Grain boundary design based on fractal theory to improve intergranular corrosion resistance of TWIP steels

The grain size in TWIP steel had a double fractal distribution, with a uniform diameter threshold of approximately 36 μm. Based on this threshold value, the grains were divided into fine and coarse grain sets. A good linear relationship was found between the fractal dimension of the fine grain set (Dg1) and the fraction of Σ3 gain boundaries (GBs) (FΣ3). The distribution characteristics of the three types of GBs satisfy multifractal and generalized fractal characteristics. Importantly, the fractal structural parameters of the Σ3 GBs control the distribution characteristics and complexity of the total grain boundary network (GBN). Combined corrosion test, a quantitative relationship between the corrosion thickness loss and the Σ3 GBs fractal parameter as well as corrosion time was established. In the end, the optimal microstructure characteristics for improving the intergranular corrosion resistance of TWIP steel are discussed from the GB perspective. GB design based on fractal theory provides a promising solution to optimize material corrosion properties through analyzing complex GBN.