JPS6315967B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a 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 about 96% of the theoretical value are manufactured. It's here.
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. The inventors of the present invention have repeatedly conducted various studies on reducing the iron loss of unidirectional electrical steel sheets in order to meet the needs of the times for low iron loss materials. As a result, a silicon steel slab containing Al and N is hot-rolled, annealed and rapidly cooled before final cold rolling, final cold rolled with strong reduction of 80% or more, and decarburized annealed. Continuing to include N ₂
In the production of unidirectional electrical steel sheets that undergo high-temperature finish annealing by raising the temperature in an _H2 atmosphere, annealing is performed by changing the composition, dew point, and annealing time of the atmosphere gas for decarburization annealing, and the oxygen of the steel sheet after decarburization annealing is changed. By relating the content to the plate thickness,
It has been found that iron loss can be significantly improved by controlling it within a certain range. The present invention will be explained in detail below. First, we will discuss based on experimental data. C: 0.075%, Si: 3.25%, Mn: 0.070%, S:
0.024%, acid soluble Al (hereinafter referred to as solAl): 0.026%,
Contains N: 0.0085%, Cu: 0.08%, Sn: 0.12%,
A silicon steel slab, the remainder of which is iron and unavoidable impurities, is heated to a high temperature, hot rolled, and rolled to a thickness of 2.30m/m.
The hot rolled sheet is made into a thick hot rolled sheet, and this hot rolled sheet is annealed, and after annealing, it is rapidly cooled, and then 0.225 m / m,
It was cold rolled to three thicknesses: 0.260 m/m and 0.285 m/m. In decarburization annealing of cold-rolled sheets, the annealing temperature is
The temperature was 840°C, and the annealing atmosphere was a wet hydrogen atmosphere.
Change the dew point of the atmosphere and annealing time to different types, and roughly
Decarburized annealed plates with different oxygen contents ranging from 400PPM to 1000PPM were obtained. By the way, the oxygen content of the hot coil was about 20 PPM. These decarburized annealed plates were coated with an annealing separator mainly containing MgO, and then heated to 1200°C at a rate of 20°C/hr in an atmosphere of 75% H ₂ and 25% N ₂ .
Finish annealing was performed in an _H2 atmosphere for 20 hours. After annealing, the annealing separator was removed and the surface glass film was observed. The surface glass coatings were all good. Thereafter, the magnetic properties were measured, the surface glass film was removed, and the macrostructure of the product was observed. Figure 1 shows the results of iron loss measurement and macrostructure observation. In Fig. 1, the horizontal axis is the oxygen content of the decarburized plate, and the vertical axis is the iron loss value (W _17/50 ) of the product. In other words, it has been found that there is a close relationship between oxygen content and iron loss value, and that there is an optimum oxygen content that optimizes the iron loss value. The optimum oxygen content varies depending on the thickness of the steel plate.
The optimum oxygen contents at 0.260 m/m and 0.285 m/m were approximately 750 PPM, 650 PPM, and 600 PPM, respectively. In addition, the marks ○ and × in FIG. 1 indicate the results of macroscopic observation of the product. The mark ○ means good secondary recrystallization, and the mark x means poor secondary recrystallization. On the curve showing the oxygen content and iron loss value in FIG. 1, A ₁ , A ₂ , and A ₃ are critical points where secondary recrystallization failure occurs. _{The three} points B ₁ , B ₂ , and B are points where secondary recrystallization is good and the iron loss is 10% higher than the best value. a ₁ ,
At points a ₂ , a ₃ and b ₁ , b ₂ , _b , the iron loss is 5% lower than the best value.
% increase. When the above points are organized and analyzed with the board thickness on the horizontal axis and the oxygen content on the vertical axis, the result is as shown in Figure 2. As is clear from Fig. 2, the point groups A ₁ , A ₂ , A ₃ ,
B ₁ , B ₂ , B ₃ , a ₁ , a ₂ , a ₃ , b ₁ , b ₂ , and b ₃ are plotted on approximately straight lines, .
In other words, in the region between the straight lines, secondary recrystallization is good and the iron loss value is 10, which is the best value.
A good value of less than % increase. Furthermore, it has been found that in the region between the straight lines, the iron loss value becomes an extremely good value, less than 5% higher than the best value. Where X=thickness of the steel plate (m/m) and Y=oxygen content of the decarburized plate (PPM), the area between the straight lines is expressed by the following formula. -2500X+1163Y-2500X+1413...(1) The preferable area sandwiched by the straight lines is expressed by the following formula. -2500X+1213Y-2500X+1363...(2) The present invention is constructed based on this knowledge, and its gist is that C: 0.02~
0.12%, Si: 2.5~4.0%, Mn: 0.03~0.20%,
S: 0.01~0.05%, solAl0.01~0.05%, N: 0.004
~0.012%, and if necessary further contains up to 0.30% of each of Cu and Sn, with the balance consisting of iron and unavoidable impurities. Hot rolled silicon steel slabs are annealed and rapidly cooled before final cold rolling. Processing and reduction rate of 80%
After final cold rolling under strong reduction as described above, decarburization annealing is performed,
In the production of grain-oriented electrical steel sheets that are subsequently subjected to high-temperature finish annealing in an H ₂ atmosphere containing N ₂ , in order to obtain good magnetic properties, the final cold-rolled sheet thickness is
A device with excellent magnetic properties characterized by controlling the oxygen content of the decarburized plate within the range of formula (1) above by changing the composition, dew point, and annealing time of the atmospheric gas during decarburization annealing. It is in the manufacturing method of grain-oriented electrical steel sheet. The present invention is applied to a high magnetic flux density unidirectional electrical steel sheet that utilizes AlN as a main inhibitor. AlN, which is uniformly and finely precipitated by hot rolling and annealing and quenching treatment before final cold rolling, undergoes the growth of normal primary recrystallized grains during the heating process in a H ₂ atmosphere containing N ₂ during high-temperature finishing annealing. This is thought to contribute to the development and growth of secondary recrystallization in the (110) [001] orientation, which has a high degree of integration. Quantitative and theoretical elucidation of the secondary recrystallization mechanism in relation to AlN will have to wait for future research, but AlN is exposed to an atmosphere consisting of H ₂ and N ₂ during the heating process of high-temperature finish annealing. It is thought that the inhibitor effect is exerted while undergoing subtle changes under the influence of N, and then, through the aggregation process, it is finally decomposed and the [N] component is released outside the steel base. In the case of the unidirectional electrical steel sheet of the composition related to the present invention, the oxygen content of the decarburized annealed sheet is mostly Si,
It exists in the surface layer as an oxide with Al, Fe, etc.
This surface oxidation layer becomes a kind of wall between the internal part of the steel sheet and the atmosphere consisting of H ₂ and N ₂ during the heating process of high-temperature finish annealing, and is thought to have a considerable effect on the reaction between the steel sheet and the atmosphere. It will be done. Product samples marked with ○A, ○B, and ○C in Figure 1 (hereinafter referred to as
The macrostructure of the samples (referred to as ○a, ○ro, and ○ha) is shown in Figure 4. These samples ○A, ○B, and ○C are the same as those used in the above experiment, C = 0.075%, Si = 3.25%,
Mn=0.070%, S=0.024%, sol.Al=0.026%,
Contains N = 0.0085%, Cu = 0.08%, Sn = 0.12%,
The starting material was a silicon steel slab, the balance of which was iron and unavoidable impurities. As is clear from this Figure 4, fine grains were observed in sample ○A, and in samples ○RO and ○C.
100% secondary recrystallization. Also, compared to sample ○○,
Sample ○C had almost the same grain size, but
It was observed that the grain boundary lines were monotonous and the grain shape tended to be round. Table 1 shows the magnetic flux density _B10 values of samples ○A, ○B, and ○C. From this table, it is recognized that the magnetic flux density B ₁₀ is also excellent for sample ○○.

[Table] Sample ○A contains fine grains, so it is thought that the overall directionality was poor and the iron loss was poor. Sample ○C had 100% secondary recrystallization, but the degree of integration of the (110) [001] orientation was inferior to sample ○B, and it is thought that the iron loss was poor accordingly. Next, in order to investigate the cause of the difference in the secondary recrystallization conditions mentioned above, decarburized annealed plates similar to those of samples ○A, ○B, and ○C in Figure 1 were prepared separately, and annealing separator was applied to them to reduce _H2 to 75%. +N ₂ 25
% atmosphere at a heating rate of 20℃/hr,
The AlN of the as-decarburized annealed material was analyzed when it reached 900℃ and 1000℃. The analysis results are shown in Figure 3.
As is clear from Figure 3, it was found that AlN during high-temperature finish annealing changes depending on the oxygen content of the decarburized plate. Although there is no definitive relationship between the oxygen content of the decarburized plate and the increase in AlN during high-temperature finish annealing, it is likely that when the oxygen content is high, the surface oxide layer becomes slightly porous and the increase in AlN during high-temperature finish annealing increases. As the temperature rises, more nitrogen is absorbed into the steel sheet from the atmosphere, indicating a tendency for AlN to increase. From the above, when the oxygen content of the decarburized plate is appropriate (in the case of sample ○), the absorption of nitrogen from the atmosphere during the temperature rise during high-temperature finish annealing becomes appropriate, and AlN as an inhibitor is the most effective. acts on,
Secondary recrystallization with a high degree of accumulation of (110) [001] orientations can be obtained, but if the oxygen content is less than the appropriate amount (in the case of sample ○A), nitrogen absorption during the temperature rise during high-temperature finish annealing may be insufficient. , the inhibitor effect of AlN is insufficient,
It is thought that the grain growth of normal primary recrystallized grains progresses and becomes fine grains. As mentioned above, when the oxygen content is higher than the appropriate amount (in the case of sample ○), there is a lot of nitrogen absorption during the temperature rise during high-temperature finish annealing, and AlN also increases. It is still unclear whether crystals are the cause. In addition, the influence of the oxygen content of the decarburized plate on the secondary recrystallization during the heating process during high-temperature finish annealing is as described above.
In addition to changes in AlN, it is also possible that the oxide itself near the surface layer of the steel sheet has an effect. However, this mechanism will have to wait for future research. Next, we will discuss the reasons for determining the component ranges. C
If it is less than 0.02%, secondary recrystallization will be poor.
If it exceeds 0.12%, it is unfavorable from the viewpoint of decarburization and magnetic properties. If Si is less than 2.5%, good iron loss cannot be obtained, and if it exceeds 4%, cold rollability is significantly deteriorated.
Mn and S are necessary elements to form MnS, and are necessary to obtain an appropriate inhibitor effect.
The appropriate amount of Mn is 0.03-0.20%, preferably 0.05%
~0.15%. If S is less than 0.01, a sufficient inhibitor effect cannot be obtained, and if it exceeds 0.05%, desulfurization during purification annealing becomes difficult, which is not preferable. If solAl is less than 0.01%, a sufficient AlN effect cannot be obtained, and if it exceeds 0.05%, secondary recrystallization becomes unstable. If N is less than 0.004%, a sufficient AlN effect cannot be obtained, and if it exceeds 0.012%, blisters will occur. Furthermore, if necessary, in addition to the above elements, Cu and Sn may each be contained in an amount of 0.30% or less. Sn has the effect of reducing crystal grain size and reducing iron loss, and Cu is included to improve the glass coating. When the upper limit values of these elements are exceeded, hot-rollability, pickling properties, cold-rollability, decarburization properties, etc. deteriorate, and workability deteriorates. A silicon steel slab consisting of the above components and the balance being 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. Next, the steel sheet is decarburized and annealed, and as described above, the oxygen content of the steel sheet is controlled in relation to the thickness of the steel sheet. This control is performed by changing the dew point of the annealing atmosphere, the annealing time, and the composition of the atmospheric gas. The dew point is set at 50 to 75°C, but the reason for this is that a low dew point may result in poor decarburization, increase the annealing time, and cause the steel plate to have an excessive oxygen content.
℃. On the other hand, as the dew point increases, the oxide film formed on the surface of the steel sheet becomes coarse (porous), making it difficult to adjust the oxygen content, so the upper limit is set at 75°C. The annealing time is 1 to 6 minutes. If this time is short, there will be insufficient decarburization and the oxygen content of the steel plate will be low, so set it to more than 1 minute.On the other hand, if the time is too long, the oxygen content of the steel plate will be excessive, which is also unfavorable in terms of productivity. minutes or less. The annealing temperature is 800 to 860℃, which is well known for decarburization annealing, but the reason is that if it is less than 800℃, the time required for decarburization will be longer, while if it exceeds 860℃, it will be difficult to thread the sheet, resulting in poor shape. This is because there is no improvement in the decarburization effect. After that, an annealing separator is applied, dried, and finish annealed. 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 No. 55-65367 relates to a method for forming a forstellite insulating film, and is a method for forming a forsterite insulating film.
A nitrate aqueous solution containing more than 100% of SiO2 is applied and decarburized and annealed to produce mainly _SiO2 with an oxygen basis weight of 1.0 to 2.0g/ ^m2.
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 present invention related to iron loss improvement method is:
The basic way of thinking is different. Furthermore, the invention described in Japanese Patent Application Laid-Open No. 110726/1983 relates to a method for forming an insulating film on a high magnetic flux density unidirectional silicon steel sheet containing Sb as an inhibitor,
A MgO-based annealing separator is applied to a steel plate with an oxygen density of 0.7 to 2.8 g/ ^m2 through decarburization annealing.
This is a technology for improving glassy coatings, which consists of annealing at a specific temperature of 800 to 920 degrees Celsius for a long period of time in an inert neutral gas. The basic idea is different from that of the present invention, which concerns a method for improving iron loss in unidirectional electrical steel sheets that does not require crystal annealing and utilizes AlN as an inhibitor, which has an inherently good glassy coating. 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 is a technology that aims to improve the forsterite insulating coating by providing a quantitative relationship between The basic idea is different from invention. Next, examples of the present invention will be described. Example 1 C: 0.060%, Si: 3.00%, Mn: 0.085%, S:
Contains 0.025%, solAl: 0.028%, N: 0.0080%,
A silicon steel slab, the remainder of which is iron and unavoidable impurities, is finished into a 2.3 m/m thick hot-rolled plate, annealed at 1130°C for 4 minutes, rapidly cooled after annealing, and then cold-rolled to a thickness of 0.260 m. /m, cold rolled to 0.285m/m. The obtained cold-rolled sheets were decarburized annealed at 850°C by changing the dew point of the wet hydrogen atmosphere and the annealing time. After decarburization annealing, an annealing separator mainly containing MgO is applied, and H ₂ 75
%, at a rate of 25°C/hr in an atmosphere of 25% _N2 .
The temperature was raised to 1200°C, and then purification annealing was performed in an H ₂ atmosphere for 20 hours. The magnetic properties of the product were as follows.

[Table] Example 2 C: 0.074%, Si: 3.25%, Mn: 0.075%, S:
0.025%, solAl: 0.026%, N: 0.0083%, Cu:
A silicon steel slab containing 0.08% Sn, 0.12% Sn, and the balance consisting of iron and unavoidable impurities was finished into a 2.3 m/m thick hot rolled plate, annealed at 1120°C for 4 minutes, and then rapidly cooled after annealing. , then cold rolled thickness 0.225m/m,
Cold rolled to 0.260m/m. The obtained cold-rolled sheets were decarburized and annealed at 840° C. for 4 minutes while changing the dew point of a moist hydrogen atmosphere. After decarburization annealing, apply an annealing separator mainly containing MgO and heat at 20℃/hr in an atmosphere of 80% H ₂ and 20% N ₂
The temperature was raised to 1200°C at a rate of 1,200°C, and then purification annealing was performed in an H ₂ atmosphere for 20 hours. The magnetic properties of the product were as follows.

[Table] As described above, if the oxygen content of a steel plate after decarburization annealing is specified in relation to the plate thickness according to the present invention, secondary recrystallization will stably occur even if the final thickness of the steel plate is thin. Thus, a unidirectional electrical steel sheet with excellent magnetic properties can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the iron loss W _17/50 due to the oxygen content of the decarburized plate.
FIG. 2 is a diagram showing the relationship between plate thickness and oxygen content of a decarburized plate in the present invention based on the above-mentioned FIG. 1. FIG. FIG. 4 is a diagram showing the change in AlN during the process, and FIG. 4 is a diagram showing the macrostructure of the sample.

Claims (1)

[Claims] 1 C: 0.02-0.12%, Si: 2.5-4.0%, Mn:
0.03-0.20%, S: 0.01-0.05%, Acid-soluble Al: 0.01
~0.05%, N: 0.004~0.012%, the balance Fe and unavoidable impurities are hot rolled, and annealed and quenched before final cold rolling.
In the production of unidirectional electrical steel sheets, decarburization annealing is performed in the production of grain-oriented electrical steel sheets, which are subjected to final cold rolling with a reduction ratio of 80% or more, followed by decarburization annealing, followed by high-temperature finishing annealing in which the temperature is raised in an H ₂ atmosphere containing N ₂ . After adjusting the oxygen content of the steel plate, the dew point of the annealing atmosphere is 50~75℃, and the annealing temperature is 800~860℃.
A method for producing a unidirectional electrical steel sheet with excellent magnetic properties, characterized by decarburizing annealing at 1 to 6 minutes at 1°C and controlling the annealing time within the range given by the following formula. −2500X+1163≦Y≦−2500X+1413 However, X=thickness of steel plate (mm), Y=oxygen content of steel plate (PPM) 2 C: 0.02 to 0.12%, Si: 2.5 to 4.0%, Mn:
0.03-0.20%, S: 0.01-0.05%, Acid-soluble Al: 0.01
~0.05%, N: 0.04~0.012%, and further
Contains Cu: 0.30% or less, Sn: 0.30% or less, and the balance is
A silicon steel slab consisting of Fe and unavoidable impurities is hot rolled, annealed and rapidly cooled before final cold rolling, final cold rolled with strong reduction of 80% or more, decarburized annealed, and then In the production of grain-oriented electrical steel sheets that undergo high-temperature finish annealing in an _H2 atmosphere containing _N2 , the oxygen content of the steel sheet after decarburization annealing is
The dew point of the annealing atmosphere is 50~75℃, and the annealing temperature is 800~
Decarburized annealing at 860℃ for 1 to 6 minutes,
A method for manufacturing a unidirectional electrical steel sheet with excellent magnetic properties characterized by controlling the magnetic properties within the range given by the following formula. −2500X+1163≦Y≦−2500X+1413 However, X=Thickness of steel plate (mm), Y=Oxygen content of steel plate (PPM)