Using the instrumented indentation technique for stress characterization of friction stir-welded API X80 steel

An instrumented indentation technique (IIT) appears to be a promising alternative to conventional stress measurement methods, particularly for welds with rapid microstructural gradients, because it has high spatial resolution and is non-destructive. The technique is used to characterize the residual stress of a friction stir-welded joint of API X80 steel. The indentation load - depth curve is significantly affected by the presence of residual stress and the stress-induced load change at a given penetration is converted to a quantitative stress value through an analytical model. All indentation test results show good agreement with those from an energy-dispersive X-ray diffraction performed to assess the validity of the IIT. In addition, the microstructures in various regions of the friction stir-welded joint and their effects on local microhardness are discussed.close111