Characterization of the Weld Regions within Duplex Stainless Steels using Magnetic Force Microscopy

Abstract

Standard metallography and optical microscopy are well established techniques for the characterization of duplex stainless steels (DSS), which consist of approximately 50% ferrite and 50% austenite. Recently, the use of atomic and magnetic force microscopies (AFM and MFM respectively) have been employed to differentiate between magnetic and non magnetic phases in materials. Such techniques would be valuable to identify different phases in duplex stainless steels, particularly the weld regions, and would thus compliment standard metallographic and optical microscopy techniques. In particular, AFM and MFM would be particularly valuable for identification of phases within the different weld regions (root, fill and cap). In the present study, Gas Tungsten Arc Welded (GTAW) DSS samples, as a function of heat input and weld configuration, were subject to standard metallographic practices (ferrite content determination, Vickers hardness measurements, Charpy impact studies and transverse tensile testing) in addition to MFM analysis. The metallographic tests revealed that the weld properties were acceptable in accordance with current industrial standards. The MFM results of the weld metal shows the formation of both a finer and coarse structure within the weld metal, which is dependent on the level of undercooling.