X70管线钢拉伸性能试验研究

对X70系列大口径厚壁天然气管道材料不同取样方式和取向的拉伸试样进行试验，结果表明：X70管线钢具有连续屈服特征，无明显的屈服平台，延伸率非常大。其力学性能呈现明显的各向异性，横向拉伸的屈服强度、抗拉强度及弹性模量均比纵向拉伸的高。试样的截面形状和尺寸对抗拉强度有一定的影响，对屈服强度影响很小。由于材料内部的片状缺陷引起的沿厚度方向强度降低和横向拉应力的作用，断裂时在板状试样短边中心出现分层开裂。因此，在进行结构设计和安全评定时应充分考虑X70管线钢特殊的力学性能。

Tensile Behavior of X70 Pipeline Steel

The tensile behavior of X70 pipeline steel was investigated experimentally by use of the tensile test pieces with different shapes and different orientations. It was found that X70 pipeline steel tensile characteristic is a continuous yielding, no obvious yield plateau but a large elongation. The mechanical behaviors of X70 pipeline steel vary with the change of orientation. The transverse strength and Young's modulus are the maximum. The yield strength and tensile strength are affected hardly by the test piece shape and size, but the elongations of specimens are very different for different shapes and sizes of test piece. There are delamination crack in the middle part of short side when the test piece ruptures because of the slice defect and out of plane stress in the plate. Therefore, X70 pipeline has not only the common characteristics of the general metals but also the special mechanics behavior. The special mechanics behavior of X70 pipeline steel must be taken into account during safe assessment of pipeline.