Microstructure and properties of X70 pipeline steel welded joints with hot-wire TIG welding process at steep slope
The hot-wire TIG welding process was used to weld the 25° X70 pipeline steel with two different heat inputs.In order to analyze the adaptability of the two welding parameters and the influence of slope on the microstructures and mechani-cal properties of welded joints,the microstructures of welded joints were observed with an optical microscope(OM)and a scanning electron microscope(SEM).Meanwhile,the mechanical properties of welded joints such as tension,bending,hardness and impact toughness were measured.The results show that the heat input has little effect on the microstructure type of welded joints,but affects the grain size.The slope affects the width and the grain size in the coarse-grained heat-affected zone(CGHAZ)of the cover weld.The width and the grain size in CGHAZ of the lower groove are both bigger than those of the upper groove.The mechanical properties of welded joint with a high heat input are qualified.However,the hardness of the cover weld toe with a low heat input is high,leading to cracking of bending specimens.The HAZ impact energy at both of the upper and the lower slopes does not differ much.It is suggested that welding parameters with a high heat input,which has a high welding efficiency and a good joint quality,should be used in practical projects.
万方数据
维普
