Experimental study of postcritical deformation and failure of steels at high temperature

The work is aimed to studying the strength and survivability of structures on the base of perceptions about the kinetic nature of the destruction of materials. An experimental study of the regularities and effects of the mechanical behavior of structural materials at the stages of elastoplastic and postcritical deformation at elevated temperatures has been carried out. Tests on uniaxial tension of specimens of the heat-resistant high-alloyed corrosion-resistant steel of martensitic class X15CrNi12-2 and the structural alloyed steel of pearlite class 40Cr were implemented in a wide range of temperatures: 22 °C, 200 °C, 400 °C, 500 °C and 600 °C. The methodological issues of testing on the universal servohydraulic test system Instron 8801 with using of the furnace and a high-temperature extensometer are considered. Based on the obtained experimental data, deformation diagrams with developed stages of softening were constructed, and the influence of the strain rate on the postcritical behavior of steel 40Cr was evaluated. Comparison of the main strength and deformation characteristics of the considered steels at different temperatures is carried out. Images of fracture surfaces of samples after fracture at high temperatures, which are characterized by different morphology, were obtained. On the basis of experimental data about the mechanical characteristics of steels, diagrams of the petal type have been constructed, which allow to a realize the complex analysis of properties at various temperatures. It is shown that with increasing the temperature of the test, the decreasing of the strength characteristics, associated with the provision of the static strength of the part, is take place. This is followed the increasing of the deformation resources (residual elongation and relative narrowing after rupture) and the coefficient of the postcritical deformation stage, which has a positive effect on survivability during destruction process.