多边形铁素体含量对X60、X70管线钢DWTT断口纤维率的影响

Effect of polygonal ferrite on shear-area percentage of DWTT fracture of pipeline steels X60 and X70

以X60和X70管线钢为研究对象,研究了管线钢中显微组织与断裂韧性之间的关系。结果表明,多边形铁素体对管线钢既有增韧性又有减韧性作用:当钢中分布细小的多边形铁素体晶粒时,多边形铁素体迫使裂纹分叉、弯曲和转向,导致裂纹的扩展功提高,增加了管线钢的韧性,而且随多边形铁素体含量增多,落锤撕裂试验断口纤维率也随之提高。然而,当多边形铁素体晶粒粗大且以绝对多的数量分布在基体中时,其增韧性作用消失。

Relationship between microstructure and fracuture toughness was investigated for pipeline steels X60 and X70. The results indicate that polygonal ferrite not only plays a role in increasing toughness of the pipeline steels, but also plays a role in reducing the toughness depending on the amount and distribution of the polygonal ferrite. When the fine polygonal ferrite grains in small amounts are distributed in the matrix mainly composed of granular bainite, they can lead to the bifurcation of crack to zigzag propagation. Hence, both the crack propagation energy and the ductility of pipeline steel increase, moreover, the shear-area percentage of DWTT fracture increases with the increasing polygonal ferrite amount. However, when the polygonal ferrite grains become coarser and largely distribute in the matrix, its role in increasing toughness disappears.