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Abstract
Grain boundary phenomena strongly depend on grain boundary structure and characteristics, i.e. coincidence site lattice (CSL) boundaries, as contrasted with random boundaries, are highly resistant to intergranular degradation. Grain boundary engineering (GBE) primarily intends to prevent the initiation and propagation of intergranular degradation along random boundaries by frequent introduction of CSL boundaries into the grain boundary networks in materials. A high frequency of CSL boundaries by GBE processing leads to high resistance to grain boundary degradations. Annealing twins bring CSL boundaries into austenitic stainless steels. By twin induced GBE utilising optimised single step thermomechanical processing consisting of a slight strain followed by annealing, a very high frequency of CSL boundaries was introduced into austenitic stainless steels. The resulting steels indicated remarkably high resistance to intergranular corrosion even to weld decay and knife line attack during welding. Grain boundary engineering could have a high potential to suppress a variety of grain boundary related degradations of welded austenitic stainless steels.
This work was supported by a Grant-in-Aid for Scientific Research (A) (no. 21246104), a Grant-in-Aid for Science Research (S) (no. 19106013), a Grant-in-Aid for Science Research (S) (no. 19106017), and a grant from the Global COE Program ‘Materials Integration (International Center of Education and Research), Tohoku University’, MEXT, Japan. The author wishes to thank to Professor Z. J. Wang, Professor Y. S. Sato, Dr M. Shimada, Dr W. Z. Jin, Dr M. Michiuchi, Mr T. Inoguchi, Mr K. Sakai, Mr M. Miyagi, Mr T. Yokoyama, Mr S. Sato, Mr T. Oyamada, Mr K. Kurihara, Mr G. Yamada, Professor H. T. Fujii and Mr A. Honda for their useful discussions and technical assistance.