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All papers in this issue are devoted to the 100th anniversary of the birth of the late M. N. Mikheev, corresponding member of the Russian Academy of Sciences and one of the founders of magnetic structural analysis.Abstract -Results of an experimental study of the anomalous behavior of the residual-magnetization hysteresis of ferromagnetic articles that, under local magnetization and magnetization reversal in a pulsed magnetic field with a variable amplitude, were subjected to heat treatment under different conditions are reported. Parameters of the hysteresis and their dependence on the magnetization and magnetization-reversal conditions, as well as on the magnetic properties of a material, are considered.Magnetic methods occupy a prominent place in the theory and practice of nondestructive testing of ferromagnetic articles' strength properties and heat-treatment quality [1][2][3][4][5]. Among these, a pulsed magnetic method, which was developed at the Laboratory of Magnetic Testing Methods, Institute of Applied Physics, Belarussian Academy of Sciences [2, 6], is widely used at many plants in the CIS and other countries.In a general sense, this method consists of, first, the local magnetization (or magnetization followed by magnetization reversal) of an inspected article in a pulsed magnetic field produced by an attachable solenoid and, second, subsequent measurement of the gradient of the normal component of residual-magnetization field strength (RMFS), ∇ H rn . On the basis of this value, the article's mechanical properties and structure are determined using correlation dependences, which were found beforehand in compliance with GOST (State Standard) 30415-96.The method is characterized by simple execution, high sensitivity to the tested parameters of an article, and a weak dependence on the variable gap between a probe and a test object.The pulsed magnetic method is used successfully for the nondestructive testing of strength parameters of low-carbon (08 ÍÔ , 08 û , 3 ÍÔ , 10 ÍÔ , 15 cÔ , 20 cÔ , and 18 ûA ), medium-carbon (35, 45, 50), and lowalloyed (65 É , 30 ïÉëÄ ) cold-rolled steels; medium-carbon (35, 40, 45, 50) and low-alloyed (65 É , 30 ïÉëÄ , 30 í ) hot-rolled steels; and high-alloyed high-temperature steels ( ï 5 å , 1 ï 13, 12 ï 1 åÉ ) subjected to recrystallization annealing. However, this method is unsuitable for testing the mechanical properties of steel articles containing >0.3% C and subjected to quenching followed by high-temperature (350 − 600 ° C) tempering.The aim of this series of studies is to find additional magnetic parameters of an article, which are measured during a change of the pulsed-magnetization modes and allow one to inspect materials belonging to this class. Characteristics, such as parameters of the anomalous hysteresis of RMFS H r and its gradient ∇ H rn upon local magnetization and magnetization reversal of an article in a pulsed magnetic field with a variable amplitude [7], can be used as additional parameters for testing. MAGNETIC METHODS

Effects of the tempering temperature on specimens' hardness and on the anomalous-hysteresis loop's and the recovery curves' parameters for residual magnetization are experimentally studied. Test specimens made of steel 60C2 intended for laminated springs were subject to local magnetization and magnetization reversal by a pulsed magnetic field with a variable amplitude. Parameters enabling tests of the hardness of steel within three ranges of the tempering-temperature variation (0-300, 300 − 600, and 0-600 ° C) are determined.The hardness of items made from medium-carbon, high-carbon, and alloy steels that have been quenched and tempered at low temperatures (100-300 ° C) can be efficiently determined using coercive-force-measurement methods [1][2][3]. The pulsed magnetic method [4] enables testing of the hardness, strength, relative elongation, and contraction of cold-and hot-rolled low-carbon steels after their recrystallization annealing. However, none of these methods are suitable for testing mechanical properties of items made of steels containing more than 0.3% of carbon and have been subjected to quenching and subsequent high-temperature tempering. The Institute of Metal Physics has carried out a large amount of research devoted to the use of relaxation characteristics: relaxation coercive force H r , relaxation magnetization , relaxation permeability χ r , and residual induction B d either after partial demagnetization of specimens for the same values of demagnetizing constant field H pris or B d after partial demagnetization by variable field H pris of constant amplitude. For many steel grades with a content of carbon exceeding 0.3%, it was found that these characteristics feature unique dependences on the tempering temperature over a wide range of temperatures. The results of these studies were generalized in [1, 5] and used as a basis for the development of relaxation-coercive-force meters that magnetize specimens either in the interior of a solenoid [6] or by use of an attachable magnet [7]. These devices can be successfully used to solve many practical problems. There are, however, some problems that cannot be solved using available test methods. For example, it is inexpedient to magnetize multiple-leaf springs or other bulky items inside a solenoid, while items with intricate shapes (e.g., billets for gears or sprockets, etc.) or low-quality surfaces are not suitable for a device with an attachable magnet, since the sensitivity of such a device to the deviation of the test zone from a plane or to variations in the gap results in significant errors.The pulsed magnetic method involves magnetization of an item by a pulsed magnetic field produced by an attachable solenoid and measurement of the normal component of the gradient of the residual magnetization strength along the symmetry axis of the magnetizing field. This method can be used for any specimen regardless of its shape. The error related to the variation of the gap between the probe and the tested specimen does not exceed 2% for a change in the g...

Effects of the tempering temperature on specimens' hardness and on parameters of both the anomalous-hysteresis loop and the recovery curves for the gradient of the residual magnetization field's strength are studied experimentally. Test specimens made of steel 50 ïÉîÄ intended for laminated springs are quenched in water from 850 ° C and subjected to local magnetization and magnetization reversal by a pulsed magnetic field created by an attachable solenoid whose axis is perpendicular to the surface. The amplitude of pulses changes with increment ∆ H p . Parameters enabling nondestructive testing of the hardness of multiple-leaf springs made from steel 50 ïÉîÄ within three ranges of temperingtemperature variation (0-300, 300-600, and 0-600 ° C) are determined.High-quality chrome-manganese steel 50 ïÉîÄ intended for laminated springs is used in manufacturing of critical multiple-leaf springs for vehicles. It differs from silicon steel 60C2 investigated earlier [1] by improved technological properties attained at the same cost.An increase in the content of manganese in a medium-carbon chrome-alloy steel results in improved strength properties, minor variations of plasticity, and increased hardening characteristics. Owing to the presence of vanadium, this steel has a fine-grained structure that additionally improves its hardening characteristics. If this steel is tempered in the range 400-500 ° C, vanadium carbides that dissolved when the steel was heated for quenching become deposited at the nodes of the dislocation lattice. This process slows softening of steel in the tempering process until noticeable coagulation of these carbides begins, a process which takes place at tempering temperatures above 500 ° C.Vanadium positively affects the process of nitrogen binding as well. Low sensitivity to the growth of austenite grains and a uniform distribution of carbides in the structure of steel 50 ïÉîÄ after tempering ensure increased impact viscosity [2].Manufacturing instructions stipulate that a bundle of plates made of this steel, which is intended for making a single multiple-leaf spring, should be heated for quenching in a belt furnace with a temperature of 800-810 ° C at the entry, 890-910 ° C in the central zone, and 890-910 ° C at the exit. The heated leaves are bent and tempered in oil for 15 to 20 min. The oil temperature should not exceed 90 ° C. The hardness after quenching, which is measured once every hour, should be in the range 477-712 HB (55-63.5 HRC ).The quenched leaves are tempered also in a belt furnace whose temperature at the entry and the exit is 500-520 ° C. Heating for tempering lasts 100 min. The hardness after cooling is measured at three points: at the two ends of a leaf and on the convex surface at its center. The value of hardness should be 363-444 HB (39-47 HRC ). The hardness of individual leaves within the same multiple-leaf spring must not exceed 40 HB (4 HRC ).Owing to the dimensions and weight of a multiple-leaf spring (the length is >2 m and the weight is 30 kg) and to the necessity to...