Brykov M. Development and application of material science basis for increasing wear resistance of iron-based alloys at abrasive wear

Object of research - abrasive wear of iron-based alloys. Goal of research - Development of material science basis for increasing wear resistance of iron-based alloys at abrasive wear. Methods of research - performing tests to determine the wear resistance of iron-based alloys at different structural state using standard and newly developed testing techniques along with investigations on chemical composition, structure and properties of iron-based alloys using spectral analyses, X-ray analyses, optical microscopy, standard methods for determining mechanical properties. Theoretical and practical outcomes: Determined are the regularities of abrasive wear of Fe-C alloys without heating in widest possible range of carbon content. The influence of increased temperature and alloying on wear resistance of metastable austenite are investigated also. The principles of creation of wear resistant alloys are presented using chromium and manganese as sample alloying elements. Two wear resistant steels i.e. 150X3 and120Г3 are proposed. Novelty: There are experimental and theoretical bases which are proposed in this work as a solution of material science problem of creation and utilizing of iron-base alloys with rational composition having high wear resistance at abrasive wear. This outcome is obtained on the ground of following new statements: - the dependences of wear resistance of iron-carbon alloys on their properties in maximal possible range of carbon content (0,08-4,30 %С) are determined taking into account their phase structural state. It is shown, that metal base of iron-based alloys forms the following sequence from low to high wear resistance: ferrite - martensite - austenite. High wear resistance of austenite is achieved due to simultaneous processes of phase transformations and mechanical hardening to highest possible level which take place in the surface layer during wear process; - for the first time it is established influence of sliding velocity (0,1-3500 mm/s)and increased temperatures (20-290 оС)on wear resistance of plain carbon alloys in different structural state. It is shown that austenitic structure, which is most wear resistant, is at the same time most susceptible to heating in the process of abrasive wear. The wear resistance of austenitic samples decreases twice at temperature rise as little as 130 oC. Intensive falling of wear resistance proceeds with subsequent rise of temperature. This phenomenon is explained by stabilizing of austenite and decreasing of completeness of phase transformations. In addition, the most intensive decreasing of yield stress of austenite occurs at heating to 100-150 oC. This even more decreases resistance to embedding of abrasive grains and plastic deformation of the friction surface. Nevertheless, the wear resistance of austenite is higher or equal than that of martensite at any temperature in investigated range; - for the first time the diagram "Relative wear resistance - Hardness - Temperature" is proposed. This diagram reflects the regularities of abrasive wear resistance of Fe-C alloys and allows presenting in concentrated view all possible range of wear resistance of plain carbon alloys at different temperatures of friction surface. This diagram is also suitable for estimation of wear resistance of a newly designed alloys; - it is shown that there is an optimal carbon concentration responsible for maximal wear resistance of austenite at given content of alloying element. This is due to martensite start temperature which determines completeness of phase transformations during wear process and hence level of hardening on friction surface. At the same time it is necessary to provide higher carbon content to achieve high wear resistance in alloys with a structure of metastable austenite. At that concentration of alloying element should be as little to be enough to suppress graphitization and raise the stability of austenite against diffusive transformation. - for the first time determined are the dependences of optimal carbon content from concentration of chromium and manganese. It is established that either chromium or manganese decrease optimal carbon content, but effect of manganese is much more significant. Therefore at the same concentration of alloying element chromium alloys possess higher wear resistance that manganese ones. At the same time alloying with manganese should be preferred when it is necessary to obtain deep quenched layers in massive parts at the expense of certain loss of wear resistance. Application: In-plant testing have been performed with natural press-mould plates for pressing of lime bricks. The plates were made from 150X3 steel (1.5 %C, 3 %Cr) and their wear resistance appeared to be twice greater than that of ordinary plates made from cemented and quenched 20X steel (0.2 %C, 1 %Cr). The expected economical effect at implementation of 120Г3 steel (1.2 %C, 3 %Mn) in producing of grinding balls is determined. Said effect exceeds 1 million hryvnas.