Special Features of Transformations of Supercooled Austenite in Modern Structural Steels
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SPECIAL FEATURES OF TRANSFORMATIONS OF SUPERCOOLED AUSTENITE IN MODERN STRUCTURAL STEELS M. V. Maisuradze,1 M. A. Ryzhkov,1 E. V. Antakov,1 N. A. Popov,1 and P. A. Proskuryakov1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 29 – 38, July, 2020.
Dilatometric, metallographic and durometric studies of transformations of supercooled austenite in modern commercial and experimental alloy steels under continuous cooling from the austenitization temperature at constant rates of 0.1 – 30 K/sec are performed. Thermokinetic diagrams of transformation of supercooled austenite are plotted and analyzed. The effect of alloying on the temperature and time intervals of formation of structural components in the steels is determined. Statistical analysis of the data obtained is performed to find the dependences of the critical temperatures Ac1 and Ac3 and of the critical quenching rate on the chemical composition of the steel. The behavior of the hardness of the formed structure as a function of the cooling rate is determined. Equations relating the coefficients of the function of logarithmic hardness and the chemical composition of the steels are suggested.
Key words: steel, hardness, thermokinetic diagram, chemical composition, cooling rate.
mal and thermokinetic diagrams of transformation of supercooled austenite in steels [4 – 6] commonly presents results obtained by different methods. This makes it difficult to analyze the reported data statistically adequately. The aim of the present work was to analyze the thermokinetic diagrams of transformation of austenite obtained for modern alloy steels by dilatometric and metallographic studies and hardness measurement.
INTRODUCTION Steel is the most widely used commercial metallic material. This is explainable by the fact that the adaptability of steel to manufacture and the variety of steel grades and of kinds of heat, thermomechanical and thermochemical treatment provide a wide spectrum of mechanical, physical and operating characteristics in ready articles. Structural components with substantially different morphologies and properties (ferrite, pearlite, upper and lower bainite, martensite, retained austenite) can be obtained by varying the chemical composition of the metal, the parameters of heat treatment (heating temperature, cooling rate etc.). The temperature and time ranges of formation of structural components in steels are commonly represented for heat treatment purposes in the form of isothermal and thermokinetic diagrams [1 – 3]. Diagrams of transformation of supercooled austenite in steels are plotted with the help of metallographic, durometric, magnetometric, dilatometric and other techniques. Each approach has its own advantages and disadvantages, and the methods of analysis of the results and errors obtained also differ. This makes generalization and analysis of the diagrams plotted by different methods with the use of different equipment senseless because of the possibility of substantial errors. However, the reference
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