《Table 6Mechanical performance evaluation requirement and testing quantity of the girth-welded joint

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《Automatic girth welding and performance evaluation of the joints of hot-induction-bend and line pipes with different wall thickness》

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Fig.5 depicts the microstructure at different positions of the high-strength consumable matching plan of the automatic girth-w elded joints of the hotinduction-bend and line pipes of unequal w all thickness.The girth-weld metal exhibits a coarse columnar grain in which different orientations and random distributions of strip ferrite and bainite are the predominant microstructures with general fine grains and where no quenching martensite is observed.The nonuniformly distributed M-A component can split the ferrite substrate，which results in decreased ductility and toughness of the weld metal.However，if the M-A component disperses in the ferrite substrate，the ductility and toughness of the weld metal can be improved.The austenite grain boundary is obvious in the HAZ near the fusion line in which there are different orientations of the dispersed precipitated carbonization of fine-grain ferrite and bainite.However，for the fairly low heat input of automatic girth welding，the width of the coarse grain in the HAZ is fairly narrow，therefore，any adverse effect on the ductility and toughness of the girth-welded joints will decrease.