Effect of spray cooling intensity on microstructure and mechanical properties of X80 pipeline steel multi-wire submerged arc welded joints

Objective Spray cooling technology is applied in the process of multi-wire submerged arc welding of X80 pipeline steel medium and heavy plate, the aim is to achieve precise control of cooling intensity through air pressure regulation and water flow control. Methods A multi-scale evaluation system is established based on mechanical means such as room temperature tensile test, low temperature impact test and microhardness test, as well as OM, SEM and other characterization methods. The effects of different spray cooling intensity conditions on the mechanical properties and microstructure of welded joints are analyzed. Results The results show that spray cooling can accelerate the cooling rate of weld and HAZ, reduce the area of HAZ, and the cooling effect increases first and then decreases with the increase of air pressure, and increases with the increase of water flow. Under the effect of spray cooling, the polygonal ferrite in the weld zone changes from long chain strip to short and coarse block, the grain size of granular bainite in the coarse grain zone decreases, and the proportion of lath bainite increases. Compared with the natural cooling state, the weld impact absorbed energy reached 193.7 J at the spray cooling air pressure of 0.2 MPa and the water flow rate of 0.6 L/min, which increased by 23.5%, and the shear section rate increased from 83% to 92%. Conclusion Spray cooling can refine the grain of weld and HAZ, and improve the impact toughness of weld. The cooling effect is the best when the air pressure is 0.2 MPa and the water flow is 0.6 L/min.