The Effects Of Grain Boundary Character Distribution On The SCC Of304Stainless Steel In A Simulated PWR Environment

304stainless steel is widely used as the component materials in the primarywater in the pressurized water reactor (PWR) nuclear power plant. The stresscorrosion cracking (SCC) of304stainless steel in a high temperature and highpressure water environment is one of the problems inducing nuclear power plantaccidents. The grain boundary character distribution (GBCD) and some propertiesrelated to the grain boundary of face-centered cubic metal materials with lowstacking fault energy can be improved by grain boundary engineering (GBE).In this paper, the effects of GBCD on the SCC of304stainless steel in asimulated PWR environment have been investigated. The GBE specimens andNonGBE specimens were processed with proper deformation and thermal treatment.The electron back scattering diffraction (EBSD) was used for analyzing the GBCDof GBE specimens and NonGBE specimens. The specimens were subjected tosolution annealing, thermal sensitization, or cold working for the slow strain ratetesting (SSRT). The effects of the special grain boundary network (GBN) formed byGBE treatment on the resistance to SCC have been discussed by analyzing thefracture lifetime, fracture surface morphology and crack density on sample surface.The relationship between surface crack initiation and Schmid Factor of neighboringgrains was analyzed by EBSD. The results are as follows:1. The GBCD of304stainless steel has been improved significantly with GBEtreatment. The proportion of low-Σ CSL boundaries, which mainly were of Σ3n(n=1,2,3…) types, was enhanced to more than75%in the GBE specimens. In this case,the GBN was featured by the formation of large grain-clusters produced by multipletwinning. All of the grains inside of this kind of clusters had Σ3nmutualmisorientations. In the NonGBE specimens, the proportion of low Σ CSL boundarieswas only45%, which was much lower than that in the GBE specimens. The averagegrain-cluster size of the NonGBE specimens was also much smaller than that of the GBE specimens.2. After the SSRT tests of the sensitized GBE specimen under the condition ofdissolved Oxygen of0.1ppm and strain rate of1.0×10-6s-1, and the cold workedGBE specimen under the condition of dissolved Oxygen of0.1ppm and strain rateof5.0×10-7s-1, the results obviously illustrated that the GBN formed by GBEtreatment showed better resistance to SCC in the simulated PWR environment. But,under the condition of dissolved Oxygen of8ppm and strain rate of1.0×10-6s-1,the GBN formed by GBE treatment showed inconspicuous resistance to SCC.3. EBSD was used for analyzing the areas containing micro cracks on samplesurface. The results showed that the transgranular micro cracks initiatedpreferentially in grains with larger Schmid Factor and the intergranular micro crackspreferentially initiated at grain boundaries between two grains with larger differencein Schmid factor.