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The joint effect of vanadium and nitrogen on the mechanical behavior of railroad wheels steel

Kulyk V. V., Shipitsyn S. Ya., Ostash O. P., Duriagina Z. A., Vira V. V.

Journal of Achievements in Materials and Manufacturing Engineering

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2018

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Vol. 89, nr 2

56--63

EN

Purpose: The aim of the proposed research is to investigate the regularities of the microstructure change, fracture micromechanism and mechanical service characteristics of the high-strength wheel steel with a lowered carbon content under static, impact and cyclic loading depending on the total content of vanadium and nitrogen and also the steel heat treatment modes. Design/methodology/approach: Alloying with vanadium was carried out in the range of 0.09-0.23% and nitrogen in the range of 0.006-0.018%. All steels were heat treated by normalizing and subsequent tempering at different temperatures in the range of 450-650°C. Steels microstructure was investigated by the optical metallography methods on the microscope EPITIP-2 (Carl Zeiss Jena). Scanning electron microscope Zeiss-EVO40XVP was also used for microstructural and microfractography investigations. Static strength (UTS), relative elongation (TEL), impact toughness tests (KCV) and fatigue crack growth resistance characteristics (fatigue threshold ΔKth, cyclic fatigue fracture toughness ΔKfc) were determined on standard specimens. Rolling contact fatigue testing was carried out on the model specimens. Findings: The regularities of the change of microstructure, fracture micromechanism and mechanical characteristics of the high-strength wheel steel with a lowered carbon content under static, impact and cyclic loading depending on the total content of vanadium and nitrogen and also the steel heat treatment modes are studied. Research limitations/implications: The results obtained on laboratory samples should be tested during a real railway wheels investigation. Practical implications: The steel with the optimal parameter [V∙N]∙104 = 22.1% provides high tread surface damaging resistance established on the model wheels. Originality/value: It was established that after normalization at 950°C and tempering at 550°C the increase of ultimate strength UTS and cyclic fracture toughness ΔKfc by 4% and 19%, respectively; impact toughness at room (KCV+20) and low temperature (KCV-40) in 1.5 and 3.3 times, respectively, when parameter [V∙N]∙104 changes from 7.8 to 22.1% and carbon content from 0.63 to 0.57%.

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Effect of vanadium microaddition on the microstructure and mechanical properties of casing pipes after normalizing process

Kiczor M., Przegrałek P., Grajcar A.

Journal of Achievements in Materials and Manufacturing Engineering

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2016

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Vol. 78, nr 1

11--20

EN

Purpose: The aim of the paper is to determine the impact of vanadium microaddition on mechanical properties and microstructure of two steel grades with a different content of V, applied for production of casing pipes used in the extractive industry. Design/methodology/approach: Pilger process technology with subsequent normalizing was used. The tests were carried out on an industrial batch produced in the Rurexpol Department, and the research was done with the use of industrial research laboratories of Alchemia S.A. Group. The microstructure and mechanical properties were determined in the initial state and after normalizing at two temperatures: 940°C and 880°C. Static tensile test and Charpy V impact test have been applied. Findings: Mechanical properties, macrostructure and microstructure of steel pipes, obtained during production under industrial conditions, have been analyzed in the article. The effects of V content and hot-working and normalizing treatment affect substantially the mechanical properties and microstructure of the investigated steels. Research limitations/implications: It was found that the application of vanadium microaddition to the normalizing process after the hot-rolling has a beneficial effect on a strength-toughness balance only at a narrow range of technological parameters of the normalizing. Practical implications: The knowledge of the vanadium microaddition effect on the industrial production route is indicated in the paper. Originality/value: : The effect of vanadium microaddition has been proved to be very sensitive to the temperature conditions of the heat treatment.

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Ductilization of Ni3Al by alloying with boron and zirconium

Hyjek P., Sulima I., Wierzbiński S.

Archives of Materials Science and Engineering

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2009

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Vol. 40, nr 2

69-74

EN

Purpose: The investigation of Ni₃AlBZr alloys was carried out to determine the influence of small zirconium and boron additions on the microstructure and mechanical properties, particularly with respect to room-temperature, and different strain rate conditions. Design/methodology/approach: Additions of both boron 0.26 at.% and zirconium from 0.3 to 1.5 at.% results in higher strength than exhibited by unalloyed Ni3Al. The sequence of structural changes of Ni3Al-based alloy has been correlated with mechanical properties, determined in uniaxial compression tests. Two ranges of work hardening have been identified on the stress-strain curves of these alloys. It was found that the first range of deformation corresponds to the intergranular slip system operating within individual grains, while the second one is connected with transgranular slip. Findings: Structural observations of A and B alloys showed that zirconium addition causes a decrease of the average grain size. On the mechanical properties of investigated alloys the increasing yield stress and hardness were observed in enlarging zirconium additions. However, the enlarged addition of zirconium causes a decrease of extension. Addition to an intermetallics compound Ni₃Al of such elements as boron (0.26 at.%) and zirconium (0.3 - 1.5 at.%) can be accepted as optimum from susceptibility to plastic deformation point of view. Research limitations/implications: The main limits for application of the polycrystalline Ni3Al phases is a poor strength and creep properties at high temperatures. The improvement of mechanical proprieties of Ni₃Al phase required small addition of suitable alloying elements. Practical implications: The results of investigations as well as the conclusions may be used for improvement of alloys processing based on Ni₃Al intermetallics compound. In well-considered peculiarity selection of alloyed additions and also processing parameters it is possible to steer in a limited range of mechanical properties of these alloys. Originality/value: The results of investigations expand knowledge about processing of the alloys based on Ni₃Al phase, and in consequence, to apply it in many branches of industry.