Precipitates in microalloyed ultra-high strength weld metal studied by atom probe tomography

Abstract

Gas metal arc welding with metal-cored filler wires is frequently used to weld high strength steel constructions for lightweight and transportation applications. In the current study, microalloying is considered as strengthening concept for reaching the required mechanical properties by precipitation hardening. For this purpose, the typical microalloying elements Ti, Nb, V, and Al were added to the filler metal in a comparatively high amount (up to 0.5 m.%). All-weld metal samples with a yield strength of 1000 MPa and more were produced by gas metal arc welding. Laser-pulsed atom probe tomography was used to evaluate the potential of these elements to form clusters or precipitates and strengthen the weld metal. While Al and Nb did not form clusters, a strong tendency for clustering was found for V- and Ti-alloyed samples. The cluster size evolution and changes in chemical composition depending on the microalloying contents are discussed. Furthermore, the challenges arising from local alloying element enrichments and local differences in thermal history in the all-weld metal are addressed regarding sample preparation and data evaluation.