JP2009248108A - Method of manufacturing non-oriented magnetic steel sheet for reducing occurrence of seam defect - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means by which when rolling a slab for non-oriented magnetic steel sheets with hot-rolling equipment including vertical rolls, the occurrence of seam defects in an end part of a coil after hot-rolled is reduced without affecting the magnetic properties of a product sheet even when the slab is rolled in the width direction with the vertical rolls in the early stage of hot rolling. <P>SOLUTION: Before heating the slab for the non-oriented magnetic steel sheets, corner parts extended in the longitudinal direction of the slab are chamfered over the entire length and, after heating the chamfered slab, the hot rolling is performed under the conditions that the finishing temperature of rough rolling is set to be ≥950°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to the manufacture of non-oriented electrical steel sheets used as materials such as iron cores of motors, and in particular, a hot-rolled coil having a sheet width corresponding to the product dimensions can be obtained with reduced yield by reducing the occurrence of seam wrinkles. For technology.

  In the production of non-oriented electrical steel sheets, in order to improve the production yield and lower the production cost, it is necessary to obtain a hot rolled coil having a plate width corresponding to the product dimensions. For this purpose, it is effective to perform slab width direction rolling (width reduction) with a vertical roll mill before the hot rolling to increase the dimensional accuracy of the slab.

However, continuous cast slabs for non-oriented electrical steel sheets containing 1.5% by mass or more of Si are brittle, and when width reduction is performed on such slabs, the longitudinal direction of the steel sheet after hot rolling Along the edges, elongated surface wrinkles called seam wrinkles occur.
In particular, in a slab containing 1.5% by mass or more of Si, since it does not undergo phase transformation in the middle of hot rolling, seam flaws are likely to remain until the end of hot rolling, so in such a slab for a non-oriented electrical steel sheet, It was difficult to reduce the width while suppressing the occurrence of seam wrinkles.

  This hot-rolled sheet seam remains on the product steel plate as it is and deteriorates the space factor and interlayer resistance when it is made into an iron core. Therefore, it is necessary to trim and remove the wrinkled part. . For this reason, when seam wrinkles occur, the product yield is significantly reduced.

  The occurrence of seam wrinkles can be reduced by increasing the heating temperature in hot rolling, but as the heating temperature increases, the magnetic properties of the non-oriented electrical steel sheet, particularly the iron loss, deteriorates. In the production of a large amount of non-oriented electrical steel sheet, the width reduction of the slab could not be used effectively.

  Conventionally, it has been known that seam flaws occur in high alloy steel and stainless steel in addition to non-oriented electrical steel sheets. As a technique for reducing the influence of seam flaws and increasing the production yield, for example, Technologies have been proposed.

In Patent Document 1, the relationship between the amount of edge seam penetration according to the steel type and the difference in the target sheet bar width with respect to the slab width before rough rolling is determined in advance, and the slab width obtained by measurement before rough rolling is determined. Based on this, a technique for selecting a target sheet bar width in a range in which the amount of edge seam penetration does not exceed the remaining width of the hot-rolled coil has been proposed.
However, this technique determines the hot-rolled coil width according to the slab width before rough rolling, and does not show any method for reducing the seam wrinkle itself.

In Patent Document 2, in the production of a stainless hot-rolled steel sheet, in order to reduce the occurrence of seam wrinkles caused by wrinkles formed on the side surface of the slab that is a free surface during rolling with a horizontal roll, A technique has been proposed in which a chamfered slab is used, and the slab is width-pressed with a caliber mold having a caliber groove composed of upper and lower inclined wall surfaces and a groove bottom surface.
However, this technology is a technology for reducing the occurrence of seam wrinkles caused by wrinkles formed on the side surface of the slab that is the free surface during rolling with a horizontal roll when performing width reduction with a press. There is a problem that cannot be applied when rolling with a general hot rolling facility equipped with a die roll.

  Therefore, when width reduction is performed on a slab for non-oriented electrical steel sheets by hot rolling equipment equipped with a general vertical roll, the occurrence of seam wrinkles can be reduced without affecting the magnetic properties of the product plate. Development of means is required.

JP-A-5-104121 JP 2004-25255 A

  Therefore, when rolling the slab for a non-oriented electrical steel sheet with a hot rolling facility equipped with a vertical roll, the slab width direction rolling may be performed with the vertical roll before the hot rolling. It is an object of the present invention to provide means for reducing the occurrence of seam wrinkles at the end of a steel plate after hot rolling without affecting the magnetic properties of the product plate.

  In order to solve the above-mentioned problems, the present invention can perform width reduction without deterioration of the magnetic properties of the product plate by grinding the slab corner and optimizing the end temperature of the rough rolling. The gist is as follows.

(1) In a method for producing a non-oriented electrical steel sheet in which a slab for a non-oriented electrical steel sheet is heated in a heating furnace, then the slab is width-rolled by a vertical roll, and then hot-rolled. Before heating the slab, chamfer the corner portion extending in the longitudinal direction of the slab over the entire length, heat the chamfered slab, and then hot-roll under the condition that the end temperature of the rough rolling is 950 ° C. or higher. The manufacturing method of the non-oriented electrical steel sheet characterized by these.
(2) The method for producing a non-oriented electrical steel sheet according to (1), wherein the corner portion is chamfered in a temperature range of 150 ° C. or higher and 800 ° C. or lower.
(3) The chamfering of the slab corner is performed under the condition that the distance in the width direction and the distance in the thickness direction from the slab corner are in the range of 5 to 20 mm, respectively, and the angle θ from the wide surface of the slab is 30 to 50 °. (1) The manufacturing method of the non-oriented electrical steel sheet according to (2).
(4) The method for producing a non-oriented electrical steel sheet according to any one of (1) to (3), wherein the slab heating temperature is 1000 ° C. or more and 1200 ° C. or less.

  According to the present invention, when producing a non-oriented electrical steel sheet, the width reduction of the slab can be performed by reducing the occurrence of seam wrinkles, so that the width accuracy of the hot-rolled coil is improved. The yield is improved. Further, such an effect can be obtained without deteriorating the magnetic properties of the product plate.

The present inventor analyzed the generation mechanism of seam wrinkles (FEM analysis) using a finite element method when a slab for producing a non-oriented electrical steel sheet was reduced in width by a vertical roll. FIG. 1 shows an example of the arrangement of friction stress vectors obtained during the reduction (50 mm) obtained by FEM analysis.
As shown in the figure, due to the frictional force between the vertical roll and the slab, the material near the corner of the slab during width reduction is greatly sheared and deformed in the direction in which the material inside the corner collapses toward the corner edge. The present inventors have found that seam wrinkles are generated by this shear deformation.
In particular, in a slab having a high Si content and starting phase transformation before width reduction and a slab having no phase transformation, since it does not transform after undergoing shear deformation, the seam defect remains until the end of hot rolling. I also found it easy to do.

Therefore, as a result of examining the means for reducing the frictional force between the vertical roll and the slab at the slab corner, it was found that chamfering at the corner is effective in reducing the frictional force and is effective in reducing the occurrence of seam wrinkles. I found it.
FIG. 2 shows the width reduction amount when the slab (Si: 2.0 mass%) in which the corner portion is chamfered before width reduction and the slab without chamfering are hot-rolled after width reduction. The relationship with seam wrinkle incidence is shown.
Here, the seam wrinkle occurrence rate indicates a wrinkle ratio of a score of 2 or more, which will be described later, with respect to the entire length of the plate edge portion (between 100 mm from the edge).
The chamfering amount was performed under the condition that the values of a and b in FIG.
From FIG. 2, it can be seen that the occurrence rate of seam wrinkles is reduced by chamfering.

It has also been found that the occurrence of seam wrinkles is affected by the rough rolling end temperature during hot rolling.
FIG. 3 shows the relationship between the rough rolling end temperature and the state of occurrence of seam wrinkles in the hot-rolled sheet when a slab with chamfered corners is hot-rolled after width reduction after slab heating.
In addition, the score of the scissors was evaluated as 0 to 3 according to the degree of the seam scissors by visually checking the hot-rolled sheet.
The seam ratings are as follows. 0 is no seam wrinkle, 1 is a seam wrinkle of a pattern level, 2 is a seam wrinkle having a depth of less than 10 μm, and 3 is a seam wrinkle having a depth of 10 μm or more.

  From FIG. 3, the end temperature of rough rolling is 950 ° C. with a rating of 1 and 960 ° C. or higher with a score of 0, and after slab chamfering, the rough rolling end temperature is further 950 ° C. or higher, more preferably 960 ° C. or higher. It can be seen that the occurrence of seam wrinkles is reduced.

  Next, the manufacturing conditions of the present invention based on the above knowledge will be described.

  In the present invention, a slab produced using a molten steel whose components are adjusted for a non-oriented electrical steel sheet is heated in a heating furnace, followed by hot rolling consisting of rough rolling and finish rolling, and further cold rolling. When manufacturing non-oriented electrical steel sheets, before heating the slab, chamfer the corners of the slab over the entire length, heat the chamfered slab, perform width rolling of the slab with a vertical roll, and then rough rolling The hot rolling is performed under the condition that the finishing temperature is 950 ° C. or higher, so that the width rolling can be performed while suppressing the occurrence of seam wrinkles.

The chamfering of the slab is performed over the entire length of the corner portion extending in the longitudinal direction of the slab. By chamfering the slab corner portion, the frictional force in the vicinity of the corner at the time of width reduction and in the sliding-down direction is relieved, so that the occurrence of seam wrinkles can be suppressed.
As shown in FIG. 4, the chamfering is efficiently performed by grinding the corner portion of the slab 1 so that the cross section is linearly formed by a hot grinder.

The amount of grinding varies depending on the material of the slab, but both the width direction distance a and the thickness direction distance b from the corner shown in FIG. If it is less than 5 mm, the effect of chamfering is small, and seam wrinkles cannot be sufficiently reduced. In addition, if the amount exceeds 30 mm, the material cost corresponding to the removal becomes a problem.
The chamfering angle is an angle θ from the wide surface of the slab shown in FIG. Outside this angle range, the chamfering effect is small.

  The slab temperature during chamfering is preferably 150 ° C. or higher in order to prevent slab cracking. Although the upper limit temperature is not particularly limited, it is set to 1300 ° C. or less at which the slab is in a solidified state. Considering workability at the time of chamfering, 800 ° C. or lower is preferable.

  As shown in FIG. 3, the rough rolling end temperature during the hot rolling is set to 950 ° C. or higher in order to suppress the occurrence of seam wrinkles. It is more preferable if it is 960 degreeC or more. When the end temperature is less than 950 ° C., the deformation resistance of the slab increases, so that seam wrinkles are generated even if the chamfering of the slab corner portion is performed.

  The upper limit of the rough rolling end temperature is not particularly restricted from the viewpoint of suppressing seam wrinkles, but is preferably set to 1200 ° C. from the viewpoint of the magnetic properties of the non-oriented electrical steel sheet. In order to finish at a temperature exceeding 1200 ° C., it is necessary to heat the slab to a temperature exceeding 1200 ° C., but at that temperature, since AlN is dissolved, AlN is finely precipitated during hot rolling. As a result, grain growth is hindered, and as a result, magnetic properties, particularly iron loss, deteriorate. For this reason, the rough rolling end temperature is preferably 1200 ° C. or lower. More preferred is 1100 ° C. or lower.

  In order to set the end temperature of rough rolling to 950 ° C. or higher, the slab heating temperature before hot rolling is set to 1000 ° C. or higher. Further, when the slab heating temperature exceeds 1200 ° C., AlN is dissolved as described above, so it is preferable to set it to 1200 ° C. or less.

  Although the width reduction by the vertical roll depends on the amount of Si in the slab, the reduction is preferably performed in the range of 20 to 80 mm. When the width reduction amount is 20 mm or less, the effect of width reduction is less than the amount of work for chamfering. Further, as the width reduction amount increases, the occurrence rate of seam wrinkles also increases.

Other conditions such as hot finish rolling and cold rolling may be performed according to conditions generally employed in the production of non-oriented electrical steel sheets.
Further, the chemical composition of the slab can be generally used for non-oriented electrical steel sheets, and is not limited to a specific chemical composition. Since it becomes a problem when manufacturing a non-oriented electrical steel sheet containing at least mass%, it is effective to apply the present invention when manufacturing such a non-oriented electrical steel sheet.

  Hereinafter, embodiments of the present invention will be further described with reference to examples.

  In mass%, C: 0.003%, Si: 1.0 to 3.5%, Mn: 0.20%, Sol.Al: 0.30%, S: 0.003%, N: 0.002 Slabs for non-oriented electrical steel sheets with a thickness of 252 mm are prepared, the corners of the slabs are chamfered under various conditions, slab heated at 1150 ° C., and the width is reduced with various width reductions. Then, rough rolling was performed at various end temperatures, and finish rolling was performed at 880 ° C. to produce a hot-rolled sheet having a thickness of 2.0 mm. The seam wrinkles of the obtained hot-rolled sheet were examined, and the degree of seam wrinkles was evaluated in the same manner as in FIG.

The results are shown in Table 1 together with the Si amount of the slab, the chamfering conditions, the width reduction amount, and the rough rolling end temperature. From Table 1, when satisfy | filling the conditions of this invention, it was confirmed that generation | occurrence | production of seam wrinkles is suppressed in all.
In addition, Comparative Example 2 is an example in which the iron loss deteriorates because the end temperature of rough rolling exceeds 1200 ° C, and Comparative Example 12 is an example in which the iron loss is deteriorated because the slab heating temperature exceeds 1200 ° C. In Example 6, the yield deteriorated because the chamfer (a) in the slab width direction exceeds 30 mm, and in Comparative Example 8, the yield deteriorates because the chamfer (b) in the slab thickness direction exceeds 30 mm. This is an example.

It is a figure which shows an example of the arrangement | sequence of the friction stress vector at the time of 50 mm reduction obtained by FEM analysis. It is a figure which shows the relationship between the amount of breadth reduction, and the seam wrinkle generation rate at the time of hot-rolling using the slab which implemented chamfering, and the slab which does not implement chamfering. It is a figure which shows the relationship between the rough rolling end temperature and the generation | occurrence | production condition of the seam wrinkle in a hot-rolled sheet at the time of hot rolling by performing width reduction of the slab which implemented chamfering. It is a figure for demonstrating the aspect of chamfering.

Explanation of symbols

1 Slab a Width distance from corner b Thickness direction distance from corner θ Chamfer angle

Claims (4)

After heating the slab for the non-oriented electrical steel sheet in a heating furnace, performing the width rolling of the slab with a vertical roll, and then performing the hot rolling in the manufacturing method of the non-oriented electrical steel sheet,
Before heating the slab, chamfer the corner portion extending in the longitudinal direction of the slab over the entire length, heat the chamfered slab, and then hot-roll under the condition that the end temperature of the rough rolling is 950 ° C. or higher. The manufacturing method of the non-oriented electrical steel sheet characterized by these.   The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the chamfering of the corner portion is performed in a temperature range of 150 ° C or higher and 800 ° C or lower.   The chamfering of the slab corner portion is performed under the condition that the distance in the width direction and the distance in the thickness direction from the slab corner are in the range of 5 to 30 mm, respectively, and the angle θ from the wide surface of the slab is 15 to 75 °. The manufacturing method of the non-oriented electrical steel sheet according to claim 1 or 2.   The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the slab heating temperature is 1000 ° C or higher and 1200 ° C or lower.

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