Study On Welding Technology Of X100 Pipeline Steel

Aimed at the practical situation of X100pipeline steel in the engineering construction, strong toughness, welding joint microstructure and mechanical properties of X100pipeline steel were investigated by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM), hydraulic tensile testing machine, impact testing machine and other equipment,and then the suitable welding material and welding procedure method were put forward The results are as followings:The composed of ferrite, bainite, martensite-austenite (M/A) of Polyphase organization makes X100pipeline steel eXhibit eXcellent strength and toughness. Granular bainite grain is relatively small, the size of M/A islands is between0.2μm and0.5μm, mainly show dotted or long strips in the matriX. Ferrite mainly show batten shape parallel arrangement, batten width is between0.5μm and0.8μm, the density of dislocation is higher in batten. The main precipitates of X100pipeline steel is NbC with small size, mostly between18.45nm and26.43run, mainly present the circular or oval diffuse distribution in grain boundary and surround the dislocation line. The ductile brittle transition temperature between-80to-100℃, mechanical performance meet the standard requirements.Crack resistance of X100pipeline steel was investigated by Y-groove cracking test. The results show that the X100pipeline steel possess eXcellent crack resistance. To avoid the cold cracking of root welding, in X100pipeline steel welding process, the preheating temperature should be kept at100℃～150℃, interpass temperature should be controlled at100℃～200℃.The results of testing the mechanical performance and corrosion resistance of X100pipeline steel welded joint by taking advantage of metal powder core wire gas shielded welding indicate that the weld seam and HAZ organization mainly contained of granular bainite, acicular ferrite and bainite ferrite, root welding, filling welding, cosmetic welding grain size increases in turn. HAZ is mildly soften. The width of lath bainite ferrite in the weld is between0.42μm and0.71μm, the batten edge mainly contain acicular or film shaped M/A islands, there is high dislocation density between internal and batten; Granular bainite lath is shorter, batten width is about250nm, relatively small M/A island size is about0.1μm; Acicular ferrite is unparallel, elongation, different direction of precipitation needle flake.Batten width is from61.66nm to129.79nm, the ratio of length to width is about5to1. The strength, hardness, toughness, resistance to HIC and CTOD performance of the welded joint can satisfy the requirements of X100pipeline steel.The result indicates that the weld joint of X100pipe prepared by taking advantage of welding process of metal cored wire of GMAW, the various performance indicators it contained meet the requirement of relevant technical standards. Which proves that the choice of welding material and welding technology parameters setting is feasible and reasonable.