Research On Microstructure And Properties Of X52 Steel Joints

In recent years, X52 pipeline steel is widely used in transporting oil and gas. Low productivity is the main problem of the pipeline in the production process. The key to solving this problem is to study the reasons for cracks or fracture in the welded joints and understand the relationship between the welding process and the microstructure and properties of welded joints.This paper investigates the microstructure and property changes of X52 pipeline steel welded joints by the means of carbon dioxide gas welding process under different welding rate. The results show that under the welding rate of 45, 55, 60 and 65 cm/min, fracture area of the sample appears in welded joints and the widmanstatten structure appears in the Coarse Grain Heat Affected Zone(CGHAZ). The optimized surface of the welded joint appears under the rate of 45 cm/min, at which rate the ductile fracture is the main failure mode of welded joints in the stretching process leading to the best mechanical properties, which can ensure continuous production and improve production efficiency.In addition, during the process of welding X52 pipeline steel, the copper pad will be stuck with the weldment which reduced the mechanical properties of welded joints.In the actual production process, the flatness of steel was in bad conditions and the gap between the steel plates was not easily controlled. Therefore, we should ensure the flatness of plate and control procedure to avoid the occurance of non-fusion.