Intergranular corrosion in 1.4828 | X15CrNiSi20-12 | AISI 309 | S30900

This heat-resistant steel may have a maximum of 0.20% carbon. An assembly of plate and bar stock was welded; the carbon contents differed significantly, but were all within the specification. In the bar stock, there is a higher C content of 0.13%. In the HAZ, this has resulted in finely dispersed carbide precipitations along the grain boundaries. For carbide formation, Cr has diffused from the close range and is locally < 13% here, resulting in a severe corrosive attack. After welding, the assembly was pickled for slightly longer than usual; one could also say forgotten for 4 h. The corrosive attack is now more severe. The intergranular corrosive attack resulted in a 1/3 reduction in wall thickness. The sheet material with only 0.06% C, on the other hand, exhibited only a minor corrosive attack. The component was discarded. In the future, the customer will do without pickling altogether and has switched to brushing the weld seams.