JPH09141303A - Austenitic stainless steel sheet excellent in coating film adhesion and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give a proper suggedness on a surface of steel sheet and to obtain the steel sheet having an excellent coating film adhesion by rolling under a draft in predetermined range with a roughly ground roll at least in the last pass of a finish rolling of stalinless steel sheet for coating. SOLUTION: At least in the last pass of the finish rolling of austenitic stainless steel, steel sheet surface roughness (RaL) at rolling direction is made to >=0.2μm Ra and the steel sheet surface roughness (RaT) at rectangular direction to the rolling direction is made to >=0.5μm Ra and the ratio (RaT/RaL) is made to >=2.0, by rolling at >=3->=10% draft with the roll wherein the surface roughness at the rolling direction is ground at >=0.4->=1.0μm Ra and the surface roughness at rectangular direction to the rolling direction is ground at >=0.8->=2.0μm Ra.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel sheet for painting and a method for producing the same.

[0002]

2. Description of the Related Art Stainless steel coated steel sheets have come to be used as roofing materials, exterior materials and the like because they have excellent properties such as light weight, high corrosion resistance, high weather resistance and maintenance-free properties. When used for this type of application,
Since it undergoes sheet metal working and various forming processes, it is necessary that the coating film is sufficiently adhered to the steel plate in order to satisfy the required characteristics even after the forming process.

As an attempt to obtain good coating film adhesion, there is known a technique of roughening the surface of a stainless steel plate as a base plate to obtain the adhesion between the steel plate surface and the coating film by an anchor effect. . For example, JP-A-52-225
Japanese Patent Publication No. 17 discloses that in the temper rolling process after finish annealing, a slight reduction is applied by a dull roll to give unevenness to the surface to obtain good coating adhesion by the anchor effect. However, in the method of the publication, only rolling means using a dull roll is disclosed, and when a long steel strip is continuously rolled, the entire width of the steel strip and the entire region from the leading end to the trailing end are disclosed. No technique is disclosed for obtaining good and uniform coating adhesion throughout. Further, since the method uses a dull roll, a device dedicated to dull roll processing is required, and an additional temper rolling process for forming a dull finished surface is required, which causes a problem of cost increase. Furthermore, there is a problem in that the steel is hardened by temper rolling after annealing and the softness required as a coated steel sheet is hindered.

Further, in Japanese Patent Laid-Open No. 61-84392, in a ferritic stainless steel sheet, the average roughness of the steel sheet surface is Ra of 2 μm or more by rolling using a rough surface roll in the finishing pass of the final rolling step, and annealing is performed. -It discloses a method for producing a steel sheet for coating which is excellent in coating film adhesion, which undergoes a pickling step. However, in Japanese Patent Laid-Open No. 61-84392, like the above-mentioned Japanese Laid-Open Patent Publication No. 52-22517,
No technique is disclosed for obtaining good and uniform coating film adhesion over a long steel strip.

[0005]

The present invention has been devised to solve such a problem, and is based on the finding that the surface roughness of a coated steel sheet has a great influence on the coating film adhesion. By adjusting the surface roughness of the coated steel sheet over the entire width and length of the coil in a way that does not increase the production cost without changing the manufacturing process of ordinary stainless steel sheet, the austenitic system with good coating adhesion is obtained. The purpose is to obtain a stainless steel sheet for painting.

[0006]

Means for Solving the Problems In the austenitic stainless steel typified by SUS304, the present invention is at least a finish rolling step after hot rolling, annealing / pickling or intermediate rolling, and intermediate annealing / pickling. R in the direction parallel to the roll axis (called the axial direction) in the final pass of rolling
With a having a surface roughness of 0.4 μm or more and 1.0 μm or less and Ra of 0.8 μm or more and 2.0 μm or less in the circumferential direction of the roll (referred to as circumferential direction), the rolling reduction is 3% or more and 10% or less. Surface roughness of the steel sheet obtained by rolling the steel sheet in the rolling direction followed by finish annealing and pickling.
coating film which satisfies the relationship of RaL ≧ 0.2 μm for RaL), RaT ≧ 0.5 μm for Ra perpendicular to the rolling direction (called RaT), and (RaT / RaL) ≧ 2.0. Provided are a coating steel sheet having excellent adhesion and a method for obtaining the steel sheet.

In ordinary finish rolling of a stainless steel plate, the surface roughness in the circumferential direction of the roll, which is ground by a fine-grained grindstone having a count of # 180 (hereinafter also referred to as the same) specified in JIS R6210, is 0.4 μm in Ra. The final pass of rolling was passed by using a roll having a surface roughness Ra of less than 0.8 μm in the direction parallel to the roll axis. The surface roughness of a steel sheet rolled using a roll having such a surface roughness is such that RaL is less than 0.2 μm in the rolling direction and RaT is less than 0.5 μm in the direction perpendicular to the rolling direction. Is. As the roll used for the final pass of rolling, a roll newly ground for each steel strip is usually used in order to secure the smoothness of the steel plate surface and prevent scratches. In the present invention, it was noticed that a roll newly ground for each steel strip was used. That is, in the finish roll grinding operation that is also performed in a normal rolled steel strip, the final pass rolling is performed by using a roll having a rough surface, which is ground by a grindstone having a coarser grain than in the case of the roll grinding used in the normal rolling. It has been found that the surface roughness of the steel sheet can be adjusted to a predetermined range by this, and an austenitic stainless steel sheet for coating with good coating adhesion can be produced without a separate temper rolling step.

Further, in the conventional method of imparting irregularities to the steel sheet surface by the dull roll in temper rolling, the steel sheet surface roughness of temper rolling has no anisotropy, that is, the surface roughness in the rolling direction (RaL). The ratio (RaT / RaL) of the surface roughness (RaT) in the direction perpendicular to the rolling direction is approximately 1
By so doing, it has been intended to secure the adhesion of the coating film. On the other hand, in the present invention, rather, the anisotropy of the surface roughness of the steel sheet is positively utilized, and it has been found that excellent coating film adhesion can be obtained if the ratio is 2.0 or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors examined the influence of the surface roughness of an austenitic stainless steel sheet on the adhesion of a coating film. As a result, after the finish rolling, the surface roughness R
When a steel plate having aL of 0.2 μm or more, RaT of 0.5 μm or more, and satisfying the relationship of (RaT / RaL) ≧ 2.0, the coating film adhesion that can withstand sheet metal processing and various processing It was clarified that a good steel plate for painting can be obtained.

Next, the present inventors examined means for obtaining the surface roughness of these steel sheets. In the final pass in ordinary finish rolling, a finish roll newly ground with a fine-grained grindstone for each steel strip is used. Therefore, by rolling the roll with a coarse-grained grindstone, or by using at least the final pass rolling with a roll having a large surface roughness in which the finish grinding with the fine-grained grindstone is omitted, RaL ≧ 0.
2 μm, RaT ≧ 0.5 μm and its ratio (RaT / Ra
It is possible to obtain a steel sheet which satisfies L) ≧ 2.0 and has excellent coating film adhesion.

The surface roughness of the roll used for finish rolling is
If it is smaller than an appropriate value, the steel plate surface roughness having sufficient coating film adhesion cannot be obtained. The lower limit of the roll surface roughness for obtaining the predetermined steel plate surface roughness is Ra 0.4 in the circumferential direction.
μm or more and Ra in the axial direction was 0.8 μm or more. If the surface roughness of the roll used for finish rolling is larger than an appropriate value, the amount of wear due to the contact between the rolling roll surface and the steel sheet increases, and the variation in the steel sheet surface roughness in the steel strip longitudinal direction increases. The variation in coating adhesion also becomes large.
Therefore, the upper limit roughness of the roll surface is Ra ≦ 1.0 μ in the circumferential direction.
m and Ra ≦ 2.0 μm in the axial direction.

Even if a roll having an appropriate surface roughness is used, if it is lower than an appropriate reduction ratio in the final rolling pass, a steel sheet surface roughness having sufficient coating film adhesion cannot be obtained. Therefore, the lower limit of the rolling reduction is set to 3%. Further, if the reduction ratio is higher than an appropriate value, the amount of wear due to contact with the steel plate on the surface of the rolling roll becomes large, and the steel strip (in the present invention, the term steel strip is used when the length of the raw sheet is taken into consideration during rolling). However, there is variation in the surface roughness in the longitudinal direction (substantially synonymous with steel plate). Therefore, the upper limit of the rolling reduction is set to 10%.

[0013]

Example 1 The inventors of the present invention melt-cast SUS304, and after hot rolling, annealing, pickling, and intermediate cold rolling, the sheet thickness is 0.95 mm.
After the intermediate annealing / pickling step, a cold-rolled steel strip having a plate thickness of 0.39 mm was manufactured through a finish cold-rolling step. The finishing cold rolling process was performed in 7 passes. The pass schedule is shown in Table 1. The rolling reduction of the final 7th pass is 3.2%. Six types of rolls were manufactured by changing the grindstone count so as to have different surface roughness, and a steel plate having six types of surface roughness was obtained by rolling with each roll.

Table 2 shows the surface roughness of the grinding wheel count and roll of the finishing roll used in the 7th pass and the surface roughness measurement results of the steel plates A, B, C, D, E and F thus obtained. Show. In addition, finish annealing of each steel plate
After pickling, the coating process was performed. Table 3 shows the results of examining the coating film adhesion of the coated steel sheet that was baked at a temperature of 200 to 250 ° C. after applying the urethane-modified resin-based undercoat paint and the silicone polyester resin-based topcoat paint.
In addition, the thickness of the undercoat coating film is 10 μm, and the thickness of the topcoat coating film is 15 μm. JISG3 is used for evaluation of coating film adhesion.
An impact deformation test and a bending test specified by 320 were performed. For steel plates A, B, C and D having a steel plate surface roughness within the range of the present invention, the coating film adhesion is good, whereas
Steel plates E and F having a surface roughness outside the range of the present invention had poor coating film adhesion.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

FIG. 1 shows the relationship between the surface roughness of the finishing roll used in the final pass of rolling and the steel plate surface roughness obtained as a result of rolling. In order to obtain sufficient coating film adhesion, the steel plate surface roughness RaL is 0.2 μm or more and RaT is 0.5 μm.
As described above, the ratio (RaT / RaL) needs to be 2.0 or more. RaL ≧ 0.2 μm, RaT ≧
In order to obtain a steel plate surface roughness of 0.5 μm, the roll surface roughness Ra is 0.4 μm or more in the rolling direction, and the roll surface roughness is 0.
It must be 8 μm or more.

[0019]

Example 2 The inventors cold-rolled SUS304 using rolls having different surface roughness in the circumferential direction and the axial direction, and manufactured steel sheets having various surface roughness in a laboratory. After applying a urethane-modified resin-based undercoat paint and a silicone polyester-based resin topcoat paint to these steel plates, baking was performed at a temperature of 200 to 250 ° C., respectively. The undercoat and top coat thicknesses are 9 μm and 18 μm, respectively.
Met. Then, the coating film adhesion was examined. The coating film adhesion evaluation method is the same as in Example 1. Table 4 shows the results.

The steel sheet surface roughness in the rolling direction and the direction perpendicular thereto is RaL ≧ 0.2 μm and RaT, respectively.
Steel sheets 1, 2 and 3 having a ratio (RaT / RaL) of ≧ 0.5 μm and 2.0 or more exhibit good coating film adhesion. On the other hand, RaL <0.2 μm or RaT
Steel sheets 5, 6 and 7 having a thickness of <0.5 μm had poor coating film adhesion. Also, RaL ≧ 0.2 μm and Ra
Steel sheet 4 having T ≧ 0.5 μm but a ratio (RaT / RaT) of less than 2.0 also had poor coating film adhesion.

[0021]

[Table 4]

[0022]

Example 3 A cold rolled steel sheet of SUS304 was obtained by the same process and pass schedule as in Example 1. In the sixth pass before the final pass and the seventh pass in the final pass of the finish cold rolling step, the steel plates of G to N were rolled using rolls ground by various count grindstones. Each steel sheet was finish-annealed and pickled, and then passed through a coating process to obtain a coated steel sheet. Table 5 shows the grinding counts of the rolls used for these rollings, the roll surface roughness, and the test results of the obtained steel plate surface roughness and coating film adhesion. The coating thickness of each steel sheet is 25 μm
Met.

A # 180 grinding roll (surface roughness: 0.22μ in the circumferential direction) used to obtain a normal smooth surface in the 6th pass.
m, axial direction 0.33 μm), then # 80 on the 7th pass
Grinding roll (surface roughness: 0.48 μm in circumferential direction, 0.95 μ in axial direction)
m) rolled with a # 46 grinding roll (surface roughness: 0.55 μm in the circumferential direction, 1.93 μm in the axial direction) on the 6th pass, and then # 80 grinding roll (the surface roughness: 0.53 μm on the circumferential direction: 1.93 μm in the axial direction). The steel plate K rolled by 0.48 μm in the circumferential direction and 0.94 μm in the axial direction) exhibits good coating adhesion. On the other hand, 6
# 46 grinding roll at pass (surface roughness: 0.55μ in circumferential direction)
m, axial direction 1.91 μm), # 18 on the 7th pass
0 grinding roll (surface roughness: 0.22 μm in circumferential direction, 0.31 in axial direction)
steel plate M rolled by (μm) and # 80 grinding roll in the 6th pass (surface roughness: 0.49 μm in the circumferential direction, 0.93 μm in the axial direction)
And a steel plate N rolled by a # 220 grinding roll (surface roughness: circumferential direction 0.20 μm, axial direction 0.24 μm) on the 7th pass does not have sufficient coating film adhesion. That is, in the present invention, it can be seen that a steel plate surface having good coating film adhesion can be obtained by rolling using a roll having a rough surface at least in the final pass of finish rolling.
The surface roughness of the rolling roll in the pass before the final pass does not matter.

[0024]

[Table 5]

[0025]

Example 4 SUS304 obtained by the same process as in Example 1
In the final pass of finish rolling, # 46 grinding roll (surface roughness: 0.54 μm in circumferential direction, 1.97 μm in axial direction) or # 80 grinding roll (surface roughness: 0.45 μm in circumferential direction, 0.96 μm in axial direction) was used. Then, finish rolling was carried out while changing the reduction rate. The relationship between the rolling reduction and the steel plate surface roughness at this time is shown in FIG. When the rolling reduction is less than 3%, the surface of the steel sheet is smooth, and a steel sheet having a surface roughness required to obtain good coating adhesion has not been obtained. That is, RaL <0.2 μm,
RaT <0.5 μm. Further, the surface roughness of the steel sheet increases as the rolling reduction increases until the rolling reduction reaches 10%, but the steel sheet surface roughness tends to be saturated when the rolling reduction exceeds 10%.

In FIG. 3, in the final pass of finish rolling,
# 80 grinding roll (surface roughness: 0.48 μm in circumferential direction, axial direction
The relationship between the surface roughness of the front end of the steel strip and the surface roughness of the rear end of the steel strip when rolled at various reduction ratios of 0.95 μm) is shown. When the rolling reduction exceeds 6%, the surface roughness of the tip of the steel strip remains rough with the increase, whereas
The surface roughness of the rear end portion of the steel strip becomes fine, and the difference between the surface roughness of the front end portion and the surface roughness of the rear end portion becomes large. Especially the rolling reduction is 10
%, The surface roughness is sufficient to obtain good coating adhesion at the front end of the steel strip, whereas it cannot be obtained at the rear end of the steel strip. Becomes this is,
As the rolling reduction increases, the friction between the roll and the steel plate increases and the amount of wear of the roll increases, so the surface roughness of the roll decreases when the rear end of the steel strip is rolled. Is thought to be the cause. The change in the surface roughness of the steel strip in the same steel strip means that the appearance after coating changes in the steel strip, which is not preferable in terms of quality. Therefore, in the present invention, the upper limit of the rolling reduction of the final pass is set to 10%.

[0027]

Example 5 A cold rolled steel sheet of SUS304 was obtained by the same process and pass schedule as in Example 1. In the final pass of finish rolling, the steel strips O and P were made using the # 80 grinding roll, # 46 grinding roll and # 30 grinding roll, respectively.
And Q were obtained by rolling. Table 6 shows the roll grinding count, the roll surface roughness, the surface roughness of the steel strip front end and the steel strip rear end in the final pass. Further, FIG. 4 shows the surface roughness of the steel strip front end and the steel strip rear end at this time. The surface roughness exceeds 1.0 μm in Ra in the circumferential direction and Ra in the axial direction.
Strip Q rolled with a grinding roll exceeding 2.0 μm
Then, the front end of the steel strip is in the range of surface roughness where good coating adhesion is obtained, whereas the rear end of the steel strip is in the range of surface roughness where good coating adhesion is not obtained. turn into. Therefore, in the present invention, the upper limit of the surface roughness of the roll used for the final pass rolling is Ra 1.0 μm in the circumferential direction and Ra 2.
It was set to 0 μm.

[0028]

[Table 6]

[0029]

[Effect] According to the present invention, in the final pass of the finish rolling of the austenitic stainless steel sheet, by using a roll ground so that the surface roughness becomes rough, and rolling at a reduction ratio within a predetermined range, the entire steel strip is rolled. It is possible to obtain a coating steel sheet having excellent coating film adhesion, in which appropriate unevenness is provided on the surface of the coating.

[0030]

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the surface roughness of a finishing roll used in the final pass of finish rolling and the steel plate surface roughness obtained thereby.

FIG. 2 is a diagram showing the relationship between the rolling reduction in the final pass of finish rolling and the steel plate surface roughness obtained thereby.

FIG. 3 is a diagram showing the surface roughness of the steel sheet at the leading end and the trailing end of the steel strip rolled at different reduction ratios in the final pass of finish rolling.

FIG. 4 is a diagram showing the surface roughness of the steel plate at the leading end and the trailing end of a steel strip rolled by rolls having different surface roughnesses in the final rolling final pass.

Claims (2)

[Claims] 1. The surface roughness of a steel sheet after finish rolling after hot rolling, annealing, pickling or intermediate rolling, intermediate annealing, and pickling steps is Ra defined in JIS B0601 and Ra in the rolling direction. (RaL) is 0.2 μm or more, Ra (RaT) in the direction perpendicular to the rolling direction is 0.5 μm or more, and the ratio (RaT / RaL) is 2.0 or more. Excellent austenitic stainless steel sheet 2. In finish rolling, the surface roughness Ra is 0.4 μm or more and 1.0 μm or less in the direction parallel to the roll axis, and the roll circumferential Ra is 0.8 μm or more and 2.0 μm or less.
The austenitic stainless steel sheet having excellent coating film adhesion according to claim 1, characterized in that rolling is performed at a rolling reduction of 3% or more and 10% or less in a final pass of rolling using a roll ground as described below. Manufacturing method