Problems of Ensuring Safe Operation of Freight Wagon Trolleys at Low Temperatures
The purpose of this study is to evaluate the cold resistance of 20GL steel, which is widely used for the manufacture of critical structures (in particular, freight carriage trolleys) operating at low temperatures. To achieve this goal, tests were carried out on the shock bending of the studied metals in the temperature range of climatic cold (-80 ... -20 °С), followed by study of metal fractures, an assessment of the structural state of steel, which was subjected to heat treatment according to the manufacturer’s mode and thermocyclic processing (TCP). The studies were carried out using the MK-300 pendulum specially designed for cooling camera samples, as well as optical methods (KEYENCE VHX-1000) and electron microscopy (JSM-3U), fractographic studies. During the study, data were obtained on the change in toughness, metal fracture mechanisms for a wide range of low temperatures, as well as the temperature of the viscous-brittle transition. An operation was performed for a 20GL alloy to evaluate the effect of grain refinement on working capacity at low temperatures. As a result of the work, an assessment of the cold resistance of 20GL steel is given. It was found that the heat treatment of the manufacturer, consisting of normalization and high tempering, makes it possible to ensure reliable operation of products from the studied steel up to -20 °С, which corresponds to the temperature of the viscous-brittle transition (T50). It was established that grain refinement during TCP does not improve the cold resistance of 20GL steel, but, on the contrary, the temperature of the viscous-brittle transition shifts toward higher temperatures (Т50 = -13 °С). However, the results of microhardness measurements (up to TCP 1591 MPa, after 1911 MPa) show an improvement in the strength characteristics of the steel under study after TCP.