Research On The Weldability Of X80 Pipeline Steel And Simulation Technology

High-pressure, large-diameter and high-strength pipes are inevitable trend for theoil and natural gas transporting pipeline. X80 pipeline steel, microalloyed steelproduced by TMCP process with high strength and good crack-resistance prosperity,is the main material of transporting pipeline. In this paper, physical simulation andquantitative predication of CGGHAZ for X80 pipeline steel were preformed in orderto study its mechanical prosperities and cold crack susceptivity, which will providetheoretical knowledge for its practical application. At the same time, On the basis ofheat transfer, metal physics and mechanics, the evaluating system were establishedafter calculating the distribution of temperature, microstructure and stress, which canbe used to optimize chemical composition and welding condition and predictmicrostructure and mechanical prosperities.Taking into consideration heat input, plate thickness and preheated temperature,orthogonal regression and thermal simulating technology was used to study weldCGHAZ of pipeline steel X80. The thermal cycle for different condition weremeasured. The experimental results showed the main microstructure of CGHZ wasbainite with lath and granular morphology. The size of austenite grain was about 30～40μm. With the increase of t8/5, except that crystal grains become coarse, smallquantity of second phase particles precipitated and the phenomenon of aggregationoccur. However, the impact toughness of specimens improved for the formation of acertain quantity of granular bainite and thin lath bainite when t8/5 is shorter than 6.8s,and decreased for t8/5 longer than 6.8s for the formation of lower percentage granularbainite and coarse and parallel lath bainite. M-A constituent had little influence ontoughness for its low percentage and small size. So it is concluded that lower heatinput and suitable preheated temperature should be adopted to control grain size andmicrostructure morphology.SYSWELD software was adopted to perform FEM simulation. Based on heattransfer theory, Leblond phase transformation theory and heat elastoplasticity theory,three field of temperature, microstructure and stress were coupled considering thenonlinear relationship between material prosperities and temperature, and theinteraction among temperature, microstructure and stress.The equation of thermal cycle and grain growth kinetics were establishedaccording measured thermal cycle and thermal simulation results. Adopted Voronoioriginal lattice and Radhakrishnan algorithm, grain growth of MC method wereprogrammed on MATLAB,which can simulate grain growing of different time. Thesimulated and measured results have good agreement.The evaluating system of pipeline steel weldability was designed on VB6.0. Theuser can input welding parameters, select or self-define materials and model anddisplay or output results. The system can be used to perform weldability evaluationincluding cold crack susceptibility, microstructure fraction, austenite grain size.hardness, toughness,...