JPS6248725B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a thin, high magnetic flux density unidirectional electrical steel sheet comprising crystal grains in the (110)[001] orientation. (Prior art) Unidirectional electrical steel sheets are mainly used as core materials for transformers and generators, and have the characteristics of low core loss and high magnetic flux density, but from the perspective of energy conservation, materials with even lower core loss can be used. is demanded by the market. In order to obtain low iron loss, two methods are generally used: one method is to increase Si as much as possible to increase the specific resistance of the material to reduce eddy current loss, and the other method is to reduce eddy current loss by reducing the thickness of the finished plate as much as possible. However, with the method of reducing the thickness of the finished product, secondary recrystallization during final annealing becomes unstable, and the conventional method
It is difficult to stably obtain products with excellent magnetic properties with a thickness of 0.23 mm or less on an industrial scale. In order to perform secondary recrystallization stably, it is necessary to create a fine and uniform precipitated dispersed phase in the steel before finishing annealing, and to segregate grain boundary elements at the grain boundaries. After suppressing recrystallization as much as possible, the subsequent final annealing (110)
It is important to selectively grow secondary recrystallization in the [001] orientation. As a means of suppressing primary recrystallization,
Until now, it has been thought that the pinning effect of the grain boundaries by the precipitated dispersed phase and the drag effect of the grain boundaries by the grain boundary segregated elements are considered.
Possible elements include Cu _x S, MnSe, and AlN, and common grain boundary segregation elements include Sn, Sb, Bi, Te, and Se. (Object of the invention) From this point of view, the present invention is directed to
By using MnS, Cu _x S and AlN, using Sn as a grain boundary segregation element, and applying new rolling conditions in the hot rolling process, we have created ultra-thin products with a thickness of 0.30 mm or less, especially 0.23 mm or less. This makes it possible to industrially and stably manufacture high-grade unidirectional electrical steel sheets. (Structure of the Invention) In other words, the present invention is characterized by heating a material slab at a temperature of 1250°C or higher to completely dissolve MnS, Cu _x S, and AlN, which become precipitated dispersed phases, as a solid solution.
In the subsequent hot rolling process, the finishing front temperature is
By controlling between 1150~1250℃, the amount of SasMnS from rough rolling to finishing stand is 50 ~
100ppm MnS is precipitated uniformly and finely, and then
The coils are hardened in the finishing stand.
By controlling the surface temperature after finishing between 950 and 1050℃, the amount of MnS precipitated in the finishing stand can be suppressed as much as possible, and the amount of SasCu _x S can be reduced to 35 to 65 ppm.
Cu _x S is precipitated uniformly and finely, and SasMnS/SasCu _x S
The ratio is controlled within the range of 0.8 to 2.9. The hot coil with a thickness of 2.5 mm or less that has exited the finished surface is subsequently superquenched and rolled at a winding temperature of 500 to 600°C to control the precipitation of AlN during winding from the finishing stand, and to prevent the formation of Sn. The purpose of this method is to obtain high-quality hot coils by actively precipitating grain boundaries. JP-A-48-69720 describes how to develop a uniform and fine precipitated dispersed phase in the hot rolling process.
30 to 200 within the temperature range below ℃ and above 950℃
It was proposed to hold for seconds
In the publication, it was proposed to control the finishing outlet temperature in the hot rolling process to 900-1050℃ at the head of the hot-rolled sheet and 950-1150℃ at the center and tail, and Japanese Patent Publication No. 13606/1983 proposed During hot rolling, it has been proposed that the steel sheet temperature be continuously hot rolled at a hot rolling reduction rate of 10% or more between 950 and 1200°C, and cooled at a cooling rate of 3°C/sec or more. There is. However, these methods relate to materials that do not contain Al or Sn, the method described in JP-A-48-69720 only controls MnS, and the method described in JP-A-58-42727 mainly controls MnS. This is a control of Cu _x S, and the method described in Japanese Patent Publication No. 58-13606 considers the control of MnS and MnSe. On the other hand, the present invention starts with a material containing Mn, Cu, Al, and Sn as essential components and controls all the temperatures at the front surface of finishing, after finishing, and winding within a very narrow range. Cu _x S, and
The feature is that it attempts to control the amount of fine AlN precipitation within an optimal range. Now, FIGS. 1 and 2 are examples of experimental results conducted by the present inventors. [C] 0.070%, [Si] 3.30%, [Mn] 0.080, which are in the component range according to the present invention
%, [S] 0.025%, [Sol.Al] 0.025%, [N]
A slab containing 0.0085%, [Cu] 0.10%, and [Sn] 0.10% was heated in a heating furnace at 1350℃ for more than 5 hours to fully
After solid solution of MnS, Cu _x S and AlN, 2.3 mm thick hot coils were treated at different finishing front temperature, finishing finishing temperature, and winding temperature respectively, and after cold rolling to 32%, hot rolled sheet annealing was carried out. After finishing it to a thickness of 0.23 mm by cold rolling with a final cold rolling rate of 85%, it is made into a finished product through the steps of decarburization annealing, finish annealing, and final coating. This shows the relationship between This allows the winding temperature to reach 500 to 600.
℃, it can be seen that stable and good magnetic properties can be obtained by controlling the finishing front temperature between 1150 and 1250°C and the finishing finishing temperature between 950 and 1050°C. On the other hand, as shown in Figure 2, the winding temperature is
Although good magnetic properties can be obtained in some areas when the temperature exceeds 600℃, its stability is limited by the winding temperature of 500 to 600℃.
It can be seen that it is significantly inferior to the In other words, the finishing front temperature should be between 1150 and 1250°C, the finishing back temperature should be between 950 and 1050°C, and the winding temperature should be between 500 and 1250°C.
It can be seen that only the coil processed starting from a hot coil controlled in a narrow range of 600°C can obtain good magnetic properties. By the way, Figures 3 to 5 show the relationship between the analysis values of SasMnS, SasCu _x S, and NasAlN of the hot coil and the magnetic properties of the finished product by analyzing the components of the hot coil obtained in the experiments shown in Figures 1 and 2. It is something.
From this, the analysis value of the hot coil hot rolled in the temperature range of the present invention is 75 ± 25 ppm for SasMnS,
It can be seen that the values are in the region of 50±15ppm for SasCu _x S and 40ppm or less for NasAlN, and stable low iron loss values are obtained in that region. Also, SasMnS/
The relationship between the SasCu _x S ratio and the iron loss value is shown in Figure 6, and it can be seen that a low iron loss value is obtained in the range of 0.8 to 2.9, and the lowest iron loss value is obtained at 1.5. In other words, the coil of the present invention, whose temperatures are controlled at the front surface, rear surface, and winding, has a SasMnS content of 75 ± 25 ppm.
50±15ppm in SasCu _x S and SasMnS/SasCu _x S
ranges from 0.8 to 2.9 in terms of ratio, and in NasAlN
It can be seen that the coil has less than 40ppm. On the other hand, FIG. 7 shows an example of the results of a small sample experiment conducted by the present inventors. The components are the same as those shown in FIGS. 1 and 2. 30×30×30 from slab
Starting from a sample material cut out from a small sample of 1350 mm
After soaking for 60 minutes at of the sample put in
SasMnS, SasCu _x S and NasAlN were analyzed. The horizontal axis shows the quenching temperature, and the left side of the vertical axis shows the quenching temperature.
The sum of SasMnS and SasCu _x S is taken, and NasAlN is taken on the right side of the vertical axis. From this, MnS begins to precipitate from 1300℃, and from 1200 to 1250℃
The peak appears at ℃, and then below 1150℃
Cu _x S rapidly precipitates and reaches saturation at 950℃. In other words, in the temperature range of 1250 to 950°C, which corresponds to the temperature range between the finished front surface and the finished rear surface in the present invention.
This determines the precipitation amount ratio of MnS and Cu _x S, and it can be seen that the heat treatment during this time is important.
On the other hand, it can be seen that AlN starts to precipitate at 1100°C and is almost saturated at 900°C. In other words, rapid precipitation of AlN progresses in the temperature range of 1050 to 950°C, which corresponds to the temperature range of the finished surface.
It can be seen that it is important to immediately harden hot coils with a thickness of mm or less. Based on the above two results, in order to control the amount of finely precipitated MnS, Cu _x S and AlN within the optimal range and obtain a high quality hot coil, the finishing front temperature should be 1150 to 1250℃, and the finishing rear temperature should be 950 to 1050℃. ℃ and winding temperature 500~600℃
It is important to control each of these conditions, and it can be understood that even if this one condition is missing, a high-quality hot coil cannot be obtained. Regarding Sn, it is known from known literature that the temperature range in which Sn diffuses and is most likely to segregate at grain boundaries is 500 to 700°C. For this reason, it is presumed that after winding from the finished surface and after winding, it segregates at the grain boundaries of the hot coil, improving the magnetic properties. The reasons for limiting the conditions specified in the present invention will be explained below. First, when the finished front temperature exceeds 250°C, the amount of MnS precipitated decreases, and when it becomes lower than 1150°C, the amount of MnS precipitated is too large and the magnetic properties are not good. Next, if the surface temperature after finishing is higher than 1050℃, the amount of Cu _x S precipitated is insufficient, and if it is lower than 950℃, the amount of Cu _x S precipitated is too large, and the SasMnS/SasCu _x S ratio is in the optimum range of 0.8 to 2.9. The magnetic properties deteriorate as the magnetic field deviates from the magnetic field. In addition, it is desirable to prevent the precipitation of AlN as much as possible by super-quenching the coil, which is used to obtain fine precipitation of Cu _x S and whose surface temperature after finishing is controlled at 950°C or higher and whose thickness is 2.5 mm or less. Next, if the winding temperature exceeds 600°C, the amount of precipitated AlN will be too large and the magnetic properties will not be good, and if the winding temperature falls below 500°C, the rolled shape of the hot coil will deteriorate and at the same time the Sn It is estimated that the amount of grain boundary segregation decreases and the magnetic properties deteriorate, so the winding temperature is
The temperature was limited to 500-600℃. Next, the component composition will be described. [C] is the lower limit
If it is less than 0.025%, secondary recrystallization becomes unstable, and the upper limit of 0.085% was set because if the [C] content exceeds this value, the time required for decarburization becomes longer, which is economically disadvantageous. If [Si] is less than the lower limit of 2.5%, good iron loss cannot be obtained, and if it exceeds the upper limit of 4.5%, the cold rollability deteriorates significantly. [Mn] is an element necessary to form MnS, and if it is less than the lower limit of 0.01%
If the absolute amount of MnS is insufficient and exceeds the upper limit of 0.10%,
Industrialization is difficult because the heating temperature of the slab to dissolve all MnS into solid solution is too high.
[S] is an element necessary to form MnS and Cu _x S. If it is less than the lower limit of 0.01%, the absolute amount of MnS and Cu _x S will be insufficient, and if it exceeds the upper limit of 0.03%, hot cracking will occur.
Furthermore, desulfurization becomes difficult during final annealing. [Sol.Al]
is the element required to form AlN, and the lower limit is
If it is less than 0.010%, the absolute amount of AlN is insufficient and the upper limit
If it exceeds 0.065%, an appropriate dispersed state of AlN cannot be obtained. [N] is an element necessary to form AlN, and if it is less than the lower limit of 0.005%, the absolute amount of AlN will be insufficient. Moreover, if it exceeds the upper limit of 0.0100%, secondary recrystallization becomes unstable and blisters are likely to occur. [Cu] is an element necessary to form Cu _x S. If it is less than the lower limit of 0.03%, the absolute amount of Cu _x S will be insufficient, and if it exceeds the upper limit of 0.5%, pickling properties and decarburization properties will deteriorate. . [Sn] segregates at grain boundaries and stabilizes secondary recrystallization, but if it is less than the lower limit of 0.03%, the amount of segregation will be insufficient, and if the upper limit is 0.5%, it will be bad for economic reasons and decarburization. Further, if the final cold rolling rate is less than 83%, it is impossible to obtain a high magnetic flux density unidirectional electrical steel sheet, so the lower limit is set to 83%. The reason for limiting the finished plate thickness to 0.30 mm or less is to obtain ultra-low core loss unidirectional electrical steel sheets in response to recent demand needs. Example 1 [C] 0.075%, [Si] 3.25%, [Mn] 0.080%,
[S] 0.025%, [Sol.Al] 0.025%, [N] 0.0075
%, [Cu] 0.10%, [Sn] 0.10% 250mm
The thick slab was heated at 1350° C. for 2 hours and then hot rolled under the hot rolling conditions shown in Table 1 to obtain a 2.3 mm thick hot coil. This hot coil was cold rolled at a rolling reduction of 33%, then hot rolled sheet annealed at 1120° C. for 4 minutes, and then finally cold rolled at a cold rolling reduction of 85% to give a thickness of 0.23 mm. After that, the obtained cold-rolled sheet was coated with 20% hydrogen and 80% nitrogen.
Decarburization annealing was performed at 840°C for 3 minutes in an atmosphere with a dew point of 40°C, and an annealing separation material was applied, followed by final annealing at 1200°C for 20 hours in a hydrogen stream, and then a coating liquid was applied. It was made into a finished product. The magnetic properties of the product obtained in this way are shown in Table 1. The material of the present invention can stably obtain an iron loss W of 0.92 W/Kg, and has better magnetic properties than the comparative material. I understand. Among them, the SasMnS/SasCu _x S ratio is particularly
It can be seen that the example of 21.5 (No. 7) shows the lowest iron loss. Example 2 [C] 0.080%, [Si] 3.30%, [Mn] 0.080%,
[S] 0.026%, [Sol.Al] 0.026%, [N] 0.0080
%, [Cu] 0.09%, [Sn] 0.11% 250mm
The thick slab was heated at 1350° C. for 2 hours and then hot rolled under the hot rolling conditions shown in Table 2 to obtain a 2.0 mm thick hot coil. This hot coil was subjected to hot-rolled plate annealing at 1120°C for 4 minutes, and then finally cold rolled at a cold rolling rate of 88% to a thickness of 0.23 mm. Hydrogen is then applied to the cold-rolled sheet obtained.
20%, nitrogen 80%, 840°C in an atmosphere with a dew point of 40°C
After performing decarburization annealing for 3 minutes and applying an annealing separation material, final annealing was performed at 1200° C. for 20 hours in a hydrogen stream, and then a coating liquid was applied to obtain a finished product. As shown in Table 2, the magnetic properties of the product obtained in this way are good, even without cold rolling before hot-rolled annealing, and the iron loss is stable at 0.92 W/Kg. You can see what you can get by doing this.

【table】

【table】 [Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the relationship between the finished front temperature, finished back temperature, winding temperature, and iron loss W〓 (first
Figure: Winding temperature is 500-600℃, Figure 2: Winding temperature is
600℃ or above, 〓 mark in Figures 1 and 2 is W〓
≦0.92, △ mark is also 0.93 to 0.98, × mark is 0.99
≦), Figure 3 is a diagram showing the relationship between the amount of SasMnS in the hot coil and the iron loss W〓 (● marks indicate 35ppm≦SasCu _x S≦
65ppm, NasAlN≦40ppm, 0.8≦SasMnS/SasC
Figure ₄ is a diagram showing the relationship between the amount of SasCu _x S and iron loss W〓 of hot coils (● marks are 50ppm≦).
SasMnS≦100ppm, NasAlN≦40ppm, 0.8≦
Those that passed SasMnS/SasCu _x S≦2.9,
〇 marks indicate those that fail within the above range), Figure 5 is a diagram showing the relationship between the amount of NasAlN in the hot coil and iron loss W〓 (● marks indicate
50ppm≦SasMnS≦100ppm, 35ppm≦SasCu _x S
≦65 ppm, 0.8≦SasMnS/ _SasCu
Figure 6 is a diagram showing the relationship between the SasMnS/SasCu _x S ratio and iron loss W〓 of a hot coil (● marks are 50ppm
SasMnS≦100ppm, 35ppm≦SasCu _x S≦
65ppm, NasAlN ≦ 40ppm, those that passed the test are shown, and the ○ marks indicate those that failed within the above range. FIG. 3 is a diagram showing the relationship between the quenching temperature and the amount of precipitation of SasMnS+SasCu _x S and NasAlN.

Claims (1)

[Claims] 1 [C] 0.025 to 0.085%, [Si] 2.5 to 4.5%,
[Mn] 0.01-0.10%, [S] 0.01-0.04%, [Sol.
Al〕0.010~0.065%, [N]0.005~0.0100%,
A slab containing [Cu] 0.03 to 0.5%, [Sn] 0.03 to 0.5%, the balance iron and unavoidable impurities is heated to a high temperature and then hot rolled to a specified cold rolling process with a final cold rolling ratio of 83% or more. In the manufacturing method of high magnetic flux density grain-oriented electrical steel sheets, the finishing front temperature during hot rolling is set to 1150.
A method for producing a thin, high magnetic flux density grain-oriented electrical steel sheet with a finished product thickness of 0.30 mm or less, characterized by controlling the finished surface temperature to 950 to 1050 °C, and the winding temperature to 500 to 600 °C.