【作者】 韩彦博；

【导师】 房灿峰；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2012， 硕士

【摘要】 末端电磁搅拌(Final Electromagnetic Stirring, F-EMS)技术能有效地改善钢在连铸过程中容易出现的中心偏析、枝晶偏析、裂纹、缩孔、缩松及卷气、卷渣等常见缺陷。本文针对上海宝山钢铁股份有限公司末端电磁搅拌项目,利用DJG-φ20W新型多功能电磁搅拌器,在实验室条件下模拟钢连铸坯凝固末端电磁搅拌条件,选用低熔点的Sn-Sb、 Sn-Pb合金,在金属熔体凝固过程中对其施加螺旋磁场,并在相同电参数下施加行波磁场,对比分析螺旋磁场在改变励磁电流及频率的情况下改善成分偏析、细化微观组织的效果及作用机理,为连铸凝固末端施加电磁搅拌引入螺旋磁场提供一定的理论依据。实验以金属Sn为基体,用Sn-11wt.%Sb合金分析螺旋、行波对铸锭中心轴向成分偏析的影响；用Sn-20wt.%Pb合金分析螺旋、行波及反螺旋磁场对铸锭微观组织的影响。在Sn-11wt.%Sb合金凝固过程中施加行波磁场及螺旋磁场,搅拌频率为10Hz,励磁电流分别为25A、50A、75A、100A、125A。实验证明：励磁电流增大,两种搅拌方式改善成分偏析的能力增强。行波磁场励磁电流为125A时,改善轴向偏析的效果达到最佳,铸锭上、下p相含量差为1.67vol.%；当螺旋磁场的励磁电流为100A时,铸锭上、下p相含量差仅为0.56vol.%, Sb含量为0.08wt.%。可见,螺旋磁场能有效消除铸锭的成分偏析缺陷,且效果强于行波磁场。为了模拟钢连铸末端电磁搅拌过程,通过测量合金凝固坯壳厚度与凝固时间的关系确定浇注后6.5min开始施加电磁搅拌,坯壳厚度约为19mm,凝固率约为70%。励磁电流由75A增大至150A,行波磁场作用下最佳励磁电流为150A,平均晶粒尺寸为154μm；螺旋磁场最佳励磁电流为125A,对应的平均晶粒尺寸为133μm。改变两种磁场的搅拌频率,行波磁场搅拌频率为10Hz时平均晶粒尺寸最小,约为153μm；螺旋磁场搅拌频率为10Hz时,晶粒尺寸仅为133μm。研究发现：当旋转磁场与行波磁场复合后(即螺旋磁场)相比于单一的行波磁场在相同电参数下更易驱动熔体激烈对流、碎段枝晶,即励磁电流为125A、搅拌频率为10Hz的螺旋磁场细化组织效果最佳。当螺旋磁场的励磁电流、搅拌频率超过临界值后会延长熔体的凝固时间,导致微观组织有明显的变粗、长大现象。对金属熔体施加反螺旋磁场发现：行波分量向上的反螺旋磁场不利于排出气体而形成缩孔。更多还原

【Abstract】 Defects like central gravitational and dendritic segregation in the process of continuous casting can be improved by final electromagnetic stirring (F-EMS) effectively. This subject is in the light of the FEMS installation of Baoshan Iron and Steel Company Limited. With the New-type multi-functional electromagnetic stirring installation, the process of FEMS of the continuous casting was simulated in the experiment conditions. Low melting alloys Sn-Sb and Sn-Pb were selected in this paper which were stirred on with spiral magnetic field (SPF), with comparison of alloys solidified in the travelling magnetic field (TMF). Effect and mechanism of action under SMF on macrosegregation improvement, microstructure refinement were analysed at different excitation current and frequency which was expected to provide a theoretical basis for the practical application of a novel stirring method in F-EMS. Sn was selected in this experiment to be the matrix metal, and the composition was designed to Sn-11%Sb and Sn-20%Pb. Sn-11%Sb was selected to analyse the effect of SMF and TMF on the gravity segregation of the ingot as well as Sn-20%Pb was selected to analyse the effect of SMF, TMF and anti spiral magnetic field on the micro structure of the ingot.Sn-11%Sb was selected with the stirring methods of TMF and SMF, frequency of lOHz and excitation current of25A,50A,75A,100A,125A. Ability on improving the gravity segregation becomes better with the increasing of the excitation current for both of the two magnetic field. Effect of gravity segregation improvement reach a optimal value with1.67vol%for the content of β phase difference between upper and lower part of the ingot when the excitation is125A under TMF stirring;(3phase difference is0.56vol.%when the excitation is100A under SMF stirring. Difference between upper and lower part of the ingot is only0.08wt.%for quality score of Sb analysed by XRF under SMF which means the gravity segregation of the ingot is substantially eliminated. It could be found that, from the experimental analysis, effect of SMF on gravity segregation improvement is more excellent than TMF.In order to simulate the process of FEMS in the continuous casting, relationship between the solidified shell thickness and solidified time was measured in which6.5min was confirmed to be the beginning stirring time after pouring and the shell thickness was about19mm with a solidification rate of70%. When the excitation current increase from75A to150A, the minimum value of the average grain size unde TMF is154μm when the excitation current is150A and comparatively, the minimum value of the average grain size under SMF is 133μ m when the excitation current is125A. An optimal value of frequency can also be found for both SMF and TMF when changing the stirring frequency. The minimum of the average grain size is153μm when the frequency is lOHz and13Hz under TMF while the average grain size is133μm when the frequency is lOHz under SMF. From the analysis it could be found that, compare to TMF, a more intense convection could occur in the melt when the rotating magnetic field (RMF) and travelling magnetic field (TMF) superposed with each other (SMF) which can cause the fracture of dendrites more easily, therefore SMF shows a more excellent effect on solidification structure refinement with the optimal stirring parameters of125A and10Hz. Furthermore, solidification time could be deferred under the intense convection and more induction heat will be brought in, for this reason, a higher excitation current and frequency over the optimal value will lead to a coarse microstructure and the growth of dendrites. It could be found that when the melt was stirred on with the anti spiral magnetic field with an upward direction travelling wave, a worse effect would be showed than SMF on the ability of dendrites fracture and microstructure refinement and the sinkhole could appear easily due to the gas which couldn’t be let out timely.更多还原