JPH0823044B2 - Manufacturing method of non-oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a non-oriented electrical steel sheet having excellent magnetic properties, particularly high magnetic flux density.

[Prior Art and Problems to be Solved] Heretofore, various manufacturing techniques have been disclosed in order to manufacture a non-oriented electrical steel sheet having good magnetic properties. Among the magnetic properties, the magnetic flux density is closely related to the texture of the steel sheet, and it is necessary to integrate the axis of easy magnetization <100 <axis on the surface of the steel sheet as much as possible. Therefore, the technology for improving the hot-rolled sheet structure by hot-rolled sheet annealing, the technology for controlling the recrystallization texture at the time of subsequent annealing by optimizing the cold pressure ratio, the cold pressure, the annealing twice or more There is known a technique of selecting a texture which is preferable in terms of magnetic properties by carrying out.

On the other hand, among the techniques for improving the structure of the hot-rolled sheet by the hot-rolled sheet annealing method described above, in order to further promote grain growth in the annealing step by strain induction, the hot-rolled sheet is annealed by applying a mild rolling pressure. Technology (for example, Japanese Examined Patent Publication No. S45-22211, Japanese Patent Laid-Open No. S63-18682
No. 3) is disclosed. In this way, the present technology of adding light rolling to a hot-rolled sheet undergoes an extra rolling step as compared with other techniques, but is more effective as a method for promoting ferrite grain growth during hot-rolled sheet annealing. Therefore, the secondary recrystallization structure formed during annealing of the hot rolled sheet is extremely effective for improving the magnetic flux density.

However, in this technique, if the reduction ratio of light rolling is not properly controlled, the microstructure may become nonuniform depending on the coil position. Especially, the reduction ratio (≦ 3%) at the temper rolling level
However, secondary recrystallization occurs only in the surface layer, and a sufficient magnetic flux density cannot be obtained. Therefore, generally, a reduction of about 5 to 10% is indispensable, and such a reduction rate is difficult under a single pass reduction in a normal temper rolling mill, so that there is a margin for multiple rolling or rolling load. Rolling with a cold rolling mill becomes inevitable.

[Means for solving the problem]

In view of such a conventional technique, the present invention, prior to annealing the hot rolled sheet, by light reduction rolling under specific conditions using a rolling roll having longitudinal grooves in the roll circumferential direction, the following problems. It has been resolved.

(1) By applying a uniform reduction, macroscopic unevenness of the structure is avoided.

(2) By forming a uniform and periodic high strain region, nucleation / growth of secondary recrystallized grains during subsequent hot rolled sheet annealing is promoted.

(3) By introducing a uniform and periodic high strain region, the magnetic flux density is improved over the conventional method.

(4) Effective reduction is applied with a low rolling load by reducing the contact area between the roll and the material to be rolled.

By the way, the cold rolling technology for electrical steel sheets using groove rolls (grooved rolls) has traditionally been used to produce electrical steel sheets having a (100) plane cubic texture that combines the characteristics of grain-oriented electrical steel sheets and non-oriented electrical steel sheets. Has been considered as a possible means to achieve (for example, "Iron and Steel" 63 (1977) P.828,
P.1838, P.2335, "Iron and Steel" 70 (1984) P.2065). The technical idea is that the width of the steel sheet is set during cold rolling, so that {100} <011> to (100) <0vw> after recrystallization annealing.
To develop the organization of. As one based on such a technical idea, for example, Japanese Patent Publication No. 54-10922,
Japanese Patent Publication No. 53-30098 is proposed. However, in these conventional reports, decarburization annealing and purification annealing at a temperature of 1000 ° C. or higher are added after rolling, and the steel composition (C> 0.03%,
Even if judged from Si: ~ 3%, Mn: ~ 0.2%, S> 0.01%, Al: ~ 20 ppm), it is clearly aimed at controlling the secondary recrystallization texture. On the other hand, heretofore, no example has been found in which the application of flute roll rolling to the texture control of general non-oriented electrical steel sheets was examined.

Under such circumstances, the present invention aims to improve the magnetic flux density of the non-oriented electrical steel sheet, and after annealing the hot-rolled steel strip, the non-oriented electrical steel sheet to be subjected to cold rolling or warm rolling. In the manufacturing method of, in order to form a cyclic and uniform rolling deformation region in the steel strip prior to the hot-rolled sheet annealing step, the main point is to perform rolling using a roll having longitudinal grooves in the roll circumferential direction. Is.

That is, the feature of the present invention is that, in% by weight,
C: 0.01%, Si: 7.0% or less, Mn: 0.1 to 1.5%, P: 0.1% or less, S: less than 0.01%, Al: 0.001% or less or 0.05 to 1.0
%, N: 0.005% or less, a hot-rolled steel strip having a composition consisting of balance Fe and unavoidable impurities was descaled, and then a rolling roll having longitudinal grooves in the roll circumferential direction was used to satisfy the condition below. After cold rolling or warm rolling, the steel strip was annealed at a recrystallization temperature or higher, then cold-rolled or warm-rolled to a final plate thickness with a smooth roll, and then annealed. Especially.

0.05 ≦ [(t ₀ −t) / t ₀ ] ≦ 0.25 0.25 ≦ (Wt / l) ≦ 0.75 where t ₀ : original thickness of rolled material (mm) t: rolled material after rolling with longitudinal groove Thickness of the concave portion (mm) l: groove pitch (mm) of the vertical grooved roll Wt: width of the area of the plate thickness t within the groove pitch 1 (mm) Further, in the present invention as described above, the following conditions are satisfied. Rolling is preferably performed using a fluted roll having a satisfying shape.

0.15 ≤ [S / (ld)] ≤ 0.65 d ≥ 0.5 mm where S: groove cross-sectional area per groove pitch 1 in the section passing through the roll axis (mm ² ) d: groove depth (mm) [Operation] The constituent features of the present invention will be described in detail together with the reasons for limitation.

The present invention, prior to hot-rolled sheet annealing, cold rolling or warm rolling a steel strip with a roll having longitudinal grooves in the roll circumferential direction, the effect of such longitudinal grooved roll rolling is Original thickness of rolled material: t ₀ (mm), thickness of recessed portion of rolled material after rolling with vertical groove: t (mm), groove pitch of vertical rolling with vertical groove: l (mm), groove pitch l Width of the area of the plate thickness t in: Wt (mm) is optimized by optimizing the following parameters.

Parameters to be specified: (t ₀ −t) / t ₀ , Wt / l (t ₀ −t) / t ₀ specify the amount of strain introduced locally and uniformly in the steel strip at a constant period. So, if this strain amount is below the regulation range, it is not possible to promote sufficient nucleation and growth of secondary recrystallized grains during hot-rolled sheet annealing, while if it exceeds the regulation range, the thickness direction of the steel strip Nucleation and growth of recrystallized grains from the central part began to occur, and Go from the plate surface part
Nucleation and growth of recrystallized grains containing ss grains ({110} <001>) are hindered, and after passing through the subsequent cold rolling and annealing steps, a high magnetic flux density that the present invention aims at is obtained. Disappear.

FIG. 1 shows the effect on the magnetic flux density after the final annealing (t ₀ −t) / t ₀ when the rolling before hot-rolled sheet annealing was carried out with a fluted roll and when it was carried out with a normal smooth roll. This is a study of the effects of. In this test example, with respect to the steels with the composition numbers of steel Nos. 1, 3, and 4 in Table 1, a 220 mm t slab was obtained by continuous casting after vacuum degassing, and the slab was
After heating to 150 ℃ and soaking, rough rolling and finish rolling (finishing temperature 820
C.) to obtain a 2.0 mm t hot-rolled sheet, which was wound at 610.degree.
After pickling the steel strip, it was rolled with a smooth roll and a roll with flutes at various reduction ratios ([(t ₀ −t) / t ₀ ] × 100) within a range of 40% or less, and rolled at 650 to 900. The hot rolled sheet was annealed at a temperature of ° C.
Furthermore, after cold pressing these steel strips to 0.5 mm t,
Annealing was performed in the range of ° C, and the magnetic properties of the obtained steel sheet were measured. According to FIG. 1, the rolled material with longitudinal groove is (t ₀ −t)
In the region where / t ₀ is less than 0.05 and exceeds 0.25, the magnetic flux density is not significantly improved for the reasons described above.
In contrast, in the range of 0.05 ≦ [(t ₀ -t) / t _0] ≦ 0.25, the magnetic flux density dated flutes rolling material is greatly improved compared to the normal of the smooth rolling material.

For the above reasons, in the present invention, (t ₀ −t) / t ₀ in roll rolling with flutes is defined as 0.05 to 0.25.

Needless to say, when a strain of (t ₀ −t) / t ₀ is introduced into the entire surface of the steel sheet (when rolling with a smooth roll), the sheet is rolled in a plane strain state. In the present invention, by rolling with a vertical grooved roll, deformation in the plate width direction occurs due to the inflow of the material into the groove portion within one cycle of the groove, resulting in a deformed state different from the rolling state with a normal smooth roll. . Further, since the contact area between the roll and the material to be rolled is reduced, the rolling load for introducing a predetermined strain of (t ₀ −t) / t ₀ can be significantly reduced.

In the present invention, from the two points of the effect of reducing the rolling load and the effect of improving the texture by periodically deforming the material in the plate width direction, the groove pitch l (mm) of the longitudinal grooved roll and the groove pitch l The ratio Wt / l to the width Wt (mm) of the plate thickness t (t: the plate thickness (mm) of the concave portion of the material to be rolled after rolling with longitudinal groove) is 0.25 to
Specify in the range of 0.75.

FIG. 2 shows the effect of Wt / l on the flux density and the reduction rate of the rolling load (the reduction rate for smooth roll rolling) in the above-described longitudinal groove rolling. In this test example, the fluted roll rolling before annealing of the hot rolled sheet was carried out under the condition of different Wt / l, but other conditions were the same as those shown in FIG. According to FIG. 2, when Wt / l is in the range of 0.25 to 0.75, the magnetic flux density is greatly improved, and the rolling load can be greatly reduced as compared with the smooth roll rolling. On the other hand, when Wt / l deviates from the above range, the rolling conditions are close to those of smooth roll rolling, so that the magnetic flux density is not improved much and the rolling load is increased. From the above results, in the present invention, Wt / l is defined in the range of 0.25 to 0.75.

As described above, the effect of the present invention is exerted by controlling each parameter in the range of 0.25 ≦ (Wt / l) ≦ 0.75 and 0.05 ≦ [(t ₀ −t) / t ₀ ] ≦ 0.25. .

Further, in order to make the effect of the present invention more remarkable,
It is effective to limit the shape of the rolling roll.

FIG. 4 is defined by the sectional area S of the roll groove portion, the groove pitch 1 and the groove depth d. It shows the change in magnetic flux density after final annealing, evaluated using S / (ld) as a parameter. According to this, since the amount of strain locally introduced varies depending on the degree of inflow of the material into the groove portion, variations in the effect are recognized, but 0.05 ≦ [S / (ld)] ≦ 0.
It is clear that the magnetic flux density improves in the range of 65. Therefore, using a roll having a shape defined by 0.15 ≦ [S / (ld)] ≦ 0.65 is extremely effective in ensuring the effect of the present invention.

 Next, the reasons for limiting the steel components of the present invention will be described.

C: The present invention maximizes the advantages of performing steelmaking decarburization, and moreover, focuses on solving the problem of structure formation during cold rolling, so C is a final product. As a practically acceptable limit, the upper limit is limited to 0.01%. Regarding magnetic aging, it is preferable that C is small and the lower limit is not limited, but the lower limit is practically the limit of the steelmaking degassing technology.

Si: The present invention is a more effective technique for a high Si electrical steel sheet in which a decrease in magnetic flux density poses a problem. However, the technique of the present invention is practically effective regardless of the amount of Si, and there is no restriction on the lower limit of Si. Regarding the upper limit, it is a technology that can be applied to all in the practical range of Si content, but steel with Si content over 7.0% has no merit in terms of utilization technology in addition to the difficulty of the manufacturing method. In the invention, 7.0% is the upper limit of Si.

Al: Al is a ferrite stabilizing element like Si, and when added alone, it becomes an α single phase structure at about 2.0%. In the present invention, the upper limit is set to 1.0% as a limit added to a general non-oriented electrical steel sheet. Regarding the lower limit,
There are no restrictions in exerting the effects of the present invention. However, in a non-oriented electrical steel sheet, when a small amount of Al is added, finely precipitated AlN inhibits nucleation of secondary recrystallized grains during hot-rolled sheet annealing, growth, and grain growth during final annealing. However, this causes an increase in iron loss value. Cause such problems
The Al amount is in the range of more than 0.001% to less than 0.05%, and it is essential in the present invention that the Al amount in this range is not included. For the above reasons, Al is defined as 0.001% or less or 0.05 to 1.0%.

With respect to other elements, it is not necessary to specifically limit them in relation to the action and effect of the present invention, but in consideration of the original influence of the component elements on magnetic properties, Mn: 0.1 to 1.5%, P
Specified as ≦ 0.1%, S ≦ 0.01%, N ≦ 0.005%.

In the present invention, the groove shape of the roll used in the rolling with longitudinal groove is not particularly specified except S, l, d described above. As will be apparent from the examples described below, the action and effect thereof change depending on the cross-sectional shape of the groove, the interval, and the groove depth, but compared to the conventional flat rolled material, the effect of improving the magnetic flux density is recognized under any condition. Because it will be done.

Regarding the groove pitch l, when the value exceeds 5 mm, it is 2 with respect to the hot rolled plate thickness (1.6 to 2.5 mm) of general electromagnetic steel plates.
The pitch is more than doubled, and it becomes difficult to introduce the undulation of metal flow that is uniform and periodic in the strip width direction by roll rolling with fluting. Therefore, the groove pitch 1 is preferably 5 mm or less.

The cross-sectional shape of the groove can be a V-shaped, U-shaped, trapezoidal, sinusoidal waveform, or any other suitable effect.

In addition, regarding the arrangement of the vertical grooves of the roll with vertical grooves, the angle formed with respect to the circumferential direction of the groove roll is a surface defect (microscopic baldness).
It becomes a problem in relation to the occurrence.

As described above, in the conventionally proposed manufacturing technique of the electrical steel sheet having the (100) face cubic texture, a roll having a horizontal groove as well as a vertical groove, or two intersecting directions angled with respect to the roll circumferential direction. Mostly, a roll having a groove is used. However, when a plate is rolled by a roll having such grooves intersecting with each other, the transferred convex portion is crushed by friction with the roll during flattening rolling, and a minute lamination is formed. Therefore, it is preferable to use a roll with vertical grooves that does not intersect with the vertical grooves. When grooves having an angle with respect to the circumferential direction of the roll are provided, it is necessary to symmetrically provide the grooves having the diametrically opposite inclinations due to the requirements of the threaded plate. When the grooves are provided in this manner, it becomes unavoidable that the grooves intersect each other when the inclination angle becomes large to some extent. Therefore, even when the groove is formed at an angle with respect to the roll circumferential direction, the vertical groove should be at a limit where it does not intersect. The angle of the vertical groove with respect to the roll circumferential direction is preferably 5 ° or less in consideration of the vertical groove interval and the like.

〔Example〕

The steels shown in Table 1 were vacuum degassed and then continuously cast into 220 mm t slabs. The slab was heated to 1150 ° C. and soaked, then rough-rolled and finish-rolled (finishing temperature 820 ° C.) to obtain a 2.0 mm t hot-rolled sheet, which was wound at 610 ° C. After pickling the steel sheet, it is rolled by a smooth roll and a roll with flutes in a rolling reduction ([(t ₀ −t) / t ₀ ] × 100) within a range of 40% or less, and various rolling at 650 to 900 ° C. Annealed at temperature. Further, these steel strips were cold pressed to 0.5 mm t and then annealed in the range of 700 to 1050 ° C. The magnetic properties of the steel sheet thus obtained are shown in Table 2 together with specific manufacturing conditions.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of (t ₀ −t) / t _{0 on} the magnetic flux density (B ₅₀ ) after final annealing in fluted roll rolling and smooth roll rolling. FIG. 2 is a graph showing the effect of Wt / l in fluted roll rolling on the magnetic flux density (B ₅₀ ) after final annealing and the reduction rate of rolling load. Third
The figure is a graph showing the influence of the roll groove shape in the longitudinal groove rolling on the magnetic flux density (B ₅₀ ) after the final annealing.

Claims (2)

[Claims] 1. By weight%, C: 0.01% or less, Si: 7.0% or less,
Mn: 0.1-1.5%, P: 0.1% or less, S: less than 0.01%, Al: 0.001
% Or 0.05 to 1.0%, N: 0.005% or less, a hot-rolled steel strip having a composition consisting of the balance Fe and unavoidable impurities, after descaling, using a rolling roll having longitudinal grooves in the roll circumferential direction. Cold rolling or warm rolling under conditions that satisfy the formula, after annealing the steel strip at a recrystallization temperature or higher, cold rolling or warm rolling to a final plate thickness with a smooth roll,
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, which is characterized by performing annealing thereafter. 0.05 ≦ [(t ₀ −t) / t ₀ ] ≦ 0.25 0.25 ≦ (Wt / l) ≦ 0.75 where t ₀ : original thickness of rolled material (mm) t: rolled material after rolling with longitudinal groove Thickness of the concave part of (mm) l: Groove pitch of the roll with vertical groove (mm) Wt: Width of the area of the plate thickness t within the groove pitch l (mm) 2. The method for producing a non-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the rolling is performed using a fluted roll having a shape satisfying the following conditions. 0.15 ≤ [S / (ld)] ≤ 0.65 d ≥ 0.5 mm where S: Groove cross-sectional area per groove pitch 1 in the section passing through the roll axis (mm ² ) d: Groove depth (mm)