JP3849146B2 - Method for producing unidirectional silicon steel sheet - Google Patents

Description

【００３４】
同表から明らかなように、後段２パスのスラブ表面温度が1300℃以下で、かつパス間時間が30ｓ以内であれば、圧下スケジュールの如何にかかわらず良好な磁気特性が得られている。
【００３５】
【発明の効果】
かくしてこの発明に従い、熱間粗圧延に際し、粗圧延最終スタンドとその前段スタンドにおけるスラブ表面温度を1300℃以下にすると共に、その間のパス間時間を30ｓ以内に規制することにより、高い再結晶率のシートバー組織ひいては優れた磁気特性の一方向性けい素鋼板を得ることができる。
【図面の簡単な説明】
【図１】含けい素鋼スラブの熱間粗圧延３パス時におけるスラブ中心温度およびスラブ表層温度を示した図である。
【図２】Ｃ濃度：0.06wt％のけい素鋼の状態図である。
【図３】熱間２パス粗圧延におけるパス間時間とシートバー再結晶率との関係を示したグラフである。
【図４】熱間２パス粗圧延における従来組織（図ａ）と発明組織（図ｂ）を示す模式図である。
【図５】熱間粗圧延最終２パスのパス間時間とシートバーの再結晶率ならびに製品板の磁束密度および鉄損との関係を示したグラフである。
【図６】熱間３パス粗圧延における最終２パスのパス間時間とシートバーの再結晶率ならびに製品板の磁束密度および鉄損との関係を示したグラフである。[0001]
[Industrial application fields]
The present invention relates to a method for producing a unidirectional silicon steel sheet, and in particular, by controlling the slab surface temperature and the time between passes in the latter stage of rough rolling to improve the magnetic properties, the rolling efficiency This is to be realized along with the improvement of the above.
[0002]
[Prior art]
Unidirectional silicon steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are basically required to have excellent magnetic properties such as magnetic flux density and iron loss.
Particularly important in the production of such a unidirectional silicon steel sheet is to preferentially recrystallize the primary recrystallized grains to crystal grains of {110} <001> orientation in a so-called finish annealing process. .
[0003]
In order to effectively promote such secondary recrystallization, it is important to first disperse a dispersed phase called an inhibitor that suppresses normal growth of primary recrystallized grains in steel in a uniform and appropriate size. is there.
As such an inhibitor, since a substance having extremely low solubility in steel is used, a method in which the inhibitor component is completely dissolved by heating the slab to a high temperature before hot rolling has been conventionally employed. The precipitation state is controlled between the hot rolling process and the secondary recrystallization process.
[0004]
Inhibitor precipitation in the hot rolling process greatly affects the precipitation in the subsequent process, and thus appropriate control is required to deposit uniformly and finely.
As such a technique, for example, Japanese Patent Publication No. 50-32059 discloses a method of holding a continuous cast slab in a temperature range of 1200 ° C. or lower and 950 ° C. or higher for 30 to 200 seconds in a continuous hot rolling process. Such slow cooling is performed before finish rolling. Japanese Examined Patent Publication No. 53-39852 also proposes a method of holding a material to be rolled in a continuous hot rolling process plate at a temperature range of 1200 ° C. or lower and 850 ° C. or higher for 60 to 360 seconds. All of these techniques aim to obtain a densely dispersed precipitated phase in a hot-rolled sheet by performing a continuous hot-rolling process by a slow cooling method.
[0005]
As a further developed technique, in Japanese Patent Publication No. 56-18656, when a steel ingot or slab is heated to a temperature of 1260 ° C. or higher, and hot rolled, it is in a stage from partial rolling to rough rolling, to finish rolling, While the center temperature of the slab or seat bar is 1150 ° C or higher, the surface temperature of the slab or seat bar is lowered to the range of 900 to 1100 ° C and maintained in that temperature range for 10 to 200 s. A method is disclosed in which the surface temperature is recovered to 1100 ° C. or higher by reheating and maintained at that temperature for 2 to 300 seconds.
In this method, the size distribution of the inhibitor is controlled so that the size distribution of the steel plate is large at the surface layer of the steel plate and becomes fine at the center portion. In addition, there is a problem in the process production that the temperature is too low at the end in the width direction and the characteristic is liable to occur.
In addition, such a long-time holding in a hot rolling line has a disadvantage in that the productivity is significantly reduced.
[0006]
After that, in Japanese Patent Application Laid-Open No. 59-208021, the final pass reduction ratio in rough rolling is set to 30% or more, the rough rolling end temperature is set in the range of 950 to 1150 ° C., and the finish rolling is started from the start of rough rolling. The method to control the required time to 4 minutes or less is presented. This method is intended to suppress the coarsening of the inhibitor at the rear end of the large slab by the above-described treatment.
[0007]
In Japanese Examined Patent Publication No. 58-13606, before hot rolling, the silicon steel material is heated to a temperature of 1230 ° C. or higher to completely dissolve S and Se contained in the steel, In the case of hot rolling, a method of cooling at a rate of 3 ° C./s or higher while continuously rolling at a steel sheet temperature of 950 to 1200 ° C. at a reduction rate of 10% or higher is proposed.
In this method, MnS and MnSe have the fastest precipitation rate when the steel plate temperature is in the temperature range of 950 to 1200 ° C during the cooling process, and when this is cooled while hot deformation is applied, a more uniform and fine inhibitor dispersed phase is obtained. It is based on the knowledge that can be obtained, and it is stated that it is the finish rolling stage that is continuously rolled by a tandem rolling mill or the like that easily takes such conditions.
[0008]
In any of the methods described above, the inhibitor precipitation is controlled by the rolling temperature, the cooling rate, or the like.
However, for the precipitation of the inhibitor, the influence of the matrix (structure) that becomes the precipitation site cannot be ignored, and in particular, the presence or absence of strain in the tissue immediately before the inhibitor is precipitated is a very important factor. These studies revealed this.
[0009]
However, there have been few studies on the microstructure control of rough rolling at high temperatures, and only Japanese Patent Application Laid-Open No. 3-10020 particularly relates to rolling time. In the technology disclosed in this publication, the rolling temperature of the first pass of rough rolling is set to 1280 ° C or higher, the rolling reduction is regulated within a certain range from the rolling temperature of the first pass, and then held for 30 seconds or more until the next pass. Furthermore, the rolling temperature in the final pass of the rough rolling is set to 1200 ° C. or more, and the rolling reduction is regulated within a certain range from the rolling temperature of the final pass, and in particular, a complete recrystallized structure is obtained in the first pass. The importance of.
This technology describes the recrystallization mechanism when rolling in a temperature range of 1300 ° C or higher with 3% Si steel, that is, when rolling in the α single phase range. In this case, the recrystallized grain size is relatively large. However, it is based on the idea that in rough rolling, it is more important to leave no unrecrystallized part than to refine the recrystallized structure. As a result, it is considered possible to control the structure in a considerably high temperature range.
[0010]
However, in the actual rough rolling process, all passes are not necessarily rolled at a temperature of 1300 ° C. or higher. For example, as shown in FIG. 1, the slab temperature is increased to a range of 1150 to 1300 ° C. May decrease. In particular, the temperature difference between the slab surface layer portion and the center portion is remarkable, and the temperature is considerably lowered in the surface layer portion.
Therefore, in order to optimize the rough rolling structure, it is considered important to control the structure not only in the temperature range of 1300 ° C. or higher but also in the rolling temperature range of 1300 ° C. or lower.
[0011]
[Problems to be solved by the invention]
As described above, to date, it is almost impossible to perform structure control by time regulation in high-temperature rough rolling.
In this hot rough rolling, the sheet bar is controlled by controlling the slab surface temperature in the final rough rolling stand and the rolling stand one pass before the hot rolling, and the time required between both stands, that is, the time between passes. It is an object of the present invention to propose a novel method for producing a unidirectional silicon steel sheet capable of effectively improving the structure and thereby improving both the magnetic flux density and the iron loss.
[0012]
[Means for Solving the Problems]
The elucidation process of the present invention will be described below.
The inventors first studied to obtain an optimum structure (recrystallized structure) in order to achieve the above object.
For example, in the case of C: 0.06 wt% silicon steel, according to the phase diagram shown in FIG. 2, when the Si content is 2.0 to 4.0 wt%, an almost (α + γ) two-phase structure is obtained at 1300 ° C. or lower. Yes.
In fact, when rolling a slab heated to a high temperature of 1300 ° C or higher, recrystallization unique to the α phase occurs at 1300 ° C or higher, but the γ phase precipitates at 1300 ° C or lower, which occurred in the α phase. Experiments confirmed that the growth of recrystallized grains was stopped.
In other words, in the temperature range where the γ phase precipitates, even if isothermal holding is performed once the α phase recrystallization has started, an unrecrystallized structure remains and a complete recrystallized structure cannot be obtained. I can say that.
[0013]
Therefore, it is important to eliminate unrecrystallized grains by effectively utilizing the recrystallization behavior in the (α + γ) two-phase region.
This is because, if unrecrystallized grains remain after rough rolling, preferential precipitation of the inhibitor on the sub-grain boundary is likely to occur during finish rolling, and the inhibitor becomes unevenly coarsened, resulting in magnetic failure. It is because it becomes easy.
[0014]
Therefore, paying attention to this (α + γ) two-phase region, the recrystallization behavior in this region was investigated in detail. The recrystallization in this region is different from the recrystallization behavior that occurs in the α single phase region, and the recrystallized grains do not grow so significantly even if kept isothermal after applying strain. That is, it can be said that it is close to dynamic recrystallization in which recrystallization occurs during deformation.
[0015]
Now, the inventors conducted many research experiments to obtain a more optimal structure by utilizing the recrystallization behavior.
The experiment was conducted on a 1300 mm thick silicon steel slab containing C: 0.04 wt%, Si: 3.25 wt%, Mn: 0.08 wt% and Se: 0.020 wt%, the balance being substantially composed of Fe. After heating to ° C., it was rolled to 70 mm by the first pass, and then the second pass rolling was performed with various changes in the time between passes in the range of 10 to 50 s to obtain a thickness of 40 mm.
The result of examining the recrystallization rate at this time is shown in FIG.
As shown in the figure, it was found that when the time between passes exceeds 30 s, the recrystallization rate rapidly decreases.
[0016]
4 (a) and 4 (b) schematically show the rolling structure at that time. In the conventional method (a) (inter-pass time: 40s), coarse unrecrystallized grains remained over the entire width. On the other hand, the non-recrystallized grains were greatly reduced in the invention method (b) (time between passes: 20 s).
The reason for this has not yet been clearly clarified, but the inventors consider the following.
Considering rolling in the second pass, the recrystallization nuclei are generated from the grain boundaries and around the γ phase. Therefore, the smaller the grain size before rolling, the more the γ phase is precipitated. Is considered to progress easily. In the case of this experiment, if the time between passes is long, it leads to the growth of recrystallized grains (larger grain size before rolling), but also has the conflicting effect that the precipitation of γ phase is promoted. The opposite is true if the time is short.
Therefore, the balance between the two affected by the inter-pass time is extremely important. However, if the inter-pass time exceeds 30 s, the balance is lost for some reason, and the result shown in FIG. 3 is obtained. It is considered a thing.
[0017]
Moreover, as shown in FIG. 1, the slab temperature in the latter stage of rough rolling is generally estimated to be 1150 ° C. or higher except for the edge portion. Here, since there is temperature unevenness in the slab thickness direction in rough rolling, in the same pass, α-phase recrystallization occurs in the center of thickness, and (α + γ) 2 phase recrystallization occurs in the slab surface layer. It is considered that two different forms of recrystallization occur in the middle region.
Therefore, it is preferable to increase the time between passes since the α phase is relatively large in the slab structure before the rough rolling, and conversely, it is preferable to shorten the time between passes because the γ phase precipitates in the subsequent step. It can be said that it is extremely difficult to obtain a complete recrystallized structure.
When the number of passes at 1300 ° C. or less is 1 pass, it is difficult to obtain an optimum structure because unrecrystallized grains remain considerably.
[0018]
Based on the above experimental results, C: 0.07 wt%, Si: 3.24 wt%, Mn: 0.079 wt%, and Se: 0.015 wt%, the balance being 215 mm thick silicon substantially composed of Fe After heating the steel slab to 1350 ° C, the pre-rolling slab surface temperature at the final rolling stand and the rolling stand one pass before is 1250 ° C, and the time between passes is 15 to 45 s. After controlling the matrix (structure) to be processed, after that it is hot-rolled to a thickness of 2.7 mm as usual, and then cold-rolled twice with intermediate annealing and finished to a final thickness of 0.27 mm. After decarburization annealing was performed, an annealing separator was applied to the steel sheet surface, and then final annealing was performed to obtain a manufactured plate. The results of examining the magnetic properties of the product plate thus obtained and the recrystallization rate of the sheet bar are shown in FIG. Each investigation was conducted for three positions in the width direction of the steel sheet (50 mm position from edge, 1/4 width position, center).
As is clear from the figure, when the time between passes was within 30 s, the recrystallization rate of the sheet bar was high and good magnetic properties were obtained. In addition, it has been found that numerical fluctuations in the width direction are small and unevenness in the width direction is also improved.
[0019]
As described above, the present invention achieves an improvement in the sheet bar structure by controlling the rolling temperature and the time between passes in the final two stands of the hot rough rolling, thereby obtaining good magnetic properties.
[0020]
That is, in the present invention, a slab containing C: 0.01 to 0.10 wt % and Si : 2.0 to 4.0 wt % is hot-rolled and then hot rolled into a hot-rolled sheet, and then sandwiched once or intermediately. A method for producing a unidirectional silicon steel sheet comprising a series of processes in which a cold rolling is performed to finish to the final sheet thickness, followed by decarburization annealing, followed by applying an annealing separator to the steel sheet surface and then performing final annealing. In
When performing the hot rough rolling after heating the slab to a temperature range of 900-1450 ° C,
By setting the surface temperature of the slab before rolling in the final rough rolling stand and its preceding stand to 1300 ° C or less and the time between passes between the stands within 30 s, the recrystallization rate of the sheet bar should be 60% or more. you wherein a manufacturing method of an oriented silicon steel sheet.
[0021]
[Action]
The component composition range of the steel sheet of the present invention is not particularly limited except for C and Si , and any conventionally known silicon steel material can be used. It is as follows.
C: 0.01 to 0.10 wt%
If C is less than 0.01 wt%, the γ phase is not generated, so that it is not possible to improve the structure by hot rolling. On the other hand, if it exceeds 0.10 wt%, the limit capacity in the subsequent decarburization process is exceeded. Limited to a range of ˜0.10 wt%.
[0022]
Si: 2.0 to 4.0 wt%
Si increases the specific resistance of steel sheet and contributes effectively to the reduction of iron loss. However, if the content exceeds 4.0 wt%, the cold rolling property is impaired. On the other hand, if the content is less than 2.0 wt%, the specific resistance decreases. not only in the final high-temperature annealing which is performed for secondary recrystallization, pure by alpha-gamma transformation occurs randomization crystal orientation, because no sufficient iron loss improvement effect is obtained, Si is 2.0 Limited to 4.0 wt% range .
[0023]
Mn: 0.02-0.12wt%
Mn is preferably contained in an amount of at least 0.02 wt% to prevent cracking due to hot brittleness, but if it is too much, the magnetic properties are deteriorated, so the upper limit is preferably about 0.12 wt%.
[0024]
S and / or Se: 0.005 to 0.06 wt%
Both S and Se are effective components as inhibitors for suppressing secondary recrystallization of grain-oriented silicon steel sheets. The content is preferably 0.005 wt% or more from the viewpoint of the suppressive power, but if it exceeds 0.06 wt%, the effect is rather impaired, so it is preferable to be about 0.005 to 0.006 wt%.
[0025]
Al: 0.005 to 0.10 wt%, N: 0.004 to 0.015 wt%
Al and N act as an inhibitor in the form of AlN, but if the content is less than the above lower limit, the inhibitor inhibitory power is insufficient, while if the upper limit is exceeded, crystal grains become coarse and the inhibitory power is still impaired. Therefore, it is preferable to contain each in the above range.
[0026]
As the inhibitor, in addition to the above elements, grain boundary segregation elements such as Sb, Sn, Cu, Mo, Bi, As, Pb, B, and P can be used in combination.
[0027]
Next, the manufacturing conditions of the present invention will be described.
A silicon steel slab having a suitable component composition as described above is heated by a known method. At that time, if the heating temperature exceeds 1450 ° C, the slab begins to melt, which is very dangerous. On the other hand, if the heating temperature is less than 900 ° C, the hot strength of the steel increases and a lot of energy is required for deformation. The heating temperature was limited to the range of 900-1450 ° C.
[0028]
After the slab heating, hot rolling is performed. In the present invention, the rough rolling process in the hot rolling is particularly important.
That is, in this hot rough rolling, it is important to set the slab surface temperature at the final stand and the rolling stand one pass before it to 1300 ° C. or lower and limit the time between passes between the two stands within 30 s.
[0029]
When the slab surface temperature exceeds 1300 ° C, static recrystallization seen in the α single phase occurs preferentially, so a longer interpass time is more effective in obtaining a recrystallized structure. No regulation is required.
In this respect, when the slab temperature is 1300 ° C. or lower, the dynamic recrystallization that occurs in the (α + γ) phase becomes dominant, and thus the time between passes must be regulated.
Here, a sheet bar structure having a high recrystallization rate can be obtained when the time between passes is within 30 s, whereas the effect of improving the structure is reduced when the time exceeds 30 s, so the time between passes is set within 30 s. And within this time, the recrystallization rate of the sheet bar, which is indispensable for improving the magnetic properties, can be effectively achieved.
The lower limit of the slab surface temperature is not particularly limited, but it is desirable to set the temperature to a temperature that does not hinder finish rolling (for example, 1100 ° C. or higher).
Further, the cold rolling process, the decarburization annealing process, the finish rolling process, and the like, including the subsequent finish rolling, may be performed according to ordinary methods.
[0030]
【Example】
Example 1
C: 0.06 wt%, Si: 3.25 wt%, Mn: 0.071 wt%, Se: 0.019 wt%, Al: 0.028 wt% and N: 0.0075 wt%, with the balance being substantially made of Fe Prior to hot rolling, 9 thick continuous cast slabs were heated to 1200 ° C in a gas-fired heating furnace, charged into an induction heating furnace, heated to 1350 ° C, and held at that temperature for 20 minutes. .
Next, during the three-pass hot rough rolling, the first pass was rolled under the conditions of a slab surface temperature of 1180 ° C. and a reduction ratio of 36% to a thickness of 160 mm. In the subsequent two passes, the slab surface temperature: 1300 ° C or lower (second pass: 1170 ° C, the third pass varies depending on the time between passes), the reduction schedule is the same, and the time between passes is 10 Rolling was carried out with various changes in the range of ˜50 s to obtain a 40 mm thick sheet bar. At this time, the recrystallization rate in the sheet bar was measured.
Then, after finishing rolling to make a 2.2 mm thick hot rolled coil, the thickness was 0.60 mm by the first cold rolling, and then 0.23 mm by the second cold rolling at 1100 ° C for 1 minute intermediate annealing. Finished with a product thickness of. Then, wet hydrogen 840 ° C. C. in, then subjected to decarburization annealing for 3 minutes, after applying the MgO, pure annealing of in secondary recrystallization annealing and H ₂ of 850 ° C. in in N ₂ Finished annealing consisting of
[0031]
The results of examining the magnetic properties of the product plate thus obtained are shown in FIG. 6 together with the recrystallization rate of the sheet bar.
As is apparent from the figure, when the time between passes was within 30 s, a recrystallization rate of the sheet bar structure was high, and a product with good magnetic flux density and iron loss could be obtained.
[0032]
Example 2
C: 0.08 wt%, Si: 3.30 wt%, Mn: 0.078 wt%, Se: 0.020 wt%, Al: 0.025 wt% and N: 0.0080 wt%, the balance being substantially composed of Fe 215 mm Prior to hot rolling, 12 thick continuous cast slabs were heated to 1200 ° C in a gas-fired heating furnace, then charged to an induction heating furnace and heated to 1400 ° C and held at that temperature for 10 minutes. . Next, during the hot rough rolling of 4 passes, the first two passes were rolled to 70-90mm thickness at slab surface temperatures of 1230 ° C, 1220 ° C and the time between passes: 40s, respectively, and the second pass of slab surface temperature was 1300. When the temperature was not higher than ° C., the time between passes and the rolling reduction were variously changed and rolled to form 35 mm thick sheet bars. At this time, the recrystallization rate in the sheet bar was measured.
Then, finish rolling to make a hot rolled coil of 2.2mm thickness, 0.60mm thickness by primary cold rolling, intermediate annealing at 1100 ℃ for 1 minute, then 0.23mm product thickness by secondary cold rolling Finished. Then 840 ° C. at humidity hydrogen, then subjected to decarburization annealing for 3 minutes, after applying the MgO, pure annealing of in secondary recrystallization annealing and H ₂ of 850 ° C. in in N ₂ Finished annealing.
The results of examining the magnetic properties of the product plate thus obtained are shown in Table 1 together with the recrystallization rate of the sheet bar.
[0033]
[Table 1]

[0034]
As can be seen from the table, if the slab surface temperature of the subsequent two passes is 1300 ° C. or lower and the time between passes is within 30 s, good magnetic properties are obtained regardless of the rolling schedule.
[0035]
【The invention's effect】
Thus, according to the present invention, in the hot rough rolling, the slab surface temperature in the final rough rolling stand and the preceding stage stand is set to 1300 ° C. or less, and the time between passes is regulated within 30 s, so that a high recrystallization rate is achieved. A unidirectional silicon steel sheet having a sheet bar structure and thus excellent magnetic properties can be obtained.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a slab center temperature and a slab surface temperature during three passes of hot rough rolling of a silicon-containing steel slab.
FIG. 2 is a phase diagram of silicon steel having a C concentration of 0.06 wt%.
FIG. 3 is a graph showing the relationship between the time between passes and the sheet bar recrystallization rate in hot two-pass rough rolling.
FIG. 4 is a schematic diagram showing a conventional structure (FIG. A) and an inventive structure (FIG. B) in hot two-pass rough rolling.
FIG. 5 is a graph showing the relationship between the time between the last two passes of hot rough rolling, the recrystallization rate of the sheet bar, the magnetic flux density of the product plate, and the iron loss.
FIG. 6 is a graph showing the relationship between the time between the last two passes in hot three-pass rough rolling, the recrystallization rate of the sheet bar, the magnetic flux density of the product plate, and the iron loss.

Claims (1)

C: A slab containing 0.01 to 0.10 wt % and Si : 2.0 to 4.0 wt % is hot-rolled and then hot rolled into a hot-rolled sheet, and then cold-rolled twice or once with intermediate annealing. In the manufacturing method of the unidirectional silicon steel sheet consisting of a series of steps of applying the finishing separator after applying the annealing separation agent to the steel sheet surface after finishing to the final plate thickness and then decarburizing annealing,
When performing the hot rough rolling after heating the slab to a temperature range of 900-1450 ° C,
By setting the surface temperature of the slab before rolling in the final rough rolling stand and its preceding stand to 1300 ° C or less and the time between passes between the stands within 30 s, the recrystallization rate of the sheet bar should be 60% or more. manufacturing method of an oriented silicon steel sheet shall be the features.

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