Ferrite Plates Research Articles

Core-shell structured Mn-Zn-Fe ferrite/Fe-Si-Cr particles for magnetic composite cores with low loss

A Mn-Zn-Fe ferrite layer, several hundred nanometers thick, was deposited on the surface of Fe-3.5Si-4.5Cr (mass%) powder particles as an insulating material by an ultrasonic enhanced ferrite plating method. The compositions of the Mn-Zn-Fe ferrite layer were Mn0.18Zn0.27Fe2.55O4, Mn0.38Zn0.25Fe2.37O4, and Mn0.54Zn0.24Fe2.22O4. The core loss (Pcv) performances of the compacted cores and magnetic properties of the core-shell structured powders were evaluated. All the ferrite-coated cores exhibited a saturation flux density (Bs) in the range of 1.54–1.56 T derived from their soft magnetic metal and ferrite composition. All ferrite-coated cores annealed at 773 K exhibited a constant permeability µ′ in the frequency range up to 50 MHz owing to the insulating effect of the ferrite layer, and the Mn0.54Zn0.24Fe2.22O4 ferrite-coated core exhibited the highest real permeability µ′ of 56 at 50 MHz. The core loss of the Mn-Zn-Fe ferrite-coated Fe-3.5Si-4.5Cr cores was 604–738 kW/m3 at 100 kHz and 50 mT, which was much smaller than that obtained for the Fe-3.5Si-4.5Cr core without a ferrite layer (3617 kW/m3). The eddy-current loss (Pe) of the Mn-Zn-Fe ferrite-coated Fe-3.5Si-4.5Cr cores considerably decreased compared with those of the non-coated Fe-3.5Si-4.5Cr core owing to the insulating properties of the ferrite layer.

Effects of low-temperature transformation and transformation-induced plasticity on weld residual stresses: Numerical study and neutron diffraction measurement

In this study, the weld residual stresses (RS) in a 25mm thick ferrite steel plate with newly developed low-temperature transformation (LTT) welding wire were investigated by finite element method and neutron diffraction (ND) measurement. A thermo-elastic–plastic finite element model coupled with solid-state phase transformation (SSPT) was developed to investigate the distribution and formation mechanism of RS, which has been verified by ND measurement. The results demonstrate that the developed LTT alloy can significantly reduce the RS and even generate compressive RS in the weld zone, due to the interrupted cooling shrinkage caused by the LTT. The higher inter-pass temperatures related to the microstructure evolution result in an increased region of compressive stress within the weldment. Moreover, the longitudinal RS in the weld zone gradually changes to tension as the initial temperature of martensitic transformation increases. Notably, the relaxation effect of transformation-induced plasticity on RS and its influence on model accuracy were discussed.

TRANSFORMATION OF CARBIDЕ PHASE IN RAILS AT LONG-TERM OPERATION

Evolution of carbide phase in surface layers of volume (passed gross tonnage 500 and 100 million tons) and differentially hardened rails (passed tonnage – 691.8 million tons) to a depth of 10 mm along the central axis and along the rail head fillet was studied by means of transmission electron diffraction microscopy. The grains of lamellar perlite, ferrite-carbide mixture, structurally free ferrite are analyzed. The flow of two complementary mechanisms of transformation of carbide phase of steel in the surface layers during the rails operation was identified: mechanism of cutting cementite particles and their subsequent­ transfer into the ferrite grains or plates volume (in perlite structure); mechanism of cutting and following dissolution of cementite particles, transition of carbon atoms to dislocations (into the Cottrell­ clouds and the dislocation centers), transfer of carbon atoms within dislocations to the volume of grains (or plates) of ferrite, with the following repeated formation of nanoscale cementite particles. A fragmented dislocation substructure is formed instead of former plates. Fragments boundaries decorate places where cementite-α phase interphase boundaries used to be. The main reason for dissolution of cementite is that it is energetically more preferable for carbon atoms to be on dislocation centers and on subboundaries than in cementite lattice. Binding energy of carbon atom-dislocation is 0.6 eV, for carbon atom-subboundary bond it is 0.8 eV, while in cementite it is held by 0.4 eV. Formation of elastoplastic stress fields is detected, concentrators of which are intra and interphase boundaries between grains of ferrite and perlite, cementite and ferrite plates of perlite colonies, particles of globular cementite and ferrite. The main sources of curvaturetorsion of metal lattice of rails metal are intraand interphase bounda­ries­ of grain separation of ferrite and perlite, cementite and ferrite plates of perlite colonies, particles of globular cementite and ferrite. Approaching to the rolling surface, number of stress concentrators and amplitude of internal fields of longrange stress are increasing.

Effect of Ni content on the microstructure and mechanical properties of weld metal with both-side submerged arc welding technique

The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (−40 °C and −60 °C) of the weld metal. The above influences of Ni were attributed to the formation of predominant acicular ferrite (AF), at the expense of grain boundary ferrite (GBF), ferrite side plates (FSP) and martensite/austenite (M/A) constituent in weld metal. EBSD results indicated that GBF keeps K-S or N-W relations only with the prior austensite grain that belongs to one side of the grain boundary and the variants belong to the same bain group which always forms low angle boundary. Moreover, the retained austenite as one part of M/A constituent was mainly found in the weld metal with lower Ni content. It indicated that the transformation process could be promoted more completely by the increase of Ni content. The mechanism of the toughness improvement brought by Ni increasing was ascribed to the relatively uniform transformation to final microstructure, which reduces the appearance of GBF and M/A constituents.

Transformation of Carbides in Prolonged Rail Operation

The evolution of the carbide phase in the surface layers of bulk-quenched rails (after the passage of 500 and 1000 million t of traffic) and differentially quenched rails (after the passage of 691.8 million t) to a depth of 10 mm at the central axis of the rail cross section and at the nearby rounded section is studied by transmission electron-diffraction microscopy. The grains of plate pearlite, ferrite–carbide mixture, and structure-free ferrite are analyzed. The carbide phase in the surface layers of the steel changes in two mutually complementary processes during rail operation: (1) cleavage of cementite particles with subsequent entrainment in ferrite grains or plates (in the pearlite structure); (2) cleavage and dissolution of cementite particles, with transfer of carbon atoms to dislocations (in Cottrell atmospheres and in dislocational cores), which transport them to the ferrite grains (or plates), where cementite nanoparticles are formed again. In the previous location of the plates, fragmented dislocational substructure appears. The boundaries of the fragments are found at the positions previously occupied by cementite α-phase boundaries. The solution of cementite is mainly due to the energy of carbon atoms at dislocation cores and subboundaries in comparison with the cementite lattice. The binding energy of the carbon atom and the dislocations is 0.6 eV and the binding energy of the carbon atom and the subboundary is 0.8 eV, as against 0.4 eV for the carbon atom in cementite. Elastoplastic stress fields are formed; their stress concentrators are intra- and interphase boundaries of ferrite and pearlite grains, cementite plates and ferrite of the pearlite colonies, and globular cementite and ferrite particles. Those are also the basic sources of curvature and torsion in the crystal lattice of the rail steel. On approaching the contact surface, the number of stress concentrators increases, and the internal long-range stress fields are of greater amplitude.

Conductivity Lift-off Invariance and measurement of permeability for ferrite metallic plates

In this paper, a Conductivity Invariance Phenomenon with a controlled lift-off is discovered and studied. It is found that at certain lift-off, the effect of conductivity influence on inductance is eliminated/reduced. Based on this phenomenon, a novel permeability measurement approach is proposed. The proposed approach was verified by both simulation and experimental data. And the permeability can be estimated in a reasonable accuracy (with an error of 2.86%) by the proposed approach without the influence of its conductivity.

Combined surface hardening and laser patterning approach for functionalising stainless steel surfaces

The paper reports a laser patterning method for producing surfaces with dual scale topographies on ferritic stainless steel plates that are hardened by low temperature plasma surface alloying. Nitrogen and carbon based gasses were used in the alloying process to obtain surface layers with an increased hardness from 172 HV to 1001 HV and 305 HV, respectively. Then, a nanosecond infrared laser was used to pattern the plasma treated surfaces and thus to obtain super-hydrophobicity, by creating cell- or channel-like surface structures. The combined surface hardening and laser patterning approach allowed super-hydrophobic surfaces to be produced on both nitrided and carburised stainless steel plates with effective contact angles higher than 150°. The hardened layers on nitrided samples had cracks and was delaminated after the laser patterning while on plasma carburised samples remained intact. The results showed that by applying the proposed combined approach it is possible to retain the higher hardness of the nitrided stainless steel plates and at the same time to functionalise them to obtain super-hydrophobic properties.

Surface Modification by Friction Stir Processing of Low-Carbon Steel: Microstructure Investigation and Wear Performance

A low-carbon steel sheet with a thickness of 5 mm was subjected to friction stir processing (FSP) by one to four different passes. The microstructures of different regions were characterized using the optical microscopy and electron backscatter diffraction. The Vickers micro-harness was measured at the distance of 200 μm below the processed surfaces. The influence of pass numbers (PNs) on wear resistance was studied in terms of coefficients of friction (CoFs), weight losses and wear rates. SEM topographies of the worn surfaces were also studied to evaluate the wear mechanisms. Microstructure observations showed that Widmanstatten ferrite plates were formed in stir zones (SZs) and heat affected zones. As PN increased, these grains were widened due to the increment of the carbon diffusivity and lengthened because of the high heat input and microstructure anisotropy. Besides, increasing the PN causes increasing of the hardness and wear resistance, simultaneously. Specifically, the wear rate in the SZ was reduced from 2.8 × 10−2 mm3 m−1 in base metal to 0.3 × 10−2 mm3 m−1 in sample which was subjected to 4 FSP passes. However, variation in PN had no considerable effect on CoFs. Oxidative wear mechanism was observed on the worn surface of the steel and the FSPed samples while more debris was formed by increasing the PNs.

Physical Nature of Structure and Properties Degradation of Rail Surface after Long Term Operation

By methods of optical, scanning and transmission electron diffraction microscopy and microhardness and tribology parameters measurement the changes regularities of structure-phase states, defect substructure of rails surface after the long term operation (passed tonnage of gross weight 500 and 1000 mln. tons) were established. It is shown that the wear rate increases in 3 and 3.4 times after passed tonnage of gross weight 500 and 1000 mln. tons, accordingly, and the friction coefficient decreases in 1.4 and 1.1 times. The cementite plates are destroying absolutely and cementite particles of around form with the sizes 10-50 nm are forming after passed tonnage 500 mln tons. The appearance of dynamical recrystallization initial stages is marked after the passed tonnage 1000 mln tons. It is shown that the operation of steel rails is accompanied by full fractures in surface layers with lamellar pearlite grains and the formation of ferrite–carbide mixtures with nanosized particles. The deformation of steel increases the densities of scalar and excess dislocations, the curvature–torsion values of the crystal lattice, and the amplitudes of internal stress fields. The possible mechanisms of established regularities are discussed. It is noted that two competitive processes can take place during rails long term operation: 1. Process of cutting of cementite particles followed by their carrying out into the volume of ferrite grains or plates (in the structure of pearlite). 2. Process of cutting, the subsequent dissolution of cementite particles, transition of carbon atoms to dislocations (into Cottrell atmospheres), transition of carbon atoms by dislocations into volume of ferrite grains or plates followed by repeat formation of nanosize cementite particles.

Determination of magnetoelastic oscillations in ferrite plate with different values of anisotropy constant

The maximum amplitudes of magnetic and elastic oscillations are calculated at various material parameters and parameters of external fields. Normally and tangentially magnetized anisotropic magnetic plates were considered. To obtain the maximum amplitudes with additional constraints, the simulated annealing method was used. The behaviour of the magnetic and elastic components of the oscillations was considered. The changes in the position of the magnetization vector and the equilibrium displacements as a function of the first anisotropy constant were revealed.

Magnetostatic waves in a medium with damping

By means of consistent solution of the motion equation for magnetization the consideration of energy dissipation for magnetostatic surface waves propagating on in-plane magnetized ferrite plate is regarded. The complex character of the wave number caused by the dissipation is revealed. In this case the dispersion relations for the real and imaginary parts of the wave number are obtained. It is shown that dispersion curves are limited both by the wave number and frequency, and these restrictions tighten with an increase in the damping parameter. Also, it is predicted that there is a new set of branches of the backward dissipative waves. Both for forward and backward waves there is a critical value of the damping parameter and propagation angle, beyond which it does not exist.

Hypersound excitation of magnetization and elastic displacement in case of magnetization reversal

The paper gives a description of hypersound magnetoelastic oscillations excitation along magnetisation reversal of normal magnetized single-layer and multi-layers ferrite plates, also provides definition of distinctive features of magnetic and elastic oscillations development. The relation of oscillations to the parameters of saturation magnetization, magnetic and elastic damping has been revealed.

Study on microstructures and properties of carbide-free and carbide-bearing bainitic steels

The microstructural characteristics, the mechanical and fatigue properties of carbide-free lower bainite and carbide-bearing lower bainite were studied. Moreover, the effects of the bainitic ferrite, retained austenite, and carbide phases on the properties of the tested steels were analyzed. Results show that the carbide-free lower bainite consists of fine bainitic ferrite plates and metastable retained austenite. Large amounts of C atoms are distributed in the metastable retained austenite. The carbide-bearing lower bainite consists of thick bainitic ferrite plates and stable carbides, which contain numerous C atoms. Carbide-free lower bainite exhibits higher strength, plasticity, and toughness than carbide-bearing lower bainite, and the former also exhibits longer fatigue life under total strain amplitude, the latter exhibits longer fatigue life under plastic strain amplitude. The metastable retained austenite of large size in the carbide-free lower bainite obviously undergoes strain-induced martensitic transformation during deformation. Martensitic transformation delays crack propagation by absorbing the energy required for crack propagation, thus increasing the fatigue life of carbide-free lower bainite under total strain amplitude. The stable carbide and the coarse bainite ferrite plates play positive roles for the fatigue life under plastic strain amplitude, while the fine bainite ferrite plates and metastable retained austenite are negative. The stable secondary carbide phase strengthens carbide-bearing lower bainite under uniaxial tensile deformation but may shorten fatigue life under cyclic fatigue by acting as locations of stress concentration.

EBSD Analysis of Relationship Between Microstructural Features and Toughness of a Medium-Carbon Quenching and Partitioning Bainitic Steel

A multiphase microstructure of bainite, martensite and retained austenite in a 0.3C bainitic steel was obtained by a novel bainite isothermal transformation plus quenching and partitioning (B-QP) process. The correlations between microstructural features and toughness were investigated by electron backscatter diffraction (EBSD), and the results showed that the multiphase microstructure containing approximately 50% bainite exhibits higher strength (1617 MPa), greater elongation (18.6%) and greater impact toughness (103 J) than the full martensite. The EBSD analysis indicated that the multiphase microstructure with a smaller average local misorientation (1.22°) has a lower inner stress concentration possibility and that the first formed bainitic ferrite plates in the multiphase microstructure can refine subsequently generated packets and blocks. The corresponding packet and block average size decrease from 11.9 and 2.3 to 8.4 and 1.6 μm, respectively. A boundary misorientation analysis indicated that the multiphase microstructure has a higher percentage of high-angle boundaries (67.1%) than the full martensite (57.9%) because of the larger numbers and smaller sizes of packets and blocks. The packet boundary obstructs crack propagation more effectively than the block boundary.

Numerical modelling of stainless steel preloaded bolted connections

AbstractThe use of stainless steel in construction has become more popular in recent years. It is used for a wide range of structural applications in aggressive environments where reliable performance over long periods with little maintenance is required. Although structural design standards are available for stainless steel, currently there are no rules covering the design of preloaded slip‐resistant bolted connections because of the lack of knowledge about their long‐term viscoplastic behaviour. Viscoplastic creep and stress relaxation in the preloaded bolt assemblies will lead to a certain loss of clamping force and may cause the failure of the connection if not accounted for. This paper presents the development of material models and finite element models for bolt assemblies based on an extensive experimental study of creep, relaxation and tension effects on austenitic, ferritic, duplex and lean duplex steel plates and bars for different loading rates. These models were verified against slip tests with stainless steel bolt assemblies according to EN 1090‐2 and then used in a parametric study to extend the scope of the connections investigated. Both experimental programmes were carried out in the European RFCS research project SIROCO (Execution and reliability of slip‐resistant connections for steel structures using Carbon Steel and Stainless Steel) as well as finite element calculations.

Analysis of the Corrosion Behavior of an A-TIG Welded SS 409 Weld Fusion Zone

AISI 409 (SS 409) ferritic stainless steel is generally used as the thick gauge section in freight train wagons, in ocean containers, and in sugar refinery equipment. Activating the flux tungsten inert gas (A-TIG) welding process can reduce the welding cost during fabrication of thick sections. However, corrosion behavior of the A-TIG weld fusion zone is a prime concern for this type of steel. In the present work, the effect of the A-TIG welding process parameters on the corrosion behavior of a weld fusion zone made of 8-mm-thick AISI 409 ferritic stainless-steel plate has been analyzed. Potentiodynamic polarization tests were performed to evaluate the corrosion behavior. The maximum corrosion potential (E corr) was shown by the weld made using a welding current of 215 A, a welding speed of 95 mm/min, and a flux coating density of 0.81 mg/cm2. The minimum E corr was observed in the weld made using a welding current of 190 A, a welding speed of 120 mm/min, and a flux coating density of 1.40 mg/cm2. The current study also presents the inclusive microstructure–corrosion property relationships using the collective techniques of scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction.

Effect of pressure pulsation on bond interface characteristics of 409 ferritic stainless steel diffusion bonds

In present study, impulse pressure assisted diffusion bonding (IPADB) technique was applied for diffusion bonding of 409 ferritic stainless steel plates. The effect of diffusion bonding process parameters i.e. maximum pulse pressure and pressure pulses on bond interface characteristics and mechanical properties was investigated. The bonds were analyzed by field emission scanning electron microscope (FESEM) and using these micrographs interface bonding ratio was measured, which is defined as the ratio of void free interface length to the total interface length. The pressure pulsation improved the interface bonding ratio by reducing the voids at the interface. At 40 MPa maximum pulse pressure and 18 pressure pulses, 43.7% improvement in interface bonding ratio of the diffusion bonds was observed with respect to those developed at same constant pressure. Hardness and tensile shear tests were performed on the diffusion bonds. A maximum shear load of 37 kN was obtained for the diffusion bonds developed at 40 MPa maximum pulse pressure and 18 pressure pulses, having the fracture from the base metal during tensile shear testing. The fracture surface of the diffusion bonds was also studied by FESEM.

Long-term operation surface changes in differentially quenched 100-m rails

By optical microscopy and transmission electron diffraction microscopy, the evolution of the structural and phase states in the surface layers over a depth of 10 mm in the head of differentially quenched rail (category DT350) is studied, as the rail is subjected to passed tonnage of 691.8 million t at the experimental loop of AO VNIIZhT. In the initial state, the following structural components are present in the rail head: plate-pearlite grains (relative content 0.7); mixed ferrite–carbide grains (0.25); and grains of structure-free ferrite. After experiencing a passed tonnage of 691.8 million t, this state only remains beyond a depth of 10 mm. At that depth, a large quantity of bend extinction contours is observed. That indicates elastoplastic distortion of the material’s crystal lattice. The stress concentrators in the steel are intraphase and interphase boundaries of the ferrite and pearlite grains, cementite and ferrite plates in pearlite colonies, and globular cementite and ferrite particles. Structural transformations are observed at the macro level: microcracks appear, running at acute angles from the surface to a depth of 140 μm; and a decarburized layer is formed. At the micro level, elastoplastic stress fields are formed, and the cementite plates in the pearlite colonies break down. The stress concentrators in that case are intraphase and interphase boundaries of the ferrite and pearlite grains, cementite and ferrite plates in pearlite colonies, and globular cementite and ferrite particles. In structure-free ferrite grains, cementite nanoparticles are formed. The results are compared with the evolution of the structural and phase states at the surface of a recess in bulk-quenched rail as the rail is subjected to gross loads of 500 million t: the transformation of the structural and phase states in the surface layers is more pronounced. Plate pearlite is characterized by solution of the cementite plates. That leads to the formation of chains of globular carbide particles at the sites of the cementite plates. This may be associated with transfer of the carbon atoms from the cementite lattice to dislocations.

Widening of Laths in Bainite

Units of bainite in Fe-C alloys from the upper temperature range inherit their shape from Widmanstätten plates of ferrite, which are lathlike. The thickness increases by long-range diffusion of carbon and the length by short-range diffusion of carbon from the advancing edge of the tip. Both have been studied extensively and are fairly well understood. Widening growth seems to have been much neglected, but a study of some aspects of widening is now presented. The present report is the last one in a series of four morphological studies of bainite, isothermally formed in Fe-C alloys with 0.3 or 0.7 mass pct carbon, mainly in the upper temperature range. It contains a number of morphological observations made on cross sections of packets of bainite, and it elucidated a number of interesting questions about bainite and resulted in some proposals. The ferrite plates in a packet are nucleated as a group on a grain boundary, not each one separately on the side of a prior plate. Lengthening occurs by advancement of a short edge that is formed in close contact to the grain boundary. Widening of laths does not start spontaneously. It is initiated by a modification of the structure of the long edge of the lath. When it then moves, the lattice of the new ferrite is rotated relative to the ferrite formed by lengthening and the habit plane is different. In a section through the length direction, it is difficult to recognize what part of ferrite has formed by widening growth. Furthermore, it is proposed that the individual plates in a microstructure, previously used to illustrate subunits formed by repeated nucleation, were nucleated on a hidden grain boundary.

Multiple frequency transformation in the magnetostriction transducer: Frequency division in the relaxation mode

The forced oscillations of the magnetization and elastic displacement in the normally magnetized ferrite plate with magnetoelastic properties are discussed. The process whereby the initial frequency is divided in the ratio defined by the multiplicity of the resonance frequencies of magnetic and elastic subsystems is investigated. The time and amplitude characteristics of the phenomenon are revealed on the basis of the impact excitation model of an elastic system under short-term magnetic actions. Recommendations are given for the practical implementation of excitation-frequency division in the scheme of a magnetostriction transducer.