带状组织对微合金钢应变局部化及应变强化行为的影响

Effect of Banded Microstructure on Strain Localization and Strain Hardening Behaviors of Microalloyed Steel

目的研究不同加载方向下带状结构对微合金钢塑性变形及应变强化行为的影响。方法将X80管线钢加热到1200℃后分别进行炉冷和空冷热处理,得到多边形铁素体/退化珠光体和粗/细铁素体晶粒带状组织以用于实验研究。将单轴微拉伸实验和数字图像相关方法相结合,通过零变形实验分析系统精度,获取RD、45°和TD取向带状组织试样的拉伸变形规律。同时,在DIC全场变形测量结果与实验数据统计分析结果的基础上,提出了可描述应变强化程度的参量K_(f),用于对比和分析不同加载方向下带状结构对应变强化行为的影响。结果零变形实验中位移平均值和标准差的最大值分别为0.004 pixels和0.006 pixels,系统精度较高。加载方向会影响带状组织的塑性变形演化情况,45°试样中产生了明显与带状取向一致的应变分布特征。在相同应力下45°试样首先达到了较大的应变强化程度,其抗变形能力最低。结论不均匀带状组织对局部变形的影响程度与2个组成带的力学性能差异有直接联系,参量K_(f)可在一定程度上描述应变局部化引起的各向异性特征。

The work aims to study the effect of banded microstructure on plastic deformation and strain hardening behaviors of microalloyed steel under different loading directions.Firstly,in order to obtain different types of banded microstructures of polygonal ferrite/degenerated pearlite and coarse/fine ferrite grains for experiment,the X80 pipeline steel was heated to 1200℃and then subject to furnace cooling and air cooling,respectively.By combining the uniaxial tensile test and digital image correlation(DIC)method,the tensile deformation of RD,45°and TD banded microstructure specimens was obtained after a zero-deformation experiment.Meanwhile,on the basis of full-field deformation and statistical analysis of experimental data,a parameter K_(f)was proposed to describe the evolution of strain hardening.The maximum absolute values of mean values and standard deviation in zero-deformation experiment were less than 0.004 and 0.006 pixels respectively,implying a higher system precision.The tensile results indicated that the plastic deformation evolution of the banded microstructure was affected by the loading direction.The strain distribution in 45°specimen was obviously consistent with the banding direction,which was the first to reach a greater degree of strain hardening under the same stress and had the least resistance to deformation.The degree of the uneven banded microstructure on the local deformation is directly related to the difference in mechanical properties of the two adjacent bands.K_(f)can be used to compare the anisotropy caused by strain localization.