Research On The Activated Welding For Medium-chromium Ferritic Stainless Steel

There is no or little nickel in ferritic stainless steel, which makes it cheaper thanaustenitic stainless steel. It has a broad application prospect in architectural decoration,home appliances, kitchen utensils and tableware, vehicle parts. Now it is a kind ofstainless steels of development potential.The weld penetration is small and the efficency is low when ferritic stainlesssteel was welded by TIG or laser welding methods. With the application of activatingfluxes, the welds penetration increases significantly. Research of activated weldingmainly focus on materials such as carbon steel, titanium alloy, aluminum alloy,magnesium alloy, austenitic stainless steel. There is no researchers report for ferriticstainless steel.In the paper, studies of actived welding process and the mechanism analisis ofactivated fluxes were focused on a representative steel SUS430.Firstly, some common oxides, halides and carbonates are applied in A-TIG andlaser welding tests respectively. The results showed that the effect of oxides on weldspenetration was more remarkable. B₂O₃, SiO₂, CrO₃, TiO₂and KCl performed betterin A-TIG,while ZrO₂, CaCO₃, CaO and MgO performed better in A-LBW.On the basis of experiments with single component activating fux, the bestfluxes were selected to develop the formula of multi-component activating flux. Testscheme adopts the uniform design to arrange, which greatly reduced the amount oftests.The grey theory（including the grey relational analysis and advantage analysis）and nonlinear regression method were introduced into the development of formula tofurther explore the influence regularity of the content and the interaction of eachcomponent on welds penetration, which provides powerful guidance for thecomponent optimization work.The welds penetration with A-TIG activating flux optimized by above-mentioned mathematical methods was2.22times as that without flux in the samecondition, while the optimized A-LBW activating flux could make the weldpenetration up to2.23times as that without flux. The effect was obviously superior to single componet activating flux, which prove the feasibility of mathematical methodsused in the study of activating flux.Microstructure, mechanical properties, corrosion resistance and compositionanalysis results of the welded joints with and without activating flux showed that thechanges of microstructure, elements and mechanical propoerties were not big, but thecorrosion resistance changed a lot. In TIG welding, the use of B₂O₃made thecorrosion resistance much worse than traditional TIG welds; In laser welding, all theactivating fluxes used could make the corrosion resistance better to varying degrees,among which the best were CaCO₃and the flux containing5%rare earth Y.Combined with the results of EDS detection, it was known that the use of surfactantcan effectively inhibit the loss of Cr in laser welding process, as a result the weldscorrosion resistance were improved greatly.Through the high-speed photography collection of the laser plasma forms fordifferent types of activating fluxes, it was found the use of activating fluxes resultedin no obvious changes in laser plasma which proved in the experimental condition, theinhibition of activating fluxes in laser plasma was not the main reason for the increaseof welds penetration.