Effect of grain boundary structure on weld decay of austenitic stainless steel (part 1). Grain boundary structure and intergranular corrosion in a type 304 stainless steel weld heat affected zone

Grain boundary carbide precipitation and corrosion in weld heat affected zone of a type 304 austenitic stainless steel were investigated using optical and scanning electron microscopy to discuss effects of grain boundary structure on precipitation and corrosion from a crystallographic viewpoint. In the grain boundary precipitation region, the frequency of grain boundary carbide precipitation had a maximum near the coarse grained region and decreased gradually with the distance from there to the unaffected base metal region. The frequency increased with weld heat input. Strauss test of 304 steel HAZ showed that all the cracked grain boundaries after bend test had carbide precipitates and that the frequency of cracked boundary was roughly proportional to the frequency of grain boundary precipitation. Electron channelling pattern analyses in scanning electron microscopy showed that grain boundaries with ordered atomic structures were hardly etched after 10% oxalic acid etching test. These facts have suggested that grain boundary precipitation and corrosion in stainless steel weld heat affected zone depend sensitively on crystallographic character of grain boundary.