Measurements Of Coercive Force Research Articles

Evaluation of post weld heat treatment quality of modified 9Cr–1Mo (P91) steel weld by magnetic coercive force measurements

This paper presents a novel technique for evaluation of quality of post weld heat treatment (PWHT) of modified 9Cr–1Mo (P91) steel weld by correlation with its magnetic coercive force (MCF). The MCF of modified 9Cr–1Mo steel was studied in respect of different PWHT cycles involving ordered variations of soaking temperature unto 770°C and soaking time unto 140min. It was observed that MCF of the weld metal reduced with increase in both the soaking temperature and soaking time of PWHT. The drop in MCF of welds after PWHT was found to be dependent on the drop in the hardness of the weld and on the degree of carbide precipitations seen in the weld microstructure. Based on the study, a criterion was evolved for evaluation of heat treatment quality of the weld.

ANALYSIS OF STRUCTURAL CHANGES IN THE ZONES OF LOCAL CATASTROPHIC DESTRUCTION OF PIPELINE SYSTEMS OF OIL REFINING

It has been found that the most dangerous corrosion type of pipeline systems of oil refi ning is a pitting one. Based on the volume and thickness measurements, as well as the results of the coercive force measurements, the mechanism of local catastrophic corrosion of pipeline systems of oil refining has been established. A method of non-destructive quality control of welding and subsequent heat treatment of pipeline systems of oil refining has been offered. It will prevent the emergency situations.

Material aging diagnosis system using magnetic NDE

This paper discusses material aging diagnosis what uses a non-destructiveness evaluation system. The diagnosis is based on magnetic characteristics of material. It is well known that the magnetism of strong magnetic materials is extremely sensitive with respect to the change of microstructure and to residual-stress variation. For example, coercive force and minor- loop coefficients have shown a linear relationship with rolling reduction. We have proposed a method what is an impedance measurement of a sensor. The method needs a magnetizer with one coil and an impedance meter. The method is simpler than a method what use coercive force. We have compared the method with a method what is a measurement of coercive force. Relationship between strain of carbon steels and experimental results of using coercive force or impedance measurements has measured. Carbon steel sample specimens with some strain loading in the experiment have been used. The experimental results have shown that the method can detect strain of steel just like a method of using a coercive force measurement.

Certification of hardened surface layers by magnetic and electromagnetic methods

The possibilities of certification of hardened surface layers by measurement of coercive force, eddy current inspection and analysis of the field dependence of differential magnetic permeability μ d (H) are considered. The advantages of analysis of the pattern of peaks on the μ d (H) dependence for estimating the state of surface-hardened steels subjected to subsequent force loading are shown.

Measurement of Coercive Force Enhanced by Nanometer-Sizing of Magnetic Dot by X-Ray Magnetic Circular Dichroism (XMCD)

We have studied the coercive force of fine magnetic CoPt dot enhanced by nanometer-sizing of the dot. The 39-to 106-nm-sized CoPt magnetic dot arrays were formed by30-keV-electron beam (EB) drawing with thin calixarene resist and 200-eV-Ar ion milling. Using the fine magnetic dot arrays, we measured coercive forces of the dot by x-ray magnetic circular dichroism (XMCD) with an energy of 11.56 keV, which corresponds to an energy edge of Pt-L3. It is experimentally demonstrated that a coercive force of the nanometer-sized magnetic column increased as the dot diameter decreased. Keywords: Coercive force, nanomagnetic column, XMCD, magnetic storage, EB lithography

An attachable electromagnet of a coercimeter with an indicating system between the electromagnet’s poles

The dependence of the readings of a coercimeter on the gap width between an article and the poles of an attachable electromagnet (AEM) at different magnetizing and magnetization-reversing currents is studied in the case when the indicator of the magnetic state of an article is removed from the electromagnet’s magnetic circuit and placed between the electromagnet’s poles on the surface of the article. It is shown that, during coercive-force measurements, such an indicator cannot be used for determining the demagnetized state of the article in the case of substantial fluctuations of the gap between the AEM poles and the article, although it can be used for assessing the gap width.

Angular variation of the magnetic properties and reversal mode of aligned single‐domain iron nanoparticles

We report magnetic hysteresis and back‐field demagnetization data measured at 10° intervals of the angle ψ between the applied field H and the long (magnetically easy) axes of aligned elongated single‐domain iron particles electrodeposited in regularly spaced surface pores in an Al substrate. Our three samples have identical particle diameters, d = 17 nm, but varying axial ratios l/d and spacings dc. Measured hysteresis loops resemble “hysterons” predicted by fanning, curling, and coherent rotation models of magnetization reversal, except for two features. For ψ = 0–60°, particle magnetizations do not reverse simultaneously at a single critical field: distributed particle coercivities produce steep but nonvertical loop segments. Broadened ψ = 80–90° loops indicate imperfectly aligned particles. Comparing coercive force Hc(ψ) with theoretical variations for different angular dispersions of axes and Mrs/Ms data with a theoretical cos ψ variation, we find a variance of 6–8.5° in particle alignment. The Hc(ψ) results most closely resemble the theoretical variation for fanning rotations when ψ ≤ 50° and coherent rotations when ψ > 50°. A predicted hump in the Hc(ψ) curve at intermediate angles marking the changeover from one mechanism to the other is suppressed by particle interactions (packing factors p of 0.127–0.373). Remanent coercive force measurements Hcr(ψ) show that irreversible changes, unlike reversible rotations, are incoherent at both large and small ψ. Hcr continues to rise, to a high of 340–430 mT, as ψ → 90°, whereas Hc(ψ) decreases over the same range. Hcr(ψ) results at large ψ favor fanning reversals for one sample and curling reversals for the other two. A Day plot of Mrs/Ms versus Hcr/Hc data gives a novel and distinctive trend from which ψ can determined within ±5° for aligned uniaxial particles.

Iron-cementite nanocomposites obtained by mechanical alloying and subsequent magnetic pulsed pressing

X-ray diffraction, atomic-force microscopy, and density, microhardness, and coercive force measurements were used to study bulk iron-cementite nanocomposites obtained by different regimes of magnetic pulsed pressing of mechanically alloyed samples with a total carbon content ranging from 5 to 25 at. %.

Nondestructive Testing of Mechanical Properties of Rolled Steel (Review): 1. Tests of Strength and Plastic Properties

This review considers the creation and development of a nondestructive technique based on coercive-force measurements used to determine strength and plastic properties of industrial rolling products made from Russian-produced low-carbon and low-alloy steels. The operating principle for a coercimeter equipped with a field electromagnet is described briefly. Regression lines of mechanical properties versus coercimeter readings are presented for 20Κ- and 09Γ2-steel sheets produced by Nizhni Tagil Iron and Steel Works. Different methods for considering sheet thickness and tube dimensions are discussed.

Magnetic properties of amorphous and nanocrystalline alloys based on iron

In the present paper, two amorphous alloys: Fe 74Cu 1Cr 3Si 13B 9 and Fe 74Cu 1Zr 3Si 13B 9 were studied by applying the following experimental techniques: magnetic permeability, coercive force, magnetic after-effect, Hall constant and electrical resistivity measurements. Structural changes in annealed samples have been examined by X-ray diffraction analysis and high-resolution electron microscopy technique. It has been shown that magnetic properties of the examined alloys can be significantly improved by applying a suitable thermal annealing causing formation of α-Fe(Si) nanocrystalline phase with grain size from the range 2–6 nm and/or annealing out of microvoids. It has been found that the temperature of 1-h optimisation annealing as well as the temperature of first stage of crystallisation process in the first approximation is proportional to the atomic radius of the alloying addition (Cr, Mo, Zr).

SM-401 Magnetic Structuroscope

The SM-401 magnetic structuroscope is described. Operations carried out by means of the structuroscope and technical characteristics of the device are described. Factors determining the error in measurement of the coercive force are considered. The parameters of transducer of the magnetic structuroscope are estimated and the measurement results are outlined.

Optimisation of soft magnetic properties in Fe–Cu–X–Si 13B 9 (X=Cr, Mo, Zr) amorphous alloys

In the present paper a group of Fe–Cu–X–Si 13B 9 (X=Cr, Mo, Zr) amorphous alloys has been examined by applying different experimental techniques—magnetic permeability, magnetic after-effect, coercive force and electrical resistivity measurements. It has been shown that their soft magnetic properties can be optimised by 1-h thermal annealing at the temperature close to the crystallisation temperature. This leads to an increase of permeability and a decrease of coercive force, thermal instability (magnetic after-effect intensity) and electrical resistivity of the material. The optimisation effect is discussed in terms of different processes—(i) a formation of a nanocrystalline phase with the grain size much smaller than the ferromagnetic exchange length, (ii) an annealing out of microvoids formed during the fabrication process and also (iii) a decrease of the effective magnetostriction constant. The temperature of optimisation annealing treatment is always higher than the Curie temperatures of the materials and varies approximately linearly with the atomic radius of the alloying additions.

Magnetic Measurements of Stressed-Strained States and Remaining Service Lives of Steel Structures in Hoisting Machines and Pressurized Vessels

A technique of magnetic diagnostics has been developed on the base of correlations between physico-mechanical properties of ferromagnetic materials and their coercive force Hc. Examples of practical utilization of the technique in assessing conditions of bridge cranes and oxygen cylinders are given. By solving the inverse problem, it is possible to diagnose the stage of transition to the yield region on the base of measurements of the maximal and average coercive force, which enables one to diagnose the predestruction condition of gas cylinders. Criteria for rejecting gas cylinders based on results of statistical analysis have been established.

Coercive force measurements in nondestructive testing

The paper considers applications of coercive force meters with external electromagnets to nondestructive measurements of strength, plastic, and viscous properties of rolled high-carbon and low-alloyed steels, characterization of annealed high-carbon, predominantly chromium-doped, steels, testing of the quality of quenched and tempered steels, measurements of the depth and hardness of surface hardened layers on metallic components, and their use in sorting out different steels.

Magnetic properties of pulverized titanomagnetite, Fe2.4 Ti0.6 O4 : effect of thermal fluctuations

SUMMARY The magnetic properties of titanomagnetite, Fe 2.4 Ti 0.6 O 4 , pulverized in a ball mill for times between 3.5 and 78 hr form a consistent picture if the material is treated as monodomain particles of decreasing size progressively subject to thermal fluctuations. The magnetic observations are made over a range of characteristic measurement times: 10’3 s (susceptibility measurement), 1 s (coercive force measurement) and 104 s (viscous decay of remanence). The magnetic viscosity coeYcient first rises then falls as pulverization proceeds. This is ascribed to a distribution of time constants in the assemblage of particles, the maximum viscosity occurring when the value of the time constant at the peak in the distribution, in zero field, is the same as the characteristic measurement time. The application of a field equal to the coercive force shifts the distribution so that the peak corresponds to the characteristic time of the coercive force measurement. The position of the corresponding zero-field peak can readily be calculated from the observed coercive force and the uniaxial anisotropy constant derived from hysteresis loop parameters. This shows that the calculated zero-field peak position for the degree of pulverization at which the maximum viscosity occurs is the same as the viscous decay measurement time. At maximum pulverization time, and therefore smallest particle size, the peak in the zero-field time constant distribution is five orders of magnitude bigger than the characteristic time of susceptibility measurement, which can be satisfactorily interpreted in terms of only a few per cent of the particle assemblage being aVected by thermal fluctuations. The observed eVectiveness of thermal fluctuations requires that the pulverized particles contain nanocrystals, in size about two orders of magnitude smaller than the particle envelope. The presence of the nanocrystals is supported by transmission electron microscope and X-ray line broadening observations.

Thermoremanent magnetization in monodomain monoclinic pyrrhotite Fe7S8

The intensity and stability of thermoremanent magnetization (TRM) acquired by fine particles (<1µm) of synthetic monoclinic pyrrhotite were determined. A specific TRM (magnetization per unit inducing field) of 32 with a median destructive field of 36 kA m−1 was observed. The median destructive field of saturation isothermal remanence is 42 kA m−1 and the coercive force is 62 kA m−1. The intensity of TRM has been compared to that predicted by the classical monodomain model adapted to the magnetic symmetry of pyrrhotite. If the optically determined particle size is incorporated into the model, the agreement between model and observation is poor (a factor of 100 difference); if a grain size (∼0.05 µm) inferred from the measurement of coercive force is adopted, model and observation are in agreement within experimental error.

Rapid annealing of metallic glasses under tension

Pulse heat treatment using 0.4 s current pulses was applied to Fe 80B 14Si 6 amorphous ribbons above its Curie temperature in order to avoid magnetically induced anisotropy. After relaxation the pulse heat treatment was continued while applying 128 MPa mechanical stress to obtain induced anisotropy. The results of pulse annealing were monitored by coercive force and effective anisotropy measurements carried out between the pulses at room temperature. It is shown that pulse annealing enables a magnetically soft relaxed state to be achieved and if mechanical stress is applied during the process, induced anisotropy can be developed.

A new method for measurement of coercive force in bubble garnets using microwave absorption

A new method has been developed for measurement of coercive force in bubble garnets using microwave absorption. The inflection point was observed in the derivative absorption signal when the measurement was carried out, changing the modulation field in a garnet film supporting magnetic bubbles. This inflection is related to the domain-wall absorption and the modulation field at the inflection point gives the coercive force in the garnet film. Using this method the coercive force can be determined even if the bubbles can hardly be observed. The coercive force of garnet films supporting submicron (0.3–1 μm diam) bubbles has been measured.

A Coercivity Measuring Method of Barium Ferrote Fome Powder for Particulate Perpendicular Magnetic Recording Media

A Barium ferrite platelet fine particle coercive force is affected by magnetic particle agglomeration. Investigations of a new measuring method to determine the intrinsic coercive force of Ba-ferrite particles that exclude the effect of magnetic agglomeration are reported. The new method was to make coercive force measurements for Ba-ferrite particles dispersed and attached on large SiO 2 particle surfaces. Coercive force measurement for samples of low Ba-ferrite/SiO 2 mixing ratio confirmed that it was possible to measure the intrinsic coercive force excluding the influence of magnetic agglomeration.

Structural relaxation of Co-P amorphous alloys.

The structural relaxation of ${\mathrm{Co}}_{91}$${\mathrm{P}}_{9}$ amorphous alloys is monitored using coercive-force measurements after isothermal annealing. The coercive force relaxes by 2 orders of magnitude after annealing. The relaxation is analyzed in terms of the spectra of the activation energies. We deduce that four processes contributing to relaxation can be distinguished in the activation energy range from approximately 1.18 to 1.50 eV. Our results suggest that the diffusion of P atoms from ``unstable'' to ``stable'' holes is the main source for the relaxation process. The relation between the four processes observed and the different possible holes is discussed.