Characteristics of microstructural phases relevant to the mechanical properties in structural steel weld zone studied by using indentation

The volume fraction (f) and properties of microstructural phases, the mechanical properties in the weld zone, and their relevance of commonly used steel, SM520, were investigated by using instrumented indentation. The volume fraction and properties of microstructural phases in fusion zone (weld metal -WM), heat-affected zone (HAZ), and base metal (BM) of the weld zone were identified by applying the statistical analysis for observed frequency density of hardness (H), elastic modulus (E), and yield strength (σy) spectra from nano-indentation tests. The mechanical properties distributed across the weld zone were determined from the micro-indentation tests. Two different stiffness ferrite types can be characterized in each individual weld zone from the analysis of H and E results, while two different strength ferrite types can be identified in WM from the analysis of the σy spectrum obtained from nano-indentations. The results from micro-indentations exhibited that the E, H, σy, and n values in the HAZ decrease in the direction from WM to BM region and all the average values of E, H, σy, and n in HAZ are higher than those in BM. The relevance of f, E, H, and σy of microstructural phases and E, H, and σy in the weld zone and was also discussed.