JPH10263620A - Cold rolling method of stainless steel strip excellent in surface gloss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a working rate of a rolling mill, to reduce a production cost and to increase a yield by rolling with a tension load ratio between a front side and a back side at least in a last finish pass controlled to a specified value or higher. SOLUTION: A proof stress of a material to be rolled is grasped from a tension tester, etc., by adjusting a torque of a coiling reel to coil a steel strip and a recoiling reel to recoil the steel strip, etc., of a multi-stage rolling mill, a tension of a front side and a back side is controlled, rolling is conducted under a front side/back side tension load ratio of >=0.5 or preferably >=0.6, where the tension load ratio is the value of a tension at a front side or a back side divided by a proof stress of a material to be rolled. The stainless steel strip 1 is rolled with a pair of small diameter work rolls 2, 2' which are supported by upper/lower two pairs of four intermediate rolls 3a, 3a', 3b, 3b', the intermediate rolls are supported by upper/lower three pairs of back up rolls divided into six parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cold rolling stainless steel, and more particularly to a method for rolling a stainless steel strip having excellent gloss.

[0002]

2. Description of the Related Art In general, a cluster type multi-high rolling mill using a small diameter work knurl is used for cold rolling stainless steel having excellent gloss. Gloss is an important item as the quality of stainless steel products, and high gloss products are manufactured by various means such as using a mirror-finished work opening.

In addition, such a cluster type multi-high rolling mill is provided with various shape control ends for controlling the shape of the plate. As a typical example, an AS-U mechanism is provided in the split backup port of the Sendzimir mill to control the roll crown of the split backup roll by eccentricity of the roll, or a desired roll profile pattern is formed on the intermediate roll of a multi-high rolling mill. Using an intermediate roll
A method of shifting the intermediate roll in the axial direction, an intermediate roll bender method of bending the intermediate roll corresponding to the intermediate roll in a metal chock format, and the like are generally known.

[0004] In such a cluster type multi-high rolling mill, in order to produce a high gloss stainless steel product,
Generally, as disclosed in JP-A-53-106365, after adjusting the work roll roughness of the rolling pass schedule, the viscosity of the rolling lubricant is reduced, or the rolling speed of the final finishing pass is reduced. Or let me do it. However, when the viscosity of the rolling lubricating oil is reduced, seizure flaws called heat scratches tend to occur when the rolling speed is increased, so that the rolling speed cannot be increased in all passes, and productivity is reduced. There is a problem of inhibition,
Reducing the rolling speed in the final finishing pass also has the problem of reducing productivity.

As a method for solving such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 3-133503, there is a method in which the advanced rate during rolling is set to a negative state and rolling is performed. The relative sliding speed between the material in the roll bite and the work roll increases, and the friction coefficient increases, so that heat scratches are likely to occur. There is a problem of lowering. Further, Japanese Patent Application Laid-Open No. 5-50103
As disclosed in Japanese Unexamined Patent Publication, there is a cross-rolling method using a spirally polished work roll, but it is necessary to modify a device for supporting the thrust force of the work roll, or the work roll surface Since the properties are different from those of mirror-polished work rolls generally used at the time of finish rolling, there is a problem that a steel strip having excellent gloss cannot be expected.

[0006]

As described above, a rolling method for producing a high-gloss stainless steel strip has been proposed, but a method in which the rolling speed is reduced at the time of final finish rolling causes a decrease in productivity. In addition, the method of cross rolling requires much equipment cost and has a problem that desired gloss cannot be obtained. The present invention has been made in view of the above problems, and provides a rolling method for obtaining a high-gloss stainless steel strip that is excellent in productivity and low in cost.

[0007]

According to a first aspect of the present invention, there is provided a method for cold rolling a stainless steel strip by using a multi-high rolling mill, wherein a tension load ratio between a front side and a rear side is at least 0.5 at least in a final finishing pass. , Preferably a cold rolling method of a stainless steel strip characterized by rolling at 0.6 or more, wherein the tension load ratio is a value obtained by dividing the forward or backward tension by the proof stress of the material to be rolled. According to a second aspect of the present invention, the steel strip is rolled by controlling the shape so that the steepness of the steel strip is 1.5% or more and less than 4.0%.
A method for rolling a stainless steel strip as described above.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
This will be described in detail with reference to FIG. FIG. 1 is a schematic side view of a 12-high rolling mill, in which a stainless steel strip 1 is rolled. In FIG. 1, a pair of small-diameter work rolls 2 and 2 'are upper and lower pairs of four intermediate rolls 3a, 3a',
3b, 3b ', and these intermediate rolls are
A pair of six divided backup floors 4a, 4a ', 4
b, 4b ', 4c, 4c'. A is provided for the side split backup rolls (4a, 4c) on the upper side.
An S-U mechanism is installed, and the upper split backup roll profile can be arbitrarily changed by rotating and eccentrically rotating the bearing position of each split backup roll. Further, the lower divided backup rolls 4a 'and 4c' on the lower side can change the profile of the lower divided backup roll with a certain pattern by rotating and eccentric the main shaft. Also, two pairs of upper and lower four intermediate rolls 3a,
A roll crown is provided on one side of each of 3a ', 3b, 3b', and each roll can be independently moved in the roll axis direction by a roll shift device (not shown).

On the exit side of the multi-high rolling mill, there is a roll composed of a plurality of sleeves which are divided in the axial direction and come into contact with the stainless steel strip, and a contact type which measures the plate shape by detecting the pressure applied to each sleeve. Is provided, and the tension distribution of the rolled stainless steel strip is detected and subjected to signal processing, and a steepness distribution (elongation distribution) is displayed by the shape display device 6.

[0010] In the case of rolling in the final finishing pass using the above-described multi-high rolling mill, stainless steel is usually emulsion-lubricated with a mineral oil-based low-viscosity (viscosity of about 10 cSt at 40 ° C) rolling oil. Finish rolling speed of about 1
A rolling experiment was performed by changing the front and rear tensions using a work roll polished at a low rolling speed of 00 m / min, and the friction coefficient and rolling load between the work material and the work roll during rolling, The surface gloss of the steel strip was investigated and the following findings were obtained.

FIG. 2 shows the result. FIG. 2A shows the relationship between the coefficient of friction and the tension, and FIG.
FIG. 3 is a diagram illustrating a relationship between a rolling load and a tension, and FIG. 3C is a diagram illustrating a relationship between a glossiness and a tension. In FIG. 2, the forward tension load ratio .alpha.
The rear tension load ratio β is a value obtained by dividing the output tension by the 0.2% proof stress of the material on the output side of the rolling mill.

Generally, the front tension load ratio and the rear tension load ratio are usually rolled at 0.3 to 0.4 to prevent the plate from breaking. The surface gloss is a value measured at a GS of 45 degrees using a gloss meter, and the operation is usually controlled so as to be 650 or more. If the surface gloss is lower than this value, the quality grade deteriorates. FIG. 2 (a) shows the relationship between the friction coefficient and the forward tension load ratio α and the rear tension load ratio β, but the effect of tension on the friction coefficient is almost not recognized in rolling at a normal tension load ratio level. However, when both the front tension load ratio and the rear tension load ratio become 0.5 or more, the friction coefficient sharply increases. This is because the tension is increased, oil pits in the roll bite are less likely to occur, and the already existing recesses on the surface of the stainless steel strip are smoothed, resulting in a sharp increase in the boundary lubrication region.

Further, as a result of conducting an experimental investigation similar to that described above by changing the viscosity of the rolling lubricating oil, the above phenomenon was found to be 4%.
This phenomenon occurs remarkably when boundary lubrication occupies the mainstream, as in the case of using a low-viscosity rolling lubricating oil having a viscosity of about 20 cSt or less at 0 ° C. Tallow oil or palm oil used in cold tandem rolling is used. It was found that the effect was hardly recognized in a rolling oil having a high viscosity of the lubricating oil as described above.

FIG. 2B shows the relationship between the rolling load and the forward tension load ratio and the backward tension load ratio. As is generally known, as the tension level increases, the rolling load decreases. It can be seen that the effect is greater for the rear tension than for the front tension. Here, when the front tension load ratio and the rear tension load ratio become 0.5 or more, the rolling load decreases despite the increase in the friction coefficient as shown in FIG. 2 (b). This is because the effect of decreasing the rolling load by increasing the tension is greater than the effect of increasing the rolling load by increasing the friction coefficient.

FIG. 2 (c) shows the relationship between the surface gloss and the forward tension load ratio and the backward tension load ratio. In the normal rolling at the tension load ratio level, almost no influence of the tension on the surface gloss was recognized. However, it was found that when both the front tension load ratio and the rear tension load ratio were 0.5 or more, the surface gloss was sharply improved.

From the above, in the present invention, when the stainless steel strip is cold-rolled by the multi-high rolling mill, the forward and backward tension load ratio is set to 0.5 or more, and preferably 0.1 to 0.5.
Rolling is performed with 6 or more. That is, while the yield strength of the material to be rolled is grasped from a tensile test or the like, the forward or backward tension is adjusted by adjusting the torque of a take-up reel for winding the steel strip and a rewind reel for rewinding the steel strip in a multi-high rolling mill. Is controlled so that the tension load ratio falls within the above range. The control of the tension load ratio is performed in the final finishing pass, but it is also preferable to control the tension load ratio in the range before the final pass as well.

In general, when the rolling speed is increased, the amount of rolling lubricating oil introduced into the roll bite is increased, so that oil pits are easily generated and the surface gloss is reduced. Therefore,
In order to ensure a surface gloss of a predetermined value or more, the relationship between the gloss and the rolling speed is investigated by changing only the rolling speed in advance under the same rolling conditions, and the rolling speed is more than the limit rolling speed at which the gloss is 650 or more. It is necessary to roll at a slow speed. However, by applying the present invention, a desired surface gloss can be obtained even if the rolling speed is increased beyond the limit speed at which the desired glossiness obtained experimentally described above can be obtained. In general, it is expected that heat scratches are likely to occur due to an increase in the rolling speed and an increase in the friction coefficient.
By setting it to 5 or more, there is no substantial problem since the rolling load is reduced and the frictional heat is reduced. Experiments have confirmed that the rolling speed at which the predetermined surface gloss is reduced is faster than the rolling speed at which the heat scratch limit occurs.

Although the surface gloss is improved by rolling at a high tension in this way, there is also a possibility that the plate may be broken by rolling at a high tension. Plate fracture is caused by defects at the end of the plate, for example, when using a note rim material, cracks in the plate width direction during hot rolling or when using a trim material, by performing multiple passes of cold rolling. This is caused by cracks at the plate edge. That is, when the tension is increased, stress concentration occurs at the above-described defective portion, and there is a possibility that the strip is torn from the defective portion and the plate is broken.

Therefore, using the rolling mill shown in FIG. 1, the front tension load ratio, the rear tension load ratio, and the plate shape (steepness) were changed, and the plate shape (steepness) and the presence / absence of plate breakage were tested. . FIG. 3 is a diagram showing the relationship between the steepness obtained by subtracting the steepness at the center of the steel strip from the steepness at the end of the steel strip and the plate breakage.
FIG. 3 (a) shows the effect of the forward tension load ratio and the plate shape on the occurrence of plate breakage, and FIG. 3 (b) shows the effect of the rear tension load ratio and the plate shape on the occurrence of plate breakage. Is shown. The steepness of the steel strip was measured by the shape detector described above, and the plate shape was controlled by changing the amount of eccentricity of the roll eccentricity of the upper split backup roll and the amount of shift of the intermediate roll shift. The symbol ３ in FIG. 3 indicates that the plate did not break, and the symbol X indicates that the plate broke, cracks grew or drawn. Therefore, preferably, in order to eliminate such a possibility of plate breakage, the plate shape is controlled within the scope of the present invention, that is, when the tension load ratio is 0.5 or more, the steepness is 1.5% or more and 4.0% or less. Things.

In order to control the shape in this manner, as described above, the backup roll of the multi-high rolling mill is divided and the AS-U mechanism is provided to control the roll crown of the backup roll. A method of providing a roll crown pattern to an intermediate roll of a rolling mill and providing a roll shift mechanism to shift the same in the axial direction, or a method of controlling a shape control end such as a roll bend ink method of bending an intermediate roll may be employed. it can.

In these cases, for example, a contact type shape detector is provided on the output side of the multi-high rolling mill, and based on this signal, the roll eccentricity of the divided backup roll, which is the shape control end, and the shift position of the intermediate roll It is preferable to control the bending force and the like of the intermediate roll.

[0022]

【Example】

(Example 1) The multi-high rolling mill used was the same rolling mill as that shown in FIG. 1, and the rolling conditions are shown in Table 1. Rolling lubricating oil is based on mineral oil and has a viscosity of 10 cS at 40 ° C.
t.

First, the rolling speed was increased under the normal rolling conditions of the rear tension load ratio β = 0.35 and the front tension load ratio α = 0.35. As a result, the rolling speed was 125 m · mi.
When the ^value was n ⁻¹ or more, the surface gloss after rolling was smaller than 650, and the desired gloss could not be obtained. Therefore,
In the prior art, the rolling speed had to be reduced at a speed lower than 125 m · min ⁻¹ , resulting in a decrease in productivity.

Next, applying the present invention, the rear tension load ratio β =
When the rolling speed was increased to 415 m · min ⁻¹ or more as a result of increasing the rolling speed at 0.60 and the forward tension load ratio α = 0.60, the surface gloss after rolling became smaller than 650, which was desirable. The gloss cannot be obtained. Therefore, by applying the present invention, the productivity of the final finishing pass was improved by about 3.3 times.

Example 2 The multi-high rolling mill used was the same as the one shown in FIG. 1, and the rolling conditions are shown in Table 1. The rolling lubricating oil is a mineral oil base, and has a viscosity of about 10 cSt at 40 ° C.

First, the rolling speed was increased at a rear tension load ratio β = 0.60 and a front tension load ratio α = 0.60 without controlling the plate shape. As a result, the rolling speed was 415 m · min.
^{When the value} was ^-1 or more, the surface gloss after rolling was smaller than 650, and the desired gloss could not be obtained. Therefore,
Without controlling the plate shape, the rear tension load ratio β = 0.60, the front tension load ratio α = 0.60, and the rolling speed is 400 m · mi.
30 coils were cold rolled at n ^-1 . At this time, the breaking rate of the sheet was about 0.8 times / coil.

Next, by applying the present invention and manually operating the AS-U mechanism of the divided backup roll while watching the output of the shape detector so that the steepness of the rolled sheet becomes 3%, the rear tension is adjusted. Load ratio β = 0.60, forward tension load ratio α =
As a result of increasing the rolling speed at 0.60, when the rolling speed was 415 m · min ⁻¹ or more, the surface gloss after rolling was smaller than 650, and the desired gloss could not be obtained. Accordingly, 60-coil cold rolling was performed at a rear tension load ratio β = 0.60 and a front tension load ratio α = 0.60 at a rolling speed of 400 m · min ⁻¹ while controlling the plate shape. At this time, the rate of occurrence of plate breakage was 0 times / coil.

As a result, it was possible to increase the operation rate of the rolling mill and reduce the occurrence rate at which the product quality was impaired.

[0029]

[Table 1]

[0030]

By using the rolling method of the present invention,
In a rolling mill of a small-diameter work roll for producing a stainless steel strip, it is possible to increase the operating rate of the rolling mill to reduce the production cost and to improve the yield by reducing the incidence of impairing product quality.

[Brief description of the drawings]

FIG. 1 is a diagram showing a multi-high rolling mill used to carry out the present invention.

2A is a diagram showing a relationship between a friction coefficient and a front tension load ratio and a rear tension load ratio, and FIG. 2B is a diagram showing a relationship between a rolling load and a front tension load ratio and a rear tension load ratio.
(C) is a diagram showing the relationship between the surface gloss and the front tension load ratio and the rear tension load ratio.

3A is a diagram illustrating a relationship between a steepness and a forward tension load ratio that affects a plate fracture, and FIG. 3B is a diagram illustrating a relationship between a steepness and a rear tension load ratio that affects a plate fracture.

[Explanation of symbols]

1: Stainless steel strip 2, 2 ': Work roll 4a, 4a', 4b, 4b '4c, 4c': Split backup roll 5: Shape detector 6: Shape display device

Claims (2)

[Claims] 1. A method for cold rolling a stainless steel strip with a multi-high rolling mill, wherein at least in the final finishing pass, the front and rear tension load ratio is set to 0.5 or more, preferably 0.6 or more. Characteristic cold rolling method for stainless steel strip. However, the tension load ratio is the value obtained by dividing the forward or backward tension by the proof stress of the material to be rolled. 2. The method for cold rolling a stainless steel strip according to claim 1, wherein the shape is controlled so that the steepness of the steel strip is 1.5% or more and less than 4.0%.