JPH0819468B2 - Method for producing grain-oriented electrical steel sheet with excellent magnetic and coating properties - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as core materials for transformers, generators and other electric equipment, and must have good magnetic properties, especially iron loss properties. The grain-oriented electrical steel sheet uses the secondary recrystallization phenomenon on the rolling surface (11
It can be obtained by developing crystal grains having a so-called Goss orientation, which has a [001] axis in the 0) plane and the rolling direction.

As is well known, the secondary recrystallization is caused by finish annealing, but there are fine AlN, MnS, MnSe and other so-called inhibitors which control the growth of the primary recrystallization up to the secondary recrystallization temperature range. Need to let. Therefore, the electromagnetic steel slab is heated to a high temperature of, for example, about 1350 to 1400 ° C., and a component that forms an inhibitor, for example,
Annealing is performed in which Al, Mn, S, Se, N, etc. are completely solid-dissolved and the inhibitor is finely precipitated in the hot-rolled sheet or the intermediate sheet before the final cold rolling.

By carrying out such a treatment, a grain-oriented electrical steel sheet having a high magnetic flux density is produced, but since the electrical steel slab is heated at a high temperature as described above, the amount of molten scale generated is large. Is large, which hinders the operation of the heating furnace. There are also problems such as high energy consumption per unit of the heating furnace and occurrence of surface defects. A grain-oriented electrical steel sheet manufacturing method in which the slab heating temperature is lowered is being studied. For example, Japanese Unexamined Patent Publication No.
In addition to Al, Zr, Ti, B, N
A manufacturing method is disclosed in which slab heating is performed at 1100 to 1260 ° C. by incorporating a nitride forming element such as b, Ta, V, Cr and Mo. Also, JP-A-59-56
In Japanese Patent No. 522, Mn is 0.08 to 0.45%, S is 0.007% or less, the [Mn] × [S] product is reduced, and a magnetic steel slab containing Al, P, and N is used as a material. Is proposed.

Although the low-temperature slab heating method has a certain effect, the inhibitor-forming components such as Al and M are used.
Since n, S, Se, N, and the like are not completely dissolved in the steel, it is a problem to form an inhibitor effective for the appearance of secondary recrystallization. The present applicant has previously filed Japanese Patent Application Laid-Open No. 2-20
No. 0731 proposes a manufacturing method in which a grain-oriented electrical steel sheet cold-rolled to a predetermined sheet thickness at the time of decarburization annealing is passed through strips by nitriding with NH ₃ to create an inhibitor.

[0006]

Since a decarburized annealed sheet is nitrided with a gas having a nitriding ability, an annealing separating agent containing MgO as a main component is applied, and then the coil is wound into a coil and finish annealing is performed. In the production of the grain-oriented electrical steel sheet, an exposed coating defect of the base metal called shimofuri occasionally occurs.

This shimofuri has a nitrogen content of 20 after nitriding.
It can be improved by adjusting the content to be 0 ppm or less and by optimizing the atmospheric conditions during decarburization and finish annealing, but this is not sufficient. In order to completely eliminate this shimofuri, it has been found that it is necessary to optimize the atmospheric conditions of the gas in the furnace up to denitrification treatment after decarburization annealing and during the subsequent nitriding treatment.

In the present invention, secondary recrystallization is stably expressed,
Further, it is a major object to obtain a grain-oriented electrical steel sheet having a good glass coating without shim free by a nitriding method during strip passing, and to obtain a stable coating formation.

[0009]

The gist of the present invention is that a slab of electromagnetic steel is heated to a temperature of 1200 ° C. or lower, then hot rolled, hot rolled or annealed,
In the manufacturing method of the grain-oriented electrical steel sheet, cold rolling is performed once or twice or more with intervening intermediate annealing, then inhibitors are formed by decarburization and nitriding, and then finish annealing is performed. Up to and after the nitriding treatment, the degree of oxidation of the atmosphere gas in the furnace PH ₂ O / PH ₂
^Is 5 × 10 ⁻⁴ or more, which is a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties.

The present invention will be described in detail below. The present invention is carried out as follows. An electromagnetic steel slab heated at a temperature of 1200 ° C. or lower and containing a trace amount of Al is hot-rolled, annealed if necessary, and cold-rolled. Cold rolling is 1
It is carried out twice or more with a single or intermediate annealing sandwiched between them to obtain a predetermined plate thickness, and then decarburization annealing. The cold rolling may be performed by heating at 50 to 300 ° C. between rolling passes. This decarburization annealing reduces the carbon in the steel sheet, for example 30
The content is controlled to be ppm or less and an oxide layer containing SiO ₂ is formed on the surface of the steel sheet. The amount of oxide at that time is 45 in terms of oxygen amount.
It was 0 to 650 ppm. After decarburization annealing, until nitriding treatment,
In the subsequent nitriding treatment, the degree of oxidation PH ₂ O / PH ₂ of the atmosphere gas in the furnace was changed, and the steel sheet treated under a constant condition where the nitriding amount was 200 ppm was finish annealed and the properties of the coating film were examined.

Atmospheric gas oxidation degree PH₂O / PH₂And film properties
Figure 1 shows the relationship with₂O / PH ₂As the moth grows
This reduces the frequency of occurrence of₂O / PH₂Is 5
× 10^-FourIt is known that the occurrence of shimofuri can be eliminated by the above.
I saw it. In addition, the oxide layer of the steel sheet at that time was peeled off, and FeO
Fig. 2 shows the result of analysis of the composition of
Degree of PH₂O / PH₂Of FeO in the steel sheet
It was found that the amount increased.

This is because F in the steel sheet formed by decarburization annealing.
When eO is reduced by H ₂ gas when the degree of oxidation PH ₂ O / PH ₂ in the atmosphere in the furnace is small in the process of reaching the nitriding treatment after decarburization annealing, it is not only prevented by the present invention, but rather Fe
It is estimated that the O content was increased. Regarding the relationship between the amount of FeO in a steel sheet and shimofuri, the applicant of the present invention has applied for Japanese Patent Application No. 2-3137.
As is clear from No. 74, when FeO is large, the film formation during finish annealing is accelerated, a forsterite film is formed in a low temperature range, and excessive additional nitriding during finish annealing is prevented, so that a Occurrence can be suppressed.

Usually, an atmosphere gas containing H ₂ and a nitridable gas is used up to the nitriding treatment after the decarburization annealing and thereafter, and the dew point of the gas is −5.
It is 0 to -60 ° C. Since this contributes to the occurrence of shimofuri, in the present invention, in order to satisfy the atmospheric gas oxidation degree condition PH ₂ O / PH ₂ ≧ 5 × 10 ⁻⁴ , which is a condition for suppressing the occurrence of shimofuri, moisture in the atmospheric gas is satisfied. Is effective.

By the means described above, FeO in the oxide layer in the steel sheet after decarburization annealing can be increased rather than reduced, and then MgO is applied and finish annealing is performed, whereby magnetic properties and coating properties are improved. The grain-oriented electrical steel sheet of which quality is good and whose variation is small is obtained.

[0015]

EXAMPLES Next, examples will be described. Example 1 A slab having the composition shown in Table 1 was heated under the conditions shown in the same table, hot-rolled to a thickness of 2.3 mm, hot-rolled annealed, and then cold-rolled to a thickness of 0.3 mm. And Then 8
Decarburization annealing was performed at 30 ° C. for 155 seconds in an atmosphere composed of H ₂ 75% and N ₂ 25%. Then, after cooling to 750 ° C, 75
Nitrogen was adjusted by adjusting the amount of NH ₃ so that the amount of nitrogen would be 180 ppm in an atmosphere of H ₂ 75% and N ₂ 25% at 0 ° C. for 30 seconds. Further, the degree of oxidation PH ₂ O / PH ₂ in the atmosphere gas in the furnace during the nitriding treatment after the decarburization annealing was changed as shown in Table 1. After the nitriding treatment, an annealing separator containing MgO as a main component was applied to the steel sheet, and H ₂ 60%, N ₂ 1
Heating to 880 ° C. in an atmosphere condition of 0% and Ar 30%,
After that, H ₂ 75% and N ₂ 25% were added to adjust PH ₂ O / PH ₂ to 0.00
5, and the finish annealing was performed at 1200 ° C. for 20 hours. The magnetic properties and coating properties of the obtained grain-oriented electrical steel sheet were measured, and the results are shown in Table 1.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

EFFECTS OF THE INVENTION According to the present invention, as shown in Examples, no grain defects are generated and there is no change in inhibitor strength due to additional nitriding. Can be manufactured.

[Brief description of drawings]

[Fig. 1] After decarburization annealing, up to nitriding treatment and nitriding
Atmospheric gas oxidation degree during processing PH ₂O / PH₂And film defects occur
It is a figure which shows the relationship with a rate.

[Fig. 2] After decarburization annealing, up to nitriding treatment and nitriding
Atmospheric gas oxidation degree during processing PH ₂O / PH₂And the amount of FeO
It is a figure which shows the relationship of.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Arai 1-1, Toibata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Toshihiko Uemura Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka No. 1 No. 1 within the Yawata Works, Nippon Steel Co., Ltd. (72) Nozomi Ishibashi, No. 1 No. 1 Tobita-cho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture Within the Yawata Works, Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. A slab of electromagnetic steel is heated to a temperature of 1200 ° C. or lower, and then hot-rolled, hot-rolled as it is, or hot-rolled sheet annealed, and cooled once or twice with an intermediate annealing. In the method for producing a grain-oriented electrical steel sheet in which an inhibitor is formed by decarburization and nitriding, and then finish annealing is performed in the furnace atmosphere after decarburizing and annealing until nitriding and subsequent nitriding. Gas oxidation degree PH ₂ O
/ PH _{2 is set} to 5 × 10 ⁻⁴ or more, which is a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties.