| Stainless steel composite steel is widely used due to its good strength and corrosion resistance.It is easy to cause the diffusion of the fusion zone C and the dilution of alloying elements because the two materials of stainless steel composite steel pipe have different chemical compositions and physical properties in the welding process,eventually performance of welded joints deteriorate.In the electric power industry,the stainless steel composite steel tube is usually replaced about ten years or so.As the welding rod used for the welding of the stainless steel composite steel tube is usually imported,it can be seen that the resources are wasted and the economic cost is great.Therefore,it is very important to study the welding technology of the stainless steel composite steel pipe with the domestic electrode instead of the imported electrode and explore the reutilization of the stainless steel composite steel pipe after service.This topic focuses on the study of the microstructure and properties of the welded joint of the composite steel pipe before and after the service,under the condition of using two kinds of welding materials,the domestic electrode E308-16 and the imported electrode E309L-17.The structure and properties of stainless steel composite steel tubes before and after service were analyzed.The results of metallographic observation show that the metallographic structure of the stainless steel composite steel tube before and after service is basically unchanged,the carbon steel is F+P,and the stainless steel is A,but the grain of the stainless steel composite steel tube after service is obviously coarse.The results of electrochemical corrosion test show that the corrosion performance of the cross section of the stainless steel composite steel tube before and after service is different,and the corrosion performance of the stainless steel composite steel pipe before service is obviously less than that of the stainless steel composite steel pipe after service.The stainless steel composite steel pipes before and after service were treated with heat treatment at 350,650,750,950,1200,respectively,and theelectrochemical corrosion test of the cross section was carried out.The experimental results show that the corrosion resistance decreases with the increase of heat treatment temperature,and the corrosion performance of the stainless steel composite steel pipe before and after service is obviously increased when the heat treatment temperature is 650 ?and 1200 ?.The structure and properties of welded joints of stainless steel composite pipe were analyzed.TIG welding of stainless steel composite pipe is used,the wire is ER70S-6 and the welding current is 116~117A.Then the transition electrode and cover face welding were carried out with the domestic electrode E308-16 and the imported electrode E309L-17.The arc voltage is 18 V and the welding current is 68~76A.After X ray test,the welded joints were tested for mechanical properties,metallographic examination,hardness and electrochemical corrosion.The experimental results show that the welding joints with high quality can be obtained.The weld metal structure is the same as the parent material,the bottom seam is F+P,and the transition layer and the cover seam weld is A.The difference is that the welding seam of the cover welding seam with the imported electrode E309L-17 is more finer than that of the cover layer made by the domestic electrode E308-16.The tensile and impact tests of the welded joints welded by two welding processes are carried out.The results show that the welding joint of the stainless steel composite steel tube before and after service all exceeds the minimum limit of the national standard,and the impact toughness of the welded joint of the stainless steel composite steel tube after service is better than that of the before service.The electrochemical corrosion of the weld zone and the heat affected zone of the welded joint of the stainless steel composite steel pipe material before and after service is carried out.The experimental data show that the corrosion resistance of the two welding processes obtained is less than that of the parent material.Moreover,the heat affected zone is easier to corrode than the weld area,and the weak welded joint area is over 1100?.The welded joints of stainless steel composite pipe before and after service were treated at 650?,850? and1050? respectively.It is found that the heat treatment temperature is good at 1050?,and the corrosion resistance of the welded joint obtained at 650? is the worst. |
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