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In this paper, different welding process to weld microstructure and properties . Made tests include testing sample , the microstructure observation, hardness test , impact test , scanning electron microscopy ( SEM ) , the bending test and weld heat treatment after . The products used for square and rectangular tube size is 250mm x 250mm x 11.8mm , 250mm x 250mm x 9.8mm , 200mm x 300mm x 9.8mm , 200mm x 300mm x 11.8mm , material is Q235 . By testing and microstructure observation , verify that all samples are qualified welding performance and weld heat affected zone by decarburization of overheated zone , completely recrystallized area not fully recrystallized four regions . The decarburization layer and the overheated zone are coarse widmanstatten . The impact test is commonly used test to measure metal toughness . This test uses GB2106 - 80 \The impact test instructions using high-frequency welding method , the weld the impact of poor performance . To improve the impact properties of the weld heat treatment . The GB/T2653-1983 bending test , the bending resistance of the welded joints for evaluation . Test the bending properties of the sample . And analysis of surface energy , the width of the heat-affected zone , opening angle , the impact of speed on the bending properties of the welded joints , the good welded joints bend performance suitable welding parameters . The test is used to improve the organization of the weld heat treatment after welding , in order to achieve the purpose of improving its mechanical properties . The tests showed that , after normalizing the weld metal , especially widmanstatten significantly refined, which will bring its performance greatly improved .
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