Enhancing intergranular corrosion resistance of industrial-scale QN1803 high-nitrogen austenitic stainless steel via grain boundary engineering

In the present study, grain boundary engineering (GBE), consisting of a 6% cold-rolling reduction followed by annealing at 1120 °C, was applied to industrial-scale QN1803 high-nitrogen, low-nickel austenitic stainless steel (ASS) plates to improve their intergranular corrosion (IGC) resistance. Electron backscatter diffraction analysis showed that the GBE treatment significantly optimized the grain boundary character distribution, increasing the fraction of low-Σ CSL boundaries from 32.23% to 66.51%–71.49%. Notably, coherent twin boundaries (CTBs) reached 52.70%–59.90%, accounting for 92.1%–96.5% of the total twin-boundary length. Meanwhile, the frequency of triple junctions containing two twin boundaries (mostly CTBs) increased from 2.86% to 19.61%–26.67%, which was associated with a marked reduction in the connectivity of the grain-boundary network composed of IGC-susceptible boundaries. Accordingly, immersion IGC tests showed that the corrosion mass loss and corrosion rate of the GBE-treated specimens decreased by about 60% compared with those of the as-received plate. The reactivation ratio also decreased from 35.38% to 12.31%–14.63%, indicating a substantially reduced degree of sensitization. Under the present same-gauge engineering comparison condition, in which the GBE-treated QN1803 ASS also exhibited overall superior room-temperature tensile properties to 304 ASS, the GBE-treated QN1803 ASS showed lower IGC-related mass loss, corrosion rate, and reactivation ratio than 304 ASS. These results demonstrate that industrial-scale GBE can effectively improve the IGC resistance of QN1803 ASS. This improvement arises from the coupled effects of CTB enrichment, disruption of IGC-susceptible boundary connectivity and grain/cluster-scale structural evolution, thereby indicating promising engineering application potential under selected product-specification conditions.