JPH0328320A - Finish annealing method for grain-oriented magnetic steel sheet - Google Patents

Abstract

PURPOSE:To uniformly heat a grain-oriented magnetic steel sheet coil and to improve the electromagnetic characteristics of the grain-oriented magnetic steel sheet by using a preheated gas, such as Ar or H2 to make up the loss component of the dissipated heat of an annealing furnace at the time of subjecting the above-mentioned coil to a secondary recrystallization finish annealing. CONSTITUTION:The slab of the electromagnetic steel having the compsn. contg., by weight %, 0.03 to 0.10% C, 2.5 to 4.0% Si, 0.050 to 0.090% Mn, 0.010 to 0.030% Se or S, and <0.030% Al, and consisting of the balance Fe is hot rolled and is then subjected to the annealing for relieving the strain generated by the hot rolling. This slab is subjected to >=1 passes of cold rolling and is thereby made into a sheet having 0.15 to 0.35mm final sheet thickness. After the sheet is coiled, the coil 4 is put into an inner case 12 of the batch type annealing furnace and is further covered with a furnace frame 1. The coil 4 is heated by a heater 2 until the temp. of the coil attains 800 deg.C. The preheated gas, such as Ar or H2, is thereafter supplied from pipes 8, 10 to the inside and outside of the inner case 12 and the coil is held at the secondary recrystallization temp. over a long period of time until the secondary recrystallization ends to develop the decarburized and finish annealed {110} <001> aggregated texture. The grain-oriented magnetic steel sheet having the excellent electromagnetic characteristics is thus produced.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention provides a heating method suitable for maintaining the coil temperature at a constant temperature for a long period of time when final annealing is performed in the manufacturing process of unidirectional electric liflwA sheets. It is about the method.

[Prior Art J A unidirectional electrical steel sheet is annealed in a temperature pattern as illustrated in FIG. That is, the Se. The steel is held at a constant temperature twice during secondary holding to remove S, etc. from the steel.

In this case, in order to cause secondary recrystallization grain growth of Goss-oriented grains, which are essential for grain-oriented electrical steel sheets, it is necessary to maintain the steel sheet at a secondary recrystallization temperature specific to the material. If this temperature deviates from the secondary recrystallization temperature, as shown in two examples in Figure 3,
The electromagnetic properties will be significantly degraded.

Conventionally, in order to maintain the secondary recrystallization temperature of electrical steel sheets, in an annealing furnace, a technique was used to heat the coil using electric heater wires installed at one or more locations on the ceiling, side walls, and hearth.■ Ceiling, side walls There was a technology in which the coils were heated using a combustion burner installed on one or both sides of the furnace and an electric heater wire installed in the hearth.

[Problem to be solved by the invention 1 However, the above technology has the following drawbacks. When performing secondary recrystallization, it is necessary to hold the coil at a constant temperature for a long time, but when controlling the electric heater wire on and off, the part of the coil where the heater wire is attached and the part on the opposite side. However, there was a problem in that the coil temperature became non-uniform.

Furthermore, the method (2) also has the problem that the coil temperature becomes non-uniform depending on the position where the burner is installed.

In addition, both of the above techniques (1) and (2) have the problem that when the fixed temperature is reached, the coil temperature exceeds the maintained temperature.

The problem to be solved by the present invention is to solve the non-uniformity of the temperature inside the coil that occurs when the coil temperature is maintained at a constant temperature for a long time in secondary recrystallization finish annealing of unidirectional electrical steel sheets. The aim is to improve the electromagnetic characteristics by not exceeding the holding temperature at the initial stage.

[A thousand steps to solve the problem] In order to solve the above problem, in the present invention, while the annealed coil is maintained at the secondary recrystallization temperature, the preheated Ar. It was decided to supply the loss of heat dissipated from the furnace body by using H2 alone or in a mixed gas. This allows the coil to be maintained at a constant temperature without causing uneven temperature distribution. In addition, as a measure to prevent the holding temperature from exceeding the holding temperature at the initial stage of holding, the coil temperature is heated by an electric heater or burner alone or both, until the coil temperature reaches the secondary recrystallization temperature, and then the preheated Ar. By heating the coil to the holding temperature using H2 alone or in a mixed gas, it is possible to heat the coil so that it does not exceed the holding temperature. [Function] Since the method of the present invention is formed horizontally as described above, it is possible to maintain the coil uniformly at the secondary recrystallization temperature for a long time, and to prevent the coil from exceeding the holding temperature at the initial stage of retention. , it is possible to obtain an electric lif1 steel sheet with excellent electromagnetic properties. [Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG.

A batch-type finishing annealing furnace was used in which the coil was heated by an electric heater 2. The coil 4 is placed on the coil pedestal 5 installed on the hearth 3 via the seal plate 7 and the pedestal 6, and is annealed with the inner case 12 and the furnace side 1 covered. The coil is heated by the heater 2 installed in the furnace structure until the coil temperature reaches 800°C, and then the heater power is turned off until the secondary recrystallization is completed and the temperature is maintained at a constant temperature. Ar gas supply pipe 8
, Ar gas preheated to a holding temperature from 10 to 5rn'/Hr is applied to the inside of the inner case and 50rr to the outside of the inner case. /Hr to keep the coil temperature constant at the holding temperature.

Preheating of Ar gas is performed, for example, using the recubulator device shown in Figure 4. Passing Ar gas through the recuperator l4,
Heat with preheating gas burner 13. The preheating temperature of Ar gas is determined by an exhaust gas thermometer 15 and an Ar gas exit side thermometer 16,
17, and the temperature is adjusted by controlling the gas flow rate of the combustion gas burner so that the measured value remains constant. Figures 5 and 6 show the heat patterns of the coils of the conventional example and the embodiment of the present invention, respectively. In the conventional example, a temperature rise is observed in the initial stage of holding, and there is also a difference in temperature between the heater side and the anti-heater side. On the other hand, in FIG. 6, there is no temperature rise at the initial stage of holding, and the temperatures on the heater side and the anti-heater side are uniform.

By implementing the present invention, ■ Temperature differences due to coil winding position are eliminated.

■ It can also prevent the coil temperature from exceeding the holding temperature at the start of holding. Table 1 shows plate thickness 0. The electromagnetic characteristics of a 3 mm silicon steel plate are compared between an example and a comparative example.

Table 1 [Effects of the Invention] According to the method of the present invention, while maintaining the temperature at the secondary recrystallization temperature,
Since the temperature is controlled by preheated gas, temperature differences depending on the coil winding position are eliminated.

It is also possible to prevent the coil temperature at the start of holding from exceeding the holding temperature (secondary recrystallization temperature). Therefore,
It is possible to improve electromagnetic properties.

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view of the final annealing furnace according to the present invention, Figure 2 is a graph showing the heat pattern of the final annealing process, and Figure 3 is the deterioration of electromagnetic properties due to deviation from the secondary recrystallization holding temperature. Figure 4 is a vertical cross-sectional view of the recuperator, Figure 5 is a graph showing the conventional coil heat pattern,
FIG. 6 is a graph showing the coil heat pattern of the present invention. 4... Coil 5... Coil pedestal 8... Gas supply pipe 9-... Gas recovery pipe IO... Gas supply pipe 11... Gas recovery pipe 12... Inner case l3... Preheating gas burner l4... Recuperator l5, 16, l7... Thermometer application agent Kawasaki

Claims (1)

[Claims] 1 C: 0.03-0.10% by weight Si: 2.5-4.0% by weight Mn: 0.050-0.090% by weight Se or S: 0.010-0. 030% by weight Al: 0
．． A silicon steel hot-rolled sheet containing 0.030% by weight or less and the balance consisting of Fe and unavoidable impurities is annealed and cold rolled one or more times to obtain a 0.1
After the final plate thickness is 5 to 0.35 mm, decarburization annealing and finish annealing are performed to develop the {110}<001> texture. When finish annealing a grain-oriented electrical steel sheet, the secondary recrystallization temperature While the coil is being held at
A method for finish annealing grain-oriented electrical steel sheet, characterized by circulating r, H_2 gas alone or in a mixture.