Fe-6.5wt%Si合金中有序相的形成规律及其对力学性能的影响

发布时间：2018-03-20 21:08

本文选题：Fe-6.5wt%Si电工钢　切入点：有序相　出处：《北京科技大学》2015年博士论文　论文类型：学位论文

【摘要】：Fe-6.5wt%Si合金(又称高硅电工钢)具有高磁导率、高电阻率、低铁损和几乎为零的磁致伸缩系数等优异的软磁性能,对于提高电器效率、降低设备噪音以及节约能源等具有重要意义。但是该合金的室温脆性和低的加工性能严重制约了其在工业领域的应用。本课题组已经通过逐步增塑法成功制备出0.05-0.1min厚的冷轧薄板,那么进一步明确高硅钢的脆性本质,深入分析影响高硅钢塑性的因素,研究制备过程中逐步增塑机理便成为本论文的主要目标。本文系统研究了Fe-6.5wt%Si合金中有序无序转变过程及其对各种力学性能的影响,明确了高硅钢的脆性本质；在此基础上分析了冷却速度及形变过程对有序相的影响,为高硅钢塑性的改善提供了方法和思路；探索了有序相定量计算方法,研究了高硅钢整个制备过程中有序相的演变规律,为逐步增塑法制备高硅钢薄板提供了理论依据。得到的主要结论如下： (1)确定了Fe-6.5wt%Si合金有序无序转变温度,A2-B2和B2-D03的相转变温度分别为760℃和640℃。B2有序相是在A2无序相的基础上发生Fe和Si原子的近邻有序化而形成的,B2相的长大符合经典的晶粒长大的动力学公式；而D03有序相是在B2相的基础上,进一步发生Fe和Si原子的次近邻有序化而形成的。当DO3相长大到一定程度,畴内发生分解,沿100方向析出另一种Si原子占位的D03’有序相,从而形成了规则排列的条状衬度。 (2)在D03相区做有序化处理,会使Fe-6.5wt%Si合金的力学性能恶化。将无序化后的Fe-6.5wt%Si合金分别在不同相区(B2和D03相区)保温不同时间,得到不同有序相含量的合金。在B2相区保温过程中,流变应力没有明显的规律性,合金的显微硬度值基本保持稳定,且均表现出良好的塑性：而在D03相区保温过程中,显微硬度与流变应力在lh以内,随时间的延长呈上升趋势,超过lh之后,基本保持稳定,而且合金的塑性随着有序化时间的延长是逐渐变差的,且均为脆性解理断裂。 (3)热处理或制备过程中快的冷却速度,例如淬火、空冷和快速凝固,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,比如炉冷和普通浇铸,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。 (4)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。形变诱导无序化是超位错滑移的结果,合金的无序化是从滑移面上的反相畴界(APBs)开始的。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。 (5) Fe-6.5wt%Si合金在中温有序相区变形的过程中表现出显著的加工软化现象,其加工软化机制为形变诱导无序化和动态回复。在中温形变过程中,有序相的含量、尺寸及有序度不断降低：在形变后期产生了大量的位错胞和亚晶组织,发生了明显的动态回复,使位错密度大大降低,有效消除了部分加工硬化。两方面的作用使合金得到了有效的软化。 (6)尝试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,并给出了相应的计算公式。通过验证实验证明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。结果表明,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。
[Abstract]:Fe-6.5wt%Si alloy (also called high silicon electrical steel) has high permeability, high resistivity, soft magnetic properties of low iron loss and nearly zero magnetostriction coefficient of excellent, to improve electrical efficiency, is of great significance to reduce equipment noise and save energy. But the alloy brittleness at room temperature and low processing performance seriously its applications in the industrial field. The research group has passed gradually plasticizing process successfully prepared 0.05-0.1min thick cold rolled sheet, then to further clarify the nature of brittleness of high silicon steel, in-depth analysis of the impact factors of high silicon steel, study on preparation process of gradually plasticizing mechanism has become the main target of this thesis.
This paper studies the Fe-6.5wt%Si alloy orderdisorder transition process and its impact on the mechanical properties, the brittle nature of high silicon steel; on the basis of analysis of the influence of cooling rate and deformation phase of order, provides methods and ideas for the improvement of high silicon steel; to explore the quantitative calculation method of ordered phase on the whole, high silicon steel during the preparation of ordered phase evolution, gradually plasticizing preparation of high silicon steel sheet provides a theoretical basis. The main conclusions are as follows:
(1) determine the order disorder transition temperature of Fe-6.5wt%Si alloy, A2-B2 and B2-D03 phase transition temperature were 760 degrees and 640 degrees.B2 ordered phase is between Fe and Si atoms in A2 disordered phase based on nearest neighbor ordering and the formation and growth of B2 phase dynamics formula accord with the classic grain growth; and D03 ordered phase is in B2 phase on the basis of subneighbouring further Fe and Si atoms orderly formed. When DO3 grew up to a certain extent, in the domain decomposition, along the 100 direction precipitated another Si atom occupying the D03 ordered phase, thus forming a regular arrangement of strip contrast.
(2) do the ordering in the D03 phase, will deteriorate the mechanical properties of Fe-6.5wt%Si alloy. Fe-6.5wt%Si alloy disorder after respectively in different phase (B2 and D03 phase) for different holding time, different alloy ordered phase. In the insulation of B2 phase in the process of rheological stress the obvious regularity, the microhardness values remained stable, and showed a good plasticity: while in the D03 phase insulation process, the microhardness and the flow stress within LH, with time increased, more than LH, stable, and ductility of the alloy with the extension of the ordered time is gradually deteriorated, and are brittle cleavage fracture.
(3) heat treatment or preparation process of fast cooling speed, such as quenching, cooling and rapid solidification, can inhibit the D03 brittle phase formation, is conducive to the improvement of the mechanical properties of the alloy. In slow cooling conditions, such as furnace cooling and ordinary casting, D03 ordered phase fully formed and grew up orderly the degree and the ordered phase has a high content of.D03 ordered phase reduces the mobility of superdislocations, dislocation or easily gathered in the grain boundaries, and reacts to form dislocation network, further hampering the dislocation movement, easy to cause the stress concentration, resulting in the plasticity of the alloy decreases, easily lead to brittle transgranular fracture and intergranular fracture.
(4) the deformation process can be broken or B2 D03 ordered phase, decreasing ordered domain size, lower ordered phase content and degree of order, namely deformation induced disordering. Deformation induced disordering is super dislocation slip the disordered alloy from sliding on the surface of the antiphase boundary (APBs) began. A large number of super dislocation movement will gradually expand the disordered area, orderliness of alloys. When the alloy in high temperature disordered phase zone after deformation, high density dislocations will hinder the air cooling process of ordered phase formation, reduce the content of the ordered phase.
(5) showed a significant softening deformation process of ordered phase zone of Fe-6.5wt%Si alloy in the temperature of the softening mechanism induced by disordering and dynamic recovery deformation. In the process of warm deformation, the content of the ordered phase, the size and the degree of order decreased continuously produced a large number of dislocation cells and subgrains the organization has an obvious deformation stage, the dynamic recovery, the dislocation density is greatly reduced, effectively eliminating the part of work hardening. The two aspects of the role of the alloy has been effectively softening.
(6) try to use the electron diffraction integral intensity of ordered phases in Fe-6.5wt%Si alloy were quantitatively calculated, and the corresponding formulas are given. Experimental results indicate the rationality and feasibility of this method. The quantitative analysis of the ordered phase change by electron diffraction integral intensity quantitative method of Fe-6.5wt%Si alloy in the preparation process. The results show that the alloy casting - forging and hot rolling temperature and cold rolling process, the content of ordered phase is reduced gradually, gradually plasticizing preparation of high silicon steel sheet provides a theoretical basis.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1

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