Effects of Grain Size Distribution of C-HRA-5 Austenitic Heat-resistant Steel on Intergranular Corrosion Resistance

The influence of mixed grain structure (MGS) and uniform grain size structure (UGS) on the intergranular corrosion performance of C-HRA-5 austenitic heat-resistant steel was studied through DL-EPR experiments. Grain size, special grain boundaries, carbide precipitation phases, and intergranular corrosion characteristics were analyzed using metallographic microscopy, SEM, EBSD, etc. The results showed that the intergranular corrosion resistance of samples with uniform grain size (microstructure) was higher than that of samples with mixed grain size microstructure. Both UGS and MGS samples contained low ΣCSL special grain boundaries mainly Σ3 boundaries. The special grain boundary content of UGS samples was 54.2%, which was much higher than that of MGS samples (29.5%). The reason for the high resistance of UGS to the corrosion could be regarded as the high content of special grain boundaries interrupted the connectivity of the large angle grain boundary network, which had a certain inhibitory effect on the precipitation of Cr rich M₂₃C₆ and improved the phenomenon of Cr deficiency in some grain boundaries.