Suitability analysis of thermally hardened S620Q steel sheets used for welded constructions working in lowered temperatures

S620Q steel sheets 12 mm thick that were heat treated were subjected to research. The sheets weldability was examined during semi-automatic welding by MAG method, at the welding conditions usually applied in industry for welding normalized sheets of this steel. The achievement of metallically continuous joints was confirmed by X-ray examination, the correctness of making test joints was confirmed by the measurement of transverse warp and edges of sample sections. Moreover the following tests were carried out: static tensile tests, technological bending tests and impact tests on the samples with V-notch cut in positions S, P, C2 and C5. The joints microstructure was observed in the weld axis, in SWC and in native materials with the use of Neophot-2 optical microscope. Steel microstructure was classified as low-carbon, tempered martensite of layered construction. The bend tests were carried out by means of bending arbour 36mm in diameter. The impact energy values for test temperatures -60°C, -40°C and -20°C marked in the drawings are the mean values of breaking three samples at a given test temperature. The places ofnotches cuts applied on welded joints samples are required by Det Norske Veritas regulations for welded joints. Mechanical properties ofS620Q steel were given as reference.