Babachenko O. Development of scientific statements about influence of the structural state on reliability and durability of solid-rolled railway wheels and tyres

The object of study is the formation of the structural state of ferrite-pearlite steels during hot deformation and subsequent heat treatment, its effect on the properties of steel. The purpose of the thesis is increasing the reliability and durability of solid-rolled railway wheels and tyreson the basis of control of processes of structure formation of ferrite-pearlite steels by improving their chemical composition and optimization of the deformation and heat treatment parameters. The researchmethods: light and scanning electron microscopy used to study of the structural state of steels; X-ray analysis used to study of the fine structure of steel; local X-ray analysis used to study of the composition of non-metallic inclusions, dilatometric method used to research of austenite transformation during continuous cooling; mechanical tests used for determining the mechanical properties, methods of mathematical statistics used in the processing of experimental data. The theoretical and practical results: developed and scientifically substantiated the chemical composition of the steel and the technological parameters of deformation and heat treatment of the railway wheels and that provideincreasing of the reliability and durability indices and reduction ofmanufacturing costs. The method of determination of fracture toughness of the railway wheels has been developed. Scientific novelty: for the first time the regularities of phase transformations during continuous cooling the steel for manufacturing of the railway wheels with a high content of silicon have been established. For the first timethe nonlinear dependence of the depth of the martensite layer which is formed during braking of railway wheels and determines their resistance to the formation of defects on the tread surface of thermal originon the content of carbon in the steels has been established. For the first time the dependences of the critical stress intensity factor at cyclic loading (cyclic fracture toughness) Кfc ferrite-pearlite steels on the cooling rate from the austenitic state and the carbon content have been obtained. Degree of manufacturing application: the technology of heat treatment of the tyres made of the vacuum degased steel without treatment against flakes has been developed and realized at the PJSC "INTERPIPE NTRP". The actual economic effect is equal 74 UAH / tonne (according to prices in 2009 year).At the PJSC "INTERPIPE NTRP" the manufacturing technology of railway wheels with a high silicon content providing their resistance to the formation of defects on the tread surface by 44% and the new method of accelerated cooling of the tyres and technological parameters of their heat treatment that provide increasing of wear resistance have been developed. Scope: manufacturing of metal productionmade of carbon steel at the metallurgical enterprises.