Effect of the welding technique and post-welding heat treatments on the microstructure and mechanical properties of a high silicon nanostructured carbide-free bainitic steel
Mattia Franceschi, Edoardo Bregolin, Alvise Miotti Bettanini, Luca Pasqualini, Simone Campagnolo, A. Zambon, Luca Pezzato, Manuele Dabalà
Abstract
Recently carbide free bainitic steels, with microstructure consisting in nanoscaled bainitic ferrite plates and high carbon-enriched austenite, have been developed. These steels have found commercial use in manufacturing engineering components, nevertheless, their high carbon concentration poses a limitation as they cannot be welded, restricting their potential applications, therefore the actual research has shifted to the investigation to medium carbon steels. In this work, Butt weld – V groove weldment have been realized with a novel medium carbon high silicon carbide-free bainitic steel by means GMAW and GTAW. Optical microscopy, scanning and transmission electron microscopy and X-ray diffraction were used to characterize the microstructures of both the fusion and heat affected zone. Dilatometry was utilized to study the phase transformations during post-welding heat treatment. Tensile and micro-hardness tests were carried out to evaluate the mechanical properties in the as-weld state after post-welding heat treatment. The analysis shows the possibility to obtain high strength weldments with high integrity and high strength (>1 GPa) coupled with reasonable ductility and the absence of cold or hot cracking phenomena.