Influence of size and distances between impurities on fatigue strength structural steel for agricultural machines
2018
Lipinski, T., University of Warmia and Mazury in Olsztyn (Poland)
The high-purity low carbon steel properties are influenced by the chemical composition and production technology. The morphology of impurity, its size and content is very important for the quality of high-purity steel. Hard, non-plastic microstructure of steel with impurities as non-metallic inclusions can be one of the factors that influence the fatigue strength of steel. The quantity of non-metallic inclusions results from the content of impurities in the steel, while their size, dispersion, microstructure, phase composition shape and impurity spaces are determined by the course of technological processes in liquid state. The tested material consisted of semi-finished products of high-purity, low-carbon structural steel with: boron, chromium, manganese, molybdenum, nickel and low contents sulphur and phosphorus as impurities. The experimental material obtained in industrial production consisted of structural steel obtained in three series of steel melts in furnaces: electric with desulphurized, electric with desulfurized and next argon-refined and the third series from oxygen converter with vacuum degassed of steel. The technological process consisted of two melting technologies: the first and second in a 140-ton basic industrial arc furnace and the third in a 100-ton oxygen converter. The test specimens were austenitized by treatment at temperature 880 ºC for 30 minutes. Next the samples were cooled in cold water and tempered in different temperatures: 200, 300, 400, 500 and 600 ºC for 120 minutes and cooled on air. The fatigue strength of the samples was tested on a rotary bending machine at a frequency load 6000 rotations per minute. The present work discusses the results of changes in rotary bending fatigue strength of low carbon structural steel hardened and tempered at different temperatures as the influence of size and distance proportions between the impurities of high-purity low carbon steel.
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