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In the work the comparative evaluation of mechanical properties of butt welded joints of N-A-XTRA-70 high-strength steel of 8 mm thickness, produced using arc, laser and hybrid laser-arc welding, was carried out. Mechanical tests on static tension and impact bending with V-notch showed that the values of static strength are increased with decrease in heat input of arc welding, and the values of ductility remain almost unchanged. At the same time, the values of impact toughness of weld and HAZ metal are approximately 1.5–1.8 times reduced. This is connected with the fact that at increase in welding speed from 18 to 50 m/h the phase composition of weld metal changes from ferrite-bainite to bainite-martensite. In laser welding, the values of static strength of weld metal are by 18–20 % reduced and the ductility 1.8 times increases with increase in welding speed and cooling rate of HAZ metal. With increase in speed of laser welding from 40 to 50 m/h the phase composition of weld metal changes from martensite to martensite-bainite (with martensite fraction exceeding 60 %). In hybrid welding, the increase in welding speed leads to 10–15 % increase in the values of static strength and ductility. These changes occur because of the fact that the fraction of phase components changes. In the molten metal of specimens produced using laser method, and in the deposited metal produced using arc and hybrid methods the ultra-low concentrations of diffusion hydrogen content are observed, namely 0.07, 0.2–0.3 and 0.4 ml/100 g, respectively. 10 Ref., 1 Table, 1 Figure.

Comparative evaluation of properties of high-strength N-A-XTRA-70 steel welded joints produced using arc, laser and hybrid laser-arc method