| Because of the combination of excellent comprehensive mechanical properties and corrosion resistant properties, 2507 super duplex stainless steel is widely used in field of petrochemical industry, offshore engineering and ship-building and so on. While it is difficult to control phase ratio during the welding thermal cycle, mechanical and corrosion resistance properties will clearly decline, especial when the traditional welding methods are used in the welding of 2507 super stainless steel. Therefore it is necessary to use a different welding method to solve the these problem, as an new high-energy-density welding method,applying laser welding and laser-arc hybrid welding into the welding of 2507 super stainless steel will be a good thinking deserve some research.In this research, the effect of laser welding process parameters including defocusing?laser power and welding speed on welding joint appearance, microstructure and phase ratio,the mechanical properties and pitting resistance of welded joint were studied. At the same time, the main welding process parameters of laser hybrid welding including the distance of heat resource, Heat source relative position, laser power and arc current on welding quality also studied. Regulation of phase formation and the content of each phase in welded zone and HAZ were studied. Adjust the relevant welding process and obtain the sound welded joint, and the comparative study of the difference of microstructure ? mechanical and corrosion resistance of two welded joint is the main job.Study results indicate: determined the best defocusing amount of laser welding and the appropriate heat source distance and heat source relative position of laser-arc hybrid welding. laser power and welding speed is the main factors to laser welding, a relative low heat input lead the content of ferrite in welded zone is very high, and the precipitation of intra-granular ferrite is limited. The laser-arc hybrid welding experiment results show that the weld deep is mainly affected by laser power while the weld wide is mainly controlled by arc current. With the high heat input, the content of austenite is increased while the morphology is also changed. The mechanical room temperature test of two welded joint indicate that the tensile strength and the micro-hardness are stronger than that of base metal.While the toughness of welded joint seems decreases a lot. The corrosion resistance result of welded joint show that although the phase ratio of laser welded is high than that of hybrid welded joint, the pitting and inter-granular corrosion resistance of laser welded joint are better than hybrid welded joint, Oxalic acid etching experiment also show same result. The pitting almost located in heat affected zone or around fusion line, in welded zone, the pitting appeared in ferrite, the development of pitting is hampered by austenite. |
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