The Simulation Of Weld CGHAZ Of Pipeline Steel X80 And Performance Study

The demands for pipeline steels are being increased dramatically with thenational economy development. Driven by cost considerations, gas & oiltransportation companies have readily adopted higher strength pipeline steels withthicker gauges to permit gas & oil transportation at higher pressures. As a result,recent construction of pipeline has shown a trend towards higher operation pressurewith greater wall thickness and higher strength pipe. As new generation of highstrength pipeline steel, the development and application of X80 pipeline steel has beenthought much.CGHAZ (coarse grain zone of heated affected zone) is weakness area of weldjoint. Base on physical simulation, this paper studies the welding performance of X80pipeline steel and pay more attention to the phase and performance of CGHAZ andnumerical simulation also has been studied.In this paper, a scheme about welding cycle base on linear orthogonal experimentis designed, and then welding cycles of CGHAZ for different welding conditions aremeasured. Base on the experiment result, regression equations about t8/5 and tH areestablished and numerical simulation about welding temperature field has been done,the concept that in the three main influence factors of welding temperature field, weldheat input is main influence of the parameters of double ellipse heat source model isproposed.SH-CCT diagram of X80 pipeline steel has been studied in this paper for it isuseful for the study of welding performance, in X80 steel CGHAZ there are mainlybainite and ferrite, pearlite appears only when the cooling rate is very low and thereare no martensite. Base on the SH-CCT, parameters of Leblond phase transformationmodel for X80 steel are first calculated and determined.More work about X80 CGHAZ phase and performance has been done throughphysical simulation and numerical simulation, and then the result that when weld heatinput is lower and preheating temperature is higher, the phase of X80 CGHAZ isoptimal and toughness in low temperature is higher is found.