多边形铁素体的体积分数和大小对管线钢落锤撕裂性能的影响

Effect of the Volume Fraction and Grain Size of Polygonal Ferrite on the Fracture Properties of Drop Weight Tear Test of Pipeline Steel

在天然气管线脆性断裂止裂的研究中,由于落锤撕裂试验(Drop weight tear test,DWTT)采用了全板厚试样,其试验状态接近管道在实际情况下的应力应变状态,能充分显示管材断裂的真实状况及其止裂能力,所以,DWTT已经成为评价管线钢脆性断裂止裂能力的重要方法,并以试样的断口纤维率(Shear-area percentage,SA)大小作为衡量标准。在不同的工业生产条件下轧制X70管线钢,并对它们进行落锤撕裂试验、疲劳试验、拉伸试验及冲击试验,探讨X70管线钢显微组织中多边形铁素体体积分数和大小对DWTT断口纤维率的影响。研究结果表明,当多边形铁素体作为第二相存在时,断口纤维率随着多边形铁素体体积分数的增加呈现出先上升后下降的特点;当多边形铁素体作为主要基体组织存在时,断口纤维率主要受多边形铁素体晶粒大小的影响,并且晶粒越细断口纤维率越高。

In the study on the brittle fracture arrest of natural gas pipeline,the shear-area percentage（SA） of fracture is regarded as an important measurement parameter in drop weight tear test（DWTT） which is used to evaluate the ability of brittle fracture arrest of pipeline steel,can accurately reflect the actual stress-strain state of pipeline,and show the true state of fracture and the ability to prevent fracture.X70 pipeline steels are hot rolled under different conditions of industrial production,and then the drop weight tear test,fatigue test,tensile test and impact test are carried out.Effect of the volume fraction and grain size of polygonal ferrite on the SA of DWTT fracture of X70 pipeline steel is investigated.Results indicate that the SA of fracture increases and then decreases with the increase of polygonal ferrite volume fraction when the polygonal ferrite exists as a second phase;and it is mainly affected by polygonal ferrite grain size when the polygonal ferrite exists as main matrix microstructure,and the shear-area percentage increases with the finer of the grain.