The kinetics of bainite structure formation in lowcarbon complex-alloyed steel during a cooling process

Purpose. Medium-carbon steel, alloyed with molybdenum and chromium are widely used in engineering. Chromiummolybdenum steel guaranteed with high mechanical properties of strength, ductility and toughness and very high hardenability. However, the results of systematic transformation kinetics of austenite in the large range of cooling rates are not available. Also is not available information about an additional impact of nickel and manganese on the bainite transformation kinetics in such steels. That's why, was done the work to study the kinetics of austenite transformation in a large range of cooling rates in rolled steel 23MnNiMoCr5-4, alloyed with molybdenum, nickel and chromium and to study the kinetics of acicular structures (bainite) formation in a large range of cooling rates. Methodology. The research was conducted on 24 mm diameter rod, produced according to DIN 17115 at the company TRINECKE ZELEZARNY (Czech Republic). Kinetics of austenite transformation after heating in a separate large range of cooling rates was studied with a dilatometer AD-80 and MD-83, designed by ISI. Were produced hot-rod samples with a diameters from 3 to 4 mm. Heating the samples in the dilatometer was performed to 900 °C, with the following staying during 5 min. Then samples were cooled under the program in furnaces with different thermal inertia, with air, under the fan, and with oil. Findings. Established that increased molybdenum content to 0.55% in medium-carbon steel promotes the bainitie structure formation in a large range of cooling rates that allows it to manufacture parts in machinery, metallurgy, transportation and construction industries with high complex mechanical and performance properties. Originality. Studied the kinetics of phase transformations in steel 23MnNiMoCr5-4, widely used in European industrial practice and which is having the prospect of industrial use in machine-building enterprises of Ukraine.