Study of structure of high-strength cold-resistant steel after quenching and tempering

At present time it is expedient to use high-strength weldable structural steels with guaranteed yield strength exceeding 600 MPa for manufacture of lifting and transportation equipment as well as mining machines in Russia and worldwide. Technical and economical efficiency of use of highstrength steels concludes in lowering of mass and increase of constructions bearing capacity, as well as in rise of their service life due to increased strength and cold resistance (down to −60 °С) [1–4]. It was established based on the previously conducted investigations of the new weldable high-strength steel 20G2SMRA with increased cold resistance [5, 6], that quenching from the temperature 860 °С and consequent high tempering at the temperature 600 °С is the optimal procedure of strengthening heat treatment of rolled sheet metal. The developed technology included processing of sparingly alloyed 20G2SMRA steel [5] and heat treatment procedures [6]; it provided achievement of the complex of properties which meet the requirements in structural strength (s0,2 ≥ 600 N/mm2), plasticity and impact strength at low climatic temperatures (−60 °С) of the best foreign analogies. These analogues include Weldox 700 (SSAB, Sweden, EN 10025), Quend 700, Optim 700 QL (Ruukki), shipbuilding steel HY-100, which are delivered after quenching and tempering [7–13]. Study of the structure of rolled sheet metal from the sparingly alloyed 20G2SMRA steel with determination of the required level of strength and cold resistance was the aim of this work. Materials and methods of the research