JPH0839125A - Rolling method of hot rolled steel sheet - Google Patents

Abstract

PURPOSE:To make it possible to substantially decrease the filtrating amt. of edge seam flaws and to decrease margins for edge cutting so as to improve a yield by rolling a material to be rolled in such a manner that the coeffts. of friction of both end areas of this material attain a specific value or below at the time of horizontal rolling of a slab in a hot rough rolling stage thereof. CONSTITUTION:The rolling of the material to be rolled is executed by confining the coeffts. of friction mu of the material to be rolled to <=0.25 to make the restraining force with rolls small and to make the materials on the front and rear surfaces easily deformable in a transverse direction. The material is not only deformed in the rolling direction but is deformed in the transverse direction as well at the end of the material to be rolled. The front and rear surfaces of the material to be rolled are held in contact with work rolls of the rolling mill and are restrained from above and below and, therefore, these surfaces are hardly movable in the transverse direction but the side faces thereof are free surfaces and then the material at the center in the thickness direction is deformed in the transverse direction without receiving the restraint. The material on the end face side falls into its front and rear and the linear creases existing thus far at the side faces of the material to be rolled move to the front and rear surfaces thereof and infiltrate toward the center. The fall-in to the front and rear surfaces is suppressed by making the coeffts. of friction of both end areas small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling hot-rolled steel sheet, and in particular, a linear flaw generated on the side surface of a material to be rolled in a hot rough rolling step is deformed by horizontal rolling of the material to be rolled. Therefore, it proposes an effective rolling method for avoiding wraparound on the front and back surfaces.

[0002]

2. Description of the Related Art Among surface defects in hot-rolled steel sheets, what are called edge seam flaws are linear flaws along the rolling direction which occur near the widthwise ends of the front and back surfaces of the hot-rolled coil. Since the hot rolled steel sheet having such edge seam flaws does not satisfy the required surface quality, it is necessary to cut off (edge cutting) such a region, which causes a significant decrease in yield.

In such edge seam flaws, coarse grains are generated on the side surface of the material to be rolled when the material to be rolled is heated, and flaws and the like generated during slab casting are present. Therefore, hot rough rolling of the material to be rolled is performed. While horizontal wrinkles are generated during the horizontal rolling in the process, linear wrinkles are formed, while at the time of this horizontal rolling, the edge side surface of the rolled material is deformed into a drum shape (bulging deformation), so the corners of the rolled material are front and back surfaces. It is caused by falling to the side and entering from the width end of the material to be rolled into the center thereof.

Many proposals have hitherto been made as a method of suppressing the edge seam flaws from wrapping around the front and back surfaces of the material to be rolled when rolling the hot rolled steel sheet.

As one of them, for example, Japanese Patent Laid-Open No. 1-1504
No. 03 gazette, rolling is performed while supplying a lubricant between a roll material plate side end portion and a roll in a hot rough rolling step,
As a result, a method is disclosed in which the friction coefficient between the front and back of the rolled material and the roll is reduced, and the bulging deformation of the material to be rolled is reduced to prevent the material from wrapping around to the front and back sides.

However, in this method, the value of the coefficient of friction between the material to be rolled and the roll is not specified, and the method is simply lubrication. Therefore, the prevention of edge seam flaws is still insufficient. The reality was that it was not a thing.

[0007] In addition, in this method, although there is an appropriate amount of the lubricant used from the viewpoint of efficiently using the lubricant, nothing is touched on this point, and economical rolling work is performed. It was impossible to do.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art in producing hot-rolled steel sheets, that is, during horizontal rolling in the hot rough rolling step.
A new rolling method is proposed which can prevent linear flaws generated on the side surface of the rolled material from wrapping around the front and back surfaces thereof.

[0009]

According to the present invention, when a hot rolled steel sheet is manufactured by using a slab, the friction coefficient (in both end regions of the material to be rolled during horizontal rolling in the hot rough rolling step of the slab ( μ) is 0.25 or less, and is a rolling method for a hot-rolled steel sheet, wherein during horizontal rolling in the hot rough rolling step, the average friction coefficient in the width direction of the material to be rolled. A method of rolling such that (average μ) satisfies the following formula is particularly preferable.

Mean μ> tan θ θ = cos ⁻¹ (1-Δh / 2R) where θ: contact angle between rolled material and roll Δh: amount of reduction of rolled material (sheet thickness at inlet side-sheet thickness at outlet side) R : Work roll radius

[0011]

In horizontal rolling in the hot rough rolling step, not only the material is deformed in the rolling direction but also in the width direction at the width end of the material to be rolled. At that time, the front and back surfaces of the material to be rolled contact the work rolls of the rolling mill and are constrained from above and below, so it is difficult to move in the width direction, but since the side surface is a free surface, The material deforms in the width direction without being restrained.

Then, as such deformation progresses, the material on the end face side including the vicinity of the corner portion of the material to be rolled falls down to the front and back as shown in FIG. 1, whereby the material to be rolled is rolled. The linear wrinkles existing on the side surface of the material 1 move to the front and back surfaces thereof, and the wrinkles relatively wrap around from the end in the width direction toward the center every horizontal rolling.

In the present invention, during horizontal rolling in the hot rough rolling step, the coefficient of friction μ of the material to be rolled, particularly at both ends, is set to 0.25 or less, and the constraint between the material and the roll on the front and back surfaces of the material is reduced. Since the materials on the front and back surfaces are also easily deformed in the width direction, the amount of bulging deformation is small as shown in FIG. 2, and the side surfaces of the rolled material are prevented from falling to the front and back surfaces.

FIG. 3 is a graph showing the relationship between the friction coefficient (with the roll) and the bulging amount at both ends of the material to be rolled.

The results shown here are the results obtained by applying various lubricants to the front and back surfaces of a rectangular pure lead material to change the surface condition and rolling in one pass at room temperature. Height D of the convex portion on the side surface after rolling and plate thickness H
The friction coefficient μ is calculated based on the rolling load from the following equations (1) to (3) using the rolling theory under the mixed friction condition.

H · (dq / dφ) = R ′ · K · (2φ · ω ± λ) --- (1) λ = min (2μ · s / K, 1) --- (2) s = q + K・ Ω --- (3) where h: plate thickness K: two-dimensional yield stress of material R ′: flat roll radius q: horizontal pressure s: normal pressure φ: normal angle of roll surface ω: roll surface Function defined by the frictional stress of the material and the yield stress of the material

From the results shown in FIG. 3 above, it is general that the coefficient of friction between the material to be rolled and the roll becomes 0.3 to 0.4 particularly in the hot rough rolling step in the hot rolling of the slab. On the other hand, when the friction coefficient (μ) is 0.25 or less, the collapse of the material due to the bulging deformation becomes extremely small, which is advantageous for preventing the occurrence of edge seam flaws.

If the friction coefficient is too small during horizontal rolling, there is a possibility that the material to be rolled slips when it is bitten by the rolls and cannot be rolled. Therefore, the average coefficient of friction in the width direction of the material to be rolled ( Average μ) is (4),
It is preferable to set so as to satisfy the expression (5).

Average μ> tan θ --- (4) θ = cos ^-1 (1-Δh / 2R) --- (5) θ: Contact angle between rolled material and roll Δh: Reduction amount of rolled material ( Inlet plate thickness-Ejection plate thickness) R: Work roll radius

The coefficient of friction μ at both ends of the rolled material is 0.25
By satisfying the following expression and satisfying the above expression, it is possible to roll a hot-rolled steel sheet of good quality while ensuring good biting.

The region where the coefficient of friction μ is 0.25 or less is
The width of the material to be rolled is preferably about 100 mm from the width end, and more preferably about 50 mm from the width end.

As means for reducing the friction coefficient μ to 0.25 or less, the lubricating oil in the above range is supplied under the conditions applied to the plate width end portion, or the descaling before rolling is performed. Do not do.

[0023]

【Example】

Example 1 In order to produce a stainless hot-rolled steel sheet (steel type: SUS 430, finished sheet thickness: 4.0 mm, width: 1200 mm) in which the surface quality is strict and edge seam flaws are likely to occur, the slab is subjected to hot rough rolling 7 When rolling from a thickness of 200 mm to 30 mm in a pass, rolling is performed in the second to fourth passes while supplying lubricating oil to the region of 50 mm from the width end of the material to be rolled (friction coefficient is 0.21, before rolling No descaling was performed), and then final rolling was performed to obtain a product plate, and the resulting plate (pickled) was examined for the occurrence of edge seam flaws.

The results are shown in the case of performing descaling before rolling and rolling without lubrication (conventional method: friction coefficient of
32), when descaling was performed before rolling and lubrication rolling was performed (Comparative method 1: friction coefficient 0.26) and when non-lubricating rolling was performed without descaling before rolling.
It is shown in FIG. 4 together with the result of (Comparative method 2: Friction coefficient 0.28). The results in FIG. 4 are the average values of the 10 coils obtained by each method at both ends of the coil.

As is clear from FIG. 4, when rolling is carried out in accordance with the present invention, it is confirmed that the wraparound amount of the linear flaw is about 7 mm, which is about 40% smaller than the conventional one. It was

Example 2 The same stainless hot-rolled steel sheet as in Example 1 (finished plate thickness 4.
0 mm, width 1200 mm), when rolling the slab from 200 mm to 30 mm in thickness by 7 passes of hot rough rolling, the width of the rolled material is 50 mm from the width end of the second pass through 4 passes. Rolling is performed while supplying lubricating oil (friction coefficient is 0.19, average friction coefficient μ in the plate width direction is 0.
26, the condition that descaling before rolling is not performed), and then finish rolling was performed to obtain a product plate, and the occurrence state of edge seam flaws in the obtained plate (pickled) was investigated.

The results obtained were subjected to descaling before rolling and rolling without lubrication (conventional method: coefficient of friction of 0.
32), when descaling was performed before rolling and lubrication rolling was performed (Comparative method 1: friction coefficient 0.26) and when non-lubricating rolling was performed without descaling before rolling.
It is shown in FIG. 5 together with the results of (Comparative method 2: Friction coefficient 0.28). Note that the results in FIG. 5 are the same as in FIG. 4 above, showing the average values at both ends of the 10 coils obtained by each method.

As is clear from FIG. 5, it was confirmed that when rolling was carried out according to the present invention, the wraparound amount of the linear flaw was further reduced to about 6 mm.

[0029]

As described above, according to the present invention, the wraparound amount of the edge seam flaw can be reduced by about 40% as compared with the conventional one, so that the yield of the hot rolled steel sheet product can be greatly improved by reducing the edge margin. I was able to do it.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a deformation state of a material to be rolled when a conventional rolling method is applied.

FIG. 2 is an explanatory diagram of a deformation state of a material to be rolled when the rolling system according to the present invention is applied.

FIG. 3 is a graph showing a relationship between a friction coefficient and D / H.

FIG. 4 is a diagram showing a comparison of wraparound amounts of edge seam flaws.

FIG. 5 is a diagram showing a comparison of wraparound amounts of edge seam flaws.

Front page continued (72) Inventor Kunio Isobe 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.

Claims (2)

[Claims] 1. When manufacturing a hot rolled steel sheet using a slab, during horizontal rolling in the hot rough rolling step of the slab,
A method for rolling a hot-rolled steel sheet, which comprises rolling so that a friction coefficient (μ) in both end regions of a material to be rolled is 0.25 or less. 2. The average friction coefficient (average μ) in the width direction of the material to be rolled during horizontal rolling in the hot rough rolling process.
The rolling method according to claim 1, wherein the rolling is performed so as to satisfy the following formula. Note Average μ> tan θ θ = cos ⁻¹ (1-Δh / 2R) where θ: contact angle between rolled material and roll Δh: amount of reduction of rolled material (sheet thickness at entry side-sheet thickness at exit side) R: workpiece Roll radius