Influence of heat input and preheating on the cooling rate, microstructure and mechanical properties at the hybrid laser-arc welding of API 5L X80 steel

This study investigates the influence of hybrid laser-arc welding parameters: heat input and preheating on the cooling rates, microstructure and mechanical properties of the welding joint. Samples from API 5L X80 steel with root thickness 14 mm were welded using welding wire MF 940 M. Decreasing cooling rate of welds from 588 degrees C/sec up to 152 degrees C/sec, weld metal hardness from 343 +/- 12 HV up to 276 +/- 6 HV and ultimate tensile strength from 1019.5 +/- 14 MPa up to 828 +/- 10 MPa and increasing bainite phase term of the weld metal was detected at the increasing preheating temperature up to 180 degrees C and maximal heat input. The mathematical relations of the input and output parameters were created using linear regression equations. Preheating temperature 180 degrees C allows increasing maximal welding speed up to more than 3.0 m/min with acceptable welding joint quality. (C) 2018 The Authors. Published by Elsevier Ltd.