X65Pipeline Steel Flash Welding Process Parameters Optimization And Study Of Joint Performance

Abstract:Because of its high degree of automation, excellent and stable welding quality, high production efficiency, flash butt welding technology can be widely used in petroleum and natural gas pipeline construction, optimization of pipeline flash welding process parameters has important practical significance. In this paper we use the quadratic orthogonal regression test method, in the case of X65pipeline steel, to optimize the flash butt welding process parameter. We select distance Si of flash phase1, current I1of flash phase1, distance S2of flash stage2, electric upsetting time tp, terminal velocity Vf of the flash accelerate stage as the test factors, each factor of three levels,30groups of experiment are carried out. After welding, testing tensile strength, bending properties and the impact toughness of the welded joint, analysis the joint mechanical properties, and establish quadratic regression equation at the target of impact energy of the center of weld seam center and heat affected zone, discuss the relationship between flash welding process parameters and the joint impact toughness. Observe the microstructure of weld joint and analyzes the relationship between the microstructure and welding technology parameters, observe the macro and micro morphology of the fracture of grooving and hammer breaking experiment, analysis of weld defect and put forward possible preventive measures, get the following conclusion:(1) Tensile strength of welded joint of X65pipeline steel flash butt welding can meet the requirements, although there is no obvious welding defects in welded joint, but plastic of the joint is poor, the reason is that the microstructure of the joint is too bulky, and at the same time part of the joint have grey spot of different area also led to the decrease of the joint performance.(2)The flash butt welding joint microstructure of X65pipeline steel is ferrite and pearlite mainly, it can be divided into four areas:the weld zone, heat affected-coarse grain, and heat affected-fine grain area and the parent metal, with the farther from the fusion line, the microstructure becomes more and more small, due to welding heat and the deformation force, the heat affected-fine grain area happens grain recrystallization, the grains are smaller than the parent metal.(3) The fracture of the welded joint is brittle fracture, the river pattern and fan-shaped pattern of cleavage fracture morphology can be found under electron microscope; some of the sample fracture resistant grey spot, energy spectrum test shows it is oxide slag of SiO2and MnO, it was due to the residual liquid metal was not completely extruded before upsetting, it can be avoided by appropriate measures.