KR20130101099A - Manufacture method of oriented silicon steel having good magnetic performance - Google Patents

Abstract

The process for producing oriented silicon steel with good magnetic properties comprises the following steps: 1) general smelting and casting to form steel blanks; 2) heating the steel blank and hot rolling the steel blank with a steel strip; 3) standardizing; The normalizing step is performed with a standardization process having two stages, the strip is first heated to 1100-1200 ° C. and cooled to 900-1000 ° C. for 50-200 seconds; The strip is then rapidly cooled in water with a temperature of 10-100 ° C .; During this period, a tensile force is applied to the steel strip, and the steel strip has a stress of 1 to 200 N / mm ² in the temperature range of 900 to 500 ° C .; 4) cold rolling; The cold rolling step may be performed by double cold rolling with main cold rolling or intermediate annealing; 5) performing a primary recrystallization annealing, and coating an annealing separator having a main composition of MgO to carry out annealing comprising secondary recrystallization annealing and purifying annealing to the final product. The present invention provides a steel sheet after standardization by adjusting the tensile force applied to the steel sheet during the standardization conversion, in order to make the content of martensite within the range to ensure better magnetic properties of the final product and to optimize the magnetic properties of the final products. Optimize the content and distribution of martensite.

Description

MANUFACTURE METHOD OF ORIENTED SILICON STEEL HAVING GOOD MAGNETIC PERFORMANCE

TECHNICAL FIELD The present invention relates to a method for producing grain-oriented silicon steel, and more particularly, to a method for producing oriented silicon steel having excellent magnetic properties.

Directional silicon steel is an essential and important soft magnetic alloy that is mainly used in the electrical, electronic, and military industries, mainly the iron core of transformers, and electrical generators and large electric machines. A grain-oriented silicon steel is required to have good magnetic properties, in particular a reduction of iron loss.

In oriented silicon steel, the Goss texture (Gos texture: {110} means that the crystal plane is parallel to the rolling plane, and <001> means that the crystal direction is parallel to the rolling direction. Excellent in the rolling direction by using secondary re-crystallizing technology, which causes abnormal grain growth to merge the grains in different directions. It may have magnetic properties.

The method for producing grain-oriented silicon steel with general high magnetic induction is as follows. To promote sufficient solid solution impurities AlN, MnS, or MnSe, the steel blank is heated to a temperature of 1350 ° C. to 1400 ° C. in a special high temperature furnace, and the temperature is maintained for at least one hour, after which the steel blank is The rolled, roll-finishing temperature is above 950 ° C., and the hot-rolled steel strip is quickly splashed, cooled with water and then coiled. In the following normalizing process, good and diffusive phase particles (called grain growth inhibitors) are separated from the body of the steel and removed to remove ferric oxide skin from the surface of the steel. Pickling is performed on hot-rolled steel after normalization. After further cold rolled to the thickness of the final product, the steel sheet is decarburized to reduce the carbon [C] content in the steel sheet to the extent that it does not affect the magnetic properties of the final product (≤30 ppm). A decaburizing and annealing process is performed, and then an annealing separator having a main composition of MgO is coated on the steel sheet to perform high temperature annealing, the steel sheet is formed to form an undercoating of Mg 2 SiO 4 and Secondary recrystallization is performed to purify and finally the steel sheet is coated, stretched, and annealed with an insulating coating, resulting in high magnetic induction, low iron loss, And high-quality grain-oriented silicon steel products with good insulation are obtained.

The above manufacturing method involves the following problems.

1. The heating temperature is high, and the burning loss of the steel blank is large;

2. Furnace has to be repaired frequently, production efficiency is low;

3. The hot rolling temperature is high and the creak of the flange of the hot rolling is large.

To solve these problems, some foreign companies have searched for and developed several methods of producing directional silicon steels that heat steel blanks at relatively low temperatures, for example:

1.Method of producing grain-oriented silicon steel at medium temperature, some steel plants, such as Russian Novolipetsk Iron & Steel Corporation (NLMK), and VIZ, Using oriented silicon steel manufacturing technology, the steel-blank-heating temperature is 1200 ° C to 1300 ° C, the chemical composition contains relatively high copper (Cu) (0.4% -0.7%), and AiN and CuS are used as inhibitors do. This method avoids some of the problems of heating the steel blank at high temperatures, but has the disadvantage of only producing general oriented silicon steel.

2. Nitrogen inside the steel sheets to form inhibitors in the form of NH ₃ acquired after cold rolled plates pass through decarburization and annealing furnaces by means of steel blank heating and nitriding at low temperatures. Inject). Using this method, the steel-blank-heating temperature can be reduced to 1250 ° C. or lower, and this method can be used to produce not only general oriented silicon steel but also oriented silicon steel with high magnetism.

3. In the process of producing grain-oriented silicon steels without inhibitors, in the process of smelting, the materials are controlled to be highly purified, and the contents of Se, S, N, O are Se, S, N, O, etc. It is controlled to 30ppm or less to eliminate any effects due to segregation of. Thus, oriented silicon steel can be produced using the difference between the high energy grain boundary and the speeds of progression of other grain boundaries.

M. Barisoni et al., When silicon steel is cooled from 800 ° C. to 850 ° C. at a rate of 20 ° C./s after being standardized, has a volume percentage of about 8% and a hardness of Hv ≧ 600. In order to form a martensite phase (hardness of the steel sheet matrix Hv ≧ 230) and to segregate a large amount of AlN of about 10 nm, the steel sheet is quenched at a cooling rate of 100 ° C./s. ). Martensite is formed such that the stored energy is increased, thus the stored energy is increased after cold rolling, and the stored energy allows the [110] grains to more easily crystallize and grow in the decarburization and annealing treatment, and after decarburization and annealing is performed [110] ] The composition is strengthened and the magnetic properties of the final product are improved.

Martensite phase transitions can be induced by rapid cooling (? Ching) called thermally induced martensite phase transitions. Martensite phase transition can also be induced due to stress or strain called stress or strain induced in martensite phase transition. In terms of the free energy of phase transition, the work by which stress induces martensite phase transition is in line with the change of free energy due to phase transition. Therefore, the power of martensite phase transition consists of two parts: chemical power and mechanical power.

In a stressed state, the temperature of the martensite phase transition decreases. At curie temperatures (770 degrees C) or less, oriented silicon steels exhibit spontaneous ferromagnetic elongation, which may partially interfere with the automatic contraction in volume to increase the temperature decrease of the martensite phase transition. (enlongation).

Martensite phase transition undergoes two phases of nucleation and growth.

As can be seen according to solid state phase transition theory, by modifying the stored energy, the rate of nucleation of martensite is greatly increased in the range of tens to hundreds of times. The stored energy does not significantly affect the growth rate of crystal nucleation of martensite.

In US Patent No. 3959033, the amount of martensite is controlled by controlling the standardization treatment after hot rolling, in particular by adjusting the cooling rate from 700 ° C to 900 ° C to room temperature in the standardization treatment, As a result, the magnetic properties of the final product are improved. A disadvantage of this patent is that it is difficult to achieve cooling rate consistency in the direction of the plate thickness resulting in heterogeneity of the distribution of martensite in the direction of the plate thickness, and martensizy because of its inhomogeneous presence. It is difficult to achieve effective control of the amount of traces. In addition, in this patent, water is used to control the cooling rate from 700 ° C. to 900 ° C. to room temperature, firstly the control of the air which may destabilize site conditions, for example cooling rate. Can be limited by temperature, nozzle damage or obstacles, and secondly, the temperature of the steel sheets cannot be accurately measured due to artificial factors, making it difficult to achieve accurate control and thus fine tuning of the cooling rate. Is difficult to achieve.

It is an object of the present invention to provide a method for producing oriented silicon steel with excellent magnetic properties, wherein the content of martensite and its distribution in the steel sheet after standardization is that the content of martensite has better magnetic properties of the final product. It can be optimized by adjusting the stress on the steel plate in a standardized phase transition so that it is obtainable and within the range that optimization of the magnetic properties of the final product is realized.

In order to achieve the above object, the technical solution of the present invention is as follows.

Methods for producing oriented silicon steel with good magnetic properties are:

1) general smelting and casting to form steel blanks;

2) heating the steel blank and hot rolling the steel blank with a steel strip;

3) standardizing; The normalizing step is performed with a standardization process having two stages, the strip is first heated to 1100-1200 ° C. and then cooled to 900 ° C.-1000 ° C. for 50-200 seconds; The strip is then rapidly cooled in water with a temperature of 10-100 ° C .; During this period, a tensile force is applied to the steel strip, and the steel strip has a stress of 1 to 200 N / mm ² in the temperature range of 900 to 500 ° C .;

4) cold rolling; The cold rolling step may be performed by double cold rolling with main cold rolling or intermediate annealing;

5) coating an annealing separator having a main composition of MgO to perform an initial recrystallization annealing and an annealing comprising secondary recrystallization annealing and purifying annealing to the final product; .

In addition, the tensile force can be applied to the steel strip by disposing a tension roller in the standardizing furnace, or by varying the front and rear tension rollers.

According to the present invention, by regulating the stress on the steel sheet in the normalized phase transition, the stress or strain forces the martensite phase to change in order to achieve reasonable and effective control of the amount of martensite after standardization and, as a result, The magnetic properties of the product are improved. According to the invention, a relatively homogeneous martensite structure is derived in the thickness direction of the steel sheet. Due to the use of tension control, the limits due to site conditions are small, and in sample plates with the same thickness, the desired amount of martensite can be obtained stably, and the tension control has less artificial elements It is quantified, easy to control accurately and good regulation is achieved.

By controlling the stress on the hot rolled plate in the normalized phase transition, the amount of martensite after standardization is optimized so that the content of martensite in the standardized steel sheet is within a range to obtain better magnetic properties of the final product. Better magnetic properties of the final product are obtained.

Reasons why the appropriate content of martensite can help to improve the magnetic properties B ₈ of the final product are as follows.

(1) Since martensite exists to improve the stored energy after cold rolling, the stored energy is increased, which facilitates recrystallization and growth of (110) grains in the decarburization and annealing treatment, and the content of the (110) composition Increases and the magnetic properties can be improved.

(2) The presence of martensite after cold rolling and decarburization and annealing increases the amount of high angle grain boundaries, which helps the goth set to merge grains in different directions and facilitates secondary recrystallization. Let's do it.

(3) After martensite is annealed with cold rolling and decarburization, the γ fiber texture is formed of a material that facilitates the treatment of secondary recrystallization. Because of the comparative elements analyzed above, an improvement in the degree of grain orientation of the final product can be achieved and the magnetic properties B ₈ of the final product are improved.

If the compositions of the steel sheets are the same, the conditions of the manufacturing processes are the same, the method of measuring the amount of martensite is the same, and the amounts of martensite in the plates are also the same. Thus, the relationship between the amount of martensite and the magnetic properties of the final product can be precomputed according to the amount of martensite in the steel sheet after standardization and before cold rolling, measured by the same measurement method on the pre-produced sample plate and The target range of the amount of martensite in the steel sheet after standardization and before cold rolling can be calculated.

As a means of controlling the amount of martensite, there are three methods.

(1) The content of martensite can be changed by changing the stress in the steel sheet in the phase transition in order to change the nucleation number of martensite in the phase transition.

(2) The content of martensite can be changed by changing the highest temperature of normalization in order to change the amount of austenite at the highest temperature.

(3) The content of martensite can be changed by varying the rate of secondary cooling upon standardization. After standardization, the measured value of the amount of martensite in the steel sheet is compared with the target value according to the difference from the target value, and the stress (1 to 200 N / mm2) of the steel sheet at the normalized phase transition (range of 900 ° C to 500 ° C) Changed by at least one of adjusting the tension roller disposed in the furnace or changing the winding tension, and after standardization, the purpose of optimizing the content and distribution of martensite in the steel sheet can be achieved, The amount of zit is within a range in which better magnetic properties of the final product can be obtained.

Steps (1), (2), (3) and (4) of the method according to the invention are all general technical means for producing oriented silicon steel, the description of which will be omitted.

Advantages of the present invention are as follows:

According to the present invention, rational and effective control of the amount of martensite in the steel sheet after standardization is realized, which finally improves the magnetic properties of the final product by controlling the stress in the steel sheet in the standardized phase transition, so that the tensile force or strain Allow the phase of martensite to transition.

The present invention can obtain a relatively homogeneous martensite set in the direction of the plate thickness, and can perform excellent control over the content of the desired martensite.

The present invention uses tension control with small limits due to site conditions, and for sample plates having the same thickness, the desired amount of martensite can be obtained stably; Tensile control is more quantified, the influence of artificial factors is reduced, accurate control is easy, and good adjustment can be realized.

1 shows the relationship between the content (vol%) of martensite having the magnetic properties B ₈ of the final product for standardized oriented silicon steel, according to the present invention.
FIG. 2 schematically shows the distribution of martensite with respect to the plate thickness at the cross section of oriented silicon steel, in accordance with the present invention.

Hereinafter, the present invention will be described through embodiments.

Example 1

Steel sheets containing various compositions are standardized. The main compositions of the steel sheet are shown in Table 1.

                                                          (weight%) number Si C Als N Mn S One 3.03 0.0456 0.0264 0.0078 0.12 <0.0060 2 3.22 0.0507 0.0261 0.0081 0.12 <0.0060 3 3.41 0.0542 0.0269 0.0083 0.12 <0.0060

The steel sheet containing the above described compositions is heated to 1200 ° C. and the temperature is maintained for 180 minutes. The steel sheet is then rolled directly to 2.0 mm. Two stage normalization processing is performed on the hot rolled plate. First, the steel sheet is heated to 1200 ° C., cooled to 900 ° C. within 200 seconds, and then the steel sheet is rapidly cooled to water having a temperature of 100 ° C. The stress in the steel sheet (1 to 200 N / mm ² ) at the normalized phase transition (range from 900 ° C to 500 ° C) is optimized to achieve a range of magnetic properties with better martensite content and distribution in the standardized steel sheet. To this end, it may be varied by adjusting at least one of the tension rollers disposed in the furnace or by varying the front and rear tension rollers.

After pickling, single-stage cold rolling is performed on the steel sheet in five rolling passes, and the third and fourth treatments are pressed at 220 ° C. so that the steel sheet has a thickness of 0.30 mm. Decarburization and nitriding annealing are performed at 850 ° C. on cold rolled plates. After nitriding, the annealing separator with the main composition of MgO is coated on the surface of the plate heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , the atmosphere is changed to pure H ₂ , and the plate is 30 at this temperature. Maintained for hours.

The content of martensite after normalization, the tensile force applied to the steel sheet in the phase transition, and the magnetic properties are shown in Table 2.

Applied Tensile Force and Magnetic Property of End Product Furtherance Martensite Content
(% by area) Applied tensile force
(N / mm ² ) B ₈ (T) One Comparative Example 1 2.9 0 1.87 Example 1 8.8 30 1.93 2 Comparative Example 2 3.2 0 1.87 Example 2 10.7 40 1.92 3 Comparative Example 3 25 60 1.86 Example 3 9.2 20 1.92

Example 2

The major chemical compositions of the steel sheet are% by weight, Si 3.05%, C 0.060%, Als 0.0290%, N 0.0077%, Mn 0.13%, and S <0.006%.

The steel sheet containing the above-described compositions is heated to 1200 ° C., and this temperature is maintained for 180 minutes. The steel sheet is then directly rolled to 2.0 mm. Two stage normalization treatments are performed on the hot rolled plate, first the steel sheet is heated to 1100 ° C., cooled to 1000 ° C. for 50 seconds, and then the steel sheet is rapidly cooled in water having a temperature of 50 ° C. In order to optimize the stress (1 ~ 200N / mm ² ) in the steel sheet in the normalized phase transition (900 ℃ to 500 ℃), the martensite content and distribution in the standardized steel sheet can be achieved within a range that can achieve a better magnetic property range. It can be changed by at least one of adjusting the tension roller disposed in the furnace or changing the winding tension.

After pickling, single-stage cold rolling is performed on the steel sheet in five rolling treatments, and the third and fourth treatments are pressed at 220 ° C., so that the steel sheet has a thickness of 0.30 mm. Decarburization and nitriding annealing are performed at 850 ° C. on cold rolled plates. After nitriding, the annealing separator with the main composition of MgO is coated on the surface of the plate heated to 1220 degrees in an atmosphere of 25% N ₂ and 75% H ₂ , the atmosphere is changed to pure H ₂ , and the plate is 30 hours at this temperature. Is maintained.

The content of martensite after normalization, the tensile force applied to the steel sheet in the phase transition, and the magnetic properties are shown in Table 3.

Applied Tensile Force and Magnetic Property of End Product Martensite Content Applied tensile force
(N / mm2) B8 (T) Comparative example 20 50 1.86 Example 8 15 1.92

Example 3

The major chemical compositions of the steel sheet are Si 2.9 wt%, C 0.048 wt%, Als 0.0255 wt%, N 0.0073 wt%, Mn 0.10 wt%, and S <0.006 wt%.

The steel sheet containing the above-described compositions is heated to 1200 ° C., and the temperature is maintained for 180 minutes. The steel sheet is then directly rolled to 2.0 mm. Two stage normalization treatments are performed on the hot rolled plate, first the steel sheet is heated to 1100 ° C. and cooled to 900 ° C. for 100 seconds. The steel sheet is then rapidly cooled in water having a temperature of 80 ° C. The stress (1 ~ 200N / mm ² ) in the steel sheet at the normalized phase transition (range of 900 ℃ to 500 ℃) is optimized to the extent that the magnetic properties of the martensite content and distribution can be achieved in the standardized steel sheet. To this end, it can be varied by adjusting at least one of the tension rollers disposed in the furnace or by varying the winding tension.

After pickling, single-stage cold rolling is performed on the steel sheet in five rolling treatments, and the third and fourth treatments are pressed at 220 ° C., so that the steel sheet has a thickness of 0.30 mm. Decarburization and nitriding annealing are performed at 850 ° C. on cold rolled plates. After nitriding, the annealing separator with the main composition of MgO is coated on the surface of the plate heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , the atmosphere is changed to pure H ₂ , and the plate is 30 at this temperature. Maintained for hours.

The content of martensite after normalization, the tensile force applied to the steel sheet in the phase transition, and the magnetic properties are shown in Table 4.

Applied Tensile Force and Magnetic Property of End Product Martensite Content Applied tensile force
(N / mm ² ) B ₈ (T) Comparative example 1.5 0 1.85 Example 9 18 1.93

Example 4

The major chemical compositions of the steel sheet are Si 3.41 wt%, C 0.0542 wt%, Als 0.0269 wt%, N 0.0083 wt%, Mn 0.12 wt%, and S <0.006 wt%.

The steel sheet containing the above-described compositions is heated to 1200 ° C., and the temperature is maintained for 180 minutes. The steel sheet is then directly rolled to 2.0 mm. Normalization annealing is performed in the manner described below respectively.

First, the steel sheet is heated to 1180 ° C., cooled to 920 ° C. for 200 seconds, and then the steel sheet is rapidly cooled in water having a temperature of 100 ° C.

(1) a tensile force of 60 N / mm 2 is applied to the steel sheet during the cooling period (comparative example);

(2) A tensile force of 60 N / mm ² is applied to the steel sheet during the cooling period (900 ° C. to 500 ° C.) to maintain the normalized martensite content within the range in which good magnetic properties of the final product can be obtained (example). ).

After pickling, single-stage cold rolling is performed on the steel sheet in five rolling treatments, and the third and fourth treatments are pressed at 220 ° C., so that the steel sheet has a thickness of 0.30 mm. Decarburization and nitriding annealing are performed at 850 ° C. on cold rolled plates. After nitriding, the annealing separator with the main composition of MgO is coated on the surface of the plate heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , the atmosphere is changed to pure H ₂ , and the plate is 30 at this temperature. Maintained for hours.

The results are shown in Table 5.

Applied Tensile Force and Magnetic Property of End Product Martensite Content Applied tensile force
(N / mm ² ) B ₈ (T) Comparative example 25 60 1.86 Example 9.2 20 1.92

The distribution of platen versus plate thickness in the cross section of the comparative example and the example is shown in FIG. 2.

As can be seen in the drawing, a relatively homogeneous martensite set in the plate-thickness direction can be obtained by tension control. In sample plates having the same thickness, the desired amount of martensite can be obtained stably, and better magnetic properties of the final product can be obtained.

Claims (2)

1) general smelting and casting to form steel blanks;
2) heating the steel blank and hot rolling the steel blank on the steel strip;
3) standardized process steps; The normalization process step performs a standardization process with two stages, the strip is first heated to 1100-1200 ° C. and cooled to 900-1000 ° C. for 50-200 seconds; The strip is then rapidly cooled in water with a temperature of 10-100 ° C .; During this period, a tensile force is applied to the steel strip, and the steel strip has a stress of 1 to 200 N / mm ² in the temperature range of 900 to 500 ° C .;
4) cold rolling; The cold rolling step may be performed by double cold rolling with main cold rolling or intermediate annealing;
5) coating an annealing separator having a main composition of MgO to perform an initial recrystallization annealing and an annealing comprising secondary recrystallization annealing and purifying annealing to the final product;
Method for producing a directional silicon steel having excellent magnetic properties comprising a. The method of claim 1,
Tensile force is applied to the steel strip by placing tension rollers in a standardizing furnace or by varying the front and rear tension rollers,
A method for producing oriented silicon steel with good magnetic properties.

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