Investigation on thermo-mechanical processing and intergranular corrosion of TP347H stainless steel

The grain boundary character distributions of TP347H stainless steel after different thermo-mechanical processes in terms of grain boundary engineering (GBE) were investigated by EBSD. DL-EPR and electrolytic oxalic acid etch tests were carried out to evaluate the improvement of GBE treatment on intergranular corrosion. The low-Σ CSL grain boundary proportion of the TP347H can be increased to about 90% through a single-step thermo-mechanical treatment consisted of a slight tensile deformation (3%) and subsequent annealing process at 1150°C for 1 h. Compared with conventional TP347H, the optimum GBE microstructure suppressed intergranular corrosion due to the high proportion of low-Σ CSL grain boundaries, particularly the twin (Σ3) boundaries which is almost immune to intergranular corrosion.