JPS6253572B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method for manufacturing unidirectional electrical steel sheets that are easily magnetized in the rolling direction and are composed of secondary recrystallized grains in which the orientation of each grain is expressed as {110}<001> by the crystallographic Miller index. The present invention relates to a method for ensuring excellent magnetic properties by imparting characteristics to the rolling method during the manufacturing process. By the way, the manufacturing methods for grain-oriented electrical steel sheets are roughly divided into two types: the double rolling method, which has been around for several decades, and the single rolling method, which was newly developed over 10 years ago. Ru. Since the single-rolled material has particularly excellent magnetic flux density, the iron loss in a high magnetic field, for example, the iron loss W ₁₇ when the magnetic flux density value is 1.7T under 50 cycles of an alternating magnetic field.
Since the value of _/50 is excellent, it is becoming widespread in the field of use of conventional double-rolled materials. However, in the current era where demands for energy conservation are becoming stronger and stronger, consideration is being given to lowering the design magnetic flux density value of transformers, etc., and the requirements for the iron cores used are There is also a movement to reconsider double-cold-rolled materials, which have better material properties, so-called medium and low magnetic field iron loss (for example, W _15/50 ) compared to the purchase price of the steel sheet. In view of this background, the present invention provides a method for improving the core loss of a grain-oriented electrical steel sheet by double rolling. In other words, hot-rolled steel sheets containing C0.08% or less, Sl4.0% or less, and other components required for grain-oriented electrical steel sheets are annealed as necessary and then pickled. , first rolling at a reduction rate of 30~75%, intermediate annealing at a temperature of 750~1150℃, 40~
After a second rolling to achieve the final plate thickness at a rolling reduction of 80%, decarburization annealing in a humid hydrogen stream, and application of an annealing separator if necessary,
In the production of grain-oriented electrical steel sheets, which consists of a series of processes including final annealing at a temperature of 800 to 1250°C for the development and slowing of secondary recrystallization, the first rolling process or the first and second rolling processes are performed. At at least one of the intermediate plate thickness stages, the steel plate to be rolled is heated within the holding temperature range of 100 ^{to 600} °C. 〓)... It is characterized by being held for a time that satisfies the following formula (where T means the absolute temperature of the holding temperature of the rolled steel plate). The present invention is also characterized in that, in order to make the above-described method of the present invention even more effective, the thermal history of the rolled steel sheet from the intermediate annealing step to the second rolling is regulated. In other words, after the completion of the intermediate annealing process and before entering the second rolling process, the relationship between the absolute temperature of the steel plate and the holding time at that temperature is: holding time (seconds) ≦3.5×10 ^-12 exp12800/T (〓
)... The purpose is to regulate the thermal history of the rolled steel plate so that it satisfies the following inequality. Although the mechanism of the improvement effect on magnetism of the method according to the present invention described above is not clear in detail, it is thought to be as follows. Generally, grain-oriented electrical steel sheets consist of secondary recrystallized grains having an orientation close to the {110}<001> orientation. These secondary recrystallized grains are primary recrystallized grains that have grown larger under certain specific conditions prior to the growth of other surrounding primary recrystallized grains. One of these specific conditions is that the steel sheet base consisting of primary recrystallized grains is appropriate, that is, the grain orientation size and homogeneity are appropriate, and the other is that the steel sheet substrate made of primary recrystallized grains is appropriate, and the other is that the steel sheet substrate consisting of primary recrystallized grains is appropriate, and the other is that the steel sheet substrate consisting of The so-called inhibitor effect exists, which has the role of inhibiting the growth of other primary recrystallized grains while the primary recrystallized grains grow rapidly. Such inhibitors usually include
There are fine precipitated dispersed phases represented by MnS, MnSe, AlN, etc., and grain boundary segregated elements represented by S, N, Se, Sb, Sn, P, etc. The secondary recrystallization consisting of grains oriented close to the {110}<001> orientation can occur over the entire surface of the steel sheet only when the two conditions of a good primary recrystallization structure and the presence of an appropriate inhibitor are met. It can be completely covered. Furthermore, it is estimated that the magnetic properties will be better when these two conditions are more perfect.
The present invention regulates the conditions of the first rolling process, intermediate annealing process, and second rolling process, particularly in relation to double-rolled materials among the manufacturing processes of unidirectional electrical steel sheets that meet these conditions. As a result, these secondary recrystallized grains have improved magnetic properties more than before, and the reason for this is thought to be due to an improvement in the primary recrystallization structure rather than an improvement in the above-mentioned inhibitor. Presumed. That is, during rolling according to the present invention,
By holding the steel plate at a temperature within a predetermined range for a predetermined period of time, solid solution elements such as C and N are fixed to lattice defects such as dislocation lines formed during rolling.
This changes the deformation mechanism during subsequent rolling, resulting in a change in recrystallized grains and texture at the final plate thickness.
That is, by further improving the primary recrystallization structure,
It is presumed that secondary recrystallized grains with good magnetic properties grow as a result. 1. By the way, during the production of electrical steel sheets in the double cold rolling method, aging treatment is performed during the second cold rolling, and in connection with this aging treatment, intermediate annealing, which is a step before the second cold rolling, is carried out. Regulation of the cooling rate is described in Japanese Patent Publication No. 56-3892. On the other hand, the present inventors have discovered that the effect is effective not only during the second cold rolling but also during the first cold rolling, and that if aging treatment is applied to both the first and second cold rolling. We found that the effect further increased,
The regulations are based on consideration of the effective conditions in such cases. In addition, in order to fully exhibit this effect, it has been discovered that the thermal history of the steel sheet from the time of completion of the intermediate annealing process to the start of the second cold rolling process should be regulated. The present invention will be explained in detail below. First, the present inventors conducted the following experiment. C0.045
%, Si3.20%, Mn0.06%, S0.026% and the balance
After pickling a hot-rolled Fe plate with a thickness of 2.5 mm, it was hot-rolled for the first time to 0.75 mm, intermediately annealed at 970°C for 4 minutes, and then rolled for the second time at a rolling reduction of 60%. The plate was rolled to a final thickness of 0.30mm, decarburized annealed at 840°C, coated with MgO, and finished annealed at 20°C per hour to 1180°C in a hydrogen stream for 20 hours. Eventually, it was made into a finished board. At that time, during the first rolling, when the plate thickness was 1.30 mm and 0.9 mm, and further during the second rolling, when the plate thickness was 0.55 mm, the steel plate was subjected to the present invention treatment at 200 ° C. for 10 minutes, A comparison was made with the case without such treatment. Figure 1 shows the iron loss value of the finished product. According to the figure, the average value of W _17/50 when the present invention is not carried out is 1.27 (w/Kg), whereas when the present invention is carried out, it is 1.16 to 1.21 (w/Kg). It can be seen that the iron loss value has improved up to Kg). In particular, when the present invention treatment was applied both for the first and second time, there was a remarkable improvement. Figure 2 shows a plate with a thickness of 1.30 mm during the first rolling process according to the method of the present invention using a sample with the same component composition as above.
and plate thickness at 0.9 mm and during the second rolling process.
The figure shows the W _17/50 value of the finished product when processed at a temperature of 100 to 600° C. for various times at 0.55 mm. In addition, if such treatment exceeds 600℃,
The processing temperature range was limited to 100 to 600°C because recrystallization occurs and it becomes difficult to obtain secondary recrystallization as a result, and the processing time becomes significantly longer at temperatures lower than 100°C. The rolled steel plate is within the scope of the present invention, i.e.
If the absolute temperature within the range of 100 to 600℃ satisfies the following formula for a specified period of time, the average value of W _17/50 of the comparative material will be 1.27 (w/Kg), as shown in Figure 1.
On the other hand, that of the example of the present invention is 1.25 (w/
It can be seen that the value has become smaller than Kg). 0.13exp1700/T(〓)≦Holding time (seconds) ≦3.7×10 ^-4 exp8100/T(〓)...The steel plate that has gone through the intermediate annealing process is wound into a coil shape,
It is then subjected to the second rolling process. Due to the process schedule during actual factory production,
Such steel strips may be left in this state for several days or more, and the steel strip temperature may reach 40° C. or higher in summer. Furthermore, if the Si content is 3.2% or more, the coil is likely to break during the next rolling, so the temperature of the coil may be raised in advance. However, it has been found that the thermal cycle history from the intermediate annealing step to the second rolling step affects the heat treatment effect of the steel plate in the middle of rolling, which is a feature of the present invention. In other words, Fig. 3 shows that when conducting the same experiment as shown in Example B of the present invention in Fig. 1, intermediate annealing heating was performed at 970°C for 4 minutes, then cooling to 600°C for 20 seconds, and then The steel plate was cooled at a rate of 10°C per second from 600°C to room temperature, and then the steel plate was held at each temperature for a predetermined period of time before being rolled a second time (in the middle, it was treated at 200°C for 10 minutes at a plate thickness of 0.55 mm). This shows the W _17/50 value of the finished product when aged. As is clear from Figure 3, after the completion of the intermediate annealing process and before entering the second rolling process, the relationship between the absolute temperature of the steel plate and the holding time at that temperature is determined by the following formula: Holding time (seconds) ≦ 3.5×10 ^-12 exp12800/T(〓
)... Within the scope of the present invention that satisfies (within the range 1 in the figure)
shows good magnetism. In particular, retention time (seconds) ≦2.65×10 ^-13 exp
13300/T (〓) is more preferable (within the range 2 in the figure). The reason why the heat treatment effect of the steel sheet in the process of rolling, which is the basis of the present invention, affects the thermal history from the intermediate annealing process to the second cold rolling is probably because of carbon, nitrogen, etc. It is presumed that this is related to the behavior of solid solution elements. That is, as mentioned above, if the heat treatment effect of the steel plate during rolling is caused by the fixation of solid solution elements such as C and N to the lattice defects formed during rolling, then the second This is presumed to be because it is more effective if a large amount of C, N, etc. are dissolved in solid solution at the start of rolling. Next, the reason for limiting the composition of the hot-rolled sheet for unidirectional electrical steel sheet, which is the object of the present invention, will be explained. If C exceeds 0.08%, decarburization by continuous annealing becomes difficult and the magnetic properties of the product deteriorate.
must be below 0.08%. Si is an important element that controls iron loss, and a higher content is preferable, but if it exceeds 4.0%, the rollability will deteriorate significantly, so it is necessary to keep it below 4.0%. Moreover, if it is less than 2.5%, transformation occurs and the magnetic properties of the product are significantly deteriorated, so the Si content should be substantially in the range of 2.5 to 4.0%. Hot-rolled grain-oriented electrical steel sheets usually contain Mn, S, etc., but in the case of the present invention, they are not limited to these in any way, and may also contain other inhibitor-forming elements that are known per se. This can be easily inferred from the mechanism of the effects of the present invention described above. Next, the reasons for limiting the processing conditions of the present invention will be explained. The hot-rolled sheet containing the above components is
You can continue with the first rolling, but
It is more effective to perform normalizing annealing in the range of 750 to 1150°C. Such annealing is 750
If it is lower than 1150°C, a sufficient normalizing effect of the crystal structure cannot be obtained, while if it is higher than 1150°C, the crystals will become coarse, which is unfavorable in terms of the magnetism of the final product. The subsequent first rolling, intermediate annealing, and second rolling are the basis of the present invention, and the reasons for their limitations have already been explained based on the experimental data shown in Figures 1 to 3. However, regarding the limitation of the rolling reduction rate, secondary recrystallization cannot be obtained unless it is within this range, so the first rolling reduction is set at 30 to 75.
%, and the second round was limited to a rolling ratio of 40 to 80%. In addition, if the intermediate annealing temperature is lower than 750℃, the annealing effect cannot be obtained, and if the temperature is higher than 1150℃, the crystal grains will become excessively coarse, so it is normal to perform the intermediate annealing at a temperature of 750 to 1150℃. The atmosphere is preferably neutral or reducing, and a strongly oxidizing atmosphere is disadvantageous. In addition, it has been confirmed through another experiment that there is no significant difference in the effect of rolling after the heat treatment of the steel sheet in the process of rolling according to the present invention, even after the steel sheet has cooled to room temperature or when the temperature is close to the heat treatment temperature. ing. Also,
The heat treatment may be performed by any conventionally known heating method, or may be performed by heating by rolling.
The thus obtained cold-rolled sheet having the final thickness is subjected to decarburization annealing by a known method, and then an annealing separator is applied and final finish annealing is performed. If the final annealing temperature is below 800°C, not only will secondary recrystallized grains not be obtained, but magnetism will not be obtained due to insufficient purification, and if it is above 1250°C, it will be uneconomical in terms of thermal energy. However, since the glass properties deteriorate, the temperature was limited to 800 to 1250°C. The present invention will be described below with reference to Examples. Example 1 C0.055%, Si3.30%, Mn0.085%, Se0.022%,
A silicon steel material consisting of 0.015% As and the remainder substantially Fe was hot rolled into a hot rolled sheet with a thickness of 2.8 mm. 920℃
After annealing for 2 minutes at 980° C., it was pickled, rolled to a thickness of 0.75 mm for the first time, intermediate annealed at 980° C. for 3 minutes, and cooled to room temperature for 4 minutes. Then,
Immediately after light pickling, the plate was rolled a second time to reduce the final plate thickness to 0.30 mm. During this rolling, the following three types of treatments were performed. (1) Perform the first and second rolling using the conventional method. (2) 10 at 400℃ during the first rolling at 1.6mm, 1.2mm, and 0.9mm.
A second heat treatment was added. (3) For the first and second times, heat treatment was applied at 300°C for 3 minutes when the plate thickness was 1.2 mm and 0.50 mm, respectively. This cold-rolled sheet was subjected to decarburization annealing at 840°C for 5 minutes in wet hydrogen, coated with an annealing separator MgO, laminated, and annealed at 1180°C in a hydrogen stream for 25 hours. The magnetic properties of each product obtained by the above treatment are shown in Table 1.

[Table] Example 2 C0.038%, Si3.15%, Mn0.065%, S0.020%,
A silicon steel plate with a thickness of 2.1 mm, the remainder of which was essentially Fe, was pickled, rolled to 0.68 mm, intermediately annealed at 900°C for 7 minutes, and then rolled a second time to 0.30 mm. Summer. In addition, during the first rolling, heat treatment was performed at 200℃ for 10 minutes at the plate thickness of 1.5 mm and 0.95 mm, and then during the second rolling, at the point of 0.53 mm.
Heat treatment was performed at 250°C for 5 minutes. At this time, the following various treatments were performed after intermediate annealing. (1) Immediately after the intermediate annealing is completed, the second rolling is performed. (2) After intermediate annealing, the product is left in a constant temperature bath at 50°C for 3 hours and then rolled for the second time. (3) After intermediate annealing, it is left in hot water at 100°C for 2 minutes and then rolled a second time. (4) After intermediate annealing, it is left in a constant temperature bath at 50°C for 20 days and then rolled for the second time. (5) After intermediate annealing, it is left in hot water at 100°C for 3 hours and then rolled for the second time. This cold-rolled sheet was treated in the same manner as in Example 1 after the decarburization annealing step. The magnetic properties of the product were as shown in the table below.

[Table] As shown, good magnetism can be maintained in the cases of (1) and (2) that satisfy the formulas of the present invention, but it can be seen that the magnetic properties are inferior if the formulas of the present invention are not satisfied. .
As described above, according to the present invention, the magnetic flux density value of the final product can be improved, and the iron loss value can be greatly improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the effect of the mid-rolling heat treatment method of the present invention, Figure 2 is a diagram showing the temperature and time range of the heat treatment method, and Figure 3 is a diagram showing an intermediate effect when the mid-rolling heat treatment method is adopted. It is a figure which shows the thermal history restriction range from the annealing process to the second rolling. Figures 2 and 3 ●W _17/50 ≦1.20 (w/Kg) Legend〇1.20＜W _17/50 ≦1.25 ×1.25＜W _17/50

Claims (1)

[Claims] After annealing a hot rolled steel sheet consisting of 1% by weight, C≦0.08%, Si: 2.5 to 4.0%, and MnS as the main inhibitor, with the remainder being Fe and unavoidable impurities, pickling was performed for 30 minutes. First cold rolling at ~75% reduction, intermediate annealing at a temperature range of 750~1150℃, 40~80℃
% of the rolling reduction and decarburization annealing in a wet hydrogen atmosphere, further applying an annealing separator and finishing annealing, the method for producing a grain-oriented electrical steel sheet, comprising: In at least one intermediate plate thickness stage in the second cold rolling process, the rolled steel plate is held in a temperature range of 100 to 600°C for a time that satisfies the following formula (),
In the first stage of the second cold rolling process after completion of the intermediate annealing process, the thermal history of the rolled steel plate is controlled so that the absolute temperature of the rolled steel plate and the holding time at that temperature satisfy the following formula (). A method for producing a grain-oriented electrical steel sheet. 0.13exp (1700/T(〓)≦Holding time (s) ≦3.7×10 ^-4 exp(8100/T(〓))…() Holding time (s)≦3.5× ^10-12 exp(12800/T( 〓)) ...() 2 After annealing a hot-rolled steel sheet consisting of C≦0.08%, Si: 2.5-4.0% and other MnS as the main inhibitor, and the balance being Fe and unavoidable impurities in weight%, pickling, 30% by weight. First cold rolling at ~75% reduction, intermediate annealing at a temperature range of 750~1150℃, 40~80℃
% of the rolling reduction and decarburization annealing in a wet hydrogen atmosphere, further applying an annealing separator and finishing annealing, the method for producing a grain-oriented electrical steel sheet, comprising: In at least one of the intermediate plate thickness stages in the second and second cold rolling processes, the rolled steel plate is
℃ temperature range for a time that satisfies the following formula (), and in the first stage of the second cold rolling process after the completion of the intermediate annealing process, the absolute temperature of the rolled steel plate and the holding time at that temperature are as follows: A method for producing a grain-oriented electrical steel sheet, comprising controlling the thermal history of a rolled steel sheet so as to satisfy the following formula (). 0.13exp (1700/T(〓)≦Holding time (s) ≦3.7×10 ^-4 exp(8100/T(〓))…() Holding time (s)≦3.5× ^10-12 exp(12800/T( 〓)) …()