Gas and oil pipelines for the Arctic region must sustain low temperatures and high internal pressures of a corrosive active medium. Generation of new steel compositions for oil and gas pipelines is an urgent issue in order to ensure their high reliability. Low-carbon steels with a ferritic–pearlitic structure are normally used in pipe production, but they are unable to cope with increased market demands. The main objective of this study is to investigate the influence of the cooling rate on the structure and morphological characteristics of bainite, which determines the exploitation properties of the pipe steels. Dilatometric tests were carried out using a Gleeble 3500 complex. Optical microscope and scanning electron microscope analysis, with the computer image analysis system Thixomet PRO, were used to study the microstructure of steel. Hardness was measured in accordance with ASTM E-384. Morphological characteristics of bainite components that were formed at various cooling rates from 0.05 to 100 °С/s were defined. The novel result of this study is the continuous cooling transformation diagram of undercooled austenite of the steel containing 0.062% С; 1.80% Mn; 0.120% Mo; 0.032% Cr, 0.90% Ni and other elements (Al, Cu, V, Nb, Ti).

Problem Statement: As part of the comprehensive project of creating a hi-tech production process, which is carried out by Nosov Magnitogorsk State Technical University together with Termodeform-MGTU LLC at the request of Magnitogorsk Iron and Steel Works, a process is being developed for the production of nanostructured flat rolled products having a unique combination of mechanical properties and capable of substituting similar imported products. Objectives: The objective is to look at how the chemical composition and the heat treatment conditions effect the hardness and the impact strength of nanostructured high-strength rolled sheet steel. Methods Applied: With the help of the Termodeform-MGTU laboratory facilities, a number of ingots were produced, which had various chemical compositions and which were later exposed to hot deformation and different modes of heat treatment. After the heat treatment, a number of samples were prepared from the sheets for hardness and impact testing. The results of the mechanical tests were then analysed for statistics. Originality: The originality of this work includes the mathematical dependences established which show how the chemical composition and the heat treatment conditions can effect the hardness and the impact strength in high-strength rolled sheet steel. Findings: Following the statistical analysis of the experimental data, equations were obtained that show how the chemical composition and the heat treatment conditions effect the hardness and the impact strength of high-strength rolled sheet steel. Also, it was found that the temperature range of 250 to 400 °C does not prove to be a good tempering temperature for high-strength Cr-Ni-Mo-V steel with 0.3% of carbon as it can lead to constant temper brittleness. Practical Relevance: The mathematical dependences established enable to create new or improve the current high-strength rolled sheet steel production processes.

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