Effect of Thermoelectric Magnetic Convection on Shrinkage Porosity at the Final Stage of Solidification of GCr18Mo Steel
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inkage porosity of steel due to the volume shrinkage effect at the final stage of solidification plays a negative role in the hot rolling and final performance of the steel.[1–3] This shrinkage porosity can be a severe problem for wide-ranging mushy zones, such as in GCr18Mo steel, due to the fluid flow of the liquid steel compensating uneasily into the root of the dendrite. Effective techniques to control this problem at the final solidification stage of steel can be mainly categorized into two groups: (1) mechanical techniques such as ‘‘soft reduction’’[4] and ‘‘heavy reduction’’[5] and (2) electromagnetic stirring techniques such as ‘‘final electromagnetic stirring.’’[6,7] Among the abovementioned measures, stirring of the melt by time-varying magnetic fields is particularly fascinating due to the completely
YUAN HOU, SANSAN SHUAI, YUANHAO DONG, WEIDONG XUAN, JIANG WANG, ZHENQIANG ZHANG, XINGFU REN, and ZHONGMING REN are with the State Key Laboratory of Advanced Special Steel & School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China. Contact e-mails: [email protected]; [email protected] Manuscript submitted August 13, 2018.
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contactless feature and flexible tailoring of the magnetic fields themselves. The fluid flow driven by the melt stirring can penetrate the mushy zone, thus favoring solidification feeding. However, due to the skin effect and the location of the final electromagnetic stirring, the time-varying magnetic fields have some limitations for eliminating the shrinkage porosity at the end of the solidification range.[6,8] By contrast to the time-varying magnetic fields, static magnetic fields without the skin effect are applied to suppress the fluid flow due to the braking effect of the Lorentz force.[9,10] Based on the Seebeck effect, however, a thermoelectric magnetic convection (TEMC) can be induced by a thermoelectric magnetic force (TEMF) resulting from the interaction between the thermoelectric current (TEC) near the liquid/solid interface and the applied static magnetic field in the mushy zone.[11] Recent evidence suggests that this TEMC can alter both the solidification structures and component distributions of alloys. With regard to the transition of the solidification structures, the columnar-to-equiaxed transition (CET) under axial static magnetic field (ASMF) was obtained in the directional solidification of alloys, such as Al-based alloys,[12,13] Pb-Sn alloys,[14] and Ni-based superalloys.[15] However, in terms of the component distribution, the TEMC under an ASMF can modify the macrosegregation of the primary silicon
phase of an Al-Si alloy.[16] In addition, the CET for GCr18Mo under an ASMF was investigated in our previous work.[17] The results showed that the TEMC can facilitate the CET and a more uniform distribution of alloying elements. However, few studies have reported the effect of the TEMC, a fluid flow in the mushy zone, on solidification feeding. The purposes of this paper are described below. First, to assess the influence of the
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