低压脉冲磁场凝固硅钢的组织性能及热变形研究

IMR OpenIR

	低压脉冲磁场凝固硅钢的组织性能及热变形研究
	陶文哲
学位类型	硕士
导师	杨院生
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料工程
关键词	硅钢低压脉冲磁场凝固元素分布热变形组织力学性能 Silicon Steel Low Voltage Pulsed Magnetic Field Solidification Solute Distribution Hot Deformation Structure Mechanical Properties
摘要	"硅钢作为一种重要的金属功能材料，在磁性材料中用量最大。采用连铸法生产大于2wt.%Si的硅钢遇到的主要问题就在于产品表面沿轧向常出现瓦楞状缺陷，使叠片系数和磁性能降低。产生瓦楞状缺陷的原因是铸坯中粗大的柱状晶在热轧过程中由于动态回复和再结晶缓慢而不能彻底细化，热轧板的板厚中心附近为粗大伸长的形变晶粒，以后冷轧过程中变形不均匀。防止瓦楞状缺陷的有效方法是对凝固过程进行控制，获得等轴晶率更高的铸坯。低压脉冲磁场凝固技术是一种新的凝固控制方法，已在部分合金中取得了良好的晶粒细化效果。本文主要通过在硅钢凝固过程中施加低压脉冲磁场，系统研究了低压脉冲磁场的脉冲频率、励磁电压、脉冲磁场施加时间等脉冲参数以及浇注温度、模具预热温度等热控制参数对硅钢凝固组织的影响，并进一步研究了脉冲磁场对硅钢元素分布、力学性能及热变形组织和性能的影响。研究结果表明，低压脉冲磁场能够显著细化硅钢凝固组织，提高等轴晶率。在优化的脉冲磁场作用参数下，能够使等轴晶尺寸从未施加脉冲磁场时的2.37mm细化至1.22mm，等轴晶比率从10%提高到100%。脉冲频率对脉冲磁场的作用效果影响很大，频率为5Hz时，对硅钢凝固组织的细化效果最好。随着脉冲磁场的延迟施加时间从10s增至160s，脉冲磁场的细化效果逐渐减弱，脉冲磁场的有效作用时间段为整个凝固过程的初期阶段。此外，施加低压脉冲磁场可以扩大硅钢的浇注温度工艺窗口，在较大的浇注温度范围内获得尺寸变化不大的细小完全等轴晶组织。硅钢铸坯的元素宏观偏析不严重，凝固过程中未施加和施加脉冲磁场时，Si、Mn、Al元素的宏观分布均较均匀，但Si元素在铸锭表层的含量略高，产生轻微的正偏析，但施加脉冲磁场后，Si、Mn、Al元素在晶内的分布较未施加脉冲磁场更均匀。施加脉冲磁场凝固硅钢的室温综合力学性能显著提高，屈服强度由未施加脉冲磁场时的331MPa提高到361MPa，提高了9.1%；抗拉强度由414MPa提高到484MPa，提高了16.9%；延伸率由19.2%提高到30.0%，提高了56.2%。未施加脉冲磁场所得试样热压缩变形后的组织中存在伸长的形变晶粒。施加脉冲磁场所得试样在一定的热压缩变形条件下可发生完全再结晶，组织细小均匀。多道次热轧实验表明，施加脉冲磁场所得凝固硅钢在热轧过程中更易发生再结晶，未施加脉冲磁场所得硅钢轧制过程中存在难以消除的形变晶粒"
其他摘要	"As an important functional metal material, silicon steel is widely used for electromotor cores, dynamotor cores and transformer cores. In order to obtain excellent electromagnetic properties, silicon steel is mainly used in the form of thin silicon steel sheet whose thickness is usually 0.5mm, even less to 0.02mm. A key point during producing silicon steel sheet is how to prevent the formation of corrugated-liked defects on the sheet surface, which will affect the laminated coefficient and magnetic properties. It is known that, due to the inadequate recrystallization, coarse columnar grains are difficult to refine during the hot rolling process. Therefore, the center of the hot-rolled plates exists coarse elongate grains, which will induce the formation of corrugated-liked defects in the following cold rolling process. In addition, the larger size difference between columnar grains and equiaxed grains in solidification structure is generally corresponding to the higher grain ununiformity in the cold-rolled structure, which will seriously influence the magnetic properties. Therefore, to avoid the formation of corrugated-liked defects and improve the structural ununiformity, it is necessary to control the solidification process to obtain higher ratio of equiaxed grains in original as-cast structure. In recent years, a series of investigations have proved that the low voltage pulsed magnetic field (LVPMF) is an effective method to refine the solidification structure of some metal materials, such as aluminum alloys, magnesium alloys and super alloys. In this article, the effects of the LVPMF parameters (frequency, exciting voltage and applying time) and casting conditions (pouring temperature and mold temperature) on the solidification structure of silicon steel is investigated. Moreover, the effects of LVPMF on the distribution of solute, mechanical properties and hot deformation behavior are also studied. The experimental results show that the fine solidification structure of silicon steel can be obtained by applying LVPMF. The average size of equiaxed grains can be refined from 2.37mm to 1.22mm, and the ratio of equiaxed grains in the as-cast structure is increased from 10% to 100%. The solidification structure of silicon steel is remarkable refined at the frequency of 5Hz and in range of exciting voltage 50V to 200V. With the delay of LVPMF imposed from 10s to 160s, the refinement effect of LVPMF is gradually weakened, which means that the refinement effect of LVPMF is more obvious in the early stage of the solidification process. Based on the LVPMF technique, the complete equiaxed grain structure is obtained under higher pouring temperature, which is beneficial to enlarge the casting temperature range of silicon streel. The macrosegregation of ingots is not serious both in the presence and absence of LVPMF, except the surface layer is slightly enriched in Si element, resulting in a slight positive segregation. It does not exist serious microsegregation in the grains solidified without LVPMF, but with the application of LVPMF, Si, Mn and Al elements distribute more uniform inside grains. The mechanical properties of silicon steel are significantly improved by applying LVPMF. The yield strength is increased by 9.1% from 331MPa to 361MPa; The tensile strength is increased by 16.9% from 414MPa to 484MPa; The elongation is increased by 56.2% from 19.2% to 30.0%. Strip-shaped grains are formed in the samples solidified without LVPMF after thermal compressing. The samples solidified with LVPMF can be fully recrystallized and form fine grains after certain thermal compressing condition. The multistage hot-rolled experiments show that the recrystallization occurs more easily in the silicon steel solidified with LVPMF, but there are strip-shaped grains in the silicon steel solidified without LVPMF which are hard to be eliminated."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64552
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	陶文哲. 低压脉冲磁场凝固硅钢的组织性能及热变形研究[D]. 北京. 中国科学院金属研究所,2012.