For QSTE700 high-strength steel rectangular welded tube, the mechanical properties of the weld zone vary with the distance from the centerline of the weld. Therefore, the accurate description of constitutive relationship of the weld zone is of great significance for the study of formability of QSTE700 rectangular welded tube. Firstly, the mechanical properties of parent and mixed specimens containing weld zone and parent zone were obtained by uniaxial tensile test. And based on the microhardness test, the width and the microhardness distribution of the weld zone were determined. Secondly, by subdividing the weld zone into several small areas, and combining with the rule of mixtures and nanoindentation test, the continuous functional relationships of strength coefficient K, hardening coeffecient n and elastic modulus E were obtained, and then, the continuous constitutive relationship of QSTE700 rectangular welded tube was established. Finally, the validity and reliability of the continuous constitutive relationship of welded tube were verified by nanoindentation test and rotary draw bending of rectangular welded tube. Besides, it was found that the finite element model of rotary draw bending of QSTE700 rectangular welded tube established by using the continuous constitutive relationship can well simulate the cross section deformation and wall thickness variation.

对于QSTE700高强度钢矩形焊管，焊接区的机械性能会随着距焊缝中心线的距离而变化。因此，准确描述焊缝本构关系对研究QSTE700矩形焊管的可成形性具有重要意义。首先，通过单轴拉伸试验获得了包含焊接区和母体区的母体和混合试样的力学性能。并根据显微硬度测试，确定了焊接区的宽度和显微硬度分布。其次，通过将焊接区划分为几个小区域，并结合混合规则和纳米压痕试验，得出强度系数K，硬化系数n的连续函数关系。得到弹性模量E，然后建立QSTE700矩形焊管的连续本构关系。最后，通过纳米压痕试验和矩形焊管的旋转拉伸，验证了焊管连续本构关系的有效性和可靠性。此外，发现利用连续本构关系建立的QSTE700矩形焊管旋转拉伸弯曲的有限元模型可以很好地模拟截面变形和壁厚变化。