JP5845275B2 - Method for producing grain-oriented silicon steel having magnetic performance - Google Patents

Description

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

  Oriented silicon steel is an indispensable and important soft magnetic alloy in the electrical industry, the electronics industry, and the military industry, and is mainly used for the iron core of a transformer, as well as a generator, a large electrical machine, and the like. Grain-oriented silicon steel is desired to have excellent magnetic performance, and particularly to reduce iron loss.

  Oriented silicon steel can have excellent magnetic performance by utilizing secondary recrystallization technology, and causes abnormal grain growth to form grains with other orientations (goth structure: {110} means a crystal plane parallel to the rolling surface, and <001> means a crystal direction parallel to the rolling direction).

The traditional method for producing grain oriented silicon steel with high magnetic induction is as follows. The steel base is heated to a temperature of 1350 ° C. to 1400 ° C. in a special high-temperature heating furnace, and the temperature is maintained for more than 1 hour to promote sufficient solid solution of impurities of AlN, MnS or MnSe, Then, the steel base material is rolled, the rolling end temperature is higher than 950 ° C., and the hot-rolled steel strip is rapidly cooled by being sprayed with water, and then wound on a coil. In the subsequent normalization process, fine and diffusible second phase particles (ie, grain growth inhibitors) are separated and discharged from the steel body and oxidized from the surface to the hot rolled steel after normalization. Pickling is performed to remove the iron skin. After further cold rolling to the final product thickness, the steel sheet is decarburized and annealed to reduce the [C] content in the steel sheet to a range that does not affect the magnetic properties of the final product (≦ 30 ppm). In order to perform high temperature annealing, an annealing separator whose main component is MgO is applied to the steel sheet, and the steel sheet forms a base film of Mg ₂ SiO ₄ and secondary recrystallization so as to purify the steel. And finally the steel sheet is coated with an insulating coating, stretched, annealed, and thus grain orientation with high performance with high magnetic induction, low iron loss and good insulation A silicon steel product is obtained.

The following problems occur with the above manufacturing method.
1. The heating temperature is high and the combustion loss of the steel base is large;
2. The furnace must be repaired frequently and production efficiency is low;
3. The hot rolling temperature is high and the ringing squeak noise of hot rolling is large.

  In order to solve these problems, some foreign companies are exploring and developing several methods for producing grain oriented silicon steel at a relatively low temperature with respect to heating of the steel matrix. For example, it is the following method.

1. Method for producing grain oriented silicon steel at intermediate temperatures
Some steel factories such as Russian Novolipetsk Iron & Steel Corporation (NLMK) and VIZ utilize intermediate temperature grain oriented silicon steel manufacturing technology, steel base heating temperature is 1200-1300 ° C, chemical composition is Cu It contains a relatively high content (0.4% to 0.7%) and AlN and CuS are used as inhibitors. This method can avoid some problems due to heating of the steel matrix at high temperature, and the disadvantage is that only commonly oriented silicon steel can be produced.

2. Method of nitriding at a low temperature by heating a steel base material When cold-rolled sheets pass through a furnace for decarburization and annealing, NH ₃ is introduced so that the inside of the steel sheet is nitrided and obtained afterward Forms a type of inhibitor. By utilizing this method, the steel base heating temperature can be reduced to below 1250 ° C., and the method can be utilized to produce not only general oriented silicon steel but also highly magnetic oriented silicon steel.

3. Method for producing grain-oriented silicon steel without inhibitor Se, S, N so that the material is controlled to be highly purified in smelting and the effects of segregation such as Se, S, N, O are eliminated. , O content is controlled to be less than 30 ppm. And grain orientation silicon steel can be manufactured by utilizing the difference in the moving speed of a high energy grain boundary and another grain boundary.

  M.M. Barisoni et al., After the steel sheet has been normalized, cooled to 800-850 ° C. at a rate of 20 ° C./sec, and the steel sheet was quenched and dispersed at a cooling rate of 100 ° C./sec. It is proposed that the volume ratio is about 8% and the hardness Hv ≧ 600 (the hardness Hv ≧ 230 of the steel plate mother phase), and a large amount of about 10 nm of AlN is segregated. Martensite is formed to increase the stored energy, and therefore the stored energy after cold rolling is increased, and the stored energy grows easily by recrystallizing {110} grains during the decarburization and annealing process. And the {110} composition is strengthened after being decarburized and annealed, thus improving the magnetic performance of the final product.

  The martensitic phase transition can be induced by rapid cooling (quenching), which is referred to as a thermally induced martensitic phase transition. The martensitic phase transition can also be induced by stress or strain, which is referred to as stress or strain induced martensitic phase transition. Considering the free energy of the phase transition, the work due to the stress that induces the martensitic phase transition is the same as the free energy change that drives the phase transition. The driving force of the martensite phase transition is composed of two parts, that is, a chemical driving force and a mechanical driving force.

  Under certain stress conditions, the martensitic phase transition temperature decreases. When below the Curie temperature (770 ° C.), grain oriented silicon steel exhibits spontaneous ferromagnetic elongation, which can partially counter the automatic volume shrinkage upon cooling, and the temperature of the martensitic phase transition. Increase the reduction of

The martensitic phase transition proceeds through two phases: nucleation and growth.
As can be seen from the solid state phase transition theory, the introduction of deformation accumulated energy greatly increases the nucleation rate of martensite, and its range is several tens to several hundreds of times. The stored energy does not significantly affect the growth rate of martensite crystal nuclei.

  In US Pat. No. 3,959,033, the amount of martensite is controlled by controlling the normalizing treatment after hot rolling, in particular, by controlling the cooling rate from 700 to 900 ° C. to room temperature in the normalizing treatment. As a result, the magnetic performance of the final product is improved. The disadvantage of this patent is that it is difficult to achieve a consistent cooling rate in the plate thickness direction, which results in a non-uniform martensite distribution in the plate thickness direction. Because it exists, it is difficult to achieve effective control of the amount of martensite. In addition, in this patent, water is utilized to control the cooling rate from 700-900 ° C. to room temperature, and firstly this control is limited by site conditions such as air temperature, nozzle damage or obstruction. This can cause the cooling rate to become unstable, and secondly, the temperature of the steel sheet cannot be accurately measured due to human factors, making it difficult to achieve accurate control. And therefore it is difficult to achieve a fine adjustment of the cooling rate.

  It is an object of the present invention to provide a method for producing a grain-oriented silicon steel having excellent magnetic performance, and the content and distribution of martensite in the steel sheet after normalization is a normalization phase transition. Can be optimized by adjusting the stress in the steel sheet, and the martensite content can be brought into the range where better magnetic performance of the final product can be obtained, realizing optimization in the magnetic performance of the final product Is done.

In order to achieve the above object, the technical solution of the present invention is as follows.
A method for producing grain oriented silicon steel with good magnetic performance,
(1) Perform conventional melting and casting to form steel base material;
(2) heating the steel base material and hot rolling the steel base material into a steel strip;
(3) In the normalizing process, a two-step normalizing process is performed, and the band is first heated to 1100 to 1200 ° C. and then cooled to 900 to 1000 ° C. in 50 to 200 seconds; Is rapidly cooled in water at a temperature of 10-100 ° C; during this period, a tensile force is applied to the steel strip, and within a temperature range of 900 ° C-500 ° C, the steel strip is 1-200N. having a stress of / mm ² ;
(4) In cold rolling, primary cold rolling or double cold rolling with intermediate annealing is performed;
(5) Primary recrystallization annealing is performed, and then an annealing separator is applied. The main composition is MgO for annealing the final product, and the annealing includes secondary recrystallization annealing and purification annealing. ,Method.

  Furthermore, the tensile force is applied to the steel strip by placing tension rollers in a normalizing furnace or by changing the front and rear tension rollers.

  According to the present invention, by adjusting the stress in the steel sheet at the normalization phase transition, the stress or strain induces martensite, which is reasonable for the martensite content in the steel sheet after normalization. Effective control is achieved and ultimately the magnetic performance of the final product is improved. According to the present invention, a martensite structure that is relatively uniform in the thickness direction of the steel sheet can be obtained. By utilizing tension control, there is less restriction due to site conditions, the desired amount of martensite is stably obtained for the same thickness of sample sheet, and tension control is quantified with less human factors and accurately Easy to control and fine tuning can be achieved.

  By controlling the stress in the hot-rolled sheet at the normalization phase transition, the amount of martensite after normalization is optimized and the martensite content in the normalized steel sheet is the final product In the range where a better magnetic performance is obtained, and finally a better magnetic performance of the final product is obtained.

Why would help proper content of martensite improves magnetic properties B ₈ of the final product is as follows.

  (1) The presence of martensite improves the stored energy, increases the stored energy after cold rolling, and promotes (110) grain recrystallization and growth in the decarburization and annealing processes. , (110) composition content can be increased and magnetic performance can be improved.

  (2) The presence of martensite increases the amount of high angle grain boundaries after decarburization and annealing and cold rolling, which helps the goth structure to merge grains of other orientations, Promote crystals.

(3) After the martensite is cold-rolled and decarburized and annealed, a gamma fiber structure is formed in the material, which accelerates the secondary recrystallization process. The relative factors are above analysis, improvements in the degree of grain orientation of the final product is achieved, the magnetic performance B ₈ of the final product is improved.

  If the composition of the steel sheet is the same, the manufacturing process conditions are the same, the method for measuring the amount of martensite is the same, and the amount of martensite in the sheet is the same. Therefore, the relationship between the amount of martensite in the final product and the magnetic performance depends on the amount of martensite in the steel sheet after normalization and before cold rolling measured by the same measurement method in a pre-made sample sheet. The target range of martensite content in the steel sheet after normalization and before cold rolling can be calculated.

There are the following three methods for controlling the amount of martensite.
(1) The martensite content is changed by changing the stress in the steel sheet at the phase transition so as to change the nucleation number of martensite at the phase transition.

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

(3) The martensite content can be changed by changing the rate of secondary cooling during normalization. The measured amount of martensite in the steel sheet after normalization is compared with the target value, and according to the difference between them, the steel sheet in the normalization phase transition (in the range of 900 ° C. to 500 ° C.) The stress (1 to 200 N / mm ² ) is changed at least by adjusting a tension roller placed in the furnace or by changing the winding tension, and the martensite content in the steel sheet after normalization and The purpose of distribution optimization can be achieved and the amount of martensite is in a range where better magnetic performance of the final product is obtained.

  Steps (1), (2), (4) and (5) in the method according to the present invention are all general technical means for producing grain-oriented silicon steel and their description is omitted.

  According to the present invention, reasonable and effective control over the amount of martensite in the steel sheet after normalization is achieved, and the tensile force or strain is adjusted by adjusting the stress in the steel sheet at the normalization phase transition. Induces martensitic phase transition and ultimately improves the magnetic performance of the final product.

  The present invention can obtain a martensite structure that is relatively uniform in the plate thickness direction, and can make fine adjustments regarding a desired martensite content.

  In the present invention, there are few restrictions on the conditions of the place and the tension control is used, and the desired amount of martensite is stably obtained with respect to the sample plates having the same thickness, and the tension control is more quantified. The influence of the physical factor is small, it is easy to perform accurate control, and fine adjustment can be realized.

Martensite content of the final product regarding grain oriented silicon steel domesticated baked by the present invention and (vol%) is a diagram showing the relationship between magnetic properties B _8. It is a schematic diagram which shows distribution of the martensite with respect to sheet | seat thickness in the cross section of the grain orientation silicon steel by this invention.

In the following, the invention will be described in relation to the examples.
Example 1
Steel sheets containing various compositions are normalized. The main composition of the sheet is shown in Table 1.

The steel sheet containing the above composition is heated to 1200 ° C., and this temperature is maintained for 180 minutes. The steel sheet is then rolled directly to 2.0 mm. Normalizing process a two-step is performed on a steel sheet which has been hot rolled. The steel sheet is first heated to 1200 ° C. and then cooled to 900 ° C. within 200 seconds, and then the steel sheet is quenched in water at a temperature of 100 ° C. The stress (1 to 200 N / mm ² ) in the steel sheet at the normalizing phase transition (within 900 ° C. to 500 ° C.) can be adjusted at least by adjusting the tension roller placed in the furnace or the front and rear tension. By changing the rollers, the content and distribution of martensite in the tempered sheet is optimized to the extent that better magnetic performance can be achieved.

After pickling, the steel sheet is subjected to one-stage cold rolling in 5 rolling passes, the third and fourth passes are at 220 ° C., and the steel sheet has a thickness of 0.30 mm. Pressed. The cold-rolled sheet is subjected to decarburization and nitriding annealing at 850 ° C. After nitriding, an annealing separator having a main composition of MgO is applied on the surface of the sheet and heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , and then the atmosphere is changed to pure H ₂ The sheet is then held at that temperature for 30 hours.

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

Example 2
The main chemical composition of the steel sheet is 3.05 wt% Si, 0.060 wt% C, 0.0290 wt% soluble Al, 0.0077 wt% N, 0.13 wt% Mn, and less than 0.006 wt% S.

The steel sheet containing the said composition is heated at 1200 degreeC, and this temperature is hold | maintained for 180 minutes. The steel sheet is then rolled directly to 2.0 mm. The hot-rolled sheet is subjected to a two-step normalization process, where the steel sheet is first heated to 1100 ° C. and then cooled to 1000 ° C. in 50 seconds, and then the steel sheet is heated to 50 ° C. Quenched in temperature water. Stress (1 to 200 N / mm ² ) in the steel sheet at the normalization phase transition (at 900 ° C. to 500 ° C.) changes at least by adjusting the tension roller placed in the furnace or the winding tension The content and distribution of martensite in the normalized sheet can be optimized within a range where a better magnetic performance range can be achieved.

After pickling, the steel sheet is subjected to one-stage cold rolling in 5 rolling passes, the third and fourth passes are at 220 ° C., and the steel sheet has a thickness of 0.30 mm. Pressed. The cold-rolled sheet is subjected to decarburization and nitriding annealing at 850 ° C. After nitriding, an annealing separator having a main composition of MgO is applied on the surface of the sheet and heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , and then the atmosphere is changed to pure H ₂ The sheet is then held at that temperature for 30 hours.

  Table 3 shows the martensite content after normalization, the tensile force applied to the steel sheet in the phase transition and the magnetic performance.

Example 3
The main chemical composition of the steel sheet is 2.9 wt% Si, 0.048 wt% C, 0.0255 wt% soluble Al, 0.0073 wt% N, 0.10 wt% Mn, and less than 0.006 wt% S.

The steel sheet containing the said composition is heated at 1200 degreeC, and this temperature is hold | maintained for 180 minutes. The steel sheet is then rolled directly to 2.0 mm. The hot-rolled sheet is subjected to a two-step normalization process, where the steel sheet is first heated to 1100 ° C. and then cooled to 900 ° C. in 100 seconds. The steel sheet is then quenched in water at a temperature of 80 ° C. The stress (1 to 200 N / mm ² ) in the steel sheet at the normalizing phase transition (within 900 ° C. to 500 ° C.) can be achieved by adjusting at least a tension roller placed in the furnace or by winding tension The content and distribution of martensite in the normalized sheet is optimized within a range where a better magnetic performance range can be achieved.

After the steel sheet has been pickled, a single stage cold rolling is performed on the sheet in 5 rolling passes, the third and fourth passes are at 220 ° C., and the steel sheet has a thickness of 0.30 mm. Pressed to have. The cold-rolled sheet is subjected to decarburization and nitriding annealing at 850 ° C. After nitriding, an annealing separator having a main composition of MgO is applied on the surface of the sheet and heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , and then the atmosphere is changed to pure H ₂ The sheet is then held at that temperature for 30 hours.

  Table 4 shows the martensite content after normalization, the tensile force applied to the steel sheet at the phase transition and the magnetic performance.

Example 4
The main chemical composition of the steel sheet is 3.41 wt% Si, 0.0542 wt% C, 0.0269 wt% soluble Al, 0.0083 wt% N, 0.12 wt% Mn, and less than 0.006 wt% S.

  The steel sheet containing the said composition is heated at 1200 degreeC, and this temperature is hold | maintained for 180 minutes. The steel sheet is then rolled directly to 2.0 mm. Normalizing annealing is performed by each means of the method described below.

  The steel sheet is first heated to 1180 ° C. and then cooled to 920 ° C. in 200 seconds, and then the steel sheet is quenched in 100 ° C. water.

(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 20 N / mm ² is applied to the steel sheet during the cooling period (900 ° C. to 500 ° C.), and the normalized martensite content provides excellent magnetic performance of the final product. Maintained within range (Example).

After the steel sheet has been pickled, a single stage cold rolling is performed on the sheet in 5 rolling passes, the third and fourth passes are at 220 ° C., and the steel sheet has a thickness of 0.30 mm. Pressed to have. The cold-rolled sheet is subjected to decarburization and nitriding annealing at 850 ° C. After nitriding, an annealing separator having a main composition of MgO is applied on the surface of the sheet and heated to 1220 ° C. in an atmosphere of 25% N ₂ and 75% H ₂ , and then the atmosphere is changed to pure H ₂ The sheet is then held at that temperature for 30 hours.

  The results are shown in Table 5.

  FIG. 2 shows the distribution of martensite with respect to the sheet thickness in the cross section of the comparative example and the example.

  As can be seen from this figure, a relatively uniform martensite structure in the sheet thickness direction can be obtained by tension control. A desired amount of martensite can be stably obtained for the same thickness of the sample plate, and a better magnetic performance of the final product can be obtained.

Claims (3)

A method for producing grain-oriented silicon steel having magnetic performance,
(1) heating the steel base material and hot rolling the steel base material into a steel strip;
(2) a step of performing a two-step normalizing process, and in the two-step normalizing process, the steel strip is first heated to 1100 to 1200 ° C, and then to 900 to 1000 ° C to 50 to 200 And then the steel strip is rapidly cooled in water at a temperature of 10 to 100 ° C., and within the rapid cooling period, a tensile force is applied to the steel strip and a temperature range of 900 ° C. to 500 ° C. The steel strip has a stress of 15 to 40 N / mm 2, and the steel strip has 2.9 wt% to 3.41 wt% silicon and 0.0456 wt% to 0.06 wt%. Carbon, 0.0255 wt% to 0.0290 wt% soluble aluminum, 0.0073 wt% to 0.0083 wt% nitrogen, and 0.1 wt% to 0.13 wt% Manganese and 0.0060% by weight Consisting of less sulfur , balance iron and inevitable impurities ,
(3) including a step of performing cold rolling, wherein the cold rolling includes primary cold rolling or double cold rolling with intermediate annealing, and (4) performing primary recrystallization annealing and then annealing separation Applying the agent;
(5) a step of annealing to the final product, and annealing to the final product includes secondary recrystallization annealing and purification annealing,
The martensite content of the steel strip after the two-stage normalizing treatment is 8.8 area% or more and 10.7 area% or less.   The method according to claim 1, wherein the tensile force is applied to the steel strip by placing a tension roller in a normalizing furnace or by changing a winding tension.   The method according to claim 1 or 2, wherein a main composition of the annealing separator is MgO.