Friction Stir Welding of Thick Steel Plate Using Silicon Nitride Too

Friction stir welding (FSW) is expected to be applied as a welding technique of materials with relatively high melting temperature such as steel materials. Silicon nitride is one of the inexpensive and attractive tool materials for FSW of the thick steel plate. Therefore, in this study, the capability of the silicon nitride tool without groove scroll to weld a low carbon steel plate with a thickness of 15 mm was investigated. The suitability of a tool shape was confirmed by FSW of a thick A5052 plate using a SKD61 tool with same shape as the silicon nitride tool. The defect-free welded specimen of the thick steel plate was obtained using the silicon nitride tool under the optimum welding condition. The silicon nitride tool could be used for FSW of the 15 mm thick steel plate until the welding length of 200 mm without breaking the tool. The groove defect area in the stir zone of the thick steel plate was decreased with decreasing of the tool rota-tion speed and tool tilt angle. Especially, the tool tilt angle was effective to increase the heat input and the material flow velocity. It is considered that the defect-free weld specimen of the thick steel plate was obtained to sufficient material supply to the RS of the stir zone by decreasing tool tilt angle to 1.