Microstructure evolution and mechanical properties changes in the weld zone of a structural steel during low-cycle fatigue studied using instrumented indentation testing

Indentation for investigation of strain rate effect on mechanical properties in structural steel weld zone

“…It can be seen from this figure that both loading curvature and applied load of the indentation curves in the BM are lowest and these parameters are highest in the WM among three regions. This observation consists with the available results of indentation responses for the weld zone of other structural steels [3,6,22] and corresponds to the lowest hardness and yield strength in BM among three regions, respectively, which will be discussed below. While the hardness can be directly extracted from indentation curve P-h, the yield strength in the regions of the weld zone was determined using Eqs.…”

“…This trend is also From the applied load-depth curve of indentation test, the contact area Ac and maximum load P m can be easily measured and then the hardness was computed using Eq. (6). The calculated results are presented in Fig.…”

“…(7) and (8), in which an unknown parameter corresponding to the yielding part of the structural steel's σ-ε curve (α) needs to be pre-estimated for each region. The α value of each region is estimated using the results from the analysis of indentation FE simulation, which are detailed in previous works [3,6,22]. In present work, by applying such approach, the α values at each strain rate values for BM, HAZ, and WM regions were estimated and the yield strength in each region of the weld zone was extracted for certain strain rate level.…”

“…However, the welding joints are also considered as the weakest parts of structures [4]. The heating or cooling stages influence the microstructures in the weld zone, including the weld metal (WM) region, the heat-affected zone (HAZ), and base metal (BM) region near the weld due to the transformation of solid-state phases, leading to the change of material properties in the weld zone [5][6][7][8]. Thus, the properties in the local regions of weld joints need to be evaluated.…”

A comparative study on the cyclic plasticity and fatigue failure behavior of different subzones in CrNiMoV steel welded joint

“…For the advantages of high capacity and design manufacture flexibility, welded structures have been widely used in the areas of energy production, aerospace, navigation, bridge engineering, and so on. As the critical parts of a welded structure, welded joints always contains a heat affected zone (HAZ) sandwiched between the weld metal (WM) and base metal (BM) due to the thermal welding, which induces its heterogeneity in both the microstructure and mechanical properties [1,2]. Hence, welded joints are generally considered as the weak regions in the engineering structures.…”