Grain Boundaries Character Distribution And Its Effect On Intergranular Corrosion Resistance In Fe-20Cr-19Mn-2Mo-0.82Nhigh-Nitrogen Austenitic Stainless Steel

High nitrogen austenitic stainless steelhaving excellent mechanical properties,corrosion resistance,oxidization resistance and wear resistance etc.is more and more widely used in energy resources,chemical industry,fertilizer product,oil,natural gas,mining and communication and transport etc..As a result,great attention is now focused onhigh nitrogen austenitic stainless steel by scholars of many countries.however,the precipitation of carbides,nitrides and intermetallics in austenite of this steel material during thermal processing,will affect the microstructure stability of austenite.The precipitation of carbonitride and intermetallics in the steel will seriously affect various properties of materials,especially resistance to intergranular corrosion.The Fe-20Cr-19Mn-2Mo-0.82Nhigh nitrogen austenitic stainless steel with different deformation andheat treatment was adopted as the target materials in the present work.The GBCD of the experimental steel and its effect on intergranular corrosion resistance were investigated by various analytical and testing techniques,such as EBSD,optical microscope(OM),scanning electron microscope(SEM),oxalic acid etch test and ferric sulfate-sulfuric acid test.The effects of GBCD optimization on the mechanism of intergranular corrosion resistance in thehigh nitrogen austenitic stainless steel were discussed.Cold-rolling by 5%followed by annealing at 1150? for 72h is the most feasible for the optimization of GBCD in the experimental steel under the current experimental conditions.The proportion of special boundaries increases from 47.3%for the solid solution treatedhigh-nitrogen austenitic stainless steel specimen to 79.4%for the specimen cold-rolled by 5%and then annealed at 1150? for 72h.The fraction of the special boundaries(SBs)increases 32.1%.The corrosion grooves are shallow,own smaller width and the corrosion level is low in the experimental steel of cold rolling by 5%followed by annealing at 1150? for 72h.After immersing in boiling ferric sulfate-sulfuric acid solution for 24h,48h and 72h,the corrosion level of the surface and cross-section in the experimental steel of cold rolling by 5%followed by annealing at 1150? for 72h is lower than the specimen with solid solution treatment.The SBs of the experimental steel mainly consists of ?3,?9 and ?27 boundaries.Under the experimental condition,only ?3 boundary is corrosion-resisting and can be termed as "effective special grain boundary".?3 boundaries ofhigh proportion effectively interrupt the connectivity of no corrosion-resisting grain boundary(?9,?27 and generalhigh angle ones etc.)network,thus improving the intergranular corrosion resistance for thehigh-nitrogen austenitic stainless steel.