Retained austenite in multipass high-strength weld metal with a yield strength exceeding 1100 MPa

Retained austenite is an essential phase in various types of steel due to its ability to positively influence mechanical properties. However, in the research field of high-strength weld metals, it is typically considered only as part of martensite-austenite constituents. A detailed quantification of this metastable phase in different heat-affected zone regions and an assessment of its morphology is largely missing. To address this, the present study investigates the distribution and morphology of retained austenite in high-strength multipass all-weld metal with a yield strength exceeding 1100 MPa. A quantitative 2D phase map of retained austenite was generated using high-energy X-ray diffraction and Rietveld refinement. Regardless of the former microstructure, the highest retained austenite contents - up to 7.0 % - are observed in the intercritically reheated zones. These zones replicate the layer structure of the multipass all-weld metal and are surrounded by tempered regions containing less than 2.0 % retained austenite. Using transmission Kikuchi diffraction and electron backscatter diffraction, only minor amounts of stand-alone retained austenite were detected. Consequently, it is expected that the volume fractions of retained austenite may have been underestimated in many former research works about low-alloyed high-strength steels and weld metals.