Microstructure formation regularity in complexalloyed steel 25hgnma

Purpose. Investigation of the microstructure formation in complex-alloyed steel 25HGNMA, containing 0.15 % molybdenum, during decomposition of austenite in the wire rod in the range of cooling rates in different environments after austenitizing with thermokinetic diagrams construction. Methodology. The research was conducted on the wire rod diameter of 18,5 mm, manufactured with TC 00187895 by JSC "Oskol Electric Steel Works" (Russian Federation). 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. Research efforts revealed that low-carbon alloy steel complex 25HGNMA, produced with TC 00187895 by JSC "Oskol Electric Steel Works" with a content of molybdenum equal to the lower limit of 0,15 %, is a pearlitic steel. For thermalhardening to obtain a wire rod bainite structure should be cooled after the rolling or after austenitizing at speeds higher than 0,82 °C/sec. Originality. Studied the kinetics of phase transformations in the complex of continuous low-carbon alloy steel 25HGM, widely used in domestic industrial practice in the machine-building enterprises of Ukraine. Practical value. This research may be claimed for the machine-building enterprises of Ukraine, in particular in the manufacture of welded round link chains for mining equipment.