Study On The Influence Of The Level Of Restraint On The Performance Of S690Q High Strength Steel Welded Joint

S690Q high strength steel are widely used in the marine field,offshore platform,pressure vessel,automobile manufacturing and other fields.Welding is important for connect engineering structure steel.Weldability of S690 Q is key to control the quality of engineering structure.S690 Q is often used in restrained welding conditions.Three weld structure restraint intensity were designed and computed by ABAQUS finite element software.The influence of level of restraint on joint residual stress,organization and performance were researched.It is found that the restraint intensity of the fillet weld restraint-400 mm,fillet weld restraint-800 mm,and wed restraint structure-400 mm is 18:9:2.In the same structure,restraint intensity descends according to the lower,middle and upper order.The maximum restraint intensity is 16.28 kN/(mm.mm)in the lower position of fillet weld restraint-400 mm,while the minimum restraint intensity is 0.99 kN/(mm.mm)in the upper position of web restraint structure.The transverse residual stresses of fillet weld restraint-400 mm is higher than fillet weld restraint-800 mm and wed restraint structure-400 mm.The restraint welding significantly increases the residual stress of the welded structure.The stress release of the base metal caused by the fillet weld restraint is twice as high as that of the web restraint.And the restraint stress of the restraint distance 400 mm is about three times of restraint distance 800 mm.Restraint intensity has no effect on weld and heat affected zone organization.The heat-affected zones in all regions meet the characteristics of the heat-affected zone of typical quenched and tempered steel,and the organizational composition is greatly affected by the heat cycle.Joint hardness is mainly related to thermal cycling,and the relationship with restraint intensity is not obvious.As the hardness away from the fusion line changes to the tempering zone,the hardness value in the coarse grain zone is up to 350 HV10;while the tempering softening hardness value in the tempering zone is the lowest 220 HV10.In the same heat-affected zone,the hardness of the heat-affected zone near the weld surface is the highest,while the heat-affected zone in the middle and root of the joint undergoes a reheat cycle,their microstructure changes again and the hardness decreases.The tensile strength of the joint does not show a regularity with the change of the restraint intensity,which is basically stable at 750 MPa.There is little correlation between impact energy and external restraint level.The impact toughness increases substantially between the fusion line + 1mm and the fusion line + 5 mm,with the smallest impact toughness 130 J near the fusion line.The weld fracture is a typical ductile fracture,and the fracture is covered with different sizes of dimples.Quasi-cleavage fracture exists when the gap is at fused line and fused line + 1 mm.A number of shallow dimple in the fracture face of gap in fused line + 5 mm ensured a higher impact toughness 210 J of the sample.