CN101748259A - Method for producing high-magnetic-induction oriented silicon steel by low-temperature heating - Google Patents

Abstract

The invention discloses a method for producing high magnetic induction oriented silicon steel by low temperature heating, which comprises the steps of heating an oriented silicon steel slab produced by a common process, then carrying out hot rolling, annealing or normalizing the hot rolled slab, carrying out primary high reduction cold rolling to the thickness close to a finished product, carrying out decarburization annealing in a wet atmosphere, then carrying out nitriding, coating a separant, and finally carrying out high temperature annealing, and is characterized in that: the heating temperature of the plate blank is controlled below 1280 ℃; before nitriding of decarburization annealing plate, 1.5% -3% critical deformation cold rolling is carried out under the condition of no lubrication to destroy SiO₂A film; the separant is Al with the size less than 10 mu m₂O₃Fine particles, wherein 5 to 30 weight percent of TiO is added₂. The invention solves the problem of SiO formed on the surface of the decarburization annealing plate₂The film can prevent nitriding and obtain excellent performance of the bottom layer of the glass film.

Description

A method for producing high magnetic induction grain-oriented silicon steel by low-temperature heating

technical field

The invention relates to a production method of high magnetic induction oriented silicon steel, in particular to a method for producing high magnetic induction oriented silicon steel by heating at low temperature.

Background technique

At present, the production process of oriented silicon steel is generally: blast furnace ironmaking→converter smelting→external refining→continuous casting+electromagnetic stirring→slab spraying anti-oxidation film→heating and hot rolling→normalization (Hi-B)→cold rolling→ Intermediate annealing (GO)→secondary cold rolling (GO)→decarburization annealing and coating of MgO release agent→high temperature annealing of finished products→thermal leveling stretch annealing and coating of insulating film→rewinding packaging.

On an industrial scale, control techniques for inhibitors can be divided into two categories. One is a common technique, that is, the slab is heated above the solid solution temperature of inhibitors (such as AlN and MnS), so that they are dispersed and precipitated, which is called "internal inhibitor method" (> 1300 ° C); the other is The "obtaining inhibitor method" (1100-1200 °C) developed by Nippon Steel Corporation, that is, the heating temperature of the slab is low enough, and the inhibitor necessary for secondary recrystallization is the secondary annealing process from the completion of decarburization annealing to the final product annealing. Formed before secondary recrystallization begins, the means is to nitriding the steel to combine with the original elements in the steel to form (Al, Si)N precipitates with inhibitor function.

When manufacturing Hi-B oriented silicon steel with AlN+MnS as the inherent inhibitor, the heating temperature of the cast slab is >1300°C, and the rolling with a large reduction ratio of more than 85% in the first cold rolling is adopted. The most important point is Ensure the dispersion and precipitation of AlN from steelmaking to normalization.

In the hot rolling process, the final rolling temperature must be above 1100°C, because the silicon steel must be cooled rapidly from the region where the γ-phase volume fraction is greater than a given value; because the γ-phase with a volume fraction of 40% to 50% is required, Si When the content is 3.25%, the required C content is 0.07% to 0.08%. These characteristics lead to the following difficulties in developing new products.

Difficulty heating at high temperature

High-temperature heating causes more iron oxide scales, resulting in low yield; high furnace repair rate, reduced output; high fuel consumption; short furnace life; high manufacturing costs; and increased product surface defects.

(1) It is difficult to increase the Si content

To reduce the iron loss by increasing the silicon content, the C content must also be increased. However, increasing the C content makes decarburization of silicon steel difficult, resulting in hysteresis in the finished product.

(2) It is difficult to produce thin gauge silicon steel products

To produce thin gauge products with a cold rolling reduction of about 87%, it is necessary to reduce the thickness gauge of hot rolled coils. However, high finishing temperatures cannot be maintained for hot rolled coils below a certain grade.

In order to avoid the metallurgical problems of using AlN as an inherent inhibitor to manufacture Hi-B oriented silicon steel, and to manufacture new products, the method of obtaining inhibitors by heating slabs at low temperatures is often used now. The manufacturing process of the inherent inhibitor and the method of obtaining the inhibitor are basically the same, and the Hi-B product is manufactured by a cold rolling method. The essential difference between the two methods is shown in Table 1. The method for obtaining the inhibitor uses AlN as the inhibitor, heating the slab at a low temperature, and nitriding after decarburization annealing.

Table 1 Characteristics of the two manufacturing methods

Mn formed MnO after decarburization annealing can be used as a catalyst for the reaction between MgO and SiO ₂ , improving the quality of the glass film. MnS plays an effective role in forming a glass film. With AlN as the main inhibitor, MnS is no longer used in the production of grain-oriented silicon steel by the above method of obtaining the inhibitor, and the formation of a 10-20nm thick _SiO2 film on the surface after decarburization annealing is a great obstacle to nitriding.

Contents of the invention

The object of the present invention is to provide a method for producing high magnetic induction oriented silicon steel by heating at low temperature, solve the problem that the _SiO2 film formed on the surface of the decarburized annealed plate hinders nitriding, and simultaneously obtain a glass film bottom layer with excellent performance.

In order to achieve the above object, the main technical solutions taken by the present invention are as follows:

(1) The oriented silicon steel slab produced by the usual process is heated below 1280°C, followed by hot rolling, and the hot-rolled plate is annealed or normalized, and then cold-rolled at a large reduction rate, rolled to a thickness close to the finished product, and then rolled to a thickness close to the finished product. Decarburization annealing in wet atmosphere;

(2) The decarburized annealed plate is subjected to 1.5% to 3% critical deformation cold rolling without lubrication to destroy the _SiO2 film, followed by nitriding treatment, and the nitriding temperature is 830 to 870°C; the nitriding time is 5 ~50 seconds; the nitriding medium is NH ₃ ;

(3) On the surface of the steel plate after nitriding, apply fine particles of Al ₂ O ₃ with a size <10um by electrostatic method, wherein 5% to 30% TiO ₂ by weight is added;

(4) After high-temperature annealing, hot-stretching leveling annealing and insulating coating, it is finally manufactured into Hi-B oriented silicon steel with excellent performance.

When using the inhibitor method to produce low-temperature Hi-B oriented silicon steel with AlN as the inhibitor, the inhibitory ability of AlN must be strengthened by nitriding after decarburization annealing, but the dense _SiO2 film formed during decarburization annealing , will make the nitriding ability deteriorate rapidly. Under the condition of no lubrication, the _SiO2 oxide film is broken through cold rolling with 1.5%~3% critical deformation, so that the nitriding process can be carried out more easily.

MgO reacts with _SiO2 during the high-temperature annealing process to form the bottom layer of the magnesium silicate glass film. Now the _SiO2 film is destroyed by critical deformation and cold rolling, and the quality of the formed glass film becomes poor. Because Al ₂ O ₃ does not react with SiO ₂ , fine particles of Al ₂ O ₃ with a size of <10um are used as the main release agent for high-temperature annealing. After high-temperature annealing, no glass film is formed, the surface is metallic, and the punching performance is significantly improved. P _1.7 also decreased.

Compared with the prior art, the present invention has the following beneficial effects:

1) The decarburized annealed sheet is cold-rolled with a critical deformation of 1.5% to 3% without lubrication, which can effectively destroy the _SiO2 surface oxide film formed after decarburization annealing and improve the nitriding efficiency;

2) Excellent Al ₂ O ₃ coating, does not form the bottom layer of glass film, the surface layer is uniform, and good magnetic properties are obtained;

3) It ensures the implementation of subsequent heat leveling annealing and insulating coating.

Detailed ways

The present invention will be further described below by way of examples.

1. Overall process requirements

(1) Process flow:

Blast furnace ironmaking→converter smelting→external refining→continuous casting→heating and hot rolling→high reduction ratio primary cold rolling→decarburization annealing→critical deformation cold rolling→nitriding treatment→coating Al ₂ O ₃ release agent→high temperature of finished product Annealing → heat leveling stretching annealing and insulating film coating → rewinding packaging

(2) Chemical composition of molten steel (weight percent): 0.02% to 0.09% C, 2.8% to 3.8% Si, 0.01% to 0.2% Mn, ≤0.035% P, 0.001% to 0.02% S, ≤0.01% N, ≤ 0.03% Als, the rest is iron and a small amount of inclusions;

(3) The temperature of casting slab into the heating furnace is ≥ 300 °C, preferably ≥ 900 °C, and it is kept in the range of 1200 °C to 1280 °C for <3 hours, followed by hot rolling. Rolling, rolling to the thickness close to the finished product, and then performing decarburization annealing in a wet atmosphere;

(4) Before the nitriding process, the decarburized annealed sheet is cold-rolled with a critical deformation of 1.5% to 3% without lubrication, and then decomposed NH ₃ atmosphere for 5 to 50s at a temperature of 830 to 870°C. Nitriding treatment;

(5) Coating fine particles of Al ₂ O ₃ with a size <10um on the surface of the nitrided steel plate by electrostatic method, wherein 5% to 30% TiO ₂ by weight is added;

(6) After high-temperature annealing, hot-stretching leveling annealing and insulating coating, it is finally manufactured into Hi-B oriented silicon steel with excellent performance.

2. Specific examples

Take the cast slab whose composition is shown in Table 2, cut the head and tail, and divide it into 6 pieces on average, and carry out the test according to the above-mentioned process respectively. The process parameters and magnetic performance test results of the test are shown in Table 3.

Chemical composition (wt%) of steel used in table 2 experiment

C Si Mn P S Als N 0.055 3.3 0.20 0.033 ≤0.005 0.03 0.008

Claims (4)

1. the method for a producing high magnetic induction grain-oriented silicon steel by low temperature heating, to heat with the directional silicon steel slab of common explained hereafter, then carry out hot rolling, hot-rolled sheet annealing or normalizing are rolled down near finished product thickness after a heavy reduction rate is cold rolling, carry out decarburizing annealing again in wet atmosphere, carry out nitriding afterwards, the coating separant carries out high temperature annealing at last, and it is characterized in that: slab heating temperature is controlled at below 1280 ℃; The decarburizing annealing plate carries out 1.5%～3% the cold rolling SiO that destroys of critical strain before the nitriding under not lubricated situation ₂Film; Described separant is Al ₂O ₃Fine particle, wherein adding weight percent is 5%～30%TiO ₂

2. the method for producing high magnetic induction grain-oriented silicon steel by low temperature heating according to claim 1, it is characterized in that: slab is gone into furnace temp and is 〉=300 ℃, and heating and temperature control is at 1200 ℃～1280 ℃ scopes, insulation＜3h.

3. the method for producing high magnetic induction grain-oriented silicon steel by low temperature heating according to claim 1, it is characterized in that: the nitriding temperature of decarburizing annealing plate is 830～870 ℃, and nitriding time is 5～50 seconds, and nitriding medium is NH ₃

4. the method for producing high magnetic induction grain-oriented silicon steel by low temperature heating according to claim 1 is characterized in that: separant Al ₂O ₃Fine particle size＜10um, and apply with electrostatic method.