Phase quantification in a duplex stainless steel welds using NDT techniques

Duplex stainless steels are composed of ferrite and austenite in equal volume fractions of these phases, which provides an excellent combination of mechanical properties and corrosion resistance, especially when compared with conventional stainless steel grades. When these steels are welded, there are significant changes in the austenite-to-ferrite ratio therefore in their final properties. Nowadays, the ferritoscope is the unique non-destructive technique used to quantify these two phases content in situ. This tester instrument is limited to the evaluation of large areas, is not suitable for the heat affected zone and is also very sensitive to the surface finish, being considered an intermediate precision technique. So, it is necessary to develop more reliable field techniques. In this research, thermoelectric power measurements and induced current techniques are proposed to evaluate the phase quantification in S32205 welds. According to the results, both techniques are reliable and highly sensitive to phase changes in the weld bead, heat affected zone and base metal. For the thermoelectric power technique, a probe with nickel tip should be used to obtain the highest sensitivity and for the induced current technique, a probe type-pencil with a central frequency of 6 MHz should be used.