Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia
O. A. Kupriyanova, Cand. Eng., Associate Prof., Dept. of Materials Processing Technologies, e-mail: o.nikitenko@magtu.ru
P. P. Poletskov, Dr. Eng., Prof., Dept. of Materials Processing Technologies, Director of the Engineering and Innovation Sector, e-mail: p.poletskov@magtu.ru

South Ural State University, Chelyabinsk, Russia

A. K. Tingaev, Cand. Eng., Associate Prof., Dept. of Equipment and Welding Technology, e-mail: tingaevak@susu.ru
M. A. Ivanov, Cand. Eng., Head of the Dept. of Equipment and Welding Technology, Director of the Polytechnic Institute, e-mail: ivanovma@susu.ru

One of the most dangerous technological defects of welded joints of structures made of high-strength cold-resistant steels are cold cracks, the development of which occurs within several hours after welding. The reason for the development of the cracks is, as a rule, the formation of hardening structures as a result of high cooling rates of the metal of the welded joint. This paper is devoted to evaluation of weldability and analysis of resistance to formation of cold cracks of new low-carbon high-strength cold-resistant steel of 20G2SMRA grade. Technological samples for Tekken-test were prepared from sheet steel with a thickness of 20-25 mm. Samples were welded on the FANUC ARC Mate robotic system 120iC by a consumable electrode of various brands (OK AristoRod 69, Sv-08A) in a protective gas environment. A comprehensive metallographic analysis of welded joints of the steel under study was carried out in various areas: weld metal, heataffected zone, at the transition from the heat-affected zone to the base metal, as well as mainly metal. The distribution of hardness over the cross-section in all zones of the welded joint is given, the relation of the hardness of the HV1 under different welding modes at each area under study. It is shown that the most dangerous areas are those of partial melting and overheating (coarse grain) of the welded joint located in the root of the weld in the zone of the structural stress concentrator. It has been found that the use of low strength filler wire for welding the root pass of thick-sheet rolled products, as well as an increase in the welding start temperature, provide resistance to the formation of cold cracks in welded joints of high-strength cold-resistant steel of grade 20G2SMRA.

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