高强硼钢高温软化机制及动态再结晶临界条件

Softening mechanism and critical conditions of dynamic recrystallization for a high strength boron steel

采用Gleeble-1500热模拟压缩试验获得了高强硼钢在880~1000℃、0.01~10 s-1、最大变形55%条件下的真应力-真应变曲线,通过对试验数据的处理和分析,研究了高强硼钢在试验条件下的软化机制及动态再结晶临界条件。结果表明：利用真应力-真应变曲线来判断高强硼钢的软化机制存在宏观判断误区,通过分析θ-σ曲线和晶粒金相可以发现,高强硼钢在本文变形条件下均可以发生动态再结晶;通过lnθ-ε曲线拐点及-（lnθ）/ε-ε曲线最小值判据可以确定高强硼钢动态再结晶临界应变,进而通过σ-ε曲线可以获得临界应力;随变形温度降低或应变速率提高,动态再结晶临界应力或应变值随之提高,且临界应力/应变与峰值应力/应变之间存在如下关系：σc=0.92σp,εc=0.57εp;临界应力/应变与变形条件的关系分别为：σc=17.4048ln Z-450.2409,εc=0.0195ln Z-0.4710。

True stress and true strain curves of a high strength boron steel（ HSBS） were obtained under the conditions of the temperature ranging from 880 to 1000 ℃,the strain rate ranging from 0. 01 to 10 s- 1,and the maximum deformation of 55% by high temperature compression test on a Gleeble-1500 thermal simulator. The softening mechanism and critical conditions of dynamic recrystallization（ DRX） for the HSBS under experimental deformation conditions were investigated by means of the processing and analysis of the test data.The results show that there are misunderstandings when determining the softening mechanism for the HSBS using true stress and true strain curves. It is evident from the strain hardening rate and true stress（ θ- σ） curves and metallographic observation that some level of DRX has occurred under all deformation conditions in this work. Critical strains of DRX can be determined using the knee of lnθ- ε curves and the minimum of- （ lnθ） / ε- ε curves. Furthermore,critical stresses can be obtained using critical strains and σ- ε curves. It turns out that critical stress or strain increases with the reducing of deformation temperature or the rising of strain rate. The relationship between the critical and peak stresses and strains can be expressed by σc= 0. 92σp,εc= 0. 57εp. Meanwhile,the relationship of critical stress and strain with deformation conditions can be expressed by σc= 17. 4048 ln Z- 450. 2409,and εc= 0. 0195 ln Z- 0. 4710,respectively.