JPH03122226A - Decarburization continuous annealing furnace for grain oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To simultaneously execute the decarburization of a grain oriented electrical steel sheet and the formation of an inhibitor consisting of a nitride and to inexpensively produce the grain oriented electrical steel sheet having excellent magnetic characteristics by providing a nitriding zone before or after the decarburizing zone of the decarburization annealing furnace having a heating zone, decarburizing zone and cooling zone for the grain oriented electrical steel sheet. CONSTITUTION:The grain oriented electrical steel sheet S contg. a small amt. of Al is fed into the decarburization annealing furnace 1 and is heated in the heating zone 2; therafter, the steel sheet is sent to the decarburizing zone 3 and the C of the steel sheet S is oxidation- decarburized by reacting with the H2O in the wet gas supplied from a supplying pipe 4. A nitriding gas formed by mixing NH3 with H2 and N2 is blown onto the steel strip S from a supplying pipe 6 in a nitriding zone 5 partitioned by an atmosphere partition 8 to form the Al in the steel strip to the inhibitor, such as AlN; thereafter, the partition 8 is opened to sand the steel strip into the cooling zone 7. The nitriding zone 5 may be disposed in front of the decarburizing zone 3. Since the decarburization annealing and the inhibitor formation are simultaneously executed in the decarburization annealing furnace 1, the grain oriented electrical steel sheet having the excellent magnetic characteristics is produced at the low cost.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a continuous decarburization annealing furnace for grain-oriented electrical steel sheets.

(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% Sl, 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 obtaining a cold-rolled plate of the final thickness and then decarburizing annealing,
An annealing separator containing MgO as a main component is applied, finish annealing is performed to develop secondary recrystallized grains with Goss orientation, and S.

It is manufactured by removing impurities such as N and forming a glass coating. Furthermore, flattening annealing and insulation coating treatment are performed as necessary.

In order for secondary recrystallization to occur in the final annealing, fine AN to suppress the growth of primary recrystallized grains up to the secondary recrystallization temperature range is required.
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 the decarburization annealing is to remove C as described above, but the annealing also contains Si, which reacts with MgO in the subsequent final annealing to form a glass coating.
An oxide film containing O□ is formed on the surface of the steel sheet, and primary recrystallization also occurs.

As a conventional decarburization annealing furnace, for example, JP-A-Sho et-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. By heating the steel in a neutral gas atmosphere, it is effective in preventing a decrease in S in the steel and improving the magnetic properties.

(Problems to be Solved by the Invention) The present invention goes one step further and aims to remove C from the steel during decarburization annealing, as well as to build in an extremely effective inhibitor for secondary recrystallization into the steel. The purpose is to provide a continuous annealing furnace for decarburizing steel plates.

(Means for Solving the Problems) The gist of the present invention is that in a decarburization annealing furnace for grain-oriented electrical steel sheets provided with a heating zone, a decarburization zone, and a cooling zone, a grain-oriented electrical steel sheet is heated before or after the decarburization zone. This is a continuous annealing furnace for decarburizing grain-oriented electrical steel sheets, which is characterized by having a nitriding zone for nitriding.

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

In the drawings, reference numeral 1 denotes a decarburization annealing furnace provided in the process of processing 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 a heating zone provided in the decarburization annealing furnace 1, and 3 is a decarburization zone. The decarburization zone 3 is provided with a supply pipe 4 of atmospheric gas whose dew point is adjusted, for example, N2°N2, and decarburization is caused by the reaction between the moist atmospheric gas supplied from there and the carbon diffused onto the surface of the steel sheet. Charcoal.

A nitriding zone 5 is for nitriding the grain-oriented electrical steel sheet to form an inhibitor, and is provided after the decarburization zone 2 in this embodiment. In the nitriding zone 5, a nitriding gas supply device 6 is provided in the width direction of the steel sheet, and is configured to spray a nitriding gas such as NH, No, etc. onto the grain-oriented electrical steel sheet S. In addition to the nitriding gas, dry H2 and N2 are supplied to the nitriding zone 5.

7 is a cooling zone.

8 is an atmosphere partition, which separates the decarburization zone 3 and the nitriding zone 5.
The cooling zone 7 is provided at the boundary between the cooling zone 7 and the cooling zone 7 to prevent the atmospheres of the respective zones from mixing, so that decarburization and oxide film formation are stabilized in the decarburization zone 3, and nitridation of the steel sheet S is stabilized in the nitriding zone 5. The purpose is to ensure that the 9 is a conveyance 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. The steel sheet S preferably contains 0.01 to 0.06% of free AN so as to combine with nitrogen to form inhibitors (AN-5i)N, AIN, etc.

By the way, the steel plate S is heated to 750 to 900°C, and in the decarburization zone 3, carbon in the steel is removed by reaction with humid atmospheric gas. Next, in the nitriding zone 5, N2 and N2 mixed with a nitriding gas such as NH are sprayed onto the steel sheet S by the nitriding gas supply device 5 to nitridize the steel plate and form an inhibitor. At this time, the atmosphere of the nitriding zone 5 is separated from the decarburization zone 3 and the cooling zone 7 by an atmosphere partition 8, so that a dry atmosphere suitable for nitriding and containing a nitriding gas is maintained, and the nitriding zone is formed during the passing of the steel sheet S, so nitriding is carried out in a short period of time, and highly functional inhibitors such as (
AN-5l)N, AIN, etc. are formed. The temperature of this nitriding zone 4 is preferably 700 to 880°C, and the concentration of the nitriding gas is preferably 0.05 to 100%.

Thereafter, it is cooled in the cooling zone 7.

In this example, the nitriding zone 5 was provided after the decarburization zone 3, but instead of this, the nitriding zone 5 could be installed before the decarburization zone 3 to serve as a decarburization annealing furnace that performs decarburization after nitriding. Good too.

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

(Effects of the Invention) In the decarburization annealing furnace of the present invention, in addition to removing C from the steel sheet, nitriding is performed to form an inhibitor. Therefore, in the past, 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 a precipitation treatment on the hot-rolled sheet or intermediate sheet before the final cold rolling. Although there are various problems such as generation of a large amount of molten scale, generation of surface defects, and high heating energy consumption due to heating, in the present invention, the inhibitor can be built in in a decarburization annealing furnace, so heating of the electrical steel slab can be done at low temperature. Therefore, the above-mentioned problem can be eliminated, and it is suitable for obtaining grain-oriented electrical steel sheets having excellent magnetic properties at low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a decarburization annealing furnace in one embodiment of the present invention. 1... Decarburization annealing furnace 2... Heating zone 3.
... Decarburization zone 4 ... Supply pipe 5 ... Nitriding zone

Claims (1)

[Claims] (1) In a decarburizing annealing furnace for grain-oriented electrical steel sheets, which is provided with a heating zone, a decarburization zone, and a cooling zone, a nitriding zone for nitriding the grain-oriented electrical steel sheets is provided before or after the decarburization zone. A continuous annealing furnace for decarburizing grain-oriented electrical steel sheets.