抄録
For the purpose of improving the toughness of flash weld, the effect of upsetting conditions on the flash weld of 980MPa grade high strength steel bar has been studied. The main results obtained are as follows; (1) Characteristic features have been observed in the displacement profile when the upsetting condition is set to higher current and lower pressure during upsetting. In case of higher current conditions, the upsetting speed increases rapidly and then goes down in a short time, which phenomena is repeated several times until its upsetting process is finished. (2) According to high-speed camera observation, such rapid increase in the upsetting speed is attributed to the extrusion of molten metal layer formed at the weld interface due to excessive joule heating. The specimens showing the melting-extruding upsetting phenomena have revealed superior weld toughness rather than those produced by conventional upsetting conditions. (3) The reason of toughness improvement in the high current condition where the melting and extruding upsetting mode is observed is considered to be the extrusion of both oxides defects and base metal inclusions, and the achievement of small upset deformation due to the lower upsetting pressure.
