JPH03122225A - Variable zone length decarburization continuous annealing furnace for grain oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To make stable decarburization and nitriding treatments of stable steel sheets having different sheet thicknesses and C contents by providing freely openable/ closable partitions between the respective zones of the continuous annealing furnace having a decarburizing zone, reducing zone, primary cooling zone and nitriding zones for the grain oriented electrical steel sheet and freely changing the lengths of the respective zones. CONSTITUTION:The many freely openable/closable partitions 3 are provided between the decarburizing zone 2, the reducing zone 5, the primary cooling zone 7, and the nitriding zone 9 at the time of continuously subjecting the grain oriented electrical steel sheet S in a decarburizing furnace 1 to a decrburization treatment and a nitriding treatment for forming an inhibitor. The lengths of the respective treating zones 2, 5, 7, 9 are freely adjusted to adequately form the inhibitor by the decarburization reaction and the nitriding reaction in the nitrizin zone 9 by adequately opening/closing the many partitions 3 when the sheet thickness and C content of the grain oriented steel sheet S to be treated are changed. Thus, the grain oriented electrical steel sheet having the excellent magnetic characteristics is thereby stably produced even if the kind of the grain oriented electrical steel sheet is varied.

Description

[Detailed description of the invention] (Industrial application field) The present invention removes carbon from a grain-oriented electrical steel sheet, and
The present invention relates to a continuous decarburization annealing furnace for nitriding and building up an inhibitor, and for a grain-oriented electrical steel sheet whose zone length is variable.

(Prior Art) Grain-oriented electrical steel sheets are mainly used as core materials for electrical equipment such as transformers and generators, and it is important that they have good magnetic excitation characteristics and iron loss characteristics.

Normally, grain-oriented electrical steel sheets are produced by hot rolling silicon steel slabs containing 2 to 4% Sl, followed by hot rolling annealing once or cold rolling two or more times with intermediate annealing in between. A thick cold-rolled plate is formed, then decarburized annealed, coated with an annealing separator containing MgO as a main component, final annealed to develop secondary recrystallized grains with Goss orientation, and further, It is manufactured by removing impurities such as S and N and forming a glass coating.

Furthermore, flattening annealing and insulation coating treatment are performed as necessary.

In order for the secondary recrystallization to occur in the final annealing, fine AJL is required to suppress the growth of primary recrystallized grains up to the secondary recrystallization temperature range.
It is known that inhibitors such as N, MnS, MnSe, etc. need to be present.

By the way, in the manufacturing process of grain-oriented electrical steel sheets, in order to control the crystal structure of the steel, for example, 0.02~
It contains 1.00% C, but since C present in the product deteriorates the magnetic properties, it is decarburized and annealed after cold rolling to the final thickness.

The main purpose of decarburization annealing is to remove C as described above, but in addition to this annealing, in the subsequent final annealing, Si is added to form a glass film by reaction with the annealing separator MgO. An oxide film containing , is formed on the surface of the steel sheet, and primary recrystallization also occurs.

As a conventional decarburization annealing furnace, for example, JP-A-61-485
Publication No. 29 states that the heating zone is divided from the decarburization zone by a partition wall,
A decarburization annealing furnace is disclosed in which heating is performed in a neutral gas atmosphere, such as N2, in a heating zone, and carbon is removed in a humid gas atmosphere in a decarburization zone. This prevents the reduction of S in the steel by heating in a neutral gas atmosphere and improves the magnetic properties, and has certain effects.

(Problems to be Solved by the Invention) The present invention involves continuous decarburization annealing of a grain-oriented electrical steel sheet, which removes C from the steel sheet and goes one step further to build in an inhibitor that nitrides the steel sheet and sufficiently expresses secondary recrystallization. Aiming for the furnace, but
When decarburizing and nitriding to form an inhibitor, the grain-oriented electrical steel sheets to be passed have various thicknesses and are randomly subjected to decarburization annealing. Since the amount varies, there is a possibility that decarburization and formation of the inhibitor may not be performed uniformly on each grain-oriented electrical steel sheet.

The present invention provides continuous decarburization of grain-oriented electrical steel sheets that can sufficiently decarburize each steel sheet and nitride inhibitor formation even when grain-oriented electrical steel sheets with different plate thicknesses, carbon contents, etc. are passed through. The purpose is to provide an annealing furnace. In addition, there are cases where it is desired to intentionally change the amount of nitridation of the steel sheet to produce grain-oriented electrical steel sheets with different grades of magnetic properties. Another object of the present invention is to provide a continuous decarburization annealing furnace that can meet such demands.

(Means for Solving the Problems) The gist of the present invention for achieving the above object is to provide a decarburization zone, a reduction zone, a primary cooling zone, and a nitriding zone in a decarburization continuous annealing furnace for decarburizing grain-oriented electrical steel sheets. A grain-oriented electrical steel sheet, comprising a nitriding zone equipped with a gas injection device for nitriding the grain-oriented electrical steel sheet, and atmosphere partitions that can be opened and closed at intervals in each zone so that the length of the zone can be changed. in a continuous annealing furnace with variable zone length decarburization.

Other points include a decarburization zone, a primary cooling zone,
A zone of a grain-oriented electrical steel sheet that is equipped with a nitriding gas injection device and has a nitriding zone for nitriding the grain-oriented electrical steel sheet, and each zone is provided with atmosphere partitions that can be opened and closed at intervals, so that the length of the zone can be changed. Located in a variable length decarburization continuous annealing furnace.

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

In FIG. 1, 1 is a decarburization annealing furnace, in which a grain-oriented electrical steel sheet rolled to the final thickness is decarburized prior to final annealing. 2 is a decarburization zone provided in the decarburization annealing furnace 1, and in the decarburization zone 2, openable and closable atmosphere partitions 3 are provided at intervals. It is desirable that the atmosphere partition 3 is not just a partition wall, but has a structure that prevents the atmosphere from mixing with the adjacent zone when the movable wall is closed.

4 is a humid atmosphere gas supply device, for example, H2. N2 gas is supplied, and the humid atmospheric gas reacts with carbon diffused onto the surface of the steel sheet, resulting in decarburization.

Reference numeral 5 denotes a reduction zone, in which a device 6 for supplying reducing gas, such as dry H2, is provided in order to give a reducing effect to the oxidized layer formed on the surface of the steel sheet in the decarburization zone 2.

Also within the reduction zone 5, openable and closable atmosphere partitions 3 are provided at intervals.

7 is a primary cooling zone, and the nitriding temperature is set to 700 to 800, for example, to facilitate the formation of an inhibitor in the next nitriding.
Cool to ℃. 8 is a refrigerant supply pipe.

The primary cooling zone 7 is also provided with openable and closable atmosphere partitions 3 at intervals. In this cooling, if dry N2 or a mixed gas of N2 and N2 is used as a refrigerant, reduction is also carried out, although to a lesser extent, and depending on the sheet material, the reduction zone 7 can be omitted as in the decarburization annealing furnace shown in FIG.

9 is a nitriding zone in which the grain-oriented electrical steel sheet S is nitrided to form an inhibitor, and a nitriding gas such as NH
. is being used.

From the injection device lO, a nitriding gas or dry N is used.
2 or N2. Can be sprayed mixed with N2. The nitriding zone 9 is also provided with openable and closable atmosphere partitions 3 at intervals. ! I is the secondary cooling zone.

An example of the openable/closable atmosphere partitions 3 provided at intervals in the furnace is shown in FIG. The projecting walls 15 are rotatably provided in line with the tips of the protruding walls 15 provided on the hearth 14, respectively, and partition zones.

1G is a conveyance roll.

The rotating wall 12 is rotatable in the direction of the arrow by a drive device (not shown) about a fulcrum 17, and shuts off the atmosphere by opening and closing, effectively controlling the atmosphere and temperature of each zone. In order to prevent the upper rotating wall 12 from damaging the steel plate S when its tip comes into contact with it, it is preferable to cover it with a soft refractory material or the like. Reference numeral 18 denotes a device for adjusting the atmospheric pressure between the openable and closable partitions 3, which discharges atmospheric gas leaking from the partitioned adjacent zones to the outside of the furnace.

The openable and closable atmosphere partition 3 is not limited to the above-mentioned one, and as shown in FIG. 4, a movable wall 19 that moves forward and backward in the sheet passing line may be provided in place of the rotating wall, and in short, it can be opened and closed to control the atmosphere of the zone. It is fine as long as it can be partitioned so that they do not mix.

Therefore, the atmosphere partitions 3 that can be opened and closed at intervals are provided.
Activate one of these to decarburize and anneal each zone.

Next, we will discuss the effect.

The grain-oriented electrical steel sheet S rolled to the final thickness is decarburized in the annealing furnace 1.
Although the steel sheet S is passed through, it combines with the nitrogenized nitrogen to form inhibitors (Al2-5i)N and A47N.
0.01~0.0 of the free 8 ohms to form etc.
It is desirable that it contains 6%.

By the way, the final thickness of the grain-oriented electrical steel sheet S is, for example, 0.
The thickness varies from 15 to 0.35 mm, and the C content of the raw steel sheet S also varies, for example from 0.02 to 0.09%. Therefore, it is important to perform decarburization and nitriding according to the plate thickness, C content, etc. in order to obtain a grain-oriented electrical steel sheet S having excellent magnetic properties and coating properties.

For example, if the grain-oriented electrical steel sheet S to be passed is thick and has a high C content, the lengths of the decarburization zone 2 and nitriding zone 9 may be made large. The openable and closable atmosphere partitions 3-1 on the inner end side provided in each of the zones 9 and 9 are closed, and zone quality is performed. As a result, a product with desired magnetic properties can be obtained without insufficient inhibitor formation due to insufficient decarburization or insufficient nitriding. Also, if the decarburization zone 2 is short and the nitriding zone 9 needs to be long,
It is only necessary to select one of the openable/closable partitions 3 provided at intervals in the furnace and open/close the partition.

The surface of the steel sheet S decarburized in the decarburization zone 2 is subjected to a reducing action in the reduction zone 5, the oxidized layer is thinned, and the steel sheet S is cooled in the primary cooling zone 7 to a temperature suitable for nitriding. Further, in a site Kari S where forced reduction is not required, cooling is performed in a primary cooling zone 7 in a decarburization annealing furnace as shown in FIG. 5 in which the reduction zone 5 is omitted.

Next, when a nitriding gas such as NH3 is sprayed over the entire width of the M-plate in the nitriding zone 9 whose zone length is changed depending on the material to be passed through, an inhibitor with a strong secondary recrystallization effect, such as (Ag-5t), is sprayed over the entire width of the M-plate. N.

ApN etc. are stably formed.

After nitriding, it is cooled in a secondary cooling zone 11. Thereafter, an annealing separator is applied to the grain-oriented electrical steel sheet S and finish annealing is performed.

(Effects of the Invention) The present invention provides partitions that can be opened and closed at intervals in the decarburization annealing furnace, so that the decarburization zone, reduction zone, and
The length of the next cooling zone and nitriding zone can be changed, and even if the grain-oriented electrical steel sheet to be passed changes, decarburization and inhibitor-forming nitriding can be performed to suit the change, resulting in stable directionality with the desired properties. Electrical steel sheets can be obtained.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is an explanatory diagram of a variable zone length decarburization continuous annealing furnace of the present invention; FIG. 2 is an explanatory diagram showing a nitriding gas supply device seen from a cross section of the furnace; FIG. 3 is an enlarged explanatory diagram showing a partition that can be opened and closed, FIG. 4 is a diagram showing another example of a partition that can be opened and closed, and FIG. 5 is an explanation of a variable zone length decarburization continuous annealing furnace in another embodiment of the present invention. It is a diagram. 1... Decarburization annealing furnace 2... Decarburization zone 3.
... Atmosphere partition that can be opened and closed 4 ... Humid atmosphere gas supply device 5 ... Reduction zone 6 ... Reduction gas supply device 7 ... Primary cooling zone 8 ... Refrigerant supply pipe 9 ... Nitriding zone 10
... Nitriding capable gas injection device 11 ... Secondary cooling zone 30 12 ... Rotating wall 14 ... Hearth floor 16 ... Transport roll 18 ... Discharge 13 ... Furnace ceiling 15 ...・Protrusion wall 17... fulcrum

Claims (2)

[Claims] (1) A nitriding zone is provided in the furnace, which is equipped with a decarburization zone, a primary cooling zone, and a nitriding gas injection device for nitriding grain-oriented electrical steel sheets, and each zone is provided with atmosphere partitions that can be opened and closed at intervals. A variable zone length decarburization continuous annealing furnace for grain-oriented electrical steel sheet, characterized in that the zone length can be changed freely. (2) A nitriding zone is provided in the furnace, which is equipped with a decarburization zone, a reduction zone, a primary cooling zone, and a nitriding gas injection device for nitriding grain-oriented electrical steel sheets, and an atmosphere that can be opened and closed at intervals in each zone. A variable zone length decarburization continuous annealing furnace for grain-oriented electrical steel sheet, characterized by having a partition so that the zone length can be freely changed.