SMn28 alloy is a stepwise solidification mode under water cooling condition.…”

“…In addition, the convection flows pick up the freefloating, solute-lean solid grains and transport them within the slurry region until the moment when these grains become heavy enough to settle down. 1) Coupled convective and morphological instabilities during directional solidification of an alloy have also been simulated using the phasefield method. [2][3][4] Cellular automaton (CA) techniques have also become available.…”

Predictive Capabilities of Multiphysics and Multiscale Models in Modeling Solidification of Steel Ingots and DC Casting of Aluminum

“…The fast-growing grains packed immediately after settling from the descending flow current, and the slow-growing grains settled to the bottom only after a prolonged trajectory in the stagnant growth region. The two types of grains form a duplex structure, observed in many experiments [29,[34][35][36][37][38][39][40]. …”

Mechanisms and Control of Macrosegregation in Dc Casting

“…As the primary solid in hypoeutectic aluminum alloys is always depleted of the solute, the accumulation of the floating grains has to contribute to the negative segregation. Electron-probe microanalysis (EPMA) measurements on several coarse and fine cells in the duplex structures found in the centre of 195-mm billets from 2024 and 7075 alloys clearly demonstrate that coarser cells are more solute-depleted as compared to the 'regular' finer cells [13,14]. Both grain-refined (GR) and nongrain refined (NGR) alloys were tested.…”