6.5wt%高硅钢塑性改善机制及薄带轧制基础

High silicon steel containing 6.5wt%Si is very suitable to be used in high-speed electric machines, audio-frequency transformers, as it exhibits ultra-low iron loss and near zero magnetostriction, which is significant for reducing energy losses and vibration noises. However, high silicon steel is too hard and brittle to be fabricated by conventional rolling method, which hinders its industrial fabrication by strip cold rolling all over the world. The brittleness lies on the fact that the various ordered structures appearing in this alloy are brittle in nature and are hard to be deformed. Quantitative characterization of these ordered phases or the so called degree of order is absence, without which it is hard to control these ordered phases effectively and accurately. This project focuses on the brittleness nature and toughening mechanism of high silicon steel. On the one hand, based on the fundamental research on characterization the type of the ordered structures in this alloy, the contents of the ordered structures are quantified. Type and content of the ordered structure is modified by means of micro-alloying, heat treatment, plastic deformation, et al. Relationship between modification of ordered structures and mechanical properties is established, and then the toughening mechanism is elucidated. On the other hand, based on the microstructure evolution during hot deformation and the regularity and rule of edge cracking, relationship between multiscale stress and micro-crack is established. By modifying the stress restricting condition, mechanism for the appearance of edge cracking is illuminated and the edge cracks are eliminated. Combined with the ductility improvement of the strip stock and elimination of edge cracking, integrity of strip-rolling can be guaranteed, which lay the foundation for successive and efficient fabrication of strip-rolling of high silicon steel.

含硅6.5wt%高硅钢具有超低铁损和接近于零的磁致伸缩，是高速电机、音频高频变压器铁芯的理想软磁材料，对提高电器效率、节能降噪意义重大。然而高硅钢室温下硬且脆，难以轧制成形，目前世界范围内尚未实现薄带的连续化冷轧。究其原因，是高硅钢中出现的有序结构形态复杂、具有本征脆性，目前缺乏对有序结构的定量表征及有效精确控制。本项目着眼于高硅钢的脆性机理和塑性改善机制，一方面，在前期有序结构存在类型的研究基础上，对有序结构含量或有序度进行定量表征，利用微合金化、热处理、塑性加工等方法对有序结构类型及含量进行有效调控，建立“有序结构类型及含量-有序结构调控方法-力学性能”之间的关系，阐明高硅钢塑性改善机制。另一方面，通过研究热加工过程中组织演变及裂纹形成规律，建立多尺度应力和裂纹的关联性，通过改善应力约束条件抑制边部裂纹产生。二者结合，提高基体塑性变形能力、抑制边部裂纹产生，为连续成卷轧制薄带奠定基础。

Fe-6.5wt%Si高硅钢室温下硬且脆，难以轧制成形，目前世界范围内尚未实现薄带的连续化冷轧。究其原因，是高硅钢中出现的有序结构形态复杂、具有本征脆性，目前缺乏对有序结构的定量表征及有效精确控制。本项目以高硅钢增塑增韧为目的，主要研究高硅钢的塑性改善机制，以及冷轧边裂的产生机制及抑制方法，为高硅钢连续带材室温轧制提供理论依据和改善方法。取得的成果如下：.（1）利用电子衍射积分强度对Fe-6.5wt%Si合金中的有序相进行定量计算，并验证了该方法的合理性和可行性。利用电子衍射积分强度定量法对Fe-6.5wt%Si合金整个制备加工过程中有序相的变化做定量分析，表明在合金的铸造-锻造-热轧-温轧-冷轧过程中，有序相的含量是逐渐降低的，为逐步增塑法制备高硅钢薄板提供了理论依据。.（2）热处理或制备过程中快的冷却速度，可以抑制D03脆性有序相的形成，有利于提高合金的力学性能。而在慢冷条件下，D03有序相充分形成并长大，有序化程度和有序相含量均很高。D03有序相的存在降低了超位错的可动性，位错容易在晶内或者晶界处聚集，并发生反应形成位错网络，从而进一步阻碍了位错的运动，容易引起应力集中，导致合金塑性降低，容易引起脆性穿晶断裂或沿晶断裂。.（3）形变过程可以破碎B2或D03有序相，不断减小有序畴尺寸，降低有序相含量及有序度，即发生形变诱导无序化。大量超位错的运动会逐渐扩大无序化面积，降低合金有序度。当合金在高温无序相区经过形变后，高密度位错缺陷的存在将会阻碍空冷过程中有序相的形成，降低有序相的含量。.（4）采用激光焊接的方法在高硅钢薄板两边焊接上塑性较好的材料，高硅钢位于中心、塑性材料位于边部。轧制过程中高硅钢与边部材料协同变形，可有效减少边部开裂，为带张力连续冷轧顺利实施探寻新工艺。.（5）利用快速凝固甩带法成功制备出连续的Fe-6.5wt.%Si高硅钢薄带，平均晶粒尺寸2.4μm，具有一定的室温塑性。经过850℃热处理后，随着晶粒的长大，直流性能提高，铁损降低。