Papers by Keyword: Ferrite

Abstract: The present work deals with the evolution of mechanical properties and structure of low-carbon Fe-1,12Mn-0,08V-0,07Ti-0,1C (wt.%) steel after severe plastic deformation (SPD) and high-temperature annealing. Steel in initial ferritic-pearlitic state was deformed by equal channel angular pressing (ECAP) at T=200°C and high pressure torsion (HPT) at room temperature. The evolution of ultrafine grained structure and its thermal stability were investigated after annealing at 400-700°C for 1 hour. The results shown that SPD leads to formation of structure with an average size of (sub-) grain of 260 nm after ECAP and 90 nm after HPT. Ultrafine grained structures produced by SPD reveal a high thermal stability up to 500°C after ECAP and 400°C after HPT. At higher annealing temperatures a growth of structural elements and a decrease in microhardness were observed.

Abstract: Dynamic recrystallization (DRX) of ferrite in a low carbon steel with the (α+θ) duplex microstructures was investigated using hot compression tests in combination with SEM, TEM and EBSD, and the effect of the size of cementite particles was analyzed. The results indicated that during hot deformation of the low carbon steel DRX of ferrite took place and the increase in the average size of cementite particles was of benefit to DRX. The formation of DRX grains was attributed to particle stimulated nucleation (PSN), by the well development of the subgrain near cementite particles. At the beginning of hot deformation, DRX grains were mainly formed near cementite particles with the size of about 1μm or above. With the increase in the strain, such grains were also formed around pairs or groups of particles with the size of 0.5μm to 1μm.

Abstract: The kinetics of static recrystallization in cold rolled ferritic stainless steel sheet tends to slow drastically over the last 10-20% of recrystallization. This has its origins in both the microstructure (deformed grain shape, precipitates) and in the local deformation texture. In this work we have sought to provide a physical explanation for the slow last stages of recrystallization through a texture dependent JMAK model which is informed by the microstructure of the partially recrystallized microstructure. The geometrical assumptions made in developing this JMAK model have been compared to phase field simulations using experimental observations as the source of their starting configuration.

Abstract: Nanoparticles of CoCrFeO₄ ferrite in the particle size range of 9 - 38 nm have been prepared by a sol-gel auto combustion method. Synthesized powders were annealed at four different temperatures viz. 400 °C, 600 °C, 800 °C and 1000 °C. Particle sizes are determined by X-ray analysis and TEM. The size of the nanoparticles increase linearly with sintering temperature and time, most probably due to coalescence that increases as sintering temperature increases. The saturation magnetization increases from 62 to 81 emu/g and coercivity initially increases up to 814 Oe and then decreases to 366 Oe with increase in particle size and sintering temperature. The typical blocking temperature increases from 135 to 165 K with increasing particle size.

Abstract: The self-propagating high-temperature spraying synthesis (SHSS) route is evaluated for the synthesis of ferrite powders that are subsequently processed towards the manufacturing of high initial magnetic permeability. The powder samples are used for characterization by SEM, EDS and XRD. The results show that the obtained particles are hollow microspheres from nanometer dimension to several micrometers. The phase structure of hollow microspheres is the mixtures of ferrite and Fe2O3. Permittivity and permeability measurements are made on particles dispersed in a paraffin wax matrix. The microsphere is a ferromagnetic matter with both high magnetic loss and high dielectric loss.

Abstract: In this paper, firstly, the equilibrium solubility product formula of MoC with NaCl type cubic crystal structure in ferrite has been deduced by thermodynamic method, according to the free energy change of molybdenum and carbon dissolved in ferrite and the formation energy of MoC. On the basis of deducing activity coefficients of Mo in iron, the solubility product formula of MoC in austenite has been obtained according to the relationship of solubility product of MoC in austenite and ferrite. Finally, the solubility products for MoC and NbC in iron are compared. The solubility product formulae of MoC deduced would play an important role in related theoretical research and practical production.

Abstract: Ammonia production is a capital-intensive industry as it requires high temperature (400-500oC) and also high pressure (150-300 bar) for its daily operations. An earnest effort was made to synthese ammonia gas using an in-house designed microreactor. The production of ammonia was carried out in a magnetic field reaction zone, with the reaction temperature of 30°C - 280°C and ambient operation pressure. Mn0.8Zn0.2Fe2O4 nanoparticles, synthesized using the sol gel method, were used as the catalyst for the ammonia synthesis. XRD confirmed the single phase ferrites and FESEM images revealed nanofibre-like morphology when sintered at 700oC in argon gas. Electron diffraction was performed using HRTEM and obtained diffraction patterns confirmed the crystal structure of the catalyst. By using the Kjeldahl method it was found that the reaction carried out in 1 Tesla magnetic field gave approximately 46% ammonia yield. The proposed new method could be appealing for ammonia manufacturers due to highly economical implication which may offer urea producers a potential contender in the competitive market place.

Abstract: To establish the method for determining the amount of carbon in the ferrite phase in ferrite + martensite dual-phase low-alloy steels, mechanical loss measurements have been performed on a series of Fe–C alloys with varying constitution. The observed mechanical loss spectra of two-phase alloys turned out to be simple superposition of those of single phase alloys, of ferrite and of martensite. The concentrations of carbon in solution evaluated from the magnitude of the Snoek relaxation in the two-phase alloys agree well with those expected from the Fe–C phase diagram. It is thus possible to selectively analyse the carbon dissolved in the ferrite phase in the complex structure, at least in simple binary alloys.

Abstract: A mathematical model was developed predicting the effects of alloying and thermomechanical processing on the final microstructure of steel. Various factors influencing transformation kinetics, including microalloying with Nb and plastic deformation of austenite, are considered. Subsequent stages of the model development and calibration are described.

Abstract: A new kind of bainite steel with ultra-low carbon content and Nb, Ti alloys has been developed. By applying thermomechanical control process, water quenching and tempering at different temperature, excellent properties have been obtained when tempered at 450°C, with the yield strength of 813MPa and elongation of 16.2%. The morphology observed by SEM shows that the microstructure consists of fine lath-shaped bainite, polygonal ferrite, quasi-polygonal ferrite and a small fraction of residual austenite or martensite-austenite constituents. In a TEM study plenty of precipitates with the size about 5-10nm were observed interacting with the dislocations, which is very significant for the optimization of strength and ductility.