INFLUENCE OF HYBRID LASER-ARC WELDING ON THE FATIGUE RESISTANCE OF BUTT JOINTS IN HIGH-STRENGTH STEELS

Abstract

The paper presents the results of an experimental study on the influence of hybrid laser-arc welding on the fatigue resistance of butt joints in high-strength steels compared with conventional automatic arc welding. The relevance of the study is determined by the growing industrial implementation of hybrid welding technologies in load-bearing structures subjected to long-term cyclic loading, as well as by the insufficient understanding of their effect on both crack initiation and crack propagation stages of fatigue failure. The aim of the study is to establish the regularities governing the fatigue performance of butt joints made of 14KhGN2MD and S460M steels produced by hybrid laser-arc and automatic arc welding, taking into account the influence of welding speed and joint edge geometry. Fatigue tests were carried out under cyclic bending at a frequency of 14 Hz with stress amplitudes corresponding to a fully reversed cycle of 40 and 60 MPa. The tests were continued up to 2×10⁶ cycles or until the formation of a 3 mm fatigue crack. Fractographic analysis of fracture surfaces was performed to identify the mechanisms of crack initiation and propagation. It was established that at a stress amplitude of σ−1=4 MPa, S460M joints produced by both welding methods withstood 2×10⁶ cycles without failure. At σ−1=60 MPa, joints produced by automatic arc welding demonstrated higher fatigue durability compared with hybrid laser-arc welded joints. In hybrid joints, fatigue cracks were detected after approximately (0.8–1.54)×10⁶ cycles. The fracture surface analysis revealed a two-stage failure mechanism consisting of a crack initiation zone characterized by a quasi-brittle fracture mode and a main crack propagation zone dominated by ductile dimple fracture. The influence of weld metal microstructure, particularly the formation of lower bainite, and joint geometry on fatigue performance was identified. The obtained results demonstrate that the fatigue resistance of hybrid laser-arc welded joints is governed not only by process parameters but also by the geometric configuration of the joint and the structural transformations occurring in the weld metal. The findings provide a basis for technological recommendations aimed at improving the fatigue performance of high-strength steel structures operating under cyclic loading conditions.