Experimental study of the rheological behavior of steels at the postcritical deformation stage at high temperature

Abstract

A methodological issue for carrying out the rheological tests of structural steels at the postcritical stage of deformation at high temperatures under conditions of tensile tests with the possibility of registering changes in the geometry of the strain gauge of the samples during the testing has been considered. The methodology for rheological tests at high temperatures is based on the use of the electromechanical test system, which include the cooled grips, high-temperature furnace for heating samples, cooling system for grips and extensometer, control device for measure of temperature on the sample surface using thermocouples. In accordance with the design of the used furnaces and gripping devices, sketches of samples were developed for tensile tests and tensile-torsion tests. The temperature regimes and test speeds were determined, and the sequence of loading and holding the samples was chosen in accordance with the objectives of the study. Experimental data on the effect of test temperature on creep and relaxation of structural steels, previously subjected to postcritical deformation, were obtained. Experimental diagrams of deformation of X15CrNi12-2 steel samples at a temperature of 400 °C, 500 °C and 600 °C with exposures with fixed deformation at various stages of elastoplastic and postcritical deformation were constructed. Experimental data obtained during the project implementation show that during the deformation of steel at the postcritical stage of deformation at high temperatures, rheological processes actively occur. The relaxation processes in samples at the postcritical stage of deformation substantially depend on the test temperature and the degree of elongation achieved by the time of exposure. An increase in temperature leads to a more intensive decrease in the relative load at exposures, and an increase in the degree of postcritical deformation leads to an increase in the intensity of relaxation processes, and this effect is most pronounced with increasing temperature. The revealed experimental dependences confirm the need to take into account the rheological component of the mechanical behavior of steels when studying postcritical behavior at high temperatures.