Microcrack Formation During Gas Metal Arc Welding of High-Strength Fine-Grained Structural Steel

摘要

The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc,which results in higher penetration depths and welding speed.However,microcracks occurred in the weld metal while approaching the process limits of the modified spray arc,represented by a 20-mm double layer DV-groove butt-weld.These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself.The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks.The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment.However,these microcracks do not impact the design specification for toughness in the Charpy V-notch test(absorbed energy at —40 ℃ for the present material is 30 J).