JP3188643B2 - Composite roll for stainless steel cold rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold roll of stainless steel, and more particularly to a roll capable of advantageously producing a cold rolled stainless steel strip having excellent surface gloss.

[0002]

2. Description of the Related Art Conventionally, a cold-rolled stainless steel strip is cold-rolled with a Sendzimir mill or the like using a work roll made of a steel alloy having a work roll diameter of 150 mm or less after annealing and pickling a hot-rolled steel strip. Finish annealing Pickling or finish bright annealing,
It was manufactured by a process of finish pass rolling at a rolling reduction of 1.2% or less. Stainless steel cold rolled steel strip manufactured through such a process, for example, in the case of a ferrite system represented by SUS430, is often used as it is on the surface after manufacturing,
Good surface gloss is required for the product after finish temper rolling. On the other hand, in the case of an austenitic material represented by SUS 304, buffing is often performed after finish temper rolling, and it is necessary to exhibit excellent surface gloss after buffing.

Recently, in order to efficiently produce a cold rolled stainless steel strip, a method has been adopted in which cold rolling is continuously performed in one direction by a cold tandem mill using a work roll having a large diameter of 150 mm or more. It is getting. For example, JP-A-8
Japanese Patent No. 39103 discloses a technique for increasing the production efficiency and increasing the surface gloss of a cold rolled stainless steel strip by using a WC superalloy work roll for one or more stands in such a cold tandem mill. I have.

[0004]

However, according to the method disclosed in Japanese Patent Application Laid-Open No. 8-39103, not only the surface gloss of the cold-rolled stainless steel strip has not yet reached a sufficient level, but depending on the case, the work may be difficult. There were problems that the roll was broken and the roll cost was extremely high.

A technique similar to a part of the present invention is proposed in Japanese Patent Publication No. 5-55202, Japanese Patent Application Laid-Open No. 4-41007, and Japanese Patent Application Laid-Open No. 60-11704.
However, the one disclosed in Japanese Patent Publication No. 5-55202
This is a composite roll in which carbide or high-speed steel powder is sintered to the outside of a steel cylinder by high-temperature isostatic pressing, and a steel cylinder and a diffusion-bonded sleeve are fitted with a steel arbor. It is a roll for rolling a bar and a bar between them, and there is no mention of conditions for improving the surface gloss in cold rolling. Further, the high Young's modulus material is a brittle material such as ceramics and cemented carbide, and if stress is concentrated during rolling, there is a concern that destruction may occur from that location.
Therefore, it is important to prevent stress concentration on the material during rolling. The technique disclosed in Japanese Patent Application Laid-Open No. 4-41007 is a proposal of a method for preventing this stress concentration. In this method, ceramic or cemented carbide is used for the outermost layer of the rolling roll, and a saw-tooth groove is formed in non-oxidized copper, which is an elastoplastic body, as an intermediate material between this and the core material, or a copper wire is formed. The effective elastic modulus is set to 3000 to 17000 kgf / mm ² by means such as winding. However, with this rolling roll, for example, when rolling a rolled material having extremely high deformation resistance such as a stainless steel plate at a high load and a high surface pressure, the roll cannot be eccentric due to the plastic deformation of the intermediate layer or the cylindrical shape cannot be maintained. When the rolling further proceeds, there is a fear that the rolls break and cause a serious problem. Furthermore, Japanese Patent Application Laid-Open No. 60-111704 proposes a roll having a hard metal alloy roll barrel and a steel roll neck portion, which is provided between the hard metal alloy roll barrel and the steel neck portion. The present invention relates to a roll in which an intermediate material made of cemented carbide having a higher binder content and higher strength than that of the cemented carbide of the roll barrel is provided by brazing. However, not only is there no description about the material of the cemented carbide, but since the entire roll barrel portion is made of cemented carbide, no significant cost reduction in the case of manufacturing a large-diameter roll has been solved.

An object of the present invention is to solve the above problems the prior art has had, is capable of further improvement of the surface gloss of the stainless cold-rolled steel strip, capable of stably rolling stearate
Rolls for stainless steel cold rolling. Another object of the present invention is to provide an inexpensive stainless steel cold-rolling roll which can further improve the surface gloss of a cold-rolled stainless steel strip and does not cause trouble such as roll breakage. It is in. Still another object of the present invention is to provide a roll for stainless steel cold rolling, in which each of the above characteristics is particularly effective when used in a cold tandem mill.

[0007]

According to the present invention, the roll barrel is composed of three or more concentric layers, and the outermost layer has a Young's modulus of 35,000 kgf / mm ² or more and a layer thickness of 3% of the roll radius. As described above, the intermediate layer located between the outermost layer and the shaft core is a composite roll for stainless steel cold rolling having a Young's modulus smaller than that of the outermost layer and larger than that of the shaft core.

In the above invention, when the intermediate layer is composed of two or more layers, it is preferable to arrange a material having a higher Young's modulus as the intermediate layer is relatively outer.

Furthermore, in these inventions, the outermost layer and the intermediate layer are both made of WC-based cemented carbide, ultrafine
It is desirable that the composition of the hard alloy be such that the outermost layer has a smaller binder metal equivalent.

[0010]

Embodiments of the present invention will be described below. First, the inventors have found that the surface roughness of the steel strip after cold rolling has a great effect on the surface gloss of the product, and the surface roughness of the steel strip after cold rolling has a significant effect on the steel before cold rolling. In order to obtain a steel strip with good surface gloss, a part of the surface roughness of the strip (steel strip annealed and pickled after hot rolling) remains after cold rolling, It has been found that it is better to reduce the existing recesses on the surface of the steel strip during rolling. However, in order to sufficiently reduce the concave portions of the steel strip surface before the cold rolling by sufficiently contacting the convex portions of the roll surface with the steel strip surface during the cold rolling, a cold tandem using a large-diameter work roll is required. In the mill, the roll diameter is large compared to the conventional small-diameter roll mill, so a large amount of rolling oil is interposed between the roll and the steel strip, and the convex part of the roll surface is sufficiently inserted into the concave part of the steel strip surface. Difficult to contact.

To cope with this, the inventors have found that it is effective to satisfy the following conditions (a) and (b). (a) To make the rolling oil as hard as possible to be drawn between the roll and the steel strip. (b) Create sufficient pressure between the roll and the steel strip. First, regarding (a), the cause of the rolling oil being drawn between the roll and the steel strip is a hydrodynamic force acting on the rolling oil, and this force is greatly affected by the biting angle, and
It was found that when this angle was increased, the rolling oil was less likely to be drawn. Therefore, the inventors focused on the Young's modulus of the roll, and concluded that if the Young's modulus of the roll was increased, the flatness of the roll was reduced, and as a result, the bite angle could be increased and the rolling oil could be hardly drawn. It was done.

Therefore, the relationship between the Young's modulus of the roll and the gloss of the steel sheet surface after rolling will be described. For the surface gloss of cold rolled stainless steel strip, see JIS Z8741 Glossiness measurement method (Gs
20 °), and the gloss was evaluated in the following order from 5 to 950 or higher: A: 800-950: A; 600-800: B; 400-600: C; According to the experiments performed by the inventors, as shown in FIG.
Gloss increases gradually from 000 kgf / mm ^2, but a distinct difference in gloss appears when the Young's modulus is 35,000 kgf / mm ² or more. The Young's modulus is 35000kgf / mm ²
If it is above, the higher the value, the better, 50000k
It was found that when the gf / mm ² or more was used , more excellent gloss was exhibited, which was desirable. In general, when the Young's modulus increases,
It often shows a kind of brittleness, and using a material having too high Young's modulus as a roll material is not preferable in terms of roll strength. For example, as a material having a high Young's modulus, a WC cemented carbide may be mentioned, but it is preferable to set the bonding equivalent so that the Young's modulus is 58000 kgf / mm ² or less. Further, when the Young's modulus is increased, in addition to the above-described effects, the contact length between the roll and the steel strip is reduced, and as a result, the pressure between the roll and the steel strip is increased.
It was confirmed that there was also an effect of generating a sufficient pressure as shown in (b).

When a WC cemented carbide having a high Young's modulus is used as a material for improving the gloss of a large-diameter work roll such as a cold tandem mill, an integral roll of the WC cemented carbide may be used. However, there is a problem that the cost is extremely high. In order to solve this problem, it is extremely effective to employ a composite roll in which the outer layer is made of a WC cemented carbide and the core is a steel material.

However, when such a composite roll is used, it is conceivable that the flat deformation of the roll during rolling is different from that of the WC cemented carbide integrated roll. The gloss of the steel strip surface after rolling is greatly related to the flat roll radius, and the thickness of the outer layer of the roll barrel is optimized so that the flat deformation of the composite roll does not differ greatly from that of the WC cemented carbide integrated roll. Must be a value. If the thickness of the outer layer of the roll barrel is too large, the flatness of the roll can be made different from that of the WC-based hard metal integrated roll, but the cost also increases, so the thickness that balances performance and cost Is very important.

[0015] From the above viewpoint, the inventors of the present invention have examined the thickness of the outer layer of a composite roll using a WC cemented carbide for the outer layer by FEM.
The analysis and the rolling experiment were studied diligently. Figure 2 shows a WC cemented carbide with a high Young's modulus (Young's modulus 51000kgf / m
m ²⁾ when the flat roll radius integral roll was R _1, the difference between R ₁ of the flat roll radius R of the composite roll of the thickness of the outer layer was _{varied, (R-R 1) ×} 100 / R Expressed as ₁ ,
The relationship between this ratio and the ratio of the outer layer thickness to the radius is shown. FIG. 3 shows the relationship between the surface gloss of the cold-rolled steel strip and the ratio of the outer layer thickness to the radius, which are similarly expressed. As shown in FIGS. 2 and 3, the difference in flat roll radius is about 70% for a steel integrated roll (Young's modulus: 21000 kgf / mm ² ), while the flat roll radius of the composite roll is About 3% of the radius (ie,
1.5%), the flatness difference with the WC cemented carbide integrated roll is
It was within 10%, indicating that a sufficient effect on gloss could be obtained. Also, when the thickness of the WC outer layer is set to 10% or more of the roll radius (5% or more of the diameter), the difference between the flat roll radius and the case of the WC cemented carbide integrated roll can be made within 2%, and It was also found that a higher effect was obtained with respect to. Thus, the thickness of the WC outer layer is at least 3% of the radius, preferably at least 10% of the radius. Furthermore, as a result of studying the relationship between the roll radius and the thickness of the outer layer by the inventors, it was found that this relationship was substantially the same even when the Young's modulus of the outer layer changed.

On the other hand, when the roll is compounded in this manner, the discontinuity of the Young's modulus at the boundary between the outer layer of the roll, which is a high Young's modulus material, and the steel core causes a pull on the inner peripheral surface of the outer layer of the roll during rolling. Stresses are generated, and when the stresses exceed the limits, the rolls break. In order to alleviate this stress, the present inventors used a material having a Young's modulus smaller than the outer layer and larger than the shaft core between the roll outer layer and the roll axis as shown in FIG. It was found that the above-mentioned stress can be relieved by providing an intermediate layer. FIG.
Shows the radial distribution of the stress. As shown in FIG. 5, in the case of a conventional composite roll composed of two layers of a high Young's modulus outer layer and a steel shaft core, a large tensile stress acts on the inside of the outer layer near the boundary between the outer layer and the shaft core, and the roll breaks. Easily occur. On the other hand, by providing the intermediate layer according to the present invention, the tensile stress near the boundary between the outer layer and the intermediate layer and the tensile stress near the boundary between the intermediate layer and the axis are smaller than in the conventional case. It can be used stably without being damaged.

The inventors have further studied a method for relaxing the tensile stress. Since the tensile stress is caused by the difference in the Young's modulus between the outer layer of the roll and the intermediate layer, it has been found that the tensile stress can be further reduced by reducing the difference in the Young's modulus. However, when the Young's modulus of the intermediate layer approaches the Young's modulus of the outer layer of the roll, the difference in the Young's modulus between the intermediate layer and the roll core increases, and a large tensile stress acts on the inner surface of the intermediate layer. Therefore, as a result of further study, the inventors have found that it is extremely effective to provide two or more layers as an intermediate layer in order to eliminate such a phenomenon.

Further, when the inventors use, for example, a WC cemented carbide as a material having a high Young's modulus, the structure is extremely uniform, and the roll surface roughness set low at the beginning of rolling is such that the rolling progresses and It has been found that the roughness does not increase as steel rolls do. Here, the WC cemented carbide is composed of WC (tungsten carbide) as a main component.
Ni-based alloys, Co-based alloys, Ti and Cr, etc., alone or in combination. And the binder metals Ni and C
As the bond equivalent of o, Ti, Cr, etc. is reduced,
The Young's modulus gradually increases, and the tensile stress acting between the layers is reduced. Therefore, when using a WC-based cemented carbide as outermost layers and the intermediate layer, the composition of the cemented carbide is said to be desirable to reduce the bond equivalent of the binder metal as a layer on the relatively outer side.

[0019]

[Example] SUS 43 as ferritic stainless steel strip
0 After the hot rolled steel strip is annealed and pickled using a steel strip, the fifth stand of a five-stand cold tandem mill (roll diameter φ285 mm)
To, as an invention example, the shaft core 5% Cr forged steel, the Young's modulus 51000kgf / mm ² the outermost ^layer, Co17% of WC-based cemented carbide, about 40000kgf / mm ² Young's modulus of the intermediate ^layer, Co40% of WC-based than Hard metal, diameter 285mm, outermost layer thickness 5mm (roll radius 3.5mm)
%), And a composite work roll composed of three layers having an intermediate layer thickness of 4 mm was applied, and cold-rolled from a hot-rolled steel strip thickness of 4.0 mm. At this time, the rolling reduction of the 5th stand is set at 20%, 30%, and 40%.
Set to standard. Thereafter, the steel strip was finish-annealed, pickled, and temper-rolled at an elongation of 1.0%. (Invention Example 1)
As another invention embodiment, the fifth stand, the Young's modulus of the shaft core 5% Cr forged steel, the Young's outermost layer modulus 51000kgf / mm ^2, Co17% of WC-based cemented carbide, the outer intermediate layer (intermediate layer 1) About 4500
0kgf / mm ^2, Co30% of WC-based cemented carbide, inside the intermediate layer (the intermediate layer 2) Young's modulus of about 35000kgf / mm ^2, Co50% of W
Arranged as a C-based cemented carbide, apply a composite work roll of a diameter of 285 mm, the outermost layer of thickness 5 mm, thickness 4mm the intermediate layer 1, four layers thick 3mm of the intermediate layer 2, was cold rolled . Thereafter, the steel strip was finish-annealed, pickled, and temper-rolled at an elongation of 1.0%. (Invention Example 2)

On the other hand, as a comparative example, Co was added to the fifth stand.
The consists WC-based cemented carbide containing 17%, roll diameter 285m
m and cold rolled. Thereafter, the steel strip was finish-annealed, pickled, and temper-rolled at an elongation of 1.0%. (Comparative Example 1) Also, Co was added to the fifth stand.
17%, in Ni28% WC-based cemented carbide containing Crs 7% and a Young's modulus and 33000kgf / mm ^2, by applying the integral work rolls of roll diameter 285 mm, and cold rolling. Thereafter, the steel strip was finish-annealed, pickled, and temper-rolled at an elongation of 1.0%. (Comparative Example 2) In addition, the shaft core was set to 5% Cr on the fifth stand.
And forged steel Young's modulus of about 51000kgf / mm ² the outermost ^layer, Co17%
It consists of WC-based cemented carbide, diameter 285mm, wall thickness of the outer layer 5
A 2 mm composite work roll was applied and cold rolled.
Then, the steel strip is finish-annealed and pickled, and the elongation is 1.0%.
Temper rolling. (Comparative Example 3) Also, in the fifth stand,
A WC-based cemented carbide containing 17% Co is sprayed onto a 5% Cr forged steel shaft core to apply a composite work roll with a roll diameter of 285mm with a wall thickness of 0.5mm (0.35% of the roll radius). Rolled. Thereafter, the steel strip was finish-annealed, pickled, and temper-rolled at an elongation of 1.0%. (Comparative Example 4) Further, as a conventional example, cold rolling was similarly performed in the case where a work roll using ordinary 5% Cr forged steel was applied to all stands of a five-stand cold tandem mill. Thereafter, the steel strip was subjected to finish annealing pickling and temper rolling at an elongation of 1.0%.

Table 1 shows the specifications of the fifth stand roll in each of the above examples. The surface gloss of these cold-rolled stainless steel strips was measured by the JIS Z8741 gloss measurement method (Gs20 °), and in the order of goodness, the gloss was 950 or more: A, 800-950: A, 600-800: B, 400-400. The evaluation was made on a scale of 1 to 5, with 600 being C and 400 or less being D. From the results shown in Table 2, the stainless steel cold rolled steel strip manufactured using the rolling roll of the present invention is equivalent to the steel strip manufactured using the WC-based cemented carbide integrated roll of Comparative Example 1; 4 and a significantly better gloss than the steel strips manufactured in the conventional examples. Regarding the roll strength, even when the rolling reduction was higher than in the case of Comparative Example 3 and Comparative Example 4, good results were obtained without breakage of the roll.
On the other hand, in the conventional example, when the rolling reduction was 30% or more, heat streaks (seizure flaws) occurred on the surface of the rolled material and the roll surface, and the surface gloss was rejected.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As described above, according to the present invention, the Young's modulus is 35,000 kgf / mm ² or more and the thickness is 3 mm of the roll radius.
% Of the outermost layer, a shaft core, and an intermediate layer having a Young's modulus smaller than the outermost layer and larger than the shaft core. Can be rolled without causing breakage. When the intermediate layer has two or more layers, the risk of roll breakage can be further reduced by arranging the outer layer so that the Young's modulus of the outer layer is higher than the Young's modulus of the inner layer. According to the present invention, by adjusting the Young's modulus, the circumferential stress at the layer boundary can be reduced, so that a stronger reduction can be achieved as compared with a composite roll composed of only the shaft core and the outer layer of the roll, and the efficiency can be reduced. Rolling becomes possible. The composite roll of the present invention exhibits excellent effects not only in cold rolling of stainless steel strip but also in rolling of ordinary steel strip.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Young's modulus of an outer layer material and the surface gloss of a cold-rolled steel strip.

FIG. 2 is a graph showing a relationship between a ratio of a high Young's modulus outer layer material to a roll radius and a flat roll radius.

FIG. 3 is a graph showing a relationship between a ratio of a high Young's modulus outer layer material to a roll radius and a surface gloss of a cold-rolled steel strip.

FIG. 4 is a schematic sectional view of a barrel portion of a composite roll.

FIG. 5 is a diagram showing a circumferential stress distribution at a layer boundary of a composite roll.

Continuing on the front page (72) Inventor Hajime Nagai 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Akihiko Fukuhara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corp. Inside steelworks (56) References JP-A-63-180310 (JP, A) JP-A-8-39103 (JP, A) JP-A-4-41007 (JP, A) JP-A-61-219408 (JP, A) JP-A-60-111704 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 27/00 B21B 1/22 B21B 3/02 B21B 27/03 510

Claims (3)

(57) [Claims] The roll barrel comprises three or more concentric layers, and the outermost layer has a Young's modulus of 35,000 kgf / mm ² or more,
And the thickness of the layer is 3% or more of the roll radius, and the intermediate layer located between the outermost layer and the shaft core has a Young's modulus smaller than that of the outermost layer and larger than that of the shaft core. Characteristic, composite roll for cold rolling of stainless steel . 2. The stainless steel for cold rolling as claimed in claim 1, wherein the intermediate layer is composed of two or more layers, and the Young's modulus of the intermediate layer is larger as the layer is relatively outer. Composite roll. Wherein the outermost layer and the intermediate layer are both made of WC-based cemented carbide, the composition of the ultra-hard alloy, wherein the bond equivalent of the binder metal as a layer on the relatively outer side is small, The composite roll for cold rolling of stainless steel according to claim 1 or 2.