PROSPECTS OF LASER AND HYBRID LASER -ARC WELDING OF PIPE STEEL

Abstract

One of the ways to solve the problem of welding main pipelines is to use laser radiation as a heating source. Due to the small dimensions of the welding bath and the angle of convergence of the focused laser radiation, laser welding provides an opportunity to significantly reduce the angle of development of the edges to be welded. Relatively small values of linear energy, associated with high speeds of laser welding, allow to minimize of the thermal effect on the parts being welded, and, therefore, reduce the size of HAZ and residual deformations. The fine-grained structures of the cast metal of the weld and HAZ help to increase the corrosion resistance of welded joints. Hybrid laser-arc welding of tubular steels allows for to reduction of the power of laser radiation, partially replacing it with cheaper electric arc power at the rate of 1 kW of arc instead of 0.5 kW of laser radiation for δ>5 mm. With laser radiation powers up to 3 kW, the use of the hybrid process of steel welding is expedient up to a wall thickness of δ=10 mm, beyond which the penetration depth did not increase, regardless of the reduction in welding speed. For welding larger thicknesses, it is advisable to use radiation with higher powers. For the same purposes, it is possible to use multi-pass laser or hybrid welding. In hybrid welding, the width of the seam and HAZ increases compared to laser welding. An increase in welding speeds and carbon content in the base metal leads to the formation of undesirable martensitic structures in HAZ. To eliminate this drawback, a twofold increase in arc power compared to laser power is not enough. Although the additional thermal effect of the electric arc allows you to control the thermal cycle of the process to obtain the necessary structures of the weld metal and HAZ, this point needs to be studied further. The results obtained by the authors indicate that, despite the fairly high obtained values of impact toughness, further research aimed at reducing the hardness of HAZ during hybrid laser-arc welding is necessary. During laser welding, there is a danger of the formation of hardening structures both in the HAZ and in the cast metal of the seam. The study of the structures obtained in the welded joints of pipe steels by multi-pass laser and laserarc welding, as well as the impact strength and corrosion resistance of these joints, allows us to consider the application of the specified welding methods to increase the service life of pipeline transport as promising.