Friction stir welding of ultrafine grained interstitial free steels

Friction stir welding (FSW) was applied to ultra low-carbon interstitial free steels with mean grain sizes ranging front 0.7 mu m, prepared by accumulative roll-bonding. to 27 pin. The steel with the intermediate grain size (1.8 mu m) is most preferable for obtaining the highest hardness in the stir zone with the smallest grain size.