低碳软钢拉伸变形中的微空洞

MICROVOIDS IN LOW CARBON SOFTEN STEEL SUBJECTED TO TENSILE DEFORMATION

钢的延性断裂主要是由于变形过程中微空洞的形成,长大和聚合引起的。本文用定量金相方法测定了球化20钢制光滑与轴对称缺口试样在拉伸变形中微空洞的体积分数和面密度,并结合声发射实验,确定了20钢中形成一级、二级微空洞所需要的临界应变量,得到了微空洞数量与三轴应力、等效塑性应变的关系,讨论了Rice-Tracey关于空洞长大速率公式与突验结果的差异,并指出,钢中二级微空洞的萌生,使钢的弹性模量急剧下降,使钢的低周应变疲劳循环特性发生变化。

The ductile fracture of low carbon steel has been observed to be the result of formation, growth and coalescence of microvoids.Tensile tests on smooth and axisymmetrically notched specimens of spherodized steel of 0.2% carbon content were carried out and interruped at various strain,thus a series of volume percentages of voids and the number of voids per unit area were measured by method of quantitative metallography.Combining with the acoustic emission experiment, the amount of critical strain for primary and secondary voids initiation were determined respectively, and the relation among the parameters of haractcrizing voids,triaxial stress and effective plastic strain was obtained.The difference between the void growth rate equation proposed by Rice—Tracey and the practical result obtained by the author of this paper was also discussed. Moreover,the formation of secondary voids makes the elastic modulus of the steel descend rapidly and low—cycle strain fatigue character of the steel change obviously.