Structure and Crack Resistance of N-A-XTRA-70 Steel Joints Manufactured by Hybrid Laser-Arc Welding

Abstract

Crack resistance of welded joints is one of the most important indices of service reliability of critical designation structures. The purpose of the research is the establishment of the influence of technological modes, hybrid laser-arc welding of high strength steel NA-XTRA-70 on the formation of structure in the metal welded joints, as well as analysis of the influence of this structure on their crack resistances. For the experiments the laboratory setup has been developed on which the experiments were carried out in the technological scheme that provides the location of the consumable electrode arc at a certain distance in front of the laser beam in the welding direction. Nd: YAG-laser DY 044 of company ROFIN (Germany) was a laser radiation source. Power for consumable electrode arc was carried out by welding generator PSG-500. Investigations of structural-phase changes in weld metal and HAZ were carried out by means of optical microscopy (optical microscope Versamet-2 and Neophot-32), microhardness was measured using M-400 gage of Leco company at 0.98N loading. Fractographic investigations were carried out by scanning electron microscopy (scanning electron microscope SEM-515 of PHILIPS company, Netherlands) on fractured specimens of welded joints, made as a result of impact bend tests. An analysis of crack resistance of the welded joints was carried out under different conditions of test temperatures. It was based on experimental data, received by a quantitative fractography method. It is shown that metal of a welded joint produced by hybrid laser-arc welding at Vw = 72m/h rate has mainly failure of ductile nature after external loading. This indicates sufficient level of crack resistance and further working capacity under operation conditions.