JPS6253577B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a high magnetic flux density unidirectional electrical steel sheet with excellent magnetic properties. Unidirectional electrical steel sheets are soft magnetic materials that are mainly used as core materials for transformers and other electrical equipment, and must have good magnetic properties in terms of excitation properties and iron loss properties. In order to obtain good magnetic properties, it is important that the <001> axis, which is the axis of easy magnetization, is highly aligned in the rolling direction. In addition, plate thickness, crystal grain size, specific resistance, surface coating, etc. have a large effect on magnetic properties. The directionality has been greatly improved by a method characterized by final cold rolling under heavy reduction using AlN and MnS as inhibitors, and now products with magnetic flux density of approximately 96% of the theoretical value are manufactured. I came.
Along with this, iron loss has improved significantly. On the other hand, reflecting the rise in energy prices in recent years, transformer manufacturers are increasingly turning to low core loss materials as materials for energy-saving transformers. Amorphous amorphous and 6.5% Si steel are being developed as low iron loss materials, but many problems still remain to be solved before they can be used as commercial materials for transformers. (Prior Art) In order to meet the current demand for low core loss materials, the present inventors have conducted various studies on reducing the core loss of unidirectional electrical steel sheets. Based on these research results, the present inventors first developed a high magnetic flux with excellent iron loss, which is characterized by adding Sn and Cu to silicon steel in a composite alloy, as shown in Japanese Patent Application Laid-Open No. 58-23414. A method for manufacturing density unidirectional electrical steel sheets was proposed. Furthermore, in Japanese Patent Application No. 57-166039, we proposed a method for producing unidirectional electrical steel sheets with excellent magnetic properties and a glassy coating, which is characterized by the use of an annealing separator in which antimony sulfate is added to magnesia. These methods have made it possible to manufacture products with significantly better magnetic properties than before. However, the demand from transformer manufacturers for lower core loss in materials shows no signs of stopping, and in order to meet these demands, the inventors of the present invention have continued to conduct research into ways to more stably manufacture products with superior magnetic properties. Ta. (Objective of the Invention) An object of the present invention is to provide a method for more stably manufacturing a unidirectional silicon steel plate with even better magnetic properties. (Structure and operation of the invention) The present inventors have discovered that C0.02-0.12%, Si2.5-4.0%,
Mn0.03~0.20%, S0.01~0.05%, acid soluble Al0.01
~0.05%, N0.004~0.012%, Sn0.03~0.5%,
A silicon steel slab containing 0.02~0.08% Cu with the balance consisting of iron and unavoidable impurities is hot rolled, annealed and rapidly cooled before final cold rolling, and then final rolled with a rolling reduction of over 80%. Cold rolling, decarburization annealing, application of an annealing separator containing 0.5 to 20 parts by weight of titanium oxide and 0.1 to 2.0 parts by weight of antimony sulfate per 100 parts by weight of magnesia, and high-magnetic flux density one in which high-temperature finish annealing is performed. In the method for producing a grain-oriented electrical steel sheet, the oxygen content of the steel sheet after decarburization annealing is controlled within the range given by the following formula by changing at least one of the atmospheric gas composition, dew point, and annealing time during decarburization annealing. We have discovered that it is possible to stably produce products with good secondary recrystallization and even better magnetic properties. X=Thickness of steel plate (m/m) Y=Oxygen content of steel plate (PPM) −1667X+775≦Y≦−1667X+1125 The present invention will be explained in detail below. First, I will explain based on experimental data. C0.078%, Si3.35%, Mn0.075%, S0.024%,
Acid soluble Al0.027%, N0.0084%, Sn0.12%, Cu0.08
%, with the remainder being iron and unavoidable impurities, was heated at a high temperature of 1350° C. and hot rolled to obtain a hot rolled sheet with a thickness of 2.3 m/m. The hot-rolled plate was annealed at 1100℃ for 2 minutes, and after annealing, it was rapidly cooled, and then 0.200m/m, 0.225m/m, 0.260m/m,
It was cold rolled into four different thicknesses of 0.285m/m. In the subsequent decarburization annealing, the annealing temperature was 840°C, the annealing atmosphere was moist hydrogen, and the dew point of the atmosphere and annealing time were varied to obtain decarburization annealed plates with different oxygen contents in the range of approximately 200 to 1100 PPM. . By the way, the oxygen content of the hot coil was about 20 PPM. 100 parts by weight of magnesia was added to these decarburized annealed plates.
Apply an annealing separator containing 5 parts by weight of titanium oxide and 0.3 parts by weight of antimony sulfate, and then apply H ₂ 75
%, at a rate of 20°C/hr in an atmosphere of 25% _N2 .
The temperature was raised to 1200°C, and then finish annealing was performed in an H ₂ atmosphere for 20 hours. After annealing, the annealing separator was removed and the glassy film on the surface was observed. All the surface graphite films were good. Then, the magnetic properties were measured, the surface glass film was removed, and the macrostructure of the product was observed. Figure 1 shows the measured value of magnetic flux density B ₁₀ and the observation results of the macrostructure. In FIG. 1, the horizontal axis is the plate thickness, and the vertical axis is the oxygen content of the decarburized annealed plate. Each point in the figure is sorted and plotted based on the quality of secondary recrystallization and the value of magnetic flux density _B10 . As is clear from Fig. 1, the quality of secondary recrystallization and the magnetic flux density _B10 depend on the plate thickness and the oxygen content of the decarburized annealed plate. That is,
In the region below the straight line in the figure, fine grains occur and secondary recrystallization becomes defective. In the region above the straight line, secondary recrystallization is stable. In the region above the straight line, the magnetic velocity density B ₁₀ decreases to 1.91T or less. A good range where secondary recrystallization is stable and the magnetic flux density B ₁₀ is 1.92T or more is the region between two straight lines. 1st
The numbers in the figures are as shown in the table below.

[Table] Magnetic flux density B ₁₀ at each point of plate thickness 0.260m/m in Figure 1
and iron loss values are shown in Figure 2. The horizontal axis in FIG. 2 is the magnetic flux density B ₁₀ and the vertical axis is the iron loss value W〓〓. As is clear from Figure 2, there is a strong correlation between the iron loss value and the magnetic flux density, and when the magnetic flux density B ₁₀ is 1.92T or more, the iron loss value W 〓
〓 indicates a good value of 1.00w/Kg or less. 0.260m/
For sheet thicknesses other than m, a similarly strong correlation is observed between iron loss and magnetic flux density B ₁₀ , and magnetic flux density B ₁₀ is 1.92T.
In each of the above cases, good iron loss values W〓〓 were obtained. That is, in the region between the straight lines in FIG. 1, secondary recrystallization is stable, and a product with excellent magnetic properties, which has high magnetic flux density and low core loss, can be obtained. This area is expressed by the following equation. X = Thickness of the steel plate (m/m) Y = Oxygen content of the steel plate (PPM) -1667X+775≦Y≦-1667X+1125 As shown in the figure. In case B, fine grains are generated and secondary recrystallization is poor. In B, the secondary recrystallization is complete and the grain boundary lines are intertwined, while in C, the secondary recrystallization is incomplete and the grain boundary lines are monotonous, resulting in round crystal grains. In other words, the magnetic flux density depending on the oxygen content of the decarburized annealed plate in Figure 1
It can be seen that the change in B ₁₀ is caused by the method of secondary recrystallization. The present invention has C0.02~0.12%, Si2.5~4.0%,
Mn0.03~0.20%, S0.01~0.05%, acid soluble Al0.01
~0.05%, N0.004~0.012%, Sn0.03~0.5%,
A silicon steel slab containing 0.02~0.08% Cu with the balance consisting of iron and unavoidable impurities is hot rolled, annealed and rapidly cooled before final cold rolling, and then final rolled with a rolling reduction of over 80%. Perform cold rolling, decarburization annealing,
The method for manufacturing high magnetic flux density unidirectional electrical steel sheets is based on applying an annealing separator containing 0.5 to 20 parts by weight of titanium oxide and 0.1 to 2.0 parts by weight of antimony sulfate to 100 parts by weight of magnesia and performing high-temperature finish annealing. It is something. In this manufacturing method, as shown in Figure 1, the mechanism by which the oxygen content of the decarburized annealed plate affects the secondary recrystallization and magnetic properties of the product is not fully elucidated, but at present the following It is estimated that. In manufacturing the high magnetic flux density unidirectional electrical steel sheet according to the present invention, AlN is utilized as the main inhibitor. AlN, which is uniformly and finely precipitated by the annealing and rapid cooling treatment before the final cold rolling, suppresses the growth of normal primary recrystallized grains during the heating process of high-temperature finish annealing, and has a high degree of accumulation in the rolling direction (110) [001 ]
It is thought that it plays an important role in developing and growing secondary recrystallization of orientation. On the other hand, most of the oxygen in the decarburized annealed plate forms an oxide layer on the surface of the steel base as oxides with Si, Al, Fe, etc. This oxide layer becomes a kind of wall between the annealing atmosphere and the steel base when the temperature is raised during high-temperature finish annealing, and the properties of this oxide layer have a considerable influence on the reaction between the annealing atmosphere and substances in the steel base, especially inhibitors such as AlN. It is thought that this may have a negative effect. In the case of the high magnetic flux density unidirectional electrical steel sheet according to the present invention, which is characterized by the addition of a composite alloy of Sn and Cu, and the use of an annealing separator in which titanium oxide and antimony sulfate are added to magnesia, the decarburized annealed sheet contains oxygen. A surface oxidation layer that optimizes the reaction between the annealing atmosphere and substances in the steel base, especially inhibitors such as AlN, when the temperature is raised during high-temperature finish annealing, when the amount is set as the straight line in Fig. 1 and the range between the straight lines. That is, it is thought that a wall is formed, and as a result, the inhibition effect is optimal, resulting in secondary recrystallization in the (110) [001] orientation with no fine grains and a high degree of accumulation in the rolling direction. By the way, several techniques for regulating the oxygen basis weight of a decarburized plate of a unidirectional electrical steel sheet have been disclosed. All of these relate to the formation of an insulating film and are different from the present invention. For example, the invention described in JP-A-55-65367 relates to a method for forming a forsterite insulating film, in which a nitrate aqueous solution containing one or more of Fe, Co, Ni, Cr, Zn, Mg, Mn, and Al is applied. Then, it is decarburized and annealed to produce mainly SiO ₂ with an oxygen basis weight of 1.0 to 2.0 g/m ² .
An oxide film consisting of and fayarite is formed, then an annealing separating agent is applied, and final annealing is performed to improve the forsterite insulating film. This is a technology for improving forstellite insulation coatings based on the application of a sulfate aqueous solution prior to decarburization annealing. The basic idea is different from the present invention, which is related to an iron loss improvement method. The invention described in JP-A No. 55-110726 relates to a method for forming an insulating film on a high magnetic flux density unidirectional electrical steel sheet containing 0.005 to 0.20% Sb in the base steel as an inhibitor. The basis weight
A glassy coating made by coating a steel plate with a density of 0.7 to 2.8 g/ ^m2 with an annealing separator related to MgO, and annealing it at a specific temperature of 800 to 920°C for a long time in an inert neutral gas. It is a technology related to the improvement of
Relating to a method for improving iron loss in unidirectional electrical steel sheets that does not contain Sb, does not require long-term secondary recrystallization annealing in the temperature range of 800 to 920°C, and utilizes AlN, which has a glassy coating, as the main inhibitor. The basic idea is different from the present invention. Furthermore, the invention described in JP-A No. 56-72178 is a method for forming a forsterite insulating film, and when an annealing separator is applied and final annealing is performed, the amount of oxygen permeable in the subscale and the amount of applied annealing separator are specified. This technology aims to improve the forsterite insulating coating by providing a quantitative relationship between The basic idea is different from the present invention. Next, the reasons for determining the raw material steel composition and other manufacturing conditions in the present invention will be described below. When C is less than 0.02%, secondary recrystallization becomes poor, and when it exceeds 0.12%, it is unfavorable from the viewpoint of decarburization and magnetic properties. If Si is less than 2.5%, the low iron loss that is the aim of the present invention cannot be obtained, and if it exceeds 4%, cold rollability will be significantly degraded. From the viewpoint of iron loss, the preferable range of Si is 3.0 to 4.0%. Mn and S are elements necessary to form MnS. The appropriate amount of Mn to obtain an appropriate inhibitor effect is 0.03-0.20%
and preferably 0.05 to 0.15%. S is
If it is less than 0.01%, a sufficient inhibitor effect cannot be obtained, and if it exceeds 0.05%, purification becomes difficult, which is not preferable. Acid-soluble Al and N are important elements for forming AlN as an inhibitor, and each must be controlled within an appropriate range in order to sufficiently develop secondary recrystallization with an appropriate inhibition effect and obtain excellent magnetic properties. There is a need to. acid soluble Al
If it is less than 0.01%, the product has poor orientation and is 0.05%
If it exceeds , secondary recrystallization becomes unstable. 0.020〜
A particularly preferred range is 0.040%. N is 0.004%
If it is less than 0.012%, secondary recrystallization will become unstable, and if it exceeds 0.012%, blistering will occur, so 0.005 to 0.009% is a particularly preferable range. Sn is useful for stabilizing secondary recrystallization and refining the crystal grain size of products.
If it is less than 0.03%, the effect will be weak, and if it exceeds 0.5%, cold rollability will be poor. A particularly preferred range is 0.05-0.20%. Cu helps produce a good glass film in Sn-added materials, but if it is less than 0.02%, its effect is poor, and if it exceeds 0.08%, pickling properties and decarburization properties deteriorate. A silicon steel slab consisting of the above components and the remainder iron and unavoidable impurities is heated to a predetermined temperature, hot rolled, and subjected to annealing and quenching treatment before final cold rolling. For these, known conditions for unidirectional electrical steel sheets with AlN as the main inhibitor are adopted. In the final cold rolling, strong reduction cold rolling is performed with a rolling reduction of 80% or more, because excellent magnetic properties cannot be obtained if the rolling reduction is low. Further, the plate thickness after final cold rolling is preferably 0.15 to 0.30 m/m. If the plate thickness is less than 0.15m/m, secondary recrystallization is likely to occur. If it exceeds 0.30m/m,
It is difficult to achieve low core loss, which is the objective of the present invention. Next, the steel sheet is decarburized and annealed, and the oxygen content of the decarburized annealed sheet is controlled within the range between the straight lines in FIG. 1, depending on the thickness of the steel sheet. If the oxygen content of the decarburized plate is lower than the straight line, secondary recrystallization failure will occur, and if it is higher than the straight line, the secondary recrystallization will be stable but _B10 will decrease. Note that the region between the straight lines and the straight lines' is a more desirable range. Control of the oxygen content of the decarburized annealed plate is achieved by changing the dew point of the annealing atmosphere, the annealing time, and the composition of the atmospheric gas during decarburization annealing. For example, if the atmospheric gas is 100% H ₂ , the dew point should be 55°C to 75°C, and the oxidation degree of the atmospheric gas PH ₂ O/PH ₂ should be 0.20 to 0.60.
shall be. The annealing time is 1 to 5 minutes. Also, the proportion of _H2 in the atmospheric gas decreases, for example by 20%, while others
In the case of N ₂ , the dew point is selected to achieve the above oxidation degree. H ₂ , N ₂ , and Ar are used as the atmospheric gas. Further, a trace amount of CO or CO ₂ gas may be included. Note that the annealing temperature is 750 to 950°C. After that, titanium oxide was added to 100 parts by weight of magnesia.
An annealing separator containing 0.5 to 20 parts by weight and 0.1 to 2.0 parts by weight of antimony sulfate is applied, followed by high-temperature finish annealing by a known method. The effect of adding titanium oxide to an annealing separator is disclosed in Japanese Patent Publication No. 12451/1983. According to the experience of the present inventors, if the amount of titanium oxide added is less than 0.5 parts by weight, the glassy coating will be defective, and if it exceeds 20 parts by weight, the magnetic properties will deteriorate. The effect of adding antimony sulfate to the annealing separator is to improve magnetism and glass coating properties, as described in Japanese Patent Application No. 166039/1982. If the amount of antimony sulfate added is less than 0.1 parts by weight, the magnetic properties will deteriorate, and if it exceeds 2.0 parts by weight, the magnetic properties and the glassy coating will deteriorate. (Example) Next, an example will be described. Example 1 C0.076%, Si3.34%, Mn0.076%, S0.025%,
Acid soluble Al0.028%, N0.0085%, Sn0.13%, Cu0.05
%, with the remainder being iron and unavoidable impurities, was heated to a high temperature of 1350°C and hot rolled to form a hot rolled plate with a thickness of 2.3 m/m. The hot rolled sheets were annealed at 1120° C. for 2 minutes, rapidly cooled after annealing, and then cold rolled to 0.225 m/m and 0.285 m/m. Next, in decarburization annealing, the annealing temperature was set to 840°C, the annealing atmosphere was moist hydrogen, the dew point of the atmosphere was changed to 55 to 75°C, and the annealing time was changed to 1 to 4 minutes to obtain decarburized annealed sheets with different oxygen contents. Ta. 5 parts by weight of titanium oxide and antimony sulfate for 100 parts by weight of magnesia on the decarburization plate.
Apply an annealing separator containing 0.4 parts by weight, and then
The temperature was raised to 1200°C at a rate of 20°C/hr in an atmosphere of 75% H ₂ and 25% N ₂ , and then finish annealing was performed for 20 hours in an H ₂ atmosphere. Oxygen content of decarburized annealed plate,
The magnetic properties and secondary recrystallization status of the product are as shown in Table 1.

[Table] Example 2 C0.077%, Si3.25%, Mn0.074%, Se0.023%,
Acid soluble Al0.027%, N0.0083%, Sn0.12%, Cu0.07
%, with the balance being iron and unavoidable impurities, was heated to a high temperature of 1350°C and hot rolled to form a hot rolled plate with a thickness of 2.0 m/m. The hot-rolled sheets were annealed at 1100° C. for 2 minutes, rapidly cooled after annealing, and then cold-rolled to thicknesses of 0.200 m/m and 0.260 m/m.
The treatments after decarburization annealing were performed in the same manner as in Example 1. The oxygen content of the decarburized annealed plate, the magnetic properties of the product, and the state of secondary recrystallization are as shown in Table 2.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a diagram showing the influence of the plate thickness and oxygen content of the decarburized annealed plate on the magnetic flux density and macrostructure in the present invention, and Figure 2 is the magnetic flux density and iron loss value of the plate thickness 0.260 mm in the present invention. Figure 3 is a metallurgical micrograph showing the macrostructure of the sample.

Claims (1)

[Claims] 1 C0.02-0.12%, Si2.5-4.0%, Mn0.03-0.20
%, S0.01~0.05%, acid soluble Al0.01~0.05%,
N0.004~0.012%, Sn0.03~0.5%, Cu0.02~0.08
%, with the balance consisting of iron and unavoidable impurities, is hot rolled, annealed and quenched before final cold rolling, and then final cold rolled at a rolling reduction of 80% or more, After decarburization annealing, magnesia
In a method for producing high magnetic flux density unidirectional electrical steel sheets, the annealing separator containing 0.5 to 20 parts by weight of titanium oxide and 0.1 to 2.0 parts by weight of antimony sulfate is applied to 100 parts by weight and subjected to high-temperature finish annealing. A high magnetic flux with excellent magnetic properties characterized by controlling the oxygen content of a steel sheet after charcoal annealing to a range given by the following formula by changing at least one of atmospheric gas composition, dew point, and annealing time during decarburization annealing. A method for producing density unidirectional electrical steel sheets. X = Thickness of steel plate (m/m) Y = Oxygen content of steel plate (PPM) −1667X+775≦Y≦−1667X+1125