عنوان مقاله [English]
Friction stir welding is a new and effective method for joining the alloys with welding problems and also for the dissimilar alloys. In the present study, friction stir welding is used to join st37 low carbon to 304 stainless steel plates at different tool rotation speeds. The stir zone in the 304 steel shows evidence of dynamic recrystallization with a moderate dislocation density. The stir zone in the st37 steel appears to experience dynamic recrystallization too, although the allotropic transformation during cooling cycle of the welds removes the features of dynamic recrystallization and produces a fine ferrite-pearlite microstructure with a low dislocation density. The relationship between hardness and microstructure is investigated through Hall-Petch equation for the stir zone of both steels. The results of weighted least-squares fit also show that the average hardness of austenite in the 304 steel and ferrite in the st37 steel inside the stir zones has a reverse relation with hardness according to the Hall-Petch equation. The hardness of the base metal and the stir zones of 304 steel does not stand on a same Hall-Petch line that can be attributed to the relatively higher dislocations due to the dynamic recrystallization of stir zones.
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