Chair “Material Science and Heat Treatment of Metals”, Magnitogorsk State Technical University named after G. I. Nosov (Magnitogorsk, Russia):

Sychkov A. B., Dr. Eng., Prof. absychkov@mail.ru

Zavalishin A. N., Dr. Eng., Prof.

Sheksheev M. A., Post-graduate Student

This article presents the results of comprehensive studies of the effect of arc welding technological procedures on the structure and mechanical properties of the heat affected zone of pipe steel with K56 strength grade. Chemical composition, microstructure and mechanical properties of investigated sheet metal (with 12 mm hickness), manufactured at Magnitogorsk Iron and Steel Works, are analyzed. Pack-shaped and branched acicular structures, similar to bainite-type ferrite structure, are forming in the overheating area of the metal of heat-affected zone, in a wide range of heat input; it was established by the method of bead-on-plate test during the first stage of experiments. In the case of multi-layer welding during the second experimental stage, the joint is characterized by a structural heterogeneity as a result of the effect of automatic heat treatment, therefore the lower part is characterized by a granular normalized structure and the upper part — by coarse batch and Widmanstatten pattern structures. Distribution of HV metal hardness in the welding seam area along the joint height is analyzed. It was established according to the results of mechanical tests of metal in the heat-affected zone that single-layer welding of pipe steel with K56 strength grade should be conducted at increased values of heat input, while multi-layer welding can be conducted at lowered values of welding heat input without significant deterioration of mechanical properties.

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