Papers by Keyword: Ferrite

Abstract: We have determined different phase fractions from microscopy images using semi-automated image analysis fitting technique, and in addition we have classified each phase according to its hardness. The distribution of grayscale pixels of different phases is first characterised separately for each phase, which are sampled from the microscope image. After this the distributions of the separate phases are fitted to give the corresponding distribution of the whole image. The microhardness measurement provides reliability on the classification of the different phases to ferrite, bainite or martensite. In addition to describing the applied techniques in detail, we present the results obtained from the analysis for one steel subjected to isothermal holding experiments at different temperatures.

Abstract: In the present work, the segregation degrees of ferrite and austenite stabilizer alloying elements were analyzed for a high strength steel. For this, samples were taken from the surface and center of the hot-top and the upper section of a 40 MT ingot. The results showed that the positive segregation ratios for all the investigated elements were higher in the ingot center than in the surface with higher values for austenite stabilizer elements. The increase of austenite alloying element stabilizers was accompanied by the change in the primary solidification mode of the austenite phase. The obtained results are in good agreement with the observed presence of austenite, revealed by X-ray diffraction analysis, stabilized by the austenite alloying elements.

Abstract: The present investigation intended to analyse the mechanical properties of medium carbon low alloy steel (AISI 4140) under dual phase heat treatment condition. Formation of dual phase, ferrite and martensite (F+M) from normalized condition followed by heating in the intercritical temperature range to form different volume fractions of ferrite and martensite alters tensile, hardness and impact strength of medium carbon steel. Effect of alloying elements in dual phase treatment will change the mechanical properties. Tensile strength and hardness of austempered steel shows higher value followed by dual phase condition. Ductility of normalized shows better as compared to as bought and dual phase, but austempered shows almost similar to normalized result. Impact strength of the austempered is excellent followed by dual phase condition. Heat treated specimen microstructures reveal the different phase’s present.

Abstract: With the help of the Thermo-Calc software package, arrays of calculated data were created for carbon concentrations in ferrite and austenite, corresponding to the para-equilibrium of these phases and their para-equilibrium with cementite, as well as for the corresponding temperatures A₁ and A₃. Marked arrays were obtained in wide temperature ranges for ranges of carbon concentrations and the most important substitution alloying elements (Mn; Si; Cr; Ni; Mo), covering the respective ranges for medium carbon and moderately alloyed steels. Analytical formulas were developed on the basis of the reference data arrays for calculating para-equilibrium concentrations of carbon in ferrite and austenite (depending on temperature and chemical composition), as well as temperatures A₁ and A₃ (depending on chemical composition), which allow to reproduce with high accuracy the results obtained using Thermo-Calc.

Abstract: This article shows a study of the effect of mechanical activation of the initial mixture of reagents NiO and Fe₂O₃ at different speeds of grinding bowl rotation on synthesis of nickel ferrite. Nickel ferrite was produced by the solid-phase synthesis at a temperature of 900 °C for 240 minutes. The obtained ferrite samples were investigated by thermal gravimetric and X-ray phase analysis. The Curie temperature values are obtained, as well as the magnitude of the change of detected instrument weight at the magnetic phase transition (ferromagnetic-paramagnetic) of nickel ferrite using thermal gravimetric curves (TG/DTG) with applied external magnetic field. Increasing of the homogeneity degree of ferrite materials with an increase in the mechanical activation rate is shown based on the data of X-ray phase analysis. The experimental results obtained from thermal, magnetic, and X-ray analyzes were compared.

Abstract: Mechanical alloying of a mixture of Fe₂O₃ and CoO powders has been applied for the preparation of nanocrystalline. Utilizing a ball-to-powder mass ratio of 20, milling time of 20 hours followed by annealing at 900°C, we could obtain a nanocrystalline of high crystallinity and composed of mainly CoFe₂O₄ phase with presence of Fe₂O₃ as revealed by X-ray diffraction (XRD) measurements. Magnetic measurements using vibrating sample magnetometer (VSM) reveal high saturation magnetization for the annealed sample close to CoFe₂O₄ phase value. The heating efficiency of the obtained nanocrystalline is studied under an alternating magnetic field and as a function of the concentration. It was found that the nanocrystalline generate a substantial amount of heat when exposed to an alternating magnetic field. In vitro hyperthermia experiment was carried out and our result clearly demonstrates the ability of the obtained nanocrystalline to kill cancer cell through magnetic hyperthermia.

Abstract: Sintered steels, with and without boron addition, were prepared from powder compacts of pre-alloyed Fe-1.5Mo powder mixed with varied amounts of graphite (0, 0.1, 0.2, 0.3, and 0.4 wt.%) and hexagonal boron nitride (0 and 0.5 wt.%). Sintering was performed either in hydrogen or in vacuum atmosphere at 1280 °C for 45 minutes. The post-sintering cooling was performed in a furnace that was equivalent to 0.1 °C/s. The sintered boron-free steels showed dual-phase microstructure consisting polygonal ferrite and precipitate-containing grains. Each precipitate-containing grain contained packets, each of which was characterized by lamellar structure with alternating fibrous particles and ferritic laths, when carbon contents were in the range 0.1-0.3 wt.%. All the grains containing fine needle particles decorating ferritic lath boundaries were observed in the sintered Fe-Mo-0.4C steels. Boron addition caused some effects on sintered steels. The action of boron was the formation of grain boundary boride in the vacuum-sintered steels although it was hardly observed in case of hydrogen-sintered steels. Boron also promoted precipitation inside polygonal ferrite grains and along ferritic lath boundaries. The precipitate particle shape was fine needle-like in the sintered boron-containing steels. Due to liquid phase sintering, as a result of eutectic melting, the associated grain growth was observed. Disappearance of grain boundary boride was evidenced in the hydrogen-sintered steels. Without boron addition, hardening of the sintered steels strongly depended on carbon content. With boron addition, all the sintered steels showed high tensile strength and hardness even in the case of no graphite addition. Hardening action by carbon in the sintered boron-containing steels was weaker than that in the sintered boron-free steels.

Abstract: Over the past decade, Dual Phase steels are extensively used in the automotive industry to reduce the weight of the vehicles. The Fiber laser welding has been showing superior weld quality over other laser welding methods. DP 600 grade is most widely used grade among DP steels. Influence of heat input on microstructural and mechanical properties for the given thickness has been investigated. Widths of weld zone and Heat Affected Zone have decreased with decreasing the heat input. Rapid cooling rates in the fusion zone have resulted in martensitic structure and hardness also increased in proportional. Tensile test and notch tensile test of the welded joints have been confirmed that weld joints are stronger than that the base material. From the ensile test along the weld joint of all heat inputs, it has been observed that lower heat input weld joints have shown better properties over the others.

Abstract: The paper considers theoretical aspects of the kinetics of austenite → ferrite transformation in an Fe–9 %Cr alloy, a common model of diffusionless transformation. In previous studies it was shown that this transformation under isothermal conditions shows a behaviour typical for nucleation site saturation, including the change of the Avrami exponent n (determined as the slow of transformation curve on double logarithmic scale) from 4 to 1. Activation energies determined in two ways: by the ‘nose’ temperature of the normal C-curve and by the slope of the C-curve re-drawn on a reverse temperature scale are unexpectedly similar (272–315 kJ/mole) and not temperature-dependent. But the complete TTT diagrams calculated using these values determined directly from experimental data and the precise formula of Cahn’s solution of grain face nucleated transformation problem do not provide good agreement with experiment in the whole temperature range. This may mean that the theory of site saturation needs some correction.

Abstract: A steel containing Fe-0.2C-2Mn-Si-Al was annealed using intercritical Q&P cycles. Quenching temperature and partitioning time at 440°C was varied. Analysis of microstructure evolution during such Q&P treatments was performed using different characterization tools: FEG-SEM, EBSD, dilatometer and saturation magnetization measurements. Especially, phenomena taking place during partitioning were investigated. The microstructure was analyzed at the end of soaking, before and after partitioning and at the end of the annealing cycle. It was found that bainite transformation happens during partitioning and has a significant effect on the final retained austenite fraction. Quenching temperature has an important effect on both martensitic transformation during cooling and subsequent bainite transformation during partitioning.