JPH0310020A - Production of grain-oriented silicon steel sheet excellent in magnetic property and surface characteristic - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet having superior electromagnetic properties in a rolling direction by roughing a slab of a silicon steel with a specific composition under specific conditions and then subjecting the above to hot finish rolling, cold rolling, decarburizing annealing, and finish annealing. CONSTITUTION:A slab of a silicon steel having a composition containing, by weight, 0.01-0.08% C, 2.5-4.0% Si, 0.03-0.10% Mn, and 0.01-0.06% of one or more elements among S, Se, and Al is heated, e.g. to 1350 deg.C and subjected to roughing by 5-6 passes. Successively, hot finish rolling is exerted, and the resulting hot rolled plate is cold-rolled once or cold-rolled twice or more while process-annealed between the cold rolling stages so as to be formed into the final sheet thickness and is then subjected to decarburizing annealing and to finish annealing, by which the grain-oriented silicon steel sheet is produced. At this time, rolling temp. T1 at the time of the first pass in the roughing in the above method is regulated to >=1280 deg.C and rolling reduction R1% in the above pass is regulated so that it satisfies the condition in an inequality I, and then, the slab is held for >=30sec to allow recrystallization to proceed, and further, rolling temp. T2 at the time of the final pass in the roughing is regulated to >=1200 deg.C and rolling reduction R2% in the above pass is regulated so that it satisfies the condition in an inequality II. By this method, the grain-oriented silicon steel sheet excellent in magnetic properties and surface characteristic can be stably produced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a grain-oriented silicon steel sheet having excellent electrical (fi) characteristics in the rolling direction.

<Prior art> As is well known, grain-oriented silicon steel sheets are used as core materials for transformers and other electrical equipment, and have secondary recrystallized grains with (110) planes on the plate surface and <001> axes aligned in the rolling direction. Therefore, it is composed of ゛ζ. In order to develop such secondary recrystallized grains with a weight value of +1, fine precipitates such as MnS, MnSc, AIN, etc. called inhibitors are dispersed in the steel and subjected to high temperature treatment 1:vt, dulling. It is necessary to effectively capture the growth of grains in other orientations. The inhibitor-dispersed Con I roll for this purpose is produced by temporarily dissolving these precipitates into solid solution during slab heating prior to hot rolling, and then hot rolling with an appropriate cooling pattern.

The purpose of hot rolling is to refine the slab-cast composite fibers by recrystallization and obtain an optimal texture for secondary recrystallization. Conventional techniques attempt to individually achieve inhibiting solid solution or microstructural refinement, and many patents related to this have been published so far.

For example, regarding inhibitor solid solution, JP-A-63109
As disclosed in Publication No. 11, when the slab surface temperature is held in a temperature range of 1420 to 1495°C for 5 to 60 minutes, at 1320°C or higher, 1420 to 1495°C! 4
It is stated that a unidirectional silicon steel sheet with few surface defects and good properties can be obtained by increasing the Il' temperature at a rate of 8°C/min or more until the temperature reaches 95°C. By this method, it is possible to achieve a complete solid solution of the inhibitor, and in principle, coarsening of the surface grains of the slab can be suppressed and the surface quality can also be improved. It is difficult in practice to achieve these conditions, especially since it is impossible to completely suppress grain coarsening over the entire length of the slab, and some grain refinement during hot rolling is necessary to ensure uniformity of &1IVs. It is necessary to take measures to reduce the

On the other hand, regarding the miniaturization of group Ia, °ζ is, for example,
1190-960°C disclosed in Publication No. 120214
Recrystallization method by high pressure rolling, JP-A-55-119
1230-960'C disclosed in Publication No. 12G,
A method of rolling with a high reduction of 30% or more in a state containing 3% or more of the T phase, a method of reducing the rough rolling start temperature to 1250'C or less disclosed in JP-A-57-11614, JP-A-59-1988 1050-12 disclosed in -93828 publication
00'c, strain rate 15s-' or less, reduction rate! There are already known methods for increasing the ratio to 5%/pass or more. All of these have in common that they are rolled at a high pressure in a temperature range around 200° C. to refine the structure. Zunawara, these are "remo [Tetsu to Hagane J 67 (19
81) It is based on the knowledge regarding the recrystallization limit published in S 1200 or the same technical idea. Figure 6 shows this finding. This figure shows that rolling at high temperatures does not contribute to recrystallization Lj at all, and only large strain addition in the recrystallization region at low temperatures contributes to recrystallization. In other words, even in a slab heated to a high temperature, it is essential to cool it to 1250° C. or lower and then roll it in order to achieve a finer structure due to recrystallization. In both of these techniques, the heating rate is 125
The temperature is set at 0°C or higher, and there is no upper limit specified.The point is that by keeping the slab in the furnace for a long time, the inhibitor is dissolved into solid solution, allowing slab grain growth to some extent, and refining by hot rolling. They have something in common.

However, when considering the reality of these technologies, heating the slab at high temperatures to completely dissolve the inhibitor requires a cooling device on the hot strip mill, and additional mill power is required for low-temperature hot rolling. This contradicts the idea of a hot strip mill, which aims to save energy and increase productivity. Furthermore, the effects of low-temperature rolling were not always clear.

In other words, there were too many problems to apply these methods to actual processes when the effect was small.

<Problems to be Solved by the Invention> Therefore, the purpose of the present invention is to maximize the advantage of mass production of hot strip mills, and to develop conditions that apply high temperature heating that is advantageous for complete solid solution of the inhibitor and modification of surface properties. The present invention also proposes a method for producing a grain-oriented silicon steel sheet that reliably obtains a perfectly fine and uniform assembly machine and has uniform and excellent magnetic properties and surface texture.

Means for Solving the Problems〉 The present invention has a vertical % c: o, ot~0.08%,
Sl: 2.5-4.0%, Mn: 0.03-0.
Contains 10% and further contains S, Se and 8! one or more of the following
, ot ~ o, after heating a silicon steel slab containing 6% o, it is rough rolled and then hot finish rolled, then cold rolled once or twice with intermediate annealing to obtain the final plate thickness, and then decarburized. In a method for producing a grain-oriented silicon steel sheet consisting of a series of steps of final annealing after annealing, the rolling temperature Tl ("C) of the first pass of rough rolling is set to 1280°C or higher, and the rolling reduction R1 (% ) is set to 60≧R1(%)≧-0,5TI+670, then held for 30 seconds or more until the next bath, and further the rolling temperature Tt ('c) in the final rolling pass of ↑1.1 is set to 1200°C.
or more, and the rolling reduction rate IZ2 (%) is 70≧R2 (%)
≧−0. IT! +165 Patented method for manufacturing grain-oriented silicon steel sheet The present inventors have conducted extensive research on recrystallization behavior in high-temperature ranges. We have newly discovered that even in the high temperature range, which has not been of interest at all, if the strain is large enough, recrystallization can proceed in l-min.
Regarding this point, there is no report on this:r. This is because high-temperature heating has always been difficult in industry, and even in laboratory studies, high-temperature heating is necessary for high-temperature rolling, but there are problems such as scale formation and repair of experimental furnaces. This is because there were problems and great difficulties. In addition, there are many experimental reports on Nitong steel, but it is said that the first high temperature region after 1200'c is the dynamic recovery Jl region, where recovery or dynamic recrystallization is the main process, and further studies have not been conducted sufficiently. It wasn't. In particular, in the case of grain-oriented silicon steel, it contains about 3% Si, so most of it is α phase, and since the α phase is said to be unlikely to recover, dynamic recrystallization will not occur, so it is of interest at all. It was not considered.

However, the inventors of the present invention questioned this common theory and developed a high-temperature furnace capable of ultra-high temperature heating with little influence from the thrall, conducted experiments, and found the above-mentioned results for the first time.

Next, the experiments that led to the present invention will be explained. In heavy use%,
C: 0.0.1%, Si: 3.3G%, Mn
: 0.05% Sa: A silicon steel slab containing 0.022% and the remainder substantially Fe was heated at 350°C.
The material was heated for 0 minutes, and when the temperature reached a predetermined temperature of 11, it was rolled for one pass and then cooled with water to observe the cross-sectional structure and measure the recrystallization rate. Various changes were made to the rolling temperature and reduction rate. The results thus obtained are shown in FIG.

A high temperature range where conventional knowledge suggests that there is no recrystallization at all.
For example, it was found that even at 1350°C, recrystallization progresses if the rolling reduction is 30% or more. Moreover, it was confirmed that the area where recrystallization is completed expands further by holding isothermally for 30 seconds or more, preferably 60 seconds or more after rolling.The Yago phenomenon can be understood as follows. First, it was observed that a zigzag ridge consisting of a tIl, net, and node-like dislocation structure was formed in the unrecrystallized grain after rolling. Therefore, it is determined that the recovery ends fairly quickly after rolling. Moreover, the straw dislocation density differs between crystal grains. It is thought that this difference in dislocations is the driving force for recrystallization.

At high temperatures, the ↑q field is thermally activated and becomes f>dynamic V+f, and when the moved grain boundary has a certain curvature of 2), 4I, becomes 1■i crystal nucleus i'''f. A similar phenomenon occurred, and we confirmed that recrystallization is actually possible even in the high temperature range where dynamic recrystallization does not occur and strain is unbearable in UL.However, this ili crystal behavior was described above.) However, when the mobility of grain boundaries is very large, that is, when the temperature is high (1280 Although it takes a certain amount of time, the crystal becomes fully functional.

This phenomenon is quite different from the conventional well-known static recrystallization.

The point I have mentioned so far is that when rolling 3% Si steel in a temperature range of 1300°C or higher, the recrystallization mechanism occurs in a single α-phase state, a point that has been clarified for the first time this time. ．． On the other hand, the recrystallization limit curve shown in Figure 6, which is conventionally known for 3% silicon steel, is obtained when the hard γ phase precipitates and recrystallization is promoted only in its vicinity. In other words, in the past, data had been obtained from rolling experiments, but because the heat treatment method before rolling was omitted, it can be assumed that the results obtained were different from the experimental results that formed the basis of the present invention. In other words, samples that had been melted at high temperatures were cooled to room temperature and then reheated to a predetermined rolling temperature before being rolled. In this case, some γ phase is always generated during tJIHN. The γ phase preferentially forms near the grain boundaries of α grains, where recrystallization progresses easily. However, even in this case, if the original grain size is coarse like slab cast grains, recrystallization is difficult to complete, and unrecrystallized high areas tend to remain in the center of the former, and the γ phase fraction The amount 11 depends not only on the temperature but also on C, 5tffi, strain 2, and cooling rate (holding time). Therefore, it is known that even a slight change in the treatment strip 1'1 can greatly change the effect. This was a major reason why the feature refinement effect by low-temperature hot rolling could not be stably obtained in the past.
I is determined. On the other hand, there is also the drawback that increasing Cl (increasing i11 large carbide) makes it difficult to form a rolled set ring with strong accumulation by 1Nt in the subsequent process.

However, the recrystallization behavior of a single α phase at high temperatures that the present inventors discovered is different from conventional recrystallization in the presence of a γ phase at low temperatures, and the γ phase is separated by recrystallization nuclei 41-4 noids. figure,!
Since the grain boundaries become nucleation sites in i, and the recrystallized grain size tends to become relatively large, it is difficult for unrecrystallized parts to remain,
It is easy to obtain uniform recrystallized grains.

As described above, under the recrystallization conditions of '14, even if the high-temperature heated slab is rolled as it is, coarse grains can be converted to 'IIIll'. In addition, there is no need to lower the temperature during hot rolling by waiting for rolling, etc., so the advantages of a hot strip mill can be utilized to the fullest.

The present invention has been constructed based on the above basic knowledge.

Next, the constituent elements of the present invention will be explained in more detail.

In the present invention, a silicon steel slab having a composition described later is charged into a heating furnace and heated, but the heating temperature and heating time vary depending on the type and m of the inhibitor, and the time required to achieve complete solid solution of the inhibitor is 41 However, if the furnace remains in the furnace for too long, a large amount of scale will be generated, so the heating time is sufficient to avoid adversely affecting the surface properties. The slab, which is thus heated to a high temperature and in which the inhibitor is completely dissolved, is subjected to rough rolling.

Rough rolling is usually performed in 5 to 6 passes, but the results of this experiment revealed that the first pass, subsequent holding and final pass are particularly important.

During holding after the first pass and just before the second pass, it is important to obtain completely recrystallized braided fibers. The experimental results at the factory are shown in FIG. 2. In the one-ill rolling method, the time between passes is determined by the row of rolling mills, and the time between the till stand and the second stand is about 20 seconds. Therefore, it is very difficult to obtain a recrystallization rate of 95% or more immediately after rolling, but it is possible to easily obtain a recrystallization rate of 95% or more by holding the rolling for 30 seconds or more, preferably 60 seconds or more. It turns out that it becomes possible to do this. Figure 3 shows the progress of recrystallization, and the first pass must be rolled at 1280'C or higher, at which temperature Tl('
The rolling reduction ratio R1 (%) required for recrystallization in C) needs to satisfy the conditions shown in the following formula, based on the results shown in FIG.

60≧R, (%)≧−o, s T+ 4−s7° Furthermore, in order to ensure time for recrystallization to proceed, it is necessary to hold for 30 seconds or more, preferably 60 seconds or more.

It was also found that if recrystallization is completely completed in the first pass, the occurrence of baldness due to hot cracking on the surface layer is considerably suppressed. In addition, due to the remaining unrecrystallized parts, 2
It was also found that it is effective in suppressing the defective region of subsequent recrystallization.

Note: In rolling, it is more important to avoid leaving unrecrystallized areas than to refine the recrystallized structure. Therefore, it is necessary to perform recrystallization in the α single phase region also in the final pass of rough rolling. This is because in (α+r) two-phase region rolling, the γ grains are harder, so the strain concentrates near one grain, and in MJr1, the vicinity of the γ grains preferentially recrystallizes, but the T grains mainly This is because tu ta inevitably becomes non-uniform since it appears at α grain boundaries.

Immediately before the fi1m Hiiragi bath, the crystal grains are recrystallized and refined due to the effect of rolling, so the recrystallization limit is shifted slightly downward from Fig. 2 based on the experimental results at the factory, and becomes as shown in Fig. 4. . In Figure 4, the region where the γ phase appears is indicated by diagonal lines, and as the rolling reduction rate increases, the °ζTζ superposition temperature increases (this is due to strain-induced transformation. To apply pressure in α single phase without appearing, 1
A rolling temperature T (°C) of 200°C or higher is required. In addition, the rolling reduction R1 (%) required to stably obtain a recrystallization rate of 75% or more immediately after rolling must satisfy the conditions shown in the formula below, based on the results shown in Figure 4. It is.

70≧1?2(%)≧-0, I Tz1165 I1
The upper limit of the rolling reduction in one rolling is as follows:
It was necessary to provide this in order to ensure a sufficient rolling reduction ratio, and the first pass was 60% and the final pass was 70%.

The hot finish rolling conditions after this are not much different from usual, and the finish rolling nQ is uniform &I! If m (no unrecrystallized grains) is obtained, (αtr)2 is obtained in the first stage of finish rolling.
Recrystallization occurs in the phase region, and Illllll refinement can be easily achieved. The finish-rolled hot-rolled steel strip is annealed and pickled if necessary, and cold-rolled once or twice with intermediate annealing to achieve a 0.15
~0.50mm thicker than the final plate thickness.

Next, the reason for limiting the ingredients will be explained below.

The reason why the range of C was limited to 0.010-0.080% by weight was intended to improve the hot rolling & (1 weave) by passing through the (α and γ) regions during hot rolling. , which is limited to its appropriate range.

Si is effective in increasing the resistivity of the steel sheet and reducing the iron oxide, but if it exceeds 4.0%, the cold rollability deteriorates.
If it is less than % by weight, the effect of reducing iron tn is weakened, and in the final high-temperature finish annealing performed for secondary recrystallization and purification, randomization of crystal orientation occurs due to α-γ transformation, making it impossible to obtain sufficient properties.

Mnl needs to be 0.03% as the lower limit that does not cause cracking due to hot embrittlement, and the upper limit is MnS and MnSe.
In order not to increase the dissociation temperature of the solid solution, and to prevent the inhibitor from becoming coarse in the time-controlled process from slab extraction to rolling. Limited to lOm stirring %.

S, Se, and AI are microscopically present in the steel in the form of MnS, MnSe, and AIN, and act as inhibitors. Upper limit of 0.
As in the case of Mn, 1% by weight was determined from the viewpoints of suppressing the dissociation and solid solution of the inhibitor and preventing coarsening during hot rolling. Note that when Al is used as an inhibitor component,
It goes without saying that Nl is needed to balance this, and the preferred amount of N is 0.001 to 0.065 mff1%
It is.

- In addition to the above elements, sb and Sn can be used as inhibitors.

Grain boundary segregation elements such as As, r'b, Cu, Mo, and B are known, and it is also possible to use these in combination.

Note that in order to efficiently and effectively achieve the present invention in a factory, it is effective to use 3 to 4 rough rolling mills instead of the usual 5 to 6 rough rolling mills for each stand. desirable. Particularly suitable are rolling methods such as omitting the rolling on the second stand after one-pass rolling on the first stand and omitting rolling on the fourth stand 1' after two-pass rolling on the third stand.

<Example> Example 1 C: 0.04+1% by weight, Si: 3.30% by weight, Mn: 0.054% by weight, Se: 0
．． A continuously cast slab containing 0.022ffiffi% and sb: 0.024 double layer%, with the remainder substantially consisting of Fe, was charged into a heating furnace, kept soaked in a N2 atmosphere, and rough rolled immediately after the soaking was completed. Served. Note that these conditions are shown in Table 1. After the rough rolling was completed, the sheet bar was made into a sheet bar with a thickness of 30+W, and thereafter, it was made into a hot-rolled g slope with a thickness of 2.0ffi using a finishing tandem mill. This hot rolled steel sheet was pickled, first cold rolled, intermediate VF, tempered, and then second cold rolled to a product thickness of 0.23 m. After this, decarburization annealing was performed and NGO was applied, followed by secondary recrystallization and a final finish annealing process for purification to obtain a final product.

The characteristics of the product are also listed in Table 1. The surface properties and the ratio of defective secondary recrystallization areas in the width direction are also shown. Data on longitudinal properties are shown in FIG.

As is clear from Table 1 and Figure 5, raw rolling is carried out under high temperature input pressure F.
It can be seen that the specimens which were maintained in the same manner as above are superior in terms of magnetic properties, surface texture, uniform progression of secondary recrystallization in the width direction, and uniformity of magnetic properties in the longitudinal direction.

Example 2 C: 0.035% by weight, Si: 2.98mm%
, Mn: [1,072% weight loss, s: o
A continuous cast slab containing 0.5% by weight and the remainder substantially consisting of FO was charged into a heating furnace, kept soaked in an atmosphere of 1 yen, and immediately subjected to rough rolling after soaking, but the conditions were not met. are shown in Table 2. After rough rolling, it becomes a sheet bar of 35nml￥,
Thereafter, a hot rolled steel plate with a thickness of 2.4 mm was produced using a finishing tandem mill. This hot rolled steel sheet was pickled, first cold rolled, intermediate annealed, and then second cold rolled to a product thickness of 0.35 mm. After this, decarburization annealing was performed, MgO was applied and dried, and a final finish annealing process was performed for the purpose of secondary recrystallization and purification to obtain a final product.

The characteristics of the product are also listed in Table 2. In addition, as is clear from Table 2, which also shows the surface texture and the ratio of secondary recrystallization defective areas in the width direction, those that are rough rolled at high temperatures and under large pressure have uniform magnetic properties, surface texture, and uniformity in the width direction. It can be seen that the progress of secondary recrystallization is excellent.

Example 3 C: 0.050% by weight, Si + 3.10% by weight
, Mn: 0.078 ffi%, S: 0.
024 heavy ffi%, Al O,032! [t1%.

A continuously cast slab containing 0.06% by weight of N j O, and the remainder consisting essentially of r'e was charged into a heating furnace and kept soaked in an atmosphere of h. After soaking, the slab was immediately rough rolled. The conditions are shown in Table 3. After the in-rolling was completed, it was made into a 30-thick sheet bar, and after that, it was made into a 2.3-thick hot rolled steel plate using a finishing Kundem mill. After pickling this hot rolled steel plate 1
The product was then cold-rolled, intermediately annealed, and then subjected to secondary cold-rolling to a product thickness of 0.23mm. After decarburization annealing and coating with MgO, a final annealing process for the purpose of secondary recrystallization and purification was performed to obtain a final product.

The characteristics of the product are also listed in Table 3. In addition, as is clear from Table 3, which also shows data on surface texture and longitudinal properties, those that are rough rolled at high temperatures and large reductions have uniform secondary regeneration in magnetic properties, surface texture, and width direction. It can be seen that it is excellent in terms of the progress of crystallization.

<Effects of the Invention> The method of the present invention makes it possible to take full advantage of the advantages of a hot strip mill and to advantageously produce oriented silicon*i with excellent magnetic properties and surface properties in a stable manner.

[Brief explanation of drawings]

Figure 1 shows the recrystallization limit in α single phase (recrystallization rate 95% or more)
Figure 2 is a graph showing the recrystallization limit in the α single phase after the first pass of rough rolling, Figure 3 is a graph showing the progress of the recrystallization rate over time after rolling, Figure 4 is a graph showing the experimental results of The figure is a graph showing the recrystallization limit in the α single phase after multiple rough rolling passes.
FIG. 5 is a graph showing changes in properties in the longitudinal direction between the present invention and a comparative example, and FIG. 6 is a graph showing the recrystallization limit in the (α+γ) two-phase region.

Claims (1)

[Claims] In weight%, C: 0.01~0.08%, Si: 2.5~
After heating a silicon steel slab containing Mn: 4.0%, Mn: 0.03 to 0.10%, and further containing 0.01 to 0.06% of one or more of S, Se, and Al, subsequent to rough rolling. In a method for producing a grain-oriented silicon steel sheet, which comprises a series of steps of hot finish rolling, then cold rolling once or twice with intermediate annealing to achieve the final thickness, decarburization annealing, and final finish annealing. The rolling temperature T_1 (℃) of the first pass of rough rolling is 128
The temperature is 0°C or higher, and the rolling reduction rate R_1 (%) is 60≧R_1
(%)≧-0.5T_1+670, then hold for 30 seconds or more before the next pass, further set the rolling temperature T_2 (℃) in the final pass of rough rolling to 1200℃ or less, and set the rolling reduction R_2 (%) to 70≧ R_2 (%) ≧ -0.1T_2
+165. A method for producing a grain-oriented silicon steel sheet with excellent magnetic properties and surface properties.