Generation mechanism of lack of fusion in X70 steel welded joint by fully automatic welding under steep slope conditions based on numerical simulation of flow field

X70 pipeline steel is butt welded by fully automatic welding at 25° slope, and the characteristic information of process collected. A 3D transient heat mass transfer model weld pool established. This was verified means shape two-dimensional weld, then, flow field under steep slope conditions simulated to clarify mechanism lack fusion defect. The results show that arc deflected when it stays on both side walls groove. makes liquid metal tend gather lower When gravity plays a leading role in molten pool, some begins out from groove front end, resulting an overflow phenomenon. generation phenomenon deflection cause formation “void zone” structure mutation position In process, tends for various thermal effects, forms large range eddy current walls. has positive effect sidewall melting. addition, surface tension more obvious than upper groove, trend upward along wall stronger, so difficult high-temperature center area” located bottom Therefore, likely