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Journal ArticleDOI

Effect of tensile deformation on micromagnetic parameters in 0.2% carbon steel and 2.25Cr–1Mo steel

23 Apr 1999-Acta Materialia (Newcastle University)-Vol. 47, Iss: 6, pp 1869-1878
Abstract: The influence of prior tensile deformation on the magnetic Barkhausen emission (MBE) and the hysteresis (B-H) curve has been studied in 0.2% carbon steel and 2.25Cr-1Mo steel under different tempered conditions. This study shows that the micromagnetic parameters can be used to identify the four stages of deformation, namely (i) perfectly elastic, (ii) microplastic yielding, (iii) macroyielding and (iv) progressive plastic deformation. However, it is observed that the MBE profile shows more distinct changes at different stages of tensile deformation than the hysteresis curve. It has been established that the beginning of microplastic yielding and macroyielding can be identified from the MBE profile which is not possible from the stress-strain plot. The onset of microplastic yielding can be identified from the decrease in the MBE peak height. The macroyielding can be identified from the merging of the initially present two-peak MBE profile into a single central peak with relatively higher peak height and narrow profile width. The difference between the variation of MBE and hysteresis curve parameters with strain beyond macroyielding indicates the difference in the deformation state of the surface and bulk of the sample.
Topics: Deformation (engineering) (56%), Carbon steel (51%), Hysteresis (50%)
Citations
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Journal ArticleDOI
Abstract: We report the effect of initial pH and temperature of iron salt solutions on formation of magnetite (Fe3O4) nanoparticles during co-precipitation. We synthesized nanoparticles by keeping the initial pH at 0.7, 1.5, 3.0, 4.7, 5.7, 6.7 for two different temperatures of 30 and 60 ◦ C. When the initial pH (prior to alkali addition) of the salt solution was below 5, the nanoparticles formed were 100% spinel iron oxide. Average size of the magnetite particles increases with initial pH until ferrihydrite is formed at a pH of 3 and the size remains the same till 4.7 pH. The percentage of goethite formed along with non-stoichiometric magnetite was 35 and 78%, respectively, when the initial pH of the solution was 5.7 and 6.7. As the reaction temperature was increased to 60 ◦ C, maintaining a pH of 6.7, the amount of goethite increased from 78 to 100%. These results show that the initial pH and temperature of the ferrous and ferric salt solution before initiation of the precipitation reaction are critical parameters controlling the composition and size of nanoparticles formed. We characterize the samples using X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results of the present work provide the right conditions to synthesis pure magnetite nanoparticles, without goethite impurities, through co-precipitation technique for ferrofluid applications. © 2007 Elsevier B.V. All rights reserved.

264 citations


Journal ArticleDOI
Abstract: The dependence of Barkhausen noise on elastic and plastic deformations, achieved in tension and in compression, has been investigated both in Armco iron and a low carbon steel These materials exhibit quite different behaviours, especially with regard to the effect of plastic deformation: a tensile plastic deformation (>1%) induces a marked increase in Barkhausen noise for Armco iron while it induces a steep decrease in the low carbon steel The comparison between the tensile and compressive behaviours, as well as between the elastic and plastic regimes of deformation enables us to attribute these effects to two underlying mechanisms, ie effect of residual internal stresses through magneto-elastic coupling and dislocation–domain wall interaction In Armco iron, the latter mechanism seems to have the strongest influence on the Barkhausen noise, while in the low carbon steel the influence of residual internal stresses prevails

96 citations


Journal ArticleDOI
Abstract: Non-destructive evaluation (NDE) of materials for characterising various key microstructural features, mechanical properties (tension, creep, fatigue crack growth, hardness and fracture toughness), deformation and damage mechanisms has attracted considerable attention in the past 20 years as a primary step towards ensuring structural integrity of components. However, until recently, the correlations between the various NDE parameters and material properties have been only empirical and based on physical principles. The interaction between the NDE probing medium and the mechanical behaviour is not yet fully understood. The purpose of this review is to discuss the progress made in the application of non-destructive testing (NDT) techniques in evaluating various microstructural features and mechanical properties with emphasis on recent studies. Reinterpretation of older data, in the light of present understanding of the interaction of the NDE probing medium with material parameters, is carried out selectively. The NDT techniques evaluated include acoustic emission, ultrasonic attenuation and velocity, magnetic hysteresis parameters, magnetic Barkhausen emission, acoustic Barkhausen emission, laser interferometry, positron annihilation, X-ray diffraction and small angle neutron scattering. Critical assessments of the applicability of the various NDE techniques for the material parameters are provided.

75 citations


Journal ArticleDOI
01 Nov 2005-Acta Materialia
Abstract: The effect of residual stress changes caused by grinding on the magnetic Barkhausen emission (MBE) has been studied in case-carburised En36 steel. Both high and low frequency MBE measurements were made on specimens with case-depth of 0.55 and 0.8 mm subjected to varying level of grinding damage. The high frequency MBE profile shows single peak while the low frequency MBE profile shows two peaks. The first peak is not affected by grinding damages. But, the second peak increases and shifts to lower field systematically indicating the changes in microstructure and residual stresses. Both high and low frequency MBE measurements have been correlated to residual stress (RS)-depth profile measured using X-ray diffraction method. The high frequency MBE indicates the changes in surface RS, but does not indicate changes in RS at depths >10 μm. The low frequency MBE profile indicates the changes in RS below the surface.

62 citations


Journal ArticleDOI
Abstract: This study presents an extended in situ magnetic characterisation of a non-oriented (NO) Fe–(3 wt.%)Si steel. An appropriate experimental device was created and magnetic measurements were performed under uniaxial tensile stresses approaching and exceeding the macroscopic elastic limit σ e and in the corresponding unloaded states. Both Barkhausen noise and B–H hysteresis loops were measured. The sensitivity to stress was found to be qualitatively similar to that of polycrystalline iron. The different stages of the tensile deformation (perfectly elastic stage, microplastic yielding stage, the two strain-hardening stages) were clearly identified by the magnetic parameters. In the plastic strain domain, the coercive field H c and the inverse of the initial relative permeability 1/ μ r i linearly increase, while the maximal relative permeability μ r max and the Barkhausen noise peak height BN max linearly decrease with the applied stress σ . The remnant induction B r keeps a low and constant value. Furthermore, a linear dependence of 1/ μ r i , H c , μ r max and BN max on the kinematic hardening X was found. By using measurements on prestrained specimens under reloaded elastic stresses, an accurate identification of the effect of dislocations acting as pinning sites and of the magnetoelastic effect of long-range internal stresses was proposed.

62 citations


References
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Book
01 Jun 1972-
Abstract: Introduction to Magnetic Materials, 2nd Edition covers the basics of magnetic quantities, magnetic devices, and materials used in practice. While retaining much of the original, this revision now covers SQUID and alternating gradient magnetometers, magnetic force microscope, Kerr effect, amorphous alloys, rare-earth magnets, SI Units alongside cgs units, and other up-to-date topics. In addition, the authors have added an entirely new chapter on information materials. The text presents materials at the practical rather than theoretical level, allowing for a physical, quantitative, measurement-based understanding of magnetism among readers, be they professional engineers or graduate-level students.

6,302 citations


Journal ArticleDOI
01 Jul 1987-Acta Metallurgica
Abstract: The effect of microstructures on acoustic and magnetic Barkhausen signals has been investigated in a quenched and tempered steel and spheroidized steels with various carbon contents. Many different features between the acoustic and magnetic Barkhausen signals were observed. A major peak of the acoustic Barkhausen signal was induced when a magnetic field was increased from zero to the saturation state. A minor peak of the acoustic signal and a single peak of the magnetic signal appeared during the decreasing field. It was found in all the steels that the peak value of the acoustic Barkhausen signal shows a linear dependence on the sweep rate of a magnetic field while that of the magnetic Barkhausen signal does a nonlinear one. The increasing tempering temperature which gives rise to a decrease in hardness and an increase in carbide size and spacing caused that acoustic and magnetic Barkhausen peak voltages to increase precipitously and gradually, respectively. In the spheroidized steels, the acoustic peak voltage monotonically decreased with increasing carbon content from 0.17 to 0.96 wt% and the magnetic peak voltage was greatest when the carbon content was 0.46 wt%. The source mechanisms of the two types of the Barkhausen signals which are affected by the nucleation and growth processes of domains in a magnetic field are discussed to explain the effect of the change in carbide precipitate morphology and hardness.

110 citations


Journal ArticleDOI
Abstract: The magnetic properties of AISI 4130 steel after eight heat treatments have been investigated. Properties such as hysteresis loss, coercivity, and initial permeability were found to be closely interrelated. Furthermore, they were each dependent on the hardness of the material. A relationship between the hardness and permeability was found which was microstructure independent. These parameters were also found to change in a systematic way with plastic deformation and this result can be used for non-destructive evaluation. Correlations between the magnetic parameters were also found to change in a systematic way with plastic deformation and this result can be used for non-destructive evaluation. Correlations between the magnetic parameters revealed relationships which depended on the microstructure of the material. The residual stress in steels can be determined from the changes in maximum differential permeability.

75 citations


Journal ArticleDOI
Abstract: Magnetic Barkhausen emission (MBE) has been used to characterize various microstructures in tempered 0.2 wt% C steel, 2.25Cr—1Mo steel and 9Cr—1Mo steel samples (where the composition is in approximate weight per cent). A two-stage process of irreversible magnetic domain wall movement during magnetization is proposed considering the lath or grain boundaries and second-phase precipitates as the two major obstacles to domain-wall movement. The domain walls overcome these two major obstacles over a range of critical field strengths with some mean values, characteristic of the obstacles. If these two mean values are close to each other, then a single peak, sometimes associated with slope changes, appears in the MBE behaviour. On the other hand, if the mean values are widely separated, then two-peak MBE behaviour appears to indicate the influence of these two major obstacles separately. Based on this, the influence of the dissolution of martensite and/or bainite and the precipitation and growth of the...

69 citations


Journal ArticleDOI
Abstract: Magneto-acoustic emission (MAE) and Barkhausen emission (BE) have been measured from polycrystals of pure iron which had been strained by 4.9%. The specimens were then heat-treated at successively higher temperatures. The heat treatments resulted in stress recovery and, at higher temperatures, a reduction in the dislocation density. BE activity and MAE activity profiles were measured after each anneal as a function of the magnetizing field, and the number of Barkhausen events was counted as a function of their peak amplitude. At low fields the intensity of the BE and MAE activities shows a strong trend as a function of the annealing temperature, which is in agreement with the temperature dependence of the dislocation density. At higher fields there are additional fluctuations in the BE and MAE activities as a function of the annealing temperature which occur at temperatures below those of dislocation recovery. These results show that both MAE and BE are sensitive to the dislocation density, and t...

62 citations