Grain Boundary Character Distribution And Its Effect On Intergranular Corrosion Resistance Of C-HRA-5 Austenitic Heat-resistant Steel

C-HRA-5 is a type Fe-22Ni-25Cr high alloy austenitic heat resistant steel and is an important alternative for the reheater and superheater of the 650～700℃supercritical power station.after multiple certification,due to the high chromium content and alloy content,C-HRA-5 has a good high temperature lasting strength and antioxidant performance at high temperature.The addition of a large number of alloy elements plays the role of strengthening,but also analyzes the harmful phase at high temperature and leads to the deterioration of material performance,especially the intercrystal corrosion resistance.The C-HRA-5 austenitic thermal resistant steel with different Thermo-mechanical processing was adopted as the target materials in this paper.The influence of Thermo-mechanical processing on the grain boundary character distribution of C-HRA-5 Austenite thermal resistant steel is studied by optical microscope（OM）,scanning electron microscope（SEM）,electron back scattering diffraction（EBSD）and transmission electron microscope（TEM）;The effects of GBCD optimization on the mechanism of intergranular corrosion resistance in the C-HRA-5 austenitic thermal resistant steel were discussed by the analysis of 10%oxalic acid electrolytic corrosion and Corrosion weight loss test.The proportion of Low Coincidence Site Lattice boundary of the original sample accounted for 41.8%.The sample special crystal boundary（Σ≤29）after TMP process reaches more than 65%,which improves 24%.The small deformation high temperature short-time annealing process is more conducive to the improvement of special crystal boundary ratio.Ratio of grain cluster size to grain size（v）is often used to judge the good or not of GBCD optimization,where the 6-10 sample had the highest v value of 2.7.The results show that 6-10（6%Cold deformation+1200℃thermal insulation for 10min after water quenching）is the optimal process for optimizing the crystal boundary feature distribution in this experiment.The optimized samples by the thermo-mechanical processing significantly improved the overall intergranular corrosion resistance of the material after 10%oxalic acid electrolytic corrosion.The Corrosion grooves are shallow in the 6-10sample;in the Nitric acid-hydrofluoric acid corrosion weightlessness experiment the6-10 sample has the best intergranular corrosion resistance and more than double that of the original sample;By SEM of comparing oxalic acid corrosion,EBSD,TEM.it was found that the intergranular corrosion resistance of different proportion of grain boundaries was different,Σ3>Σ9>Σ27>ordinary high angle grain boundary;it is found that the coherentΣ3 grain boundary has the best inhibition effect on the M₂₃C₆,followed by the incoherentΣ3 grain boundary,HighΣ3 special crystal boundary ratio is conducive to improve corrosion resistance.