To explore UT and The causes of the small size equivalent density exceeding the standard detected by TOFD were studied using macroscopic and microscopic metallographic analysis

defect morphology characterization

and other methods to investigate the properties

distribution patterns

and causes of typical welding defects that passed the RT test. The results indicate that the frequent TOFD detection of small-sized equivalent density exceeding welding defects includes hydrogen induced porosity defects

slag inclusion defects

and linear defects such as reheat cracks. Its formation is related to the conditions of molten pool escape

interlayer/inter pass temperature and welding line energy control

and the degree of dehydrogenation (metallurgical reaction). By adopting

the DC pulse MAG welding method to enhance the fluidity of the molten pool and increasing the proportion of CO

2

in the welding protective gas to promote metallurgical reactions

the development of process improvement measures has effectively eliminated the generation of dense micro pores and slag inclusions in the weld seam; By controlling the interlayer/pass temperature and welding line energy

the generation of reheat cracks in the weld seam has been effectively eliminated. It is of great significance to improve the performance of 1 000 MPa high-strength steel welded joints and the service reliability of components.