Grain characteristic and texture evolution in friction stir welds of nanostructured oxide dispersion strengthened ferritic steel

Abstract

The present paper investigated the grain and texture characteristics in a nanostructured oxide dispersion strengthened ferritic steel subjected to friction stir welding. The ‘onion rings’ structure obviously exhibited in the macrostructure overview of the welds. The electron backscatter diffraction (EBSD) work revealed that the ‘onion rings’ comprised alternate layers made by coarse and fine grains, while no strong texture was exhibited in the alternate layers of the ‘onion rings’. Image quality maps of EBSD indicated that layers of fine grains were deformed under high strain conditions. Textures within the stir zone and thermomechanically affected zone were weak and exhibited some characteristics of bcc simple shear textures. Results of grain boundary revealed that the mechanical action in welding process promoted the transformation of low angle to high angle boundaries and contributed to the grain refinement.

Keywords:

• Friction stir welding
• Oxide dispersion strengthened steel
• Electron backscattering diffraction
• Texture
• Grain characteristic

This work was supported by the National Natural Science Foundation of China (grant no. 50971030), the National Basic Research Development Foundation of China (grant nos. 2008CB717802 and 2009CB109004), the China Scholarship Council and the CUP Program in Japan. The authors would like to thank the staff of China FSW Center at BAMTRI (Beijing Aeronautical Manufacturing Technology Research Institute) for their support during the welding experiment. Wentuo Han would like to thank his friends in laboratory of advanced high temperature materials at Hokkaido University, Japan.