Research On Underwater Welding Technology And Welded Joint Properties Of Marine Engineering Steels

Underwater welding has become an essential means to repair and maintain marine constructions in the development and utilization of marine resources.Underwater welding can be classified as underwater wet welding,underwater dry welding or underwater local-cavity dry welding.Marine engineering steel Q690 E plays an important role in offshore structures,owing to their excellent ductility,low-temperature toughness,and weldability.And S32101 duplex stainless-steel was wildly used in shipbuilding and the construction of special offsure structures because of their high resistance to corrosion and excellent mechanical properties.In the current work,we studied on the welding technique of marine engineering steel Q690 E and S32101 duplex stainless-steel.The main contents are as following: 1)Workpieces of Q690 E HSLA steel are welded via ULCW and UDW,respectively.The characteristics and performance of these joints are evaluated by comparing the corresponding microstructures,tensile properties as well as the micro-hardness and Charpy impact toughness values.2)We contrasted the microstructure,micro-hardness and corrosion behavior of underwater dry joints and wet joints with different heat inputs and to optimize underwater processing by selecting suitable welding process parameters.The results are as follows:The main results of the underwater welding of Q690 E steel are as following: 1)The results indicated that the martensite and martensite-austenite components were significantly different with different underwater methods such that the micro-hardness of the HAZ and FZ in the ULCW1 specimen was higher than that of the corresponding regions in UDW1 joint.2)The yield strength and ultimate tensile strength of the ULCW1 specimen are 799 MPa and 722 MPa,respectively,than those of the UDW1.ULCW2(Post-weld heat treatment at 500℃)appeared better yield strength and ultimate tensile strength than ULCW1 and ULCW3.The HAZ of ULCW3 showed the best impact toughness(93.3J).3)The length of acicular ferrite and ferrite side plate increases with increasing depth of water,which results in the decrease of impact toughness.Tensile strength and yield strength of UDW joint reached the maximum value when the depth of water is is 40 meters,while plasticity is very poor.When the depth of water is is 0 meters,UDW joint can not only obtain good high strength strength and yield strength,but also obtain good plasticity.The main results of the underwater welding of S32101 duplex stainless-steel are as following: 1)No matter the UWW joints of S32101 duplex stainless-steel and the UDW joints,the weld metal have a better resistance to localized corrosion than the heat-affected zone.2)During S32101 welding,nitrides are the main reason for localized corrosion of HAZ.The hightemperature heat affected zones of the welds made with underwater dry welds showed a better performance than the underwater wet welds under the same heat input because of less chromium-rich nitrides.3)And the resistance to localized corrosion of the low-temperature heat affected zones increased with an increasing heat input of the UWWs whereas the UDW lowtemperature heat affected zones experienced a reverse trend.