Study On Welding Processes Of Ferritic Stainless Steel And Corrosion Behavior Of Welded Joint

Chromium content of ferritic stainless steel with a body-centered cubic structure is generally between 11%～30%. Ferritic stainless steel has been widely used in vessels, vehicles, household appliances, kitchen equipment and building decoration because of its excellent performance of chloride stress corrosion and spot corrosion resistance addition to excellent strength, magnetic performance and wear-resisting property. The effects of different welding methods on the microstructure and mechanical properties of welded-joint for ferritic stainless steel are investigated. The effects of different corrosive media on pit corrosion behavior and electrochemical corrosion properties of welded-joint of ferritic stainless steel are investigated also.The 1mm thick ferritic stainless steel was welded by tungsten inert gas arc welding （TIG）. The results showed that the welded-joint consisted of the heat affected zone, fusion zone and weld zone. The ferrite grains were coarsened in the coarse zone of HAZ and weld zone with heat input increasing. The strength and ductility of the welded-joint was changed. The ferrite grain growth in coarse zone and weld zone was hindered through the double effects of pinning up the grain boundaries and dragging the movement of grain boundary when the niobium element was added into ferritic stainless steel. The strength and ductility of the welded-joint was improved.The 1mm thick ferritic stainless steel was welded by electronic beam welding （EBW）. The results showed that the width of the EBW welded-joint was reduced significantly. Grain size in HAZ and columnar grain size of weld zone became small significantly comparing with TIG welding. Columnar grain was short and thick and showed bamboo shape. Growth direction of columnar grain is almost perpendicular to the fusion line and encounters at weld center. The strength and ductility of the welded-joint was decreased.The corrosion behavior of TIG welded-joint of the ferritic stainless steel was investigated. The results showed that the pitting corrosion occurred likely in excess Cl- containing solution. The corrosion performance of welded joint was decreased with the Cl- and OH-concentration increasing in salt and alkaline media and the corrosion resistance was worst in alkaline media. So it was not fit for application in strong alkaline conditions. The corrosion resistance of ferritic stainless steel base metal was superior to the welded-joint in acidic, neutral and alkaline media. The local corrosion occurred firstly at the weld zone of welded joint in the FeCl₃ solution and extended to welded joint.