Study On Microstructure And Properties Of Clad X70 Steel With 2209 Duplex Stainless Steel By Hot-wire TIG

As the most safe,economical and efficient transportation mode,corrosion has been a problem that can not be ignored in the transportation by pipeline.Weld cladding an alloy with good corrosion resistance is a kind of effective method to prolong the service life and improve the safety of the pipeline.Due to its excellent corrosion resistance,mechanical properties and good weldability with low alloy steel,duplex stainless steels are considered as a good choice for the weld cladding pipeline.The hot-wire TIG welding process was optimized and the effect of welding parameter on cladding appearance,dilution rate,mechanical properties and corrosion resistance properties were discussed in this study.The results showed that the bead width increased with welding current increasing;the bead width increased with the increase of hot-wire current within a certain range,when the hot-wire current was up to 60 A,the bead width decreased obviously;With the increase of weld speed,the bead width and height decreased.The dilution rate increased and the corrosion resistance properties decreased with the increase of heat input;Shear toughness and shear plasticity obtained minimum while shear intensity obtained maximum under the optimum weld parameter;The hardness testing results showed that a dramatic fluctuation in the hardness can be seen across the fusion line,and a soften region was obtained in the base metal adjacent to the fusion line while a harden region was obtained in the clad layer.The composition profile and the microstructural evolution of the transition zone were analyzed by optical microscope,scanning electron microscope equipped with energy dispersive spectroscopy and transmission electron microscope.The results showed that the composition profile of the transition zone changed greatly;and the dilution rate ranged from 99% to 14% causing the ratio of Creq/Nieq ranging from 0.36 to 2.55 across the transition zone;and the transition zone was composed of alpha ferrite + martensite,martensite,martensite + delta ferrite and austenite + martensite + delta ferrite microstructure regions corresponding to the changes of the solidification mode from A mode to F mode.