RU2049127C1 - Method for heat treatment of sheets of magnetic circuit - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: method for heat treatment of sheets of magnetic circuit includes heating, soaking, cooling and oxidation. In so doing, soaking at total content of nitrogen and sulfur up to 0.010 mas. is effected at temperature of 750-780 C, and at the total content of nitrogen and sulfur above 0.010 mas. at temperature of 781-880 C. Besides, soaking is carried out in moistened exogas at steam-to-hydrogen partial pressure ratio taken depending on total content of silicon and aluminium by formula given in invention description. Soaking in exogas is carried out at carbon monoxide-to-carbon dioxide ratio equalling 0.4-0.6. EFFECT: higher efficiency. 3 cl, 1 tbl

Description

 The invention relates to metallurgy, in particular to methods of heat treatment of sheets of magnetic cores of electrical isotropic steel.

A known method of heat treatment of sheets of the magnetic circuit, in which oxidation is carried out at 650-720 ^about With repeatedly (and.with. SSSR N 836157, CL 21 D 9/46, 1977). The disadvantage of this method is that the oxidation is carried out at a reduced temperature, which does not allow to form a sufficiently large grain in the sheets of the magnetic circuit and to obtain a high level of magnetic properties. Moreover, with repeated oxidation, a thick oxide layer is formed, which can peel off, which leads to increased metal losses.

The closest to the proposed method is the heat treatment of the magnetic circuit sheets of cold rolled electrical steel isotropic comprising annealing at 750-950 ^{° C} in the exothermic gas, purified from carbon dioxide and water vapor, oxidation is carried out at 600-650 ^{° C} [1]
The disadvantage of this method is that the holding temperature does not depend on the content of elements such as nitrogen and sulfur in steel, on the basis of which dispersed inclusions of nitrides and sulfides are formed. These inclusions effectively inhibit the migration of grain boundaries. The driving force of grain migration can be increased by selecting the holding temperature depending on the content of nitrogen and sulfur in the steel.

 The purpose of the invention is to increase the level of magnetic properties of sheets of magnetic cores.

The goal is achieved by the fact that with a total content of nitrogen and sulfur up to 0.010 wt. exposure is carried out at 750-780 ^about With, and with a total content of nitrogen and sulfur above 0.010 wt. the exposure is carried out at 781-880 ^about With, while the exposure is carried out in a "poor" moistened exogas at a ratio of partial pressures of water vapor and hydrogen, selected depending on the total content of silicon and aluminum according to the formula:
PH ₂ O: PH ₂ 0.2 (Si + Al) 0.1, where pH ₂ O is the partial pressure in a controlled atmosphere of water vapor;
PH ₂ partial pressure in a controlled atmosphere of hydrogen;
0.2 empirical coefficient, 1 wt.

 Si silicon content in steel, wt.

 Al aluminum content in steel, wt.

0.1 empirical coefficient, and if exposure is carried out in a "rich" exogas, then the ratio of the partial pressures of oxide and carbon dioxide should be
RNO: PCO ₂ 0.4-0.6
It was experimentally established that the selection of the holding temperature, depending on the nitrogen and sulfur content in the steel, as well as the oxidation of the carbon of the steel by moistening the “lean” exogas at a certain ratio of the partial pressures of water vapor and hydrogen or at a ratio of the partial pressures of oxide and carbon dioxide RSO: RSO ₂ 0.4-0.6 in the "rich" exogas forms the optimal structure of the sheets of the magnetic circuit, which provides a high level of magnetic properties and increase the energy parameters of electrical machines.

For heat treatment, steel is used, made according to the following technological scheme: steel smelting in a converter or an electric furnace, casting on a cold rolling mill, hot rolling, pickling, first cold rolling to an intermediate thickness, recrystallization annealing at 600-700 ^о С, second cold rolling with compression 1- 6% of the final thickness. After cutting down the sheets of the magnetic cores with a total content of nitrogen and sulfur up to 0.010 wt. exposure is carried out at 750-780 ^C and at a total content of sulfur and nitrogen above 0.010 wt. exposure is carried out at 781-880 ° ^C. Increased soaking temperature during the annealing of the magnetic sheets with the increase of total sulfur and nitrogen content increases the driving force for grain growth, and promotes the formation of an optimum structure to obtain a high level of magnetic properties.

Moreover, the exposure is carried out in a "poor" moistened exogas at a ratio of partial pressures of water vapor and hydrogen, selected depending on the total content of silicon and aluminum according to the formula
PH ₂ : PH ₂ O 0.2 (Si + Al) 0.1, where PH ₂ O is the partial pressure in a controlled atmosphere of water vapor;
PH ₂ partial pressure in a controlled atmosphere of hydrogen;
0.2 empirical coefficient, 1 wt.

 Si silicon content in steel, wt.

 Al aluminum content in steel, wt.

 0.1 empirical coefficient.

With an increase in the total content of silicon and aluminum in order to ensure sufficiently complete decarburization of the steel (C _rest. 0.005%), an increase in the oxidation potential of PH ₂ : PH ₂ O of the controlled atmosphere during exposure is necessary. This contributes to loosening the surface layer of silicon oxides and aluminum, which impedes the diffusion of carbon to the surface of the sheets.

Exposure in a "rich" exogas with a ratio of partial pressures of oxide and carbon dioxide of RSO: RSO _{2 of} 0.4-0.6 provides a fairly complete decarburization (C _ost ≅ 0.005%) of the sheets of the magnetic circuit.

 The selection, depending on the total sulfur and nitrogen content, of the holding temperature, which is carried out in a decarburizing atmosphere in a "poor" humidified exogas at a ratio of partial pressures of water vapor and hydrogen, selected depending on the total content of silicon and aluminum, or in a "rich" exogas at a certain the ratio of the partial pressures of oxide and carbon dioxide allows you to get the optimal structure of the sheets of the magnetic circuit and, accordingly, a high level of magnetic properties.

The method is tested in an industrial environment. The metal smelted in an electric furnace or converter had the following chemical composition, wt. carbon up to 0.06; silicon 0.7-0.2; aluminum 0.2-0.5; sulfur up to 0.025; nitrogen to 0.015. After casting on UNRS heated in reheat furnaces slabs are rolled to 1.5-2.5 mm thickness, the etched strips were cold rolled to an intermediate thickness, recrystallization annealing was performed at 650 ^{° C} was held for 20 hours, a second cold rolling was performed with transcritical by compressing 2-5%, then the strip was pulled out onto a tape from which the sheets of the magnetic circuit were cut out, the subsequent final heat treatment of the sheets of the magnetic circuit was carried out according to the proposed method and the magnetic properties were measured by standard odike.

PRI me R 1 (table). Since the total content of sulfur and nitrogen is 0.008 wt. the magnetic sheets annealed at a soaking temperature T _of 750 ^{° C} in the "rich" ekzogaze at a ratio of partial pressures of carbon monoxide and carbon dioxide RNO: RSO ₂ 0.4. Then, the sheets of the magnetic circuit were oxidized. This processing mode allows decarburization of the metal (With _approx. 0.004 wt.) And to obtain a sufficiently large homogeneous grain (d _cf. 150 microns) and a high level of magnetic properties (P _{1.5 / 50} 4.4 W / kg; B ₂₅₀₀ 1, 66 T).

PRI me R 2. Since the total content of sulfur and nitrogen is 0.010 wt. then the sheets of the magnetic circuit were annealed at a holding temperature T _in. 780 ^о С in a "poor" humidified exogas with a ratio of partial pressures of water vapor and hydrogen, determined by the formula РНО ₂ : РН ₂ 0.2 (1.4 + 0.4) 0.1 0.27. After cooling, the sheets of the magnetic circuit were oxidized in air. This treatment mode allows decarburization of the metal (C _ost. 0.003 wt.) And to obtain a sufficiently large homogeneous grain (d _cf. 170 microns) and a high level of magnetic properties (P _{1.5 / 50} 4.2 W / kg, V ₂₅₀₀ 1.65 T).

PRI me R 3. Since the total content of sulfur and nitrogen is 0.016 wt. the magnetic sheets annealed at a soaking temperature T _of 880 ^{° C} in the "rich" ekzogaze at a ratio of partial pressures of carbon monoxide and carbon dioxide RNO: RSO ₂ 0.60. Then, after cooling, the sheets of the magnetic circuit were oxidized in air. This processing mode allows decarburization of the metal (With _approx. 0.004 wt.) And to obtain a sufficiently large homogeneous grain (d _cf. 180 microns) and a high level of magnetic properties (P _{1.5 / 50} 4.0 W / kg; B ₂₅₀₀ 1064 T )

 In case of deviation from the recommended modes (table, examples 4-8), the objectives of the invention could not be achieved.

VARIATIONS decreasing soaking temperature to 730 ^C. (Example 4), i.e. below the lower limit, the process of decarburization of steel slows down, therefore, the residual carbon content increases (With _approx. 0.008 wt.) and a fine-grained structure of steel is formed, which is characterized by a reduced level of magnetic properties (P _{1.5 / 50} 4.9 W / kg; V ₂₅₀₀ 1.63 T). An increase in the holding temperature during annealing (Example 5) also slows down the decarburization of the sheets of the magnetic circuit (With a _sp. 0.007 wt.), The formation of an inhomogeneous structure with an average grain diameter d _cf. 110 microns and a reduced level of magnetic properties (P _{1.5 / 50} 4.7 W / kg; B ₂₅₀₀ 1.63 T).

The determination of the ratio of partial pressures of water vapor to hydrogen not according to empirical dependence (Example 6) leads to increased internal oxidation in the surface layers of silicon and aluminum, which contributes to the grinding of grain in these zones, slow decarburization (C _approx. 0.006 wt.) And reduce the level of magnetic properties (P _{1.5 / 50} 4.6 W / kg; B ₂₅₀₀ 1.63 T).

By reducing the partial pressure ratio of the oxide and carbon dioxide to 0.30 (example 7), i.e. below the lower limit, the oxidizing potential of the controlled atmosphere decreases, which leads to a slowdown of the decarburization process of steel, an increased content of residual carbon (C _o. 0.008 wt.), the formation of a fine-grained structure (d _cf. 115 μm) and, accordingly, a reduced level of magnetic properties ( P _{1.5 / 50} 4.8 W / kg; B ₂₅₀₀ 1.63 T). Increasing the partial pressure ratio of the oxide and carbon dioxide to 0.70 (example 8), i.e. above the upper limit, leads to increased oxidation in the surface layers of silicon, aluminum and partially iron. The oxide layer formed from the surface inhibits the decarburization of the sheets of the magnetic circuit, as a result of which the content of residual carbon increases (With _approx. 0.007 wt.) And a structure with a fine grain (d _cf. 120 microns) and with a reduced level of magnetic properties is formed (P _{1.5 / 50} 1.63 T).

 Thus, deviations from the proposed modes lead to a slowdown of the decarburization process, the formation of a fine-grained structure and a decrease in the level of magnetic properties.

When processing the sheets of the magnetic circuit according to the known method within the scope of the prototype (example 9), a high residual carbon content (C _ost. 0.030 wt.) Was obtained, a fine-grained structure with a low level of magnetic properties (P _{1.5 / 50} 6.0 W / kg; B ₂₅₀₀ 1.60 T).

 As can be seen from the table, only in case of compliance with the proposed modes (table, examples 1-3) is the goal of the invention achieved, as a result of which the parameters of the proposed method should be considered significant.

Thus, the application of the proposed method in compliance with understated parameters provides a significant increase in the level of magnetic properties in comparison with the prototype during heat treatment of magnetic core sheets. Magnetic induction (B ₂₅₀₀ ) increases by 0.04 T, specific losses (P _{1.5 / 50} ) decrease by 1.60 W / kg.

Claims (2)

1. METHOD FOR THERMAL TREATMENT OF SHEETS OF MAGNETIC WIRE, including heating sheets of steel, containing: 0.7 to 2.0 wt. silicon, 0.2 to 0.5 wt. aluminum, up to 0.06 wt. carbon, nitrogen and sulfur, aging and cooling in the atmosphere of purified and dried exogas, oxidation, characterized in that with a total nitrogen and sulfur content of up to 0.010 wt. the exposure is carried out at 750 780 ^o With, and with a total content of nitrogen and medium above 0.010 wt. - at 781 880 ^o C. 2. The method according to p. 1, characterized in that the exposure is carried out in exogas at a ratio of partial pressures of water vapor and hydrogen, corresponding to the dependence

3. The method according to p. 1, characterized in that the shutter speed is carried out in exogas at a ratio of partial pressures of carbon monoxide and carbon dioxide of 0.4 to 0.6.

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