Microstructure And Mechanical Properties Of X65 Pipeline Steel's Welded Joint Under Different Environmental Pressure

At present,X65 grade pipeline steel is used widely in Chinese submarine pipeline systems.And underwater hyperbaric dry welding is an effective method for underwater marine engineering maintenance.The microstructure and mechanical properties of welded joints in different environmental pressure are studied in this paper,so is the mechanization that how the environmental pressure affects the welded joints' microstructure and mechanical properties.The main conclusions are as following:(1)The macroscopic morphology of X65 pipeline steel's welded joints under different environmental pressure is different.There are more defects in the welded joints with the environmental pressure increases.(2)The microstructure of X65 pipeline steel's welding seam is ferrite,pearlite and little carbide.The incomplete recrystallization of heat affected zone is composed of ferrite and pearlite,and the microstructure distribution is not average;the complete recrystallization zone is composed of homogeneous and fine-grain ferrite and pearlite;the microstructure of overheated zone is coarse ferrite,pearlite and martensite.(3)The hardness distribution of welded joints under different environmental pressure is basically the same.The hardness increases from the base metal to the heat affected zone,and continues to rise in the weld seam.Environmental pressure has little effect on the hardness of the welded joints.(4)The effect of environmental pressure on the welded joints,tensile strength is not obvious.(5)The average impact energy in the weld seam shows difference;the impact fracture is dimple fracture;and the effect of environmental pressure on their impact toughness is obvious.While the average impact energy in the heat affected zone shows little difference,the impact fracture is quasi cleavage fracture;and the effect of environmental pressure on their impact toughness is not obvious.The impact toughness is higher in the welding seam than that in the heat affected zone.