JPH03122227A - Decarburization continuous annealing furnace for grain oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To easily form a nitride inhibitor and to inexpensively produce a grain oriented electrical steel sheet having excellent magnetic characteristics by providing a reducing zone and a nitriding zone via an atmosphere partition after the decarburizing zone of the decarburization continuous annealing furnace for the grain oriented electrical steel sheet. CONSTITUTION:The grain oriented electrical steel sheet S contg. a small amt. of Al passes through the decarburization annealing furnace 1 and is heated in the heating zone; thereafter, the C incorporated in the steel sheet is oxidation-decarburized by the wet atmosphere gas from a supplying pipe 4 in the decarburizing zone 3 and SiO2 films are formed on the surfaces of the steel sheet. The steel sheet is then sent into the reducing zone 5 partitioned by the atmosphere partition 10 consisting of a freely openable/closable wall 11 where the SiO2 films are decreased or removed by the reducing gas, such as H2, from a supplying pipe 6; thereafter, the next atmosphere partition 8 is opened and the steel sheet is sent into the nitriding zone 7 where the Al in the steel sheet S is formed to the inhibitor, such as AlN, by the nitridable gas, such as NH3 or NO, blown from a supplying pipe 8 and the secondary recrystallization at the time of the finish annealing is developed. The grain oriented electrical steel sheet having the excellent magnetic characteristics is thus produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a decarburization continuous annealing furnace that removes carbon from a grain-oriented electrical steel sheet and also builds in an inhibitor.

(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 a silicon steel slab containing 2 to 4% St, annealing the hot-rolled sheet if necessary, and cold-rolling it once or twice or more with an intermediate annealing in between. According to
After making a cold rolled sheet to the final thickness and then decarburizing annealing, M
Manufactured by applying an annealing separator containing gO as the main component, performing final annealing to develop secondary recrystallized grains with Goss orientation, removing impurities such as S and N, and forming a glass coating. . Furthermore, flattening annealing and insulation coating treatment are performed as necessary.

As is known, for the secondary recrystallization to occur in the final annealing, the presence of fine inhibitors such as AJN, MnS, and MnSe that suppress the growth of primary recrystallized grains up to the secondary recrystallization temperature range is required. It is.

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~
However, since the 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 mentioned above, but in this annealing, it is also accompanied by St, which is used to form a glass film by reaction with the annealing separator MgO in the subsequent final annealing. An oxide film containing 2 is formed on the steel plate surface, and 1
Next recrystallization occurs.

As a conventional decarburization annealing furnace, for example, JP-A-61-485
Publication No. 29 discloses a decarburization annealing furnace in which a partition wall is provided at the boundary between a heating zone and a decarburization zone, heating is performed in a neutral gas atmosphere, and decarburization is performed in a humid atmosphere. This method involves heating in an atmosphere and then decarburizing the steel, which prevents the reduction of S in the steel in the neutral gas atmosphere and improves the magnetic properties, and has certain effects.

(Problems to be Solved by the Invention) The present invention incorporates an inhibitor that is essential for the occurrence of secondary recrystallization and has a strong effect, and uses grain-oriented electrical steel sheets with excellent magnetic properties. The object of the present invention is to provide a continuous annealing furnace for decarburization that can be obtained without the conventional high-temperature slab heating for forming an inhibitor.

(Means for Solving the Problems) The gist of the present invention is to provide a decarburization annealing furnace for decarburizing a grain-oriented electrical steel sheet. A decarburizing continuous annealing furnace for grain-oriented electrical steel sheet, characterized in that a reduction zone that gives a nitriding effect and a nitriding zone equipped with a nitriding device that injects nitriding gas toward the steel sheet are provided through an atmosphere partition. . Further, the partition may have a structure that can be opened and closed.

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

In the drawings, reference numeral 1 denotes a decarburization annealing furnace provided during the manufacturing process of grain-oriented electrical steel sheets, in which the grain-oriented electrical steel sheets rolled to the final thickness are decarburized prior to final annealing. 2 is decarburization annealing furnace 1
A heating zone 3 is a decarburization zone provided therein. The decarburization zone 3
For example, an atmospheric gas whose dew point is adjusted is N2. A N2 supply pipe 4 is provided, and decarburization occurs through a reaction between the humid atmospheric gas from there and the C diffused onto the surface of the steel sheet.

Reference numeral 5 denotes a reduction zone, in which a reducing gas supply pipe 6 of dry reducing gas, for example N2, is provided to give a reducing effect to the oxidized layer formed on the surface of the steel sheet in the decarburization zone 3.

In the reduction zone 5, it is not necessary to completely reduce the oxidized layer on the surface of the steel sheet, and for example, intermediate reduction may be used.

Reference numeral 7 denotes a nitriding zone, which is used to nitride the grain-oriented electrical steel sheet to form an inhibitor. As shown in FIG. A nitriding gas such as NH, No, etc. is sprayed onto the electromagnetic steel sheet S in combination with dry H2°N2 or alone. Since the nitriding gas supply device 8 sprays the nitriding gas over the entire width of the steel sheet and brings it into contact with the grain-oriented electrical steel sheet S which has been subjected to the reduction action in the reduction zone 5, nitriding is carried out in a short time and secondary recrystallization is carried out. An effective inhibitor of the expression of is formed. 9
is the cooling zone.

lO is an atmosphere partition, which is the boundary between the decarburization zone 3 and the reduction zone 5,
It is provided at the boundary between the reduction zone 5 and the nitriding zone 7 and the boundary between the nitriding zone 7 and the cooling zone 9 to prevent the atmospheres of each zone from mixing. The atmosphere partition 10 is preferably openable and closable, and as shown in FIG.
2 and the fixed wall 14 provided on the hearth 13 are rotatably provided at the tips of the fixed walls 14, respectively, with a plate threading line sandwiched therebetween, so as to block the atmosphere of the adjacent zone. 15 is an atmosphere exhaust device between the atmosphere partitions 10, and 16 is a conveyor roll for the steel plate S.

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.
The board will be passed through. This steel plate S combines with the nitrogenized nitrogen to form inhibitors (1!-31)N, Af! Add 0.01 to 0.06% of negative Ag to form N, etc.
Preferably one that includes.

By the way, the steel sheet S is heated to 750 to 900° C., and C in the steel is removed by reaction with humid atmospheric gas in the decarburization zone 3. Further, an oxidized layer containing 5 in 2 is formed on the surface of the steel plate S, but the oxidized layer is reduced or eliminated when the steel plate S undergoes a reducing action in the return zone 5. Also, the quality of the oxidation layer is changed.

Next, in the nitriding zone 7, N2 and N2. Alternatively, N2 is sprayed onto the steel plate S using the nitriding gas supply device 8 to nitridize the steel plate and form an inhibitor. The atmosphere of the nitriding zone 7 is separated from the adjacent reduction zone 5 and cooling zone 9 by an atmosphere partition 10, so that the atmosphere is kept dry and containing nitriding gas suitable for nitriding.
Furthermore, since the reduction action has been applied to the steel sheet S as described above, nitriding is carried out in a short period of time, and highly functional inhibitors such as (1!-5l)N and l)N are formed.

It is desirable that the temperature of this nitriding zone 7 is 700 to 880°C, and the concentration of the nitriding gas is 0.05 to 100%.

After nitriding, it is cooled in a cooling zone 9.

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

(Effects of the Invention) The decarburization annealing furnace of the present invention is configured to decarburize a grain-oriented electrical steel sheet rolled to the final thickness and then apply a reducing action to the surface of the steel sheet to nitride it. Since the atmospheres are independent of each other, it is suitable for not only removing C but also forming an inhibitor by nitriding and obtaining a grain-oriented electrical steel sheet with excellent magnetic properties.

In addition, conventionally, in order to form inhibitors, it was necessary to heat the electromagnetic steel slab at a high temperature of, for example, 1,300 to 1,400°C, and to perform precipitation treatment on the hot-rolled plate or intermediate plate before the final cold rolling, and a large amount of melted scale was generated due to the high-temperature heating of the slab. There were problems such as surface scratches and high heating energy consumption, but
In the present invention, since the inhibitor can be built in in a decarburization annealing furnace, it is not necessary to heat the electrical steel slab at a high temperature, and there is a great effect that the grain-oriented electrical steel sheet can be obtained at low cost.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is an explanatory diagram showing a decarburization annealing furnace of the present invention, and FIG. 2 is a cross section taken along the line ■-■ of FIG. 1, showing a nitriding gas supply device. The explanatory diagram shown in FIG. 3 is an enlarged explanatory diagram of the atmosphere partition part that can be opened and closed. 1... Decarburization annealing furnace 2... Heating zone 3...
Decarburization zone 5...Reduction zone 7...Nitriding zone 8...Nitriding gas supply device 1O...Atmosphere partition 12...Furnace ceiling 14...Fixed wall 16...Transport roll 4... ... Supply pipe 6 ... Supply pipe 9 ... Cooling zone 11 ... Rotating wall 13 ... Hearth 15 ... Atmosphere exhaust device

Claims (2)

[Claims] (1) In a decarburization annealing furnace for grain-oriented electrical steel sheets, which has a heating zone, a decarburization zone, and a cooling zone, after the decarburization zone, there is a reduction zone that gives a reducing effect to the oxidized layer on the surface of the steel sheet, and a 1. A decarburizing continuous annealing furnace for grain-oriented electrical steel sheets, characterized in that a nitriding zone equipped with a nitriding device for injecting a nitriding gas is provided with an atmosphere partition interposed therebetween. (2) The continuous decarburization annealing furnace for grain-oriented electrical steel sheets according to claim 1, wherein the atmosphere partition is a wall that can be opened and closed.