用正电子寿命法研究深冲钢板不同变形路径中的微观缺陷

本文应用正电子寿命法研究了深冲钢板在单向拉伸、平面应变和等双向拉伸变形过程中的位错和微空洞增长机制。结果表明,深冲钢板的宏观失稳及成形极限与板材内部的微观缺陷的产生及发展密切相关;当变形路径不同时,缺陷的增长速率不同;当应变量小于0.2～0.35时,材料内的微观缺陷以位错增长机制为主,且平面应变的缺陷增长速率最大,当应变量大于0.2～0.35时,微空洞的形核及增长速率加快,对板材集中失稳起到促进作用。

A STUDY OF MICRO-DEFECTS IN DEEP DRAWING SHEET STEEL UNDER DIFFERENT FORMING PATHS BY USING POSITRON LIFETIME METHOD

The increase mechanism of dislocation and micro-voids in deep drawing sheet steel during forming paths of uniaxial tension, plane strain and equal biaxial stretch was studied by using positron annihilation lifetime method. The results indicated that the instability and forming limit of deep drawing sheet steel are affected by micro-defects in sheet steel. The rate of defect increase is different for different forming path. When strain is less than 0.2-0.35, the mechanism of dislocation increase plays a main role in the formation of micro-defects in the materials. Among the three forming paths the rate of micro-defect increase in plane strain path is the largest. When strain is higher than 0.2-0.35 the nucleation and the rate of micro-void increase will be accelerated, promoting the local instability of sheet steel.