Abstract
Friction stir welding was employed for joining of 12Cr heat resistant ferritic steel. Microstructure and mechanical properties in the obtained welds were examined and their relationship was established. The stir zone microstructure was found to consist of quenched martensite with numerous fine dispersoids uniformly distributed in grain interiors. The formation of this microstructure remarkably strengthened the stir zone. Tempering for 3·6 ks at 923 K reduced the as welded hardness of friction stir weld to nearly base material level.
Financial support from the Japanese Ministry of Education, Science, Sports and Culture with a Grant-in-Aid from the Global COE Program in Materials Integration International Center of Education and Research at Tohoku University and a Grant-in-Aid for Science Research B is gratefully acknowledged. The authors are also grateful to Mr A. Honda for technical assistance, Mr K. Kobayashi for help in EBSD and TEM measurements and Professor T. Furuhara and Professor K. Maruyama for fruitful discussion of obtained results.