Abstract
We present a segmented coupling model for slab casting by roller electromagnetic stirring (R-EMS) of electromagnetic, flow, heat transfer, and solidification behavior based on magnetohydrodynamics and solidification theory. A three-dimensional (3-D) segmented coupling model that included electromagnetic, flow, and heat transfer elements was established using Ansoft Maxwell and ANSYS Fluent software. The effects of the roller sleeve, magnetic shielding ring, coil, core, molten steel, and air domain on the electromagnetic, thermal and flow fields were studied numerically. The accuracy of the model was verified by measuring the magnetic flux density at the centerline in a pair of rollers and the electromagnetic force of the copper plate. Based on the numerical results of the optimal technical parameters, the effect of the R-EMS on the solidification of Fe–17 wt% Cr–0.6 wt% Ni stainless steel was explored. The results indicated that with each additional pair of electromagnetic rollers, the average electromagnetic force increased by 2969 N/m3 in the casting direction, and 5600 N/m3 in the central section of the rollers. With increasing number of pairs of rollers, the effective stirring region increased, and the velocity of molten steel at the solidification front first increased but then decreased. The strong electromagnetic swirling washing effect reduced the solidification rate of the slab shell and promoted the superheated dissipation of molten steel in the center of the strand. The center equiaxed crystal ratio of the slab was improved to 69% with two pairs of R-EMS rollers and electromagnetic parameters of 400 A/7 Hz, which was beneficial for obtaining a uniform and dense solidified structure to improve the subsequent hot working performance and product quality.
Highlights
Nickel-saving stainless steel alloys, such as Fe–17 wt% Cr–0.6wt% Ni, have a ferrite structure at room and high temperatures that causes them to develop columnar crystals during solidification with a very low ratio of equiaxed crystal in steel castings
Controlling the cast structure and obtaining a high ratio of equiaxed crystals during the continuous casting (CC) process is important to improve the product’s subsequent hot working performance and quality; this has always been a central issue for the steel industry [1,2]
The center equiaxed crystal ratio of the slab was improved to 69% with two pairs of roller electromagnetic stirring (R-Electromagnetic stirring (EMS)) rollers and electromagnetic parameters of 400 A/7 Hz, which was beneficial for obtaining a uniform and dense solidified structure to improve the subsequent hot working performance and product quality
Summary
Nickel-saving stainless steel alloys, such as Fe–17 wt% Cr–0.6wt% Ni, have a ferrite structure at room and high temperatures that causes them to develop columnar crystals during solidification with a very low ratio of equiaxed crystal in steel castings. Kunstreich et al [3] addressed the surface/subsurface quality (slivers, pipe, pinholes, blowholes, inclusion content) and diversion rate (slab casting abnormality codes) of products cast on high or low throughput thick slab machines. They found that slow speed or wide slab machines that create or maintain a stable double roll flow in the mold are key to eliminating slab defects, the intensity of the double roll flow pattern must not be excessive. The arrangement and use of EMS to control metallurgical behavior in the secondary cooling zone (SCZ) to improve the quality of strands has received less research attention
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