Results are presented for studies of deposited metal and welded joints of high-strength medium-alloy steels made by austenitic type flux-cored wire with nitrogen developed by the authors. It is found that use of this wire makes it possible to increase the strength of deposited metal by 20–30% with simultaneous retention of good ductility indices. Within the joint metal structure in the central part, after welding high-strength alloy steel, an austenitic-ferritic structure is formed with a delta-ferrite content of ~3 vol.% by an AF type crystallization mechanism, and a small amount of lower bainite is also present. Weld metal microhardness varies in the range HV 0.1 200–250. As distance from the joint metal center towards the fusion line increases the structure transforms with an increase in bainite content. At the fusion line the phase composition is g-phase in an amount of 44.7 vol.%, and α-phase in an amount of 51.8 vol.%, as well as carbides of the order of 0.5 vol.%. The structure within the fusion line is represented by large grains of austenite in the central part and lower bainite, which has carbides within the volume of the α-phase, and δ-ferrite, the amount of which remains unchanged (3 vol.%). In the heat-affected zone, the length of which is 2–2.5 mm, a structure forms that is a mixture of lower bainite and lath package martensite (the total content of the α-phase is 98.6 vol.%) with microhardness of HV 0.1 400–550. Use of austenitic class flux-cored wire with nitrogen for welding high-strength alloy steels makes it possible to obtain defect-free welded joints with an austenitic-ferritic structure.