|About this Abstract
||2017 TMS Annual Meeting & Exhibition
||Friction Stir Welding and Processing IX
||A-88: Fatigue-Strength Increase by Friction Stir Processing between Different Strength Grades of Butt-Welded High-Tensile Steels
||Hajime Yamamoto, Kazuhiro Ito, Makoto Takahashi, Kazuyuki Kohama, Hidetoshi Fujii
|On-Site Speaker (Planned)
Fatigue strength of the high-tensile steels increases with increasing their yield stress, but that of their welds does not. It is caused mainly by tensile residual stress and microstructure-related issues in heat-affected zone (HAZ) due to fusion welding. In this study, friction stir processing (FSP) was conducted on HAZ surfaces of the butt-welded joints for 490 MPa and 780 MPa grade high-tensile steels (hereafter HT490 and HT780, respectively) to investigate whether or not FSP is an effective microstructural modification technique to increase their fatigue strength. FSP for the both grade welded joints was able to increase their fatigue strength due to grain refinements. The effect on increase in fatigue strength was higher in the butt-welded joints of HT490 than that of HT780. This can be explained by increase of high angle boundary and a hard cementite layer wrapping an ultrafine ferrite grain observed in the butt-welded HT490 joints with FSP.
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