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高碳淬火钢难以在室温下发生塑性变形,人们曾将此现象归因于成分(碳含量过高)和组织(马氏体塑性差),未考虑几何尺寸的影响.为此,本研究在室温下对厚度为400?m的9Si Cr淬火马氏体钢进行微轧制实验,发现微轧制下实验钢的塑性良好,延展率达200%以上,且硬度比淬火态提高了39%.本文对此新发现进行了研究.首先,负辊缝轧制使横向压应力增大,同时由于单位体积的接触表面积变大,而引起纵向压应力和垂直方向压应力同时增大,因而静水压力增加.这些因素有利于抑制轧件边裂、头部劈裂以及轧件内部缺陷生成和扩展,致使塑性改善.这一现象可以用传统理论进行解释,属于第一类尺度效应.其次,由于位错和孔洞一旦到达试样表面就会释放和消失,所以轧件的比表面积越大对提高塑性越有利.因此,比表面积充分大的薄轧件已不能视为均匀连续、各向同性的理想材料,其表面效应属于第二类尺度效应.实验结果表明:长期以来认为高碳马氏体组织塑性差的认识在薄轧件轧制中受到挑战,需要同时考虑两种尺度效应,才能深入认识其力学表现和物理本质.
High-carbon quenched steels are hard to be plastically deformed at room temperature and this phenomenon has been attributed to the composition (high carbon content) and microstructure (poor martensite ductility), without considering the influence of geometrical dimensions.Therefore, At room temperature, the microstructure of 9Si Cr quenched martensitic steel with a thickness of 400? M was studied. The results show that the ductility of the experimental steel under micro-rolling is good, the elongation is over 200% and the hardness is 39% higher than the quenched state. In this paper, the new discoveries are studied.First, the negative rolling seam increases the transverse compressive stress, and at the same time, the vertical compressive stress and the vertical compressive stress increase at the same time as the contact surface area per unit volume increases, Increase.These factors are conducive to the suppression of rolling edge splitting, head splitting and rolling defects within the production and expansion, resulting in plasticity.This phenomenon can be used to explain the traditional theory, belong to the first kind of scale effect.Secondly, as bit Therefore, the larger the specific surface area of the rolled part is, the better it is to improve the plasticity. Therefore, a thin rolled material with a sufficiently large specific surface area can not be regarded as an ideal of uniform continuous and isotropic Material, it The surface effect belongs to the second type of scale effect.The experimental results show that the recognition of the poor plasticity of high-carbon martensite has long been challenged in the thin-rolled rolling and the two kinds of scale effects need to be considered at the same time to understand the mechanical behavior And physical essence.