Influence Of Bead Weld Procedure On Microstructure And Properties For Chemical Vessels Clad Plates

Chemical vessels clad plates, whose base metal is carbon steel or low alloy steel andthe cladding metal is stainless steel or titanium has been extensively used for chemical vessels due to the good corrosion resistance and low cost. However, it is difficult to weld for the clad plates. At present, the manual electrode arc welding method is extensively used in the bead weld of the cladding metal for longitudinal and circumferential welding seam of chemical vessels. V-type groove is cut in the cladding metal, and corrosion resistant layer is bead weldedon the groove by use of stainless steel electrode after the base metal is welded. It is difficult to meet the use requirment for the mechanical properties and intergranular corrosion resistance of bead weld layer in actual production, the is sometimes difficult to meet the requirements. There will be the serious influence to safely use of the product. In addition, the manual electrode arc welding is low efficiency in the production. Therefore, a higher efficiency of welding method and technology is urgent. This topic is that the basic layer is Q345 R and cladding metal is bead weld with S30403.The welding method is arc welding with stick electrode and CO₂ gas shield welding whose bead weld efficiency is much higher. The influence of different bead weld technology on microstructure and properties of bead weld layer will be researched respectively. Then favorable bead weld technology for mechanical properties and corrosion resistance will be obtained. The research provides foundation to improve the welding quality and efficiency of lad plates for chemical vessels.Firstly, the welding method is manual electrode arc welding. The microstructure of surfacing layer was researched, and the influence of weld heat input on chemical composition, ferrite, metallic phase of surfacing layer section and cladding metal, lateral bending and intergranular corrosion were analyzed. The results showed that surfacing layer is composed of austenite and a small amount of ferrite, and the ferrite morphology is mainly in the shape of lath ferrite and framework iron ferrite. If the weld heat input is too large, there will be adverse influence such as the content of Cr and Ni of bead weld reduced, carbon osmosis increased, crystal grain of welded seam growth, content offerrite reduced, cracks on lateral bending specimen and intergranular corrosion test appears unqualified. In the view of the attention to the production efficiency in actual manufacture, too small weld heat input will reduce welding efficiency. Therefore, it is so important to select appropriate weld heat input on basis of meeting the weld performance for production practice. Experimental results show that the ?4 electrode for manual arc welding, to choose welding current as 160 A, the welding voltage as22²6V and the welding speed as 11¹5cm/min.Further, in order to further improve welding efficiency, this topic has carried on the research of carbon dioxide gas shielded welding test on the basis of studying manual electrode arc welding. The test variate will be overlap rate and welding parameter for different groups. The chemical composition, ferrite, metallic phase, lateral bending,intergranular corrosion for metallographic sample of each group are detected. Similar as manual electrode arc welding, too large weld heat input there will be adverse influence on microstructure and properties of welded seam. Moreover, if the overlap joint ratio changed from 25% to 50%, penetration of base metal is much smaller, the chemical composition of bead weld is much more homogeneous, the overlap of each layer is much smoother, and lateral bending and intercrytalline corrosion properties are much better. From the test results, it shows that CO₂ gas shield welding shall be welded with?1.2 welding wire, 50% overlap joint ratio, 220 A welding current, 28³0V welding voltage, 32 38cm/min welding speed.