Coercimetry with Magnetization by a U-Shaped Electromagnet

Russian Journal of Nondestructive Testing - A method is proposed for measuring the coercive force using a U-shaped electromagnet with a gap between the electromagnet poles and the test sample. It...     

Hardware for Inspection of Ferromagnetic Low Coercive-Force Articles

Hardware that uses plug-in detectors and allows one to measure coercive force in the range of few to several hundred A/m in industrial products of different shapes is presented. The operating principle is based on a functional relationship between the tangential component of the magnetic field close to the surface of a residually magnetized article and the coercive force of the article material as well as a connection between the gradient of the field of a magnetic pole formed at the article surface after local magnetization and the coercive force.     

The influence of biaxial elastic deformation on the coercive force and local remanent magnetization of construction steels

The influence of biaxial elastic tension-compression and tension-tension deformation on the coercive force and remanent magnetization of Cτ3 steel and 09Γ2C pipe steel cross-shaped specimens is studied. It is shown that coercive force grows monotonically with increasing load in the direction of compression under elastic tension-compression deformation and almost does not change under elastic tension-tension deformation. The local remanent magnetization decreases for all the considered types of biaxial elastic deformation. The possibility of using these methods for the evaluation of the stressed state of complexly deformed carbon steel products is discussed.     

On new possibilities for making local measurements of the coercive force of ferromagnetic objects

The possibility of reducing the influence of both the gap in a transducer-object combined circuit and the shape of tested objects on the results of local measurements of their coercive force is investigated. It is shown that additional measurements of the maximum magnetic flux in the circuit and the tangential component of the magnetic field on the surface of the tested area of the object, which is retained after the magnetizing current is turned off, allow a substantial decrease in the corresponding errors.     

Magnetic tests of hardness and structure of rail steel

The correlation between the coercive force on the one side, and the structure and hardness of the rail steel on the other has been studied. A technique for testing rails quenched in oil based on measurements of the coercive force has been developed. The technique can be used in acceptance tests of rails by stages of main rail-roads.     

Specific Features of the Behavior of the Coercive Force in Low-Carbon Plastically Deformed Steels

The relationship between the coercive force in low-carbon steels under plastic extension and compression and the values of deformation and actual and residual stresses are studied. This relationship is investigated for both “ slow” loading (when an equilibrium deformation is attained for each load value) and “fast” loading (when such equilibrium is not attained). It is shown that (i) a comparatively small increase in the coercive force in a loaded condition is due only to an increase in the density of dislocations in the process of plastic extension; (ii) a significant steep increase in the coercive force accompanying removal of the load from a plastically stretched specimen is fully due to residual compression stresses; (iii) the values of the coercive force under “slow” and “fast” loading are significantly different in the region of small deformations less than 2.5%; (iv) these values are close to each other in the loaded state for all deformations up to 10%; (v) a relief of the compression stress that creates plastic deformations causes a steep decrease in the coercive force that is as large as its increase following relief of plastic extension; this is explained by the emergence of a significant residual tension stress. The obtained results are of importance for the use of the method based on measuring the coercive force to test steel structures under the conditions when plastic deformations develop.__________Translated from Defektoskopiya, Vol. 41, No. 5, 2005, pp. 24–38.Original Russian Text Copyright © 2005 by Kuleev, Tsar’kova, Nichipuruk.     

Nanoscale potential measurements in liquid by frequency modulation atomic force microscopy

We have developed a method for local potential measurements in liquid using frequency modulation atomic force microscopy. In this method, local potential is calculated from the first and second harmonic vibrations of a cantilever induced by applying an ac bias voltage between a tip and a sample. The use of an ac bias voltage with a relatively high frequency prevents uncontrolled electrochemical reactions and redistribution of ions and water. The nanoscale resolution of the method is demonstrated by imaging potential distribution of a dodecylamine thin film deposited on a graphite surface in 1 mM NaCl solution.     

Effect of Plastic deformation and its localization zones on magnetic characteristics of steel 45

Attachable transducers were used to measure the demagnetizing current, which is proportional to the coercive force, and Barkhausen noise parameters for steel 45 specimens depending on the degree of their plastic deformation in measuring the magnitudes along and perpendicular to the tension direction. The demagnetizing current measured along the preliminary tension direction was shown to increase monotonically; the rate of its changes is maximal at the initial stage of plastic deformation. The demagnetizing current measured perpendicular to the applied tension direction also increases monotonically but within a narrower range. Near local inhomogeneities formed during the deformation, substantial changes in the coercive force and Barkhausen noise take place. The results obtained are explained on the basis of the current concept of the anisotropy of internal stresses in preliminarily plastically deformed materials.     

Feed-forward compensation of surface potential in atomic force microscopy

We introduce a feed-forward technique for lift-mode Kelvin probe force microscopy to minimize electrostatically induced errors in topography scans. Such errors typically occur when a grounded tip is scanned over a heterogeneous sample with differences in local work function or areas of local surface charging. To minimize electrostatic forces during the topography scan we bias the tip with the surface potential recorded in the previous Kelvin probe scan line. With this method we achieve an error free topography on samples with large variations in local surface potential. Compared to conventional tapping mode, we further observe a significant reduction of tip-induced surface charge modifications on charge patterns written in electret films.     

Magnetic Properties of a Material Used to Estimate Elastic and Plastic Strains of Ferrite—Pearlite Steels

The effect of elastic and plastic strains on the magnetic properties of ferrite-pearlite steels has been studied. It has been shown that the sensitivity to elastic-tensile and bending strains is four to five times greater for remnant magnetization than for coercive force. In order to determine the degree of cold plastic deformation of high-carbon steels, a two-parametric testing technique based on the use of remnant magnetization and coercive force was suggested. An MMT-2 device was recommended for measurement of the required parameters.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: III. Magnetic properties of patented wire made of steel 25

Temperature dependences of the coercive force of mechanically alloyed cementite and wires made of patented steel 25 that were subjected to plastic deformation and subsequent annealing are presented. As is shown, cementite can be in both low-and high-coercivity states, for which the coercive force measured at room temperature is 80 and 240 A/cm, respectively; the coercive force measured at liquid-nitrogen temperature (?196°C) is 190 and 530 A/cm, respectively. Based on an analysis of the temperature dependences of the coercive force of deformed wires made of patented steel 25, the role of cementite in the formation of the coercive force of low-carbon steels was determined. It is shown that, in spite of a relatively small amount of pearlite, the contribution due to the magnetic hardness of cementite to the coercive force should be taken into account. In this case, the contribution due to the interaction of ferrite domain walls with weakly magnetic cementite inclusions is substantially lower.     

Regularities of the change in the coercive force under biaxial asymmetric deformation of steel 3

The change in the coercive force under biaxial asymmetric (tension and compression in mutually perpendicular directions) cyclic deformation of cross-shaped steel 3 specimens in the elastic region of deformations was studied. Specimens were deformed beforehand under biaxial asymmetric loading to various degrees of plastic deformation. It was demonstrated that the elastic-deformation dependences of the coercive force measured along the tension and compression directions are qualitatively similar to those under uniaxial tension or compression. It was also shown that, under cyclic elastic loading, these dependences are reversible for well-annealed steel and have a hysteresis that expands with increasing degree of plastic deformation for plastically deformed steel. The possible causes of the hysteresis in the dependence of the coercive force on the elastic cyclic deformations under biaxial loading are discussed. It was supposed that the hysteresis of the coercive force was caused by the appearance of free (not bound in carbide phases) carbon atoms playing the role of interstitial impurity atoms for the α-iron lattice in plastically deformed carbon steels. The possibility of estimating the stressed-strained state of steel under biaxial loading using a magnetic method was discussed.     

Magnetic inspection of the hardness of cast-iron milling rolls

The effects of the chemical composition and parameters of the cast-iron smelting and teeming process on the coercive force have been studied. It is shown that only chromium and carbon appreciably affect the coercive force. For rolls with cylindrical surfaces cast from ТПХН-60 iron, a reliable correlation has been established between the hardness and readings of a coercimeter with an attachable electromagnet. For flanges and blooming passes of sizing rolls made from ТШХН-50 cast iron, equations for the relation between the hardness and readings of a coercimeter have been obtained and analyzed. These equations can be used in nondestructive testing of hardness.     

A setup for measuring the magnetic characteristics of soft magnetic materials and articles

An automated setup for measuring the normal magnetization curve, the major and minor magnetic-hysteresis loops, and the main (initial permeability, maximum permeability, residual magnetic induction, induction coercive force, and saturation induction) and additional (the permeability at a field equal to the coercive force, the field strength at which the saturation induction is reached, and the induction at fields equal to the coercive force and the double coercive force) magnetic parameters of soft magnetic materials and articles produced from them is described. Measurements are performed in an open or closed magnetic circuit at a magnetization-reversal frequency of 0.05–0.5 Hz. The block diagram of the setup and its main parameters and characteristics are presented. The operation of the setup and the possibilities of its application are considered.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: II. Magnetic properties of patented wire made of steel 70

It is shown that, during discussion of the mechanism reliable for formation of the coercive force in high-carbon steel, in addition to the interaction between the domain walls and weakly magnetic cementite inclusions, the contribution from the cementite’s magnetic hardness should be considered. With the use of the temperature dependence of the coercive force in deformed and annealed specimens, the contribution of each of the considered mechanisms to the specimens’ coercive force is estimated.     

Magnetic Properties of a Body as Nondestructive Testing Parameters of Tempering Quality of Quenched Steels (a Review)

The paper considers a nondestructive method for the monitoring of middle- and high-temperature tempering quality of steel workpieces with the carbon content higher than 0.3%. The method is based on measurements of the relaxation coercive force and the secondary residual magnetic induction of the body when remagnetization of the workpieces is carried out by means of permanent and alternating magnetic fields or by their superposition. It is shown that the possibility of this monitoring is ensured by the structural susceptibility of magnetic properties due to reversible displacements of domain walls, namely, the relaxation magnetization and magnetic susceptibility. The secondary residual magnetic induction of the matter and the relaxation coercive force of the matter cannot be used for this testing. The limiting workpiece shape factor below which this testing is possible is determined.     

Effect of Deviation from Coaxiality between the Directions of Magnetization and Mechanical Strain on the Results of Magnetic Testing of Elastic Strain in Steels

The magnetoelastic effect in steels that are in the states of coercive force and residual magnetization in the saturation hysteresis loop is studied. The regularities of changes in the residual magnetization and coercive force under uniaxial tensioning and compression of specimens of 30KhGSA steel magnetized along the direction of strain application are established. It is shown that a variation in the direction of magnetization and complication of the strain pattern result in considerable deviations in the character of changes in the magnetic forces determined by a ferroprobe-type coercive force meter for elastically strained plates from St3 and R6M5 steels and for an St3 beam.     

Choice of the parameters and algorithm for the magnetic hardness testing of thermally treated carbon steels by the method of regression modeling

The possibility of testing the hardness of quenched and tempered medium-carbon steels using their magnetic properties is studied. It is shown that the two-parameter method should be applied for the reliable estimation of the hardness. The coercive return magnetization (induction) and the coercive force must be used as the basic and subsidiary parameters of testing, respectively. It is established that the content of carbon in steel influences the sensitivity of testing. It is shown that the suggested magnetic hardness testing method can be practically implemented with the use of the modernized SIMTEST-2.10 system.     

Coercive force of ferromagnetic steels under the biaxial symmetrical tension of a material

Patterns of coercive force variations of Ct.3 and X70 ferromagnetic steels under biaxial symmetrical tension within both elastic and plastic ranges of deformation were studied using X-shaped specimens. It was shown that the coercive force of isotropic polycrystalline materials increased during plastic deformation under biaxial symmetrical tension and was proportional to applied stresses (loads). Plastic deformation of materials with high initial coercive-force anisotropy along the principal directions (X70 steel) leads to an abrupt decrease in anisotropy and subsequent alternation of its sign. The patterns of a material’s coercive force behavior allow the coercive force to be used for estimating the stress-strain state (from both an increase in the coercive force and its variations during loading as compared to that of the initial material) of articles made from the studied steels under biaxial symmetrical tensile deformation.     

Magnetooptical Analysis of the Subsurface Region in a Bearing Ring Subjected to Rolling Contact Fatigue

It has been known for decades that high contact load in bearings leads to fatigue alterations of subsurface material, which can be optically visualized on etched samples. In the literature, these alterations are termed dark etching regions and white etching bands, due to their peculiar patterns and contrast. In the current work, it is proposed to study these alterations by the magnetooptical Kerr effect, expecting that the material changes associated with rolling contact fatigue also affect the magnetic properties of bearing steel. The advantage of this method is that it has good spatial resolution, allowing recording of magnetic properties on microscopic scales. Samples containing dark etching regions and white etching bands were compared in the magnetooptical test with the reference sample containing no optically visible changes. It was found that the coercive force of material reduces as result of microstructural changes caused by rolling contact fatigue.