Suitability analysis of thermally hardened S540Q steel sheets for welded constructions working in low temperatures

The conventional heat treatment is being replaced by thermal-plastic treatment. The process of steel hardening is carried out on quenching press with a double-sided water spray at the temperatures ranging from 600 to 700°C. The steel hardening process is conducted at the temperatures of 600-700°C with cooling in the air. After this, thermal hardening the steel sheets obtain the structure of a layered tempered matrensite with carbide and cyanide disperse separations The thermally hardened S540Q steel sheets 12 mm thick underwent examinations. The welding technology was presented. The sheets were welded semi automatically by means of MAG method. The usual welding conditions normally applied in industry were used after steel standardisations. The achievement of joints metallically continuous was confirmed by X-ray tests. The static tensile test was conducted to assess the applicability of this steel. The average values of the welded joints resistance to tensile strength were given. After conducting technological bend, test good ductility was noted. Steel microstructure was defined as low carbon tempered matrensite of layered construction. Microstructure observation was carried out in the joint axis, in heat affected zone and in native material. Hardness measurements were performed according to PN-EN 1043-1:2000 requirements. Impact test was conducted on the samples with a V cut notch at the temperatures of -20, -40, -60 Celsius degrees.