Cr17-type Ultra-low Carbon Ferritic Stainless Steel Sheet Welding Process And Joint Properties

Ferrite stainless steel is an economical stainless steel which doesn't contain nickel or a little nickel.It has excellent ability of stress corrosion resistance,so it has the broad prospects of application.Studying such steel's welding problem deeply and systematically is very important and valuable in the application for mastering the basic seal performance. To improve the welding technology and match the welding materials reasonably of this kind of steel,this paper obtains a good performance welding structural part.At the same time,these have important realistic significance for enlarging the application of the ferrite stainless steel and boosting the development of the steel.By using the Ultra-low Carbon Ferrite Stainless Steel 00Cr17Ti(Nb)as test materials, the paper analyses the mechanics performance of the welded joint,the microstructure of the joint,the materials of the welded joint and the microstructure of the oxide skin. Furthermore,the influence of the welding technology to the tissue and performance of the welded joint have been studied.At the same time,this paper researches the anti-corrosion techniques and the acidic washing passivation of the welded joint.At last,this paper makes an improvement for the acidic washing passivation liquid's formula with the methods of Uniform Experimental Design and the Regression Analysis.The tests indicate that:when welding the ferrite stainless steel,we should increase the welding current and speed on the basis of the welding line's energy's low enough.When the welding current is between 100-110A,welding voltage is 16-17V,welding speed is 25-30cm/min,with the way of TIG,the welding current is between 110-120A,welding voltage 17-18V,welding speed between 55-60cm/min,with the MAG,we can get a good welding joint with good Mechanical Properties and Anti-corrosion Property.In the progress of welding,we should avoid the pollution of the welding materials and melting pool.With the way of welding torch and protecting gas cover,we can make the high temperature region be in the region of the protection of the argon gas.When we use the same material for welding,the welded joint and the HAZ are mainly single-ferrite stainless steel.In the HAZ of the welded joint,from the direction of the melting line,the crystal's size will decrease with the increment of the distance between the melting lines.With the increase of the melting line's energy,the armoring degree of the weld seam columnar grain will increase.The welding seam and the HAZ precipitate is Cr or Ti,they are the main reasons of the weld joint brittleness,the existing region and the number will increase with the increase of the welding line's energy.The analysis results to the organization structure of the ferrite stainless steel and the mechanism of the acidic washing passivation technology of the welded joint show that:the main ingredients of the oxide skin are compact type oxides such as FeO,Fe₃O₄,Fe₂O₃,FeO·Cr₂O₃,FeO·Cr₂O₃·Fe₂O₃,etc.The inner layer of the oxide skin is in the dissolving,while the outer surface is in the peeling off.Through the analysis to the acidic washing passivation technology of the welded joint,this paper establishes a mathematical resolution of matching the ingredients and the rate of corrosion,and makes an improvement of the acidic washing passivation liquid.The results shows:the error between the real performance and the simulation results is 7%,the passive film in the surface of workpiece have perfect shielded effect and doesn't haverusty spots,and the effect is very good when pickling and passivating with the formula.