Friction stir welding procedure development was initiated on steel grades S460 G2+M and S690QL1 in plate wall thicknesses of 10 and 15mm. To tackle the challenges of the high mechanical loads on the tool as well as its premature wear, a combination of preheating and optimized weld backing set-up was implemented.
The inductive preheating allowed a 28% reduction in welding torque and a significant reduction of the tool wear, particularly during the critical initial plunge of the tool within the base material.
A comparison of Mo-based and W-based tool was performed, allowing identifying the W-based tool as having a better combination of high temperature strength and wear resistance. Different backing arrangements and materials were investigated. Ceramic backing inlays were used to reduce the heat loss at the root area and maintain an acceptable stirring of this zone to achieve full penetration welds.
The welds quality was assessed via metallurgical examination, bend tests and confirmed the possibility to perform sound full-penetration, one-sided welds. The contribution of the preheating to the process as well as the quality and mechanical properties of the welds will be presented here. Finally, the transfer of the process parameters to pipe welding were started and will be discussed here.... (read more)