JP2771633B2 - Continuous decarburization annealing equipment for grain-oriented electrical steel sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention removes carbon from grain-oriented electrical steel sheets,
The present invention relates to a decarburization continuous annealing furnace that produces an inhibitor by nitriding.

(Prior Art) A grain-oriented electrical steel sheet is mainly used as an iron core material of electrical equipment such as a transformer and a generator, and it is important that the magnetic property is good in terms of excitation property and iron loss property.

Normally, grain-oriented electrical steel sheets are hot-rolled from silicon steel slabs containing 2 to 4% Si, and if necessary, hot-rolled sheet annealing, and cold-rolled one or more times with intermediate annealing By
A cold-rolled sheet having the final thickness was obtained, followed by decarburizing annealing to remove C, form an oxide layer containing SiO ₂ on the surface of the steel sheet, and then apply an annealing separator containing MgO as a main component, and finish annealing To produce secondary recrystallized grains having a Goss orientation, remove impurities such as S and N, and produce a glass film.
Further, flattening annealing and insulating coating are performed as necessary.

For the appearance of secondary recrystallization in finish annealing, fine AlN, MnS, Mn that suppresses the growth of primary recrystallized grains up to the secondary recrystallization temperature range
It is known that an inhibitor such as Se needs to be present. Therefore, a treatment is performed in which the slab is heated to a high temperature to dissolve the inhibitor-forming element, and then the inhibitor is precipitated by hot-rolled sheet annealing or intermediate annealing.

By the way, in the manufacturing process of the grain-oriented electrical steel sheet, in order to control the crystal structure of the steel, C is set to, for example, 0.02.
1.01.0% must be contained. However, C present in the product steel sheet deteriorates the magnetic properties. Therefore, the steel sheet is cold rolled to the final sheet thickness and then decarburized and annealed.

The main purpose of the decarburizing annealing is to remove C and to form an oxide layer containing SiO ₂ on the surface of the steel sheet as a base for forming a glass film. Decarburization of grain-oriented electrical steel sheets is relatively easy, but the oxide layer formed during decarburization annealing affects the quality of the glass coating and also affects the magnetic properties. Regarding the decarburization annealing furnace for electrical steel sheets, in order to form a high-quality oxide film and improve the magnetic properties, for example, as shown in JP-A-54-160514, the atmosphere in the first half and the second half of the decarburization annealing furnace was changed. Some of them change the dew point. In this case, the oxide layer on the surface of the steel sheet is improved, an excellent glass film is formed, and a secondary recrystallization is stabilized through the improvement of the oxide layer, and the magnetic properties are also excellent. Japanese Patent Application Laid-Open No. 61-48529 discloses a decarburization annealing furnace divided by providing a partition wall at a boundary between a heating zone and a decarburization zone. In this method, heating is performed in a neutral gas atmosphere to prevent reduction of S in the steel, and after heating to a predetermined temperature, decarburization is performed. As a result, magnetic properties are improved, and a certain effect is achieved.

(Problems to be Solved by the Invention) The present invention can produce an inhibitor capable of sufficiently expressing secondary recrystallization, which is not found in conventional decarburization annealing furnaces,
An object of the present invention is to provide a decarburization annealing apparatus for grain-oriented electrical steel sheets having excellent magnetic properties without performing conventional high-temperature slab heating for inhibitor formation.

(Means for Solving the Problems) The present inventors have found that it is important that an inhibitor effective for secondary recrystallization by decarburizing annealing is not formed simply by nitriding, but is nitrided in a short time. I learned.

The present invention stably embodies this, and the gist of the present invention is that in a decarburizing annealing furnace for decarburizing grain-oriented electrical steel sheets, after a decarburizing zone, a heating device for heating to a temperature equal to or higher than the decarburizing zone. A reduction zone provided with a reducing gas supply device, a primary cooling zone, a nitriding zone provided with a nitriding gas injection device, and a secondary cooling zone are separated by a double openable and closable atmosphere partition at intervals. The present invention provides a decarburizing annealing apparatus for grain-oriented electrical steel sheets.

Hereinafter, the present invention will be described in detail based on an embodiment with reference to the drawings.

In the drawing, reference numeral 1 denotes a decarburizing annealing furnace provided in a process of manufacturing a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet rolled to a final thickness is decarburized prior to finish annealing. 2 is heating zone, 3
Is a decarburization zone. The decarburization zone 3 is provided with a supply pipe 4 for an atmosphere gas whose dew point is adjusted, for example, H ₂ , N ₂ , and the wet gas from this reacts with C in the steel sheet to decarbonize. . At this time, an oxidation action occurs on the surface of the steel sheet to form an oxide layer.

Reference numeral 5 denotes a reduction zone. The reduction zone 5 includes a heating device 6 for heating the temperature of the decarburization zone 3 or higher and a reducing gas such as dry H _2.
A reducing gas supply device 7 for feeding the steel is provided, and the steel plate is heated to a higher temperature than at the time of decarburization to apply a reducing action to the steel plate to make the surface of the steel plate easy to be nitrided thereafter.

Reference numeral 8 denotes a primary cooling zone, which is cooled to a nitriding temperature of, for example, 700 to 800 ° C. in the next nitriding zone so as to easily form an inhibitor. The atmosphere of the primary cooling zone 8 is dry H ₂ or H ₂ and N ₂
Is preferred.

Reference numeral 9 denotes a nitriding zone, which is a nitriding gas such as NH
_{3. This} zone is used to form an inhibitor by injecting NO, etc. and nitriding. The nitride strip 9, nitriding capability as shown by the furnace section in Figure 2 gas injector 10 is provided in the steel plate width direction, than this plain or dry the nitriding ability gas e.g. NH _3, NO, etc.
H ₂ and N ₂ and mixed e uniformly allowed to nitrided spraying short time steel sheet. 11 is a secondary cooling zone.

Numeral 12 denotes a double openable and closable atmosphere partition, which is provided between each band so as to prevent the atmosphere from being mixed and to facilitate the temperature control of each band. It is. An enlarged view of an example of the double openable atmosphere partition 12 is shown in FIG. 3, and the rotating wall 13 is provided between the furnace ceiling 14 and the hearth 15 with a gap between the steel plate S passing line. It is rotatably provided alongside the tip of the fixed wall 16 provided, and shuts off the atmosphere in the adjacent band, and effectively acts on the atmosphere control and temperature control of each band. The openable and closable atmosphere partition 12 is not limited to the above-described one, and may be provided with a moving wall that advances and retreats to the threading line in place of the rotating wall, and is an openable and closable partition that prevents the atmosphere of the adjacent belt from being mixed. I just need. In the figure, reference numeral 17 denotes an exhaust device for adjusting the atmospheric pressure between the double openable and closable atmosphere partitions 12, and 18 denotes a transport roll for the steel sheet S.

 Next, the operation of the present invention will be described.

The grain-oriented electrical steel sheet S rolled to the final sheet thickness is decarburized in the decarburizing annealing furnace 1, and the steel sheet S is combined with nitrified nitrogen to form an inhibitor (Al-Si) N, AlN, or the like. It is desirable that Al contains 0.01 to 0.06% of free Al so as to form Al.

Incidentally, the steel sheet S is heated to 750 to 850 ° C.
The C in the steel is removed by the reaction with the wet atmosphere gas. An oxide layer containing SiO ₂ is formed on the steel sheet surface,
This defect nitride, and because causes bring nitride variation, the reduction zone 5 and heated to a temperature higher than the temperature at the time of decarburization give the steel sheet a reducing action by reducing gas e.g. dry H _2. By applying a reducing action by heating to a temperature higher than the decarburizing temperature, the oxidized layer formed on the steel sheet surface under the decarburizing atmosphere is subjected to a strong reducing action and becomes thinner, and subsequent nitriding is facilitated. Then
In the primary cooling zone 8, the steel sheet S is cooled to a temperature suitable for nitriding,
At nitride strip 9 nitriding ability gas e.g. NH ₃ H ₂ or H ₂ and N ₂
When sprayed on the steel sheet S with the mixed gas, the nitriding gas reacts with the steel sheet S, N enters the steel and is nitrided, thereby forming an inhibitor such as (Al-Si) N or AlN having a high secondary recrystallization expression function. You. After nitriding, it is cooled in the secondary cooling zone 10.

Each of these zones is partitioned by a double openable and closable atmosphere partition 12 during decarburization annealing so that the atmosphere of the adjacent zones is not mixed.

After decarburizing annealing, an annealing separator is applied and finish annealing is performed.

(Effects of the Invention) In the decarburizing annealing apparatus of the present invention, after decarburizing the grain-oriented electrical steel sheet rolled to the final sheet thickness, it is reduced by heating to a higher temperature than during decarburization, and then cooled to a temperature suitable for nitriding. Since the atmosphere is independent of each zone, the atmosphere is independent of each zone. Therefore, decarburization is sufficient, of course, and nitriding is easy. It is suitable for obtaining grain-oriented electrical steel sheets having excellent magnetic properties.

In addition, conventionally, in order to form an inhibitor, an electromagnetic steel slab is heated to a high temperature of, for example, 1300 to 1400 ° C. to form a solid solution of an inhibitor-forming component, and a precipitation treatment is essential for a hot-rolled sheet or an intermediate sheet before final cold-rolling. However, there were problems such as the generation of a large amount of molten scale, generation of surface flaws, and a high unit heating energy based on high-temperature heating of the slab, but in the present invention, the inhibitor can be built in a decarburizing annealing furnace, so The slab does not need to be heated at a high temperature, and has a great effect that the grain-oriented electrical steel sheet can be obtained at low cost.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention, FIG. 1 is an explanatory view showing a decarburizing annealing furnace, FIG. 2 is an explanatory view showing a nitriding gas supply device in section II-II of FIG. 1, FIG. FIG. 4 is an enlarged explanatory view showing an openable and closable atmosphere partition. DESCRIPTION OF SYMBOLS 1 ... Decarburization annealing furnace, 2 ... Heating zone 3 ... Decarburization zone, 4 ... Gas supply pipe 5 ... Reduction zone, 6 ... Heating device 7 ... Reduction gas supply device, 8 ... Primary Cooling zone 9: Nitriding zone 10: Nitriding gas injection device, 11: Secondary cooling zone 12: Double openable and closable atmosphere partition 13: Rotating wall, 14: Furnace ceiling 15: Hearth, 16: fixed wall 17: exhaust device, 18: transport roll

Continuation of the front page (72) Inventor Yasumitsu Kondo 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works (72) Inventor Yasuo Nemoto 1 Edamitsu, Yawatahigashi-ku, Kitakyushu-shi, Fukuoka -1-1 Nippon Steel Corporation Yawata Works (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 9/46 501 C21D 8/12

Claims (1)

(57) [Claims] In a decarburizing annealing furnace for grain-oriented electrical steel sheets, a reducing zone, a primary cooling zone, and a nitriding zone provided with a heating device for heating the temperature of the decarburizing zone or higher and a reducing gas supply device after the decarburizing zone. A decarburizing continuous annealing apparatus for grain-oriented electrical steel sheets, characterized in that a nitriding zone and a secondary cooling zone provided with an active gas injection device are partitioned by double openable walls spaced apart.