Requirements for mechanical properties of steels are constantly increasing, and the combination of quenching and tempering is the method generally chosen for achieving high strength in medium carbon steels. This study examines the influence of various silicon contents from 1.06 to 2.49 wt% and the addition of copper (1.47 wt%) on the behavior of 1.7102 steel starting with the as-quenched state and ending with the tempered condition at the temperature of 500 °C. The microstructure was characterized by SEM and TEM, the phase composition and dislocation density were studied by XRD analysis, and mechanical properties were assessed by tensile and hardness testing, whereas tempered martensite embrittlement was assessed using Charpy impact test and the activation energy of carbide precipitation was determined by dilatometry. The benefit of copper consists in the improvement of reduction of area by tempering between 150 and 300 °C. The increase in strength due to copper precipitation occurs upon tempering at 500 °C, where strength is generally low due to a drop in dislocation density and changes in microstructure. The increasing content of silicon raises strength and dislocation density in steels, but the plastic properties of steel are limited. It was found that the silicon content of 1.5 wt% is optimum for the materials under study.
This paper introduces a new alloying concept for low-density steels. Based on model calculations, samples—or “heats”—with 0.7 wt% C, 1.45 wt% Si, 2 wt% Cr, 0.5 wt% Ni, and an aluminium content varying from 5 to 7 wt% are prepared. The alloys are designed to obtain steel with reduced density and increased corrosion resistance suitable for products subjected to high dynamic stress during operation. Their density is in the range from 7.2 g cm−3 to 6.96 g cm−3. Basic thermophysical measurements are carried out on all the heats to determine the critical points of each phase transformation in the solid state, supported by metallographic analysis on SEM and LM or the EDS analysis of each phase. It is observed that even at very high austenitisation temperatures of 1100 °C, it is not possible to change the two-phase structure of ferrite and austenite. A substantial part of the austenite is transformed into martensite during cooling at 50 °C s−1. The carbide kappa phase is segregated at lower cooling rates (around 2.5 °C s−1).
The main aim of this article was to describe the methodology for the measurement of specific heat using the laser flash apparatus. The obtained values are compared to results from the literature, differential scanning calorimetry and computational method (JMatPro). Measurements were taken and computations were performed for pure metal (copper), high-alloyed steel (austenitic stainless steel) and alloy with low temperature melting point (zinc-aluminium-copper alloy). Aluminium, graphite and molybdenum were used as reference materials for laser flash method. The measurements were taken with multisample system. Accuracy of the device and influence of sample thickness and mass were evaluated from measurements of molybdenum reference in temperature range 20-800°C. The influence of reference material selection on the obtained values of specific heat was evaluated for copper and austenitic stainless steel. Measurements of zinc-aluminium-copper alloy in low temperature range (20-300°C) have shown advantage of the described methodology in comparison with heat-flux differential scanning calorimetry.
The 54SiCr6 steel belongs to spring steels which excel high strength and at the same time reaches high values of reduction of area and sufficient value of elongation. Nowadays, new methods are searched and examined how to get better properties from materials, higher strength and toughness, longer fatigue resistance or better corrosion properties. In the case of silicon-chromium spring steels, innovative heat treatments are investigated such as quenching and partitioning which enables to achieve higher ductility of steel due to higher content of retained austenite. The way of modification of the chemical composition of the 54SiCr6 steel was chosen in combination with conventional heat treatment composed of quenching and tempering to get better properties. The materials with increased content of copper to 1.5 wt. % and silicon to 2.5 wt. % were prepared. The influence of alloying elements on microstructure and mechanical properties was followed up to the tempering temperature of 400 °C.
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