Investigation On Two-Electrode Electrogas Welding Technologe Of High-heat-input Welding Steel

The size of container ships has increased rapidly over the past severalyears against a background of increased long-distance ocean freight. Due tothe special hull structure design in main deck area, a lot of higher strength andheavier thickness plates have to be used. In the welding of these heaviersection plates, the newly developed two-electrode EGW procedure is adoptedto prevent the low building efficiency and unstable weld quality withconventional multi-pass CO2welding. However， the heat-input of thisprocedure is very high, could be more than300KJ/cm. That makes themicrostructure in the HAZ become extremely coarse and the toughnessdecrease drastically. So it’s the most difficult problem to be solved whileconsidering of widely using this new welding procedure on ships.The paper mainly introduced welding tests research of tow-electrodeEGW procedure and analyzed test results. Then, it explained the reason whythe toughness of HAZ decreased remarkably in high-heat-input welding,meanwhile, some measures to improve the toughness of HAZ were mentioned. Finally, application benefits were analyzed while using this high efficiencyand automatic welding procedure. Test plates in three different kindscondition of supply had been used. The test results showed that decreasingtoughness of HAZ was the most weakness part in welded joint. The conditionof supply of steel plate determined the toughness of HAZ. With advancedmicroalloying and state-of-the-art TMCP technology, high-heat-input weldingsteel used very small inclusion to control austenite grain growth at elevatedtemperature by pinning effect. While cooling the inclusion was also helpfulfor the nucleation of intragranular ferrite，so that microstructure as acicularferrite could be generated, which can increase the toughness observably. Thatsolved the big problem in high heat input welding from the basis of steel plateitself. The research results successfully developed a new kind of highefficiency and automatic welding procedure for welding the heavier thicknessplate，reached the international advanced level at similar field, and provided anew technology support for the building of large scale container ships.