Influence of energy per unit length of hybrid laser-arc welding on structure and mechanical properties of welded joints of high strength steels

Purpose. The advantages of hybrid laser-arc welding in the production of weldments of high-strength steels are: considerable (in 3-5 times) reduction in energy per unit length; increased productivity through increasing on the order the speed of welding; obtaining equilibrium fine grain structures in the welds and HAZ, which increase the toughness of weld joints and reduces the disposition to the crack formation. As the result of action of the welding thermal cycle and the influence of weld alloying the structure and phase composition of the weld metal and HAZ may change significantly, and, accordingly, influence on the level of mechanical properties and crack resistance of welded joints. The need to find solutions problem appears by conducting complex technological and materials science experiments. Therefore, the purpose of the research is the establishment of the influence of technological modes, primarily the energy per unit length, hybrid laser-arc and laser (for comparison) welding of high strength steel on the formation of structure in the metal welds, as well as analysis of the influence of this structure on their mechanical properties. Methodology. Steel NA-XTRA-70 was investigated because this steel is widely used in the EU countries in the manufacture of critical constructions for various purposes. For the experiments the laboratory stand has been created 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. Studies of structural and phase changes in the weld metal and HAZ of welds was carried out using by light microscopy (optical microscopes Versamet-2 and Neophot-32), microhardness was measured on M- 400 micro durometer of company Leco. Findings and originality. Carried out researches for the first time allowed to establish optimal technological modes of laser and hybrid laser-arc welding to produce quality and reliable welded joints of high-strength steel from the standpoint the structure formation and phase composition of the metal, providing high mechanical properties of welded joints. Practical value. Presented in the article the results of experimental studies have high practical value. They will form the basis for new perspective technological developments in the field of laser and hybrid laser-arc welding of high strength steels.