The Research Of Corrosion Resistant Properties Of Stainless Steel Welded Joint

The electrochemical corrosion and intergranular corrosion of three zones of austenitic stainless steel 304 and ferritic stainless steel 409L,410S and 430 had been researched in the different concentration solution H₂SO₄,HCl,NaOH and 6%FeCl₃. The difference in corrosion resistance of three zones((BM),(HAZ)and (WM)) of the Weld Joints had been analysised combined with its composition, microstructure and electrochemical gradients.The weakness of these Weld Joints had found out. At the same time, the four kinds of Weld Joints had been compared and analysised by the immersion corrosion test, salt spray corrosion test and ointment corrosion test. That offers theories for precautioning and relieving the corrosion of the stainless steel Weld Joints and experimental data and guide for the using of stainless steel productions under the corrosive environment.The composition and microstructure gradients of the Weld Joint of stainless steel hot rolled plates with TIG were analyzed by using Electron Probe Microanalysis(EPMA)scan the content of Cr and Ni of the Weld Joint and adopting Metallurgic Microscope to check its microstructure.Then the method of TIG and its characteristic were compared and analysised. The content of Cr and Ni of the Weld Joint distributes in the way of gradient, the content of Cr and Ni in the zone of WM is higher than BM and HAZ. The microstructural characteristic of three zones of the Weld Joint are following: The microstructures of WM are composed of austenite andδ-ferritic with branch shape;owing to the lenghth of the sample is limited, the microstructures of BM comparing with the microstructures of hot rolled plates are affected by heating to some extent in the process of welding,the grain of BM are more equidimensional,uniform and bigger; the microstructures of HAZ become much coarse due to heat heavily in the process of welding.The electrochemical corrosion behaviors and characteristics of three zones of the four kinds of stainless steel Weld Joints had been researched in different corrosive media by using the method of electrochemical. The anodic polarization curves of the Weld Joint in 10%H₂SO₄,60% H₂SO₄,80% H₂SO₄,1%Hcl,3%Hcl,10%Hcl,10%NaOH,20%NaOH,30%NaOH and 6% FeCl₃ were measured. Througth comparing and analyzing corrosive potential,corrosive current,passivation potential,critical passivation current,passivation current and over passivation potential to assess the ability of corrosion resistance. By analysis the electrochemical parameters of three zones((BM),(HAZ)and (WM)) in different solution,we can draw a conclusion that the ability of corrosion resistance in WM is better than BM as well as the BM's is better than HAZ. The sequences of the ability of corrosion resistance of the Weld Joint from high to low in different concentration corrosive solutions are following: in H₂SO₄ solutions are 10%H₂SO₄ >60%H₂SO₄>80% H₂SO₄ ;in HCl solutions are 10% HCl>3% HCl>1% HCl; There is having not sampled comparative assassment in NaOH solution because the Weld Joints has decaid slightly, at same time both losing weighth and increasing weighth occurred in that case. The sequences of the ability of corrosion resistance of the Weld Joints from high to low in different corrosive solutions are HCl>FeCl₃>H₂SO₄>NaOH.We can reach a conclusion that there are the same results between the immersion corrosion test and the electrochemical corrosion test througth adopting the immersion corrosion test at room temperature to assess the ability of corrosion resistance of the Weld Joints in different concentration solutions H₂SO₄,HCl,NaOH and 6%FeCl₃ and calculating their erosive rate and checking the corrosive macrograph meanwhile comparing with the result of the electrochemical corrosion test in different concentration solutions. The salt spray corrosion test and the ointment corrosion test have been used for testing the ability of corrosion resistance of the Weld Joints, the result of both the two corrosive methods have agreement with the electrochemical corrosion test.