Study On Microstructure And Properties Of Weld Metal Of LNG Low Temperature Steel Welded By ENi620 Electrode

In the face of increasingly serious ecological environment pollution,liquefied natural gas,namely LNG,has more optional value and wider development potential than other mineral resources such as coal and even gaseous natural gas in Stone in order to improve the environment,mitigate climate change,improve the quality of energy use structure and thoroughly implement the national strategic plan for sustainable development.With China’s policy supporting the LNG industry chain,domestic research and development of low-temperature steel for domestic production of LNG are no longer required to be imported from abroad.However,welding materials for supporting low-temperature steel for LNG are still dependent on imports,which hinders the development of LNG industry and hinders China’s energy strategy blueprint.This paper explores a series of researches on the deposited metal after welding with Ni-based ENi620 electrode for homemade LNG cryogenic storage tanks.The welding test was conducted by electrode arc welding.The microstructure of deposited metal was characterized by metallographic microscope and scanning electron microscope.The mechanical properties were characterized by tensile,impact and hardness tests.The chemical composition of deposited metal was determined by spectrometry.The results show that the content of alloying elements in the deposited metal after welding with homemade ENi620 electrode is appropriate,and the content of Si element exceeds the expected design.The reason is that the weldability is slightly weak and the slag removal efficiency in the molten pool is not high.After welding,the deposited metal has good performance,tensile strength ≥680MPa,impact energy up to 80 J at-196 ℃,and plasticity has been greatly improved,which meets the welding requirements of LNG low-temperature steel.The deposited metal is austenite plus precipitated phase structure,and its main morphology is columnar crystal with segregation.Aiming at the defects of welding pores found in the deposited metal after welding,the paper studied the influence of changing the electrode drying temperature on the deposited metal and the influence of pores themselves on the deposited metal.The morphology of pores and tissues around pores were observed by metallographic microscope and scanning electron microscope.The element distribution in pores was studied by EDS energy spectrum.The effect of pores on grain boundaries was studied by EBSD.The main phase changes were studied by XRD.The mechanical properties were characterized by tensile and impact.The chemical composition was determined by spectrometry.The results show that changing the drying temperature of thewelding rod has an effect on the composition,microstructure and properties of the deposited metal,and the porosity defect in the deposited metal can be effectively avoided by welding after drying at 450 ℃ for 3 hours.At300-450℃,increasing the drying temperature of the welding rod will change the chemical composition of the deposited metal,refine the crystal grains and improve the deposited strength and plasticity.The results of pore research show that the largest possibility of pores in the deposited metal is CO pores.The existence of pores does not change the austenite grains of the deposited metal around it,and affects the size and growth direction of the surrounding grains.