SU1267310A1 - Method of determining curie point of discontinuous ferromagnetic phase in heterogeneous ferromagnetic material - Google Patents

Abstract

The invention relates to the field of measurement technology. It can be used to determine the Curie points of individual phases in ferromagnetic alloys with two or more phases, one of which is a matrix with a higher Curie point. The purpose of the invention is to improve the accuracy of the method. The proposed method is as follows. A sample of a heterogeneous ferromagnetic material is magnetized at room temperature, then heated, and the residual magnetization is measured during the heating process. The goal is achieved by taking the sample re-magnetized, then cooled to room temperature, and the residual magnetization is measured during the cooling process. The Curie point of the dispersed ferromagnetic phase and the temperature of the end of heating of the sample are determined, based on the values of the temperature at which the decline of the residual magnetization of the sample begins during the cooling process,. Q Curie points of the matrix phase of a heterogeneous ferromagnetic material and by that (because the residual magnetization of the sample decays during heating. Thus, due to the fact that the level of residual magnetization does not change during re-magnetization of tsD with a decrease in temperature, Then the temperature of the onset of a sharp drop in the residual magnetization is revealed very clearly, which causes an increase in the accuracy of its determination. 2 Il.

Description

The invention relates to a measurement technique and can be used to determine the Curie points of individual phases in ferromagnetic alloys with two or more phases, one of co. The purpose of the invention is to improve the accuracy of the method by eliminating the error due to temperature changes in the magnetization of the domains of the matrix phase, relaxation of internal stresses and other processes occurring in the heterogeneous material during heating.

Fig. 1 shows the dependence of the residual magnetization of the sample on temperature, explaining the implementation of the method; in fig. 2 - the same relation for low alloyed steel OG2C1D,

The method is carried out as follows.

A sample of a heterogeneous alloy is magnetized at room temperature T, then it is heated (in the absence of an applied field) and the residual magnetization Id is measured during the heating process (FIG. 1, curve 1). For those: the temperature Tl, which is higher than the temperature TC of the end of a sharp drop in residual magnitude, but below the Curie point of the matrix phase 0, the sample is re-magnetised.

Excess temperature of re-magnetization T „above the temperature of the end / rot of a sharp drop in residual magnetization when heated T ;. which is the approximate value of the Cgsri point of the dispersed phase, is 50-100 ° C. Such a transformation ensures that the sample magnetizes at a temperature above the Curie point of the dispersed phase.

Then the re-magnetized sample is cooled (also in the absence of an applied field) and the residual magnetization is measured during the cooling process (Fig. 1, curve 2). The Curie point of the dispersed ferromagnetic phase 0J is determined from the temperature of the beginning of a sharp drop, and the residual magnetization upon cooling of the sample.

The temperature detection of the end of a sharp drop in residual magnetization during heating and the beginning of a sharp drop in residual magnetization at

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cooling can be carried out according to temperature dependences of residual magnetization recorded by the two-coordinate potentiometer. In this case, the measurement of the residual magnetization of the sample can be used ferrosonde,

For example, to determine the Curie point of a dispersed carbide phase

(doped cement (Fe, Me) С in low-alloy steel 10Г2С1Д with content,%: С 0.09; Mp 1.50; Si 0.95; Cu 0.04) a sample of this steel (2x2x50 mm) welded to it A thermocouple was placed in a porcelain tube (10x2 mm, length 275 mm) and magnetized using an electromagnet at 20 ° C until saturation. Then the tube with the sample was heated in

a tubular electric furnace with a bi-filar winding at a rate of 10 ° / min. During the heating process, the tube with the sample was periodically removed from the furnace and placed in the measuring coil (200

turns) for measuring, using a ballistic galvanometer, the residual magnetization of the sample in relative units (dividing the galvanometer). In this case, the dependence of the residual magnetization on temperature (Fig. 2, curve 3) was obtained and the temperature of the end, a sharp drop, which was 140 ° C, was detected. At a temperature of 240 ° C, which

 on the termination temperature, sharp drop in residual, magnetization, but below the Curie point of the matrix phase — 0 iron — 768 ° C; the sample was re-magnetized, turned off

the furnace and in the process of cooling the sample at a rate of 10 ° / min. its residual magnetization was periodically measured. The measured values were used to plot the dependence of the residual magnetization on temperature during cooling (Fig. 2, curve 4), and the temperature of the onset of a sharp drop in the residual magnetization was found (the Curie point doped with manganese and KpehiHHeM

cementite), which amounted to 155 ° C. The amount of this cementite at the indicated content of angle in steel (0.09%) is 1.4%.

The relative error in determining the Curie point of the dispersed phase according to the proposed method is 1.5%.

The temperature of the end of the sharp drop in the residual magnetization when the sample is heated is 140 ° C, is the approximate value of the Curie point,

Repeated magnetization of the sample at a temperature above the temperature of the end of a sharp drop in the residual magnetization upon heating, but below the Curie point of the matrix phase, allows one to obtain such a magnetic structure of the sample that provides enhanced stability of the residual magnetization When cooled to the beginning of the magnetic transformation of the dispersed phase. This is due to the fact that the particles of the dispersed phase in the paramagnetic state more effectively than in the ferromagnetic state prevent the displacement of domain boundaries of the matrix phase. Since particles of the dispersed phase in the paramagnetic state manifest themselves as cavities in the matrix phase, the magnetic field in the volume of these particles (the field of internal scattering) in the direction opposite to the residual magnetization of the matrix phase. Therefore, when the sample is cooled, and below the Curie point of the dispersed phase, particles of this phase are magnetized in the opposite direction to the residual magnetization of the matrix phase. As a result . there is a sharp decrease in the residual magnetization of the sample. Since the level of residual stress of the re-magnetized sample almost does not change when the temperature drops to the beginning of the temperature of the magnetic transformation of the dispersed phase, the temperature of the onset of a sharp drop in the residual magnetization caused by 1 ferrous transformation of the dispersed phase (point. Curie) is very clearly defined , as a result of which the accuracy of its determination is determined.

Thus, the proposed method provides for the determination of the Curie point of a dispersed ferromagnetic phase with its insignificant content (0.5-5%) in a heterogeneous alloy with an accuracy of at least 1.5%. In addition, the accuracy of the determination of the Curie point is improved, since the magnetic transformation is

The dispersion phase is fixed twice: during heating and cooling, as a result of which possible cases of incorrect interpretation of the decay of the residual magnetization of the sample are excluded.

This will allow the thermomagnetic analysis of the carbide and nitride phases in low carbon and low alloyed 10 steels, as well as in technically pure iron after various heat treatment and plastic deformation modes, which contributes to the improvement of hardening

15 types of thermal and thermomechanical processing of these materials.

Claims (1)

Invention Formula 20. A method for determining the Curie point of a dispersed ferromagnetic phase in a heterogeneous ferromagnetic material, including magnetizing a sample of a heterogeneous ferromagnetic material at room temperature, subsequent heating and measuring the residual magnetization of the sample during heating, characterized in that, to increase the accuracy of 3Q, after heating the sample is re-magnetized, cooled to room temperature, and the residual magnetization is measured during the cooling process, the Curie point of the dispersed fer omagnitnoy phase and 5, the heating end temperature of the sample is determined from the ratios 0e T ,,; TC TC 0 „, where Oj is the Curie point of the dispersed ferro0 magnetic phase;  the temperature of the onset of the decay of the residual magnetization of the sample during the cooling process; five © m is the Curie point of the matrix phase of a heterogeneous ferromagnetic material; T (, is the drop end temperature of the residual magnetization of the sample during the heating process; TC - temperature okaychani heating. 4j 0 40 Yew temperature (Pub t 160 200 YO 2BO Teeperature With iPus. g