Ferritic stainless steels are widely used in transportation industry due to their exceptional performance regarding mechanical and corrosion properties. However, after a welding process, joints feature the sensitizing phenomenon because of the heat exchange from the torch affecting mechanical properties and corrosion resistance. This work describes the behavior firstly of mechanical properties of weld joints of ferritic stainless steel as base material without and with filler material (AISI 308L) by gas tungsten arc welding (GTAW). Operating parameters such as arc voltage, welding currrent, welding speed, feed speed, shielding gas flow were evaluated. Secondly, samples of weld joints were coated by flame spraying of composite particles in order to reduce the weight loss induced by corrosion in a salt spray (fog) apparatus. Changes induced from GTAW on the heat affected zone and Thermal Spraying on corrosion resistance, were monitored by optical and scanning electron microscopy, microhardness and longitudinal tensile testing. Results show that GTAW helps to control the size and the microstructure of heat affected zone improving simultaneously the mechanical properties. Meanwhile, welded joints covered by composite coatings feature a lower damage provided that the ceramic phase has been homogeneously dispersed.

A protective coating was built and assessed in order to reduce the degradation of metallic substrates caused by corrosion damage. Hence, a set of coatings with different configurations, in terms of layer arrangement, was produced by flame-spraying of composite powder (AISI 316L stainless steel coated with an α-alumina layer) onto an AISI 1018 steel substrate. In order to ensure a homogeneous dispersion of phases, a correlation was established between the operating parameters of thermal spraying (roughness and surface temperature of substrate, spraying distance, passing speed) and the splat formation. Then, corrosion damage caused in the coated samples by exposure to a salt spray was monitored through weight measurements and observations with optical and scanning electron microscopy. The results show that corrosion still remains in all cases; however, it proceeds at lower rates for coatings made with composite particles plus an α-alumina layer. The weight loss due to corrosion damage was reduced in approximately 94% as compared with the substrate without protection. Coating adhesion was also improved by an increased substrate roughness, with no need for an intermediate layer.