Effect of Cooling Rate during Heat Treatment on Martensitic-Bainitic Class Alloy Steel Microstructure and Properties

The microstructure and mechanical properties of engineering steels with high supercooled austenite stability after cooling at different rates from the austenitizing temperature are studied. Thermokinetic diagrams are plotted for supercooled austenite transformation and temperature-time intervals are determined for structural component formation during continuous cooling. In order to evaluate mechanical properties trajectories and cooling rates are established by experiment for specimens in various media, i.e., oil, still air, and a special container filled with cast iron shavings. It is shown that when the experimental cooling path is superimposed on a thermokinetic curve it is necessary to consider instantaneous cooling rates in different temperature ranges. The effect of cooling intensity on mechanical properties of steels of different composition is established quantitatively. It is found that the impact strength of steels of different alloy systems depends in different ways on cooling rate.