Low alloy ferritic steels are widely used to manufacture critical components that operating at elevated temperatures in the process industry, but a better understanding of the creep responses of their weldments are still needed to provide guidance for the design of high-temperature welded structures. In the present paper, the heterogeneous creep behavior of vanadium-modified 2.25Cr1Mo ferritic steel weldments was investigated by using the digital image correlation (DIC) technique. Three-dimensional plot of creep strain across the weld joint was constructed to intuitively represent the spatio-temporal evolution of creep strain for the base metal (BM), weld metal (WM) and the heat affected zone (HAZ). Combining the analysis of strain contour evolution during creep with the microstructural examination, it is found that creep strain was primarily concentrated in the HAZ, resulting in the creep cavitation at grain boundaries of the coarse-grain bainitic HAZ. In addition, BM exhibited a faster deformation rate than WM during creep. In order to quantitatively describe the heterogeneous creep deformation, a sub-region extensometer method based on the construction of virtual extensometers was proposed to obtain the representative creep strain data of individual regions of weldments. Furthermore, a parameter identification procedure combining a global optimization method (i.e. genetic algorithm) with an initial value determination scheme, was developed to determine the model parameters of BM, WM and HAZ for the hyperbolic-sine creep constitutive model. The results show that the heterogenous creep behavior of the V-mod 2.25Cr1Mo steel weldment can be well characterized by combining the sub-region extensometer method, the hyperbolic-sine creep constitutive model and its genetic algorithm-based parameter identification method.

低合金铁素体钢在加工行业中广泛用于制造在高温下工作的关键部件，但是仍需要对它们的焊件的蠕变响应有更好的了解，以为高温焊接结构的设计提供指导。本文利用数字图像相关技术研究了钒改性的2.25Cr1Mo铁素体钢焊接件的非均质蠕变行为。构造了整个焊接接头的蠕变应变的三维图，以直观地表示基础金属（BM），焊缝金属（WM）和热影响区（HAZ）的蠕变应变的时空演变。将蠕变过程中的应变轮廓演化分析与微观结构检查相结合，发现蠕变应变主要集中在热影响区中，导致在粗晶粒贝氏体热影响区的晶界处发生蠕变空化。此外，在蠕变过程中，BM的变形速率比WM快。为了定量描述异质蠕变变形，提出了一种基于虚拟引伸计构造的子区域引伸计方法，以获取焊件各个区域的代表性蠕变应变数据。此外，开发了结合全局优化方法（即遗传算法）和初始值确定方案的参数识别程序，以确定双曲正弦蠕变本构模型的BM，WM和HAZ的模型参数。结果表明，V-mod 2的异质蠕变行为。