Study On Microstructure And Properties Of Semi Automatic Weld Metal Of Self Shielded Flux Cored Wire For X80 Pipeline Steel

X80 pipeline steel self-shielded flux-cored wire semi-automatic welding has been widely used in pipeline construction projects as an efficient,low cost welding technology suitable for outdoor work.This paper starts from the pipeline construction project reality,using the X80 pipeline steel / Q345 steel semi-automatic self-shielded flux-cored wire weld metal as the object of study,in order to solve this problems of high impact toughness and discreteness of welded joints at this stage and the problem that part of the results can't reach the appropriate standards,to make research and analysis of its organizational performance.By a series of experimental study of analysis of chemical composition of the weld metal,metallographic structure observation,scanning electron microscope and impact toughness and so on to learn about that uneven or irregular M-A component in the welded metal,metallographic structure observation,scanning electron microscope and impact toughness lead to uneven stress of weld metal and stress concentration,leading to wide discreteness of impact toughness absorption.In addition,when there is high level of carbon in weld metal,the impact toughness absorption is generally low.The rule of continuous cooling transformation of weld metal obtained using physical thermal simulation technique shows that the critical transition point AC1,AC3 of welded metal falls respectively between 680-690 ? and between 840-850 ?,with the increase of cooling time(T_8/5)of weld metal,the hardness value decreases and the grain size increases.The changes in the pattern of organization are as follows: BF/M,GB,QF and PF.Through the experimental analysis of impact toughness of the weld metal under the influence of different cooling time(T_8/5),it shows that when the cooling time(T_8/5)is 5s or 9s,the organization type of weld metal is GB or QF,the grain is relatively fine,and the number of crystal interface is larger,which effectively prevent crack propagation,in the meanwhile,the stress concentration is not easily generated,to get a better impact toughness.Therefore,to thoroughly solve the big discreteness of impact toughness at welded joint,secondary thermal simulation or multi-thermal cycling method can be used on the basis of this paper,for further study on the organization type and propertyof the welded metal.