Development Of The Agglomerated Flux Of Submerged Arc Welding For X120 Pipeline Steel

Selection of high-grade pipeline steel can not only save a lot of construction costs,but also can be better applied in poor area,which production adopt automatic submerged arc welding.Currently the varieties of welding material is single,which can match the pipeline steel.The flux that used for high-grade pipeline steel is not able to meet its requirements.According to the submerged arc welding requirements of X120 pipeline steel,this research studied ways how to improve the process performance and mechanical properties of welded joint,moreover providing the theoretical basis to the research and produce of X120 matching welding materials in the future.In this study,the system of sintered flux slag is determined,which is the fluorine base type CaF2-MgO-Al2O3-CaO-TiO2 and the rage of alkalinity 1.2-2.3.Using the uniform design method developed the flux formulation,and then filtered flux which is on the bases of the range of flux alkalinity.The based formulation of flux is choosed by the analysis of process performance assessment that has the best process performance,but the weld spots were discovered and it can be improved by adding 2%of a deoxidizer SiFe.The research of the flux slag detachability uncovered the most effective factor is the phase of slag,and lattice constant of the magnesia alumina spinel is similar with Fe2O3,which makes the flux slag detachability became difficult,while the slag detachability is also associated with expansion coefficient difference between slag shell and metal,the intermediate layer is the weak part,while the increase of expansion coefficient difference,the slag shell is more easy to fall off.Furthermore,that it can be increased the chance of obtain the flux which the slag detachability is good at t.he rage of alkalinity 1.6-2.2.Therefore,it is better to determine the alkalinity in this rage as far as possible in the design of subsequent experimental formula.This paper mainly discussed the effect of Ti?Si?Mn?RE and other major alloy elements on the microstructures and mechanical properties of the weld line.Select Si?Mn as two kinds of elements to adjust the phase transition temperature and transition time of the microstructure of weld metal.Choose RE to form carbide and nitride,which is used to improve the mechanical properties of weld metal.The content of Si was adjusted by the deoxidizer.Mn is joined as the form of manganese.RE through the form of pure rare earth to join in.The test results show as follows.When adding about 6%of manganese and 0.8%?1%of pure rare earth,the precipitation of Pro-eutectoid Ferrite can be effectively inhibited,the grain can be refined also and smaller,uniform Acicular Ferrite and Granular Bainite of weld line get are obtained,so as to improve the impact toughness of weld line.However,ZrO2 added separately can not improve the toughness of weld.