New LASER welding process for welded stainless steel pipe with excellent formability

Welded stainless steel pipes and tubes are used in chemical and thermal power plants, and in ordinary gas or water supplies, and automobile exhaust assemblies. These pipes and tubes are manufactured by continuous tube milling, and are generally seam-welded by TIG (tungsten inert gas welding), plasm arc welding or ERW (electric resistance welding). For improvements in welding quality and welding efficiency, a new seam welding process using a CO2 LASER beam has been developed. This process is characterized by a lower than usual welding heat input arc welding process. Therefore, in ferritic stainless steels, a fine-grain ferritic structure forms in the weld, and the formability and toughness of the weld is consequently improved. This characteristic is can be obtained in exhaust pipes, are bended, drawn or expanded in process of assembling. Another benefit of this LASER welding process is that the critical welding rate is improved 2-6 times in comparison with the usual process. New LASER welding process combined with high frequency induction preheating is especially effective in austenite stainless steel piping with a post solution heat treatment.