The primary phase grain size is a key parameter to understand the formation of the macrosegregation pattern in large steel ingots. Most of the characterization techniques use two-dimensional measurements. In this paper, a characterization method has been developed for equiaxed dendritic grains in industrial steel castings. A total of 383 contours were drawn two-dimensionally on twelve 6.6 cm2slices. A three-dimensional reconstruction method is performed to obtain 171 three-dimensional grains. Data regarding the size, shape and orientation of equiaxed grains is presented and thereby shows that equiaxed grains are centimeter-scale complex objects. They appear to be a poly-dispersed collection of non-isotropic objects possessing preferential orientations. In addition, the volumetric grain number density is 2.2×107 grains/normalm3, which compares to the 0.5×107 grains/normalm3 that can be obtained with estimation from 2D measurements. The 2.2×107 grains/normalm3 value is ten-times smaller than that previously used in the literature to simulate the macrosegregation profile in the same 6.2 ton ingot.

Correct prediction of composition heterogeneities and grain structure across a steel ingot is critical in optimizing the industrial processing parameters for enhanced performance. The columnar to equiaxed transtion (CET) is a microstructural transition which is strictly controlled as it affects the mechanical properties of the final product along with the macrosegregation patterns. Larger equiaxed regions are preferred for most industrial applications. CET is significantly affected by the number density of equiaxed grains and by the nucleation undercooling. 8 kg 42CrMo4 alloy steel ingots (240 mm x 60 mm x 60 mm) were cast. The cast structure was characterized by ASCOMETAL. The experiments were simulated with a process-scale model of solidification that incorporates a multiscale description of the microstructure formation. The goal of the present study is to show the capabilities of such a process-scale solidification model to explain the observed structure distributions (extent of the columnar and equiaxed zones, equiaxed-to-columnar transition).

Macrosegregation is a critical defect in industrial steel ingots in both conventional ingot castings and continuous castings. Improvements in terms of macrosegregation require to be able to precisely quantify the intensity and the repartition of macrosegregation along the cast product. However, traditional macrosegregation measurements are a tedious and time consuming process. In this study, three different product lengths of the same caster strand were taken during the same heat. Each sample was cut along the longitudinal central plane of the cast product. One additional transverse section was also cut for one of the sample. Drilling with constant spacing was performed on 50% of the area of longitudinal sections and 25% of the transverse section. Carbon and sulfur contents were then measured on each drilled location. Plotting methodologies to produce chemical maps are carefully described regarding the different parameters such as color map choices and normalization methods. Data for all the characterized sections is compared with each other and the differences are commented with the help of the process parameters.