This paper presents an example of grain boundary engineering (GBE) for improving intergranular-corrosion and weld-decay resistance of austenitic stainless steel. Transmission and scanning electron microscope (TEM and SEM) observations demonstrated that coincidence site lattice (CSL) boundaries possess strong resistance to intergranular precipitation and corrosion in weld decay region of a type 304 austenitic stainless steel weldment. A thermomechanical treatment for GBE was tried for improvement of intergranular corrosion resistance of the 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of CSL boundaries indicated a maximum at the small roll-reduction. The corrosion rate was much smaller in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface. The optimized 304 stainless steel showed an excellent resistance to weld decay during arc welding. (C) 2005 Springer Science + Business Media, Inc.