The dissertation is devoted to the creation of a methodology for the development of the chemical composition of steel and technological parameters of heat treatment of railway wheels to achieve predetermined mechanical properties, which provide a high resource in specific operating conditions.
In the work at the level of the interatomic interaction in steels for railway wheels the influence of chemical composition elements on their physical and mechanical properties is studied and forecast models for their expert evaluation are developed. In a study at the level of the interatomic interaction in steels for railway wheels, the effect of chemical composition elements on their physical and mechanical properties was studied and predictive models were developed for their expert assessment.
A methodology has been developed for the selection of the chemical composition of steel based on a predictive model using the parameters of the interatomic interaction to achieve predetermined mechanical properties of railway wheels. The obtained equations for predicting the values of critical temperatures and values of the midcritical interval ΔAc using the integral parameters of interatomic interaction. Taking into account the high accuracy of the models obtained, a computational experiment was carried out, as a result of which the total content and ratio of silicon and manganese, the carbon content in steel for railway wheels from the point of view of increasing resistance to the formation of defects of thermal origin was substantiated. Using the method of factor analysis, the improvement of the composition of steel into subsystems (matrix, alloying, micro- alloying, impurity) was carried out, which made it possible to separately take into account the influence of each of the subsystems on the level of mechanical properties of railway wheels. This made it possible to significantly improve the accuracy and stability of the obtained models.
The obtained adequate and stable models according to the "warehouse - heat treatment - mechanical properties" scheme for predicting the level of mechanical properties, taking into account the content of elements of various subsystems and the cooling rate.
Based on the developed theoretical provisions and laboratory and industrial experiments, recommendations have been developed on the chemical composition of steel and heat treatment parameters of railway wheels: for operation in light braking conditions at high loads, and which should have increased wear resistance (class D, AAR M-107 / M -208); with increased resistance to wear at high loads and high resistance to loads at negative temperatures (class D +, AAR M-107 / M-208, TTCI); with increased resistance to the formation of operational defects under high loads and difficult brakinbraking conditions (grade A to replace grade 2 and T according to DSTU GOST 10791: 2016).
The chemical composition of steel has been developed, which makes it possible to manufacture railway wheels that meet the requirements for railway wheels of class D +, the following chemical composition was recommended, wt%: С = 0.50-0.55; Si = 1.00-1.20; Mn = 0.80-0.85; V = 0.10-0.15; Cr = 0.3-0.4; Ni = 0.8-0.9; S ≤ 0.025; P ≤ 0.03; Mo ≤ 0.01; Cu ≤ 0.25; Al = 0.02-0.03; Ti ≤ 0.05. The influence of the cooling rate, temperature and duration of tempering on the formation of the microstructure and mechanical properties of low-alloy research steels was investigated.
It is established that when alloying steel for railway wheels with 0.55-0.6% C system (Al-Ti-N) during crystallization disperse refractory particles of titanium carbonitrides and aluminum nitrides are formed. The dispersed particles contributed to the grinding of the austenitic grain of cast steel during crystallization. The effect of aging duration (up to 2 hours) at 1260 °C on grain size was experimentally investigated. It was found that refractory particles inhibited the growth of grains in steel for railway wheels. The chemical composition of titanium and matrix metal carbonitrides near these particles was determined by micro-X-ray spectral analysis. It was found that the carbon content decreases around the TiC (N) particles.
According to the results of a pilot-industrial experiments, it was found that for steels with increased content of alloying and micro-alloy elements, heat treatment with a change in coolant flow rate from minimum to maximum during heat treatment allows avoiding the formation of quenching structures nears the rolling surface and achieving a high level of mechanical properties in the central volumes of the rim.
Keywords: carbon and microalloy steels, chemical composition, railway wheels, microstructure, mechanical properties, heat treatment, modeling.
