Effect of aging on the microstructure and toughness of the interface zone of a gas tungsten arc (GTA) synthesized Fe-Cr-Si-Mo-C coated low carbon steel

Fe-Cr-Si-Mo-C alloy coatings have been developed by gas tungsten arc (GTA) processing on a low-carbon steel substrate. Depending on the processing parameters, either hypoeutectic or hypereutectic microstructures were formed, and at the interface martensitic, and martensite + pearlitic structures were obtained. In the interface between coated surface and alloy, the toughness was lower than coated surface and parent metal. To increase the toughness of the interface, aging processes were performed. The aging processing (480-550 °C) resulted in an increase in toughness of the interface between coated surface and the alloy. This behavior is related to a peak-hardening shift, M₂C carbide coarsening. In addition the increased aging kinetics caused a faster dissolution of Fe₃C and rapid changes in Cr partitioning in the (Mo,Cr)₂C carbide resulting in a coherency loss. The kinetics of the secondary hardening reaction in the interface of the coating was determined by an electrical resistivity method for changes in aging parameters (time/temperature).