JP2011110594A - Method of manufacturing cold-rolled ferritic stainless steel strip excellent in surface gloss - Google Patents

Abstract

A method for stably producing a ferritic stainless steel strip having excellent surface gloss is provided.
In a method for producing a stainless cold-rolled steel strip in which steel strips subjected to cold rolling, annealing, or further pickling in this order are surface-finished by temper rolling, Cr plating is applied to the surface of the steel roll. Thereafter, the temper rolling is performed using a roll polished to have an average roughness Ra in the roll width direction of 0.003 μm or more and 0.010 μm or less so that the elongation is 0.8% or more and 2.0% or less without lubrication.
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Description

  The present invention relates to a method for producing a ferritic stainless steel cold-rolled steel strip excellent in surface gloss.

  Ferritic stainless steel cold-rolled steel strip is often used for home appliances, kitchen products, Western dishes, etc., and surface gloss is an important characteristic. Ferritic stainless steel cold-rolled steel strip is usually produced by hot rolling a slab refined by continuous casting to produce a hot-rolled steel strip, annealing (may be omitted in some cases), pickling, and cold rolling. The steel strip is manufactured by annealing (in some cases pickling) and temper rolling. In order to improve the surface gloss, it is important to smooth the surface in each step of pickling, cold rolling and temper rolling.

  Conventionally, many techniques have been disclosed for improving the surface gloss of a ferritic stainless steel cold rolled steel strip. Regarding cold rolling, for example, Patent Document 1 discloses roll roughness and lubrication of cold rolling. A method for producing a high-gloss cold-rolled steel strip by defining the state is described. On the other hand, regarding temper rolling, for example, Patent Document 2 defines roll roughness of temper rolling, or Patent Document 3 describes elongation of temper rolling as elongation by rolling. A method of manufacturing a high-gloss cold-rolled steel strip by specifying the ratio of the elongation rate by tension is described.

JP-A-2-92402 Japanese Unexamined Patent Publication No. 7-32004 JP-A-2005-230857

  However, in the method described in Patent Document 1, the oil pit in which the rolling oil is pushed into the surface of the steel sheet during cold rolling or the scratch marks transferred to the steel sheet by roll polishing are completely smoothed by temper rolling. Is difficult, and it is difficult to obtain a high-gloss cold-rolled steel strip close to a mirror surface with a glossiness (GS20 °) exceeding 1100. In the method described in Patent Document 2, although a high-gloss cold-rolled steel strip is obtained, the rolling distance of the temper rolling is increased and the roll roughness is increased to reduce the gloss after the temper rolling. Therefore, it was difficult to obtain a high-gloss cold-rolled steel strip. In the method described in Patent Document 3, it is often not sufficient to improve the surface gloss only by defining the ratio of the elongation rate due to temper rolling reduction and the elongation rate due to tension.

  As described above, the conventional technique has a problem that a ferritic stainless steel strip excellent in surface gloss cannot be stably produced.

  The present invention has been made to solve the above-mentioned problems and to provide a method for stably producing a ferritic stainless steel cold-rolled steel strip excellent in surface gloss, and the gist of the invention is as follows.

1. In the method for producing a stainless steel cold-rolled steel strip, the steel strip that has been subjected to cold rolling, annealing, or further pickling in this order is subjected to surface finishing by temper rolling.
After applying Cr plating to the surface of the steel roll, using a roll whose average roughness Ra in the roll width direction is polished to 0.003 μm or more and 0.010 μm or less, and without lubrication, the elongation becomes 0.8% or more and 2.0% or less. The method for producing a ferritic stainless steel cold-rolled steel strip excellent in surface gloss, wherein the temper rolling is performed as described above.

  According to the present invention, it is possible to stably produce a ferritic stainless steel cold-rolled steel strip that is superior in surface gloss as compared with the prior art.

Graph showing the effect of roll roughness and elongation of temper rolling on the glossiness of the steel strip surface Graph showing the effect of the present invention on the relationship between the rolling distance of temper rolling and the glossiness of the steel strip surface

  The inventors of the present invention have finally determined the surface quality of the cold-rolled steel strip, paying attention to the roll of temper rolling, and as a result of intensive studies, after the temper roll was Cr plated, the average roughness in the roll width direction The inventors have found that a ferritic stainless steel cold-rolled steel strip excellent in surface gloss can be stably produced by polishing so that the thickness Ra is 0.003 μm or more and 0.010 μm or less, and the present invention has been completed.

  That is, when a non-lubricating temper rolling is performed using a general steel roll such as high-speed steel or die steel polished to an average roughness Ra of 0.003 μm or more and 0.010 μm or less, the rolling distance is 10 km. If it exceeds the limit, the wear of the roll is remarkable, and a flaw called heat scratch in which the roll and the steel strip are baked may occur, and a high-gloss stainless cold-rolled steel strip cannot be stably obtained. On the other hand, in the present invention, a non-lubricated temper rolling is performed by applying a hard Cr plating to a steel roll such as a die steel and then polishing to a mean roughness Ra of 0.003 μm or more and 0.010 μm or less. Even when the rolling distance exceeds 20 km, the change in roll roughness due to roll wear is negligible and heat scratches do not occur. It was found that can be obtained. This utilizes the feature that the hard Cr plating layer is more excellent in wear resistance and heat scratch resistance than steel.

  An experiment for verifying the effect of the present invention will be described. In this experiment, SUS430 cold-rolled steel strip manufactured under two conditions shown in Table 1 was used for temper rolling.

  When the steel sheet surfaces are compared at the stage before temper rolling, the surface gloss of condition B with a small roll diameter during cold rolling is high, and the surface gloss of condition A with a large roll diameter during cold rolling is low. In any condition, cold rolling was performed using 10 cSt mineral oil at 40 ° C. In addition, after cold rolling, the steel strip of condition A was annealed in the atmosphere and subjected to nitric acid pickling, and the steel strip of condition B was brightly annealed.

  In addition, the glossiness of the steel sheet surface after cold rolling and temper rolling was measured according to JIS Z8741 Method 5, with the glossiness (Gs20 °) measured at 5 points in the rolling direction and in the direction perpendicular to the rolling direction. The average value was used. The surface roughness of the roll was measured in accordance with JIS B0601 under the conditions of a cutoff value of 0.25 mm and an evaluation length of 4 mm, and Ra (arithmetic average roughness) was obtained.

  Using the above-mentioned two types of steel strips as a test material, after Cr plating on the roll surface, using a roll with a diameter of 340 mm whose roll roughness was changed by polishing, the elongation was in the range of 0.3% to 2.4% The temper rolling was carried out with changing the surface, and the surface gloss of the obtained steel sheet was evaluated. The results are shown in FIG. The elongation was determined from the change in length of the steel sheet before and after temper rolling.

  As shown in FIG. 1, when a roll polished to an average roughness Ra of 0.003 μm or more and 0.010 μm or less is used, the elongation is 0.8% or more regardless of the surface quality of the steel sheet before temper rolling. It was found that a very excellent surface gloss with a glossiness (Gs of 20 °) of 1100 or more can be obtained under the above conditions.

  In the present invention, the reason why the average roughness Ra in the roll width direction is limited to 0.003 μm or more and 0.010 μm or less is as follows. This is because it is practically difficult to polish the temper rolling roll to an average roughness of less than 0.003 μm, and when polished to less than 0.003 μm, the gloss is almost the same as that of 0.003 μm. On the other hand, when it was larger than 0.010 μm, glossiness (Gs20 °) of 1100 or more could not be obtained.

  The reason for limiting the elongation of temper rolling to 0.8% or more and 2.0% or less is as follows. With an elongation of less than 0.8%, a glossiness (Gs20 °) of 1100 or more could not be obtained. If the elongation exceeds 2.0%, heat scratches are likely to occur, and even if the elongation is further increased, the gloss is almost the same. In addition, since the roll smooth surface is easily transferred onto the steel strip surface and effective in improving the gloss when the elongation rate is increased under tension, it is preferable that the elongation rate due to reduction is large.

  In the present invention, cold rolling, annealing, and pickling conditions are not particularly limited. In cold rolling, the steel sheet surface gloss after rolling changes depending on conditions such as roll diameter and rolling reduction, but the present invention is a condition for producing a stainless steel cold-rolled steel strip with excellent gloss, That is, any suitable roll diameter, roll roughness, and production conditions using rolled oil that suppress the drawing of rolled oil into the roll bite are applicable. Similarly, the annealing and pickling conditions may be bright annealing, atmospheric annealing, or pickling.

  In the case of bright annealing, annealing can be performed in an appropriate temperature range and time in an inert atmosphere or reducing atmosphere according to the steel type and application so that no temper color is attached. The oxide film may be removed with an appropriate acid, concentration, temperature, and immersion time so that the oxide film on the surface generated by annealing can be removed.

  In order to show the effect of the present invention in comparison with the conventional example, a SUS430 cold-rolled steel strip having a thickness of 0.8 mm and a width of 1250 mm, cold-rolled and bright-annealed under the same conditions, Ten coils were prepared for each example. Each was subjected to continuous temper rolling under the following conditions, and the surface gloss of the obtained steel strip was arranged together with the distance of temper rolling.

  The temper rolling was performed using a roll having a roll diameter of 570 mm under conditions of no lubrication and an elongation of 1.0% to 1.2% while applying a tension of 50 to 80 MPa. In the example of the present invention, a roll obtained by applying hard Cr plating to the die steel and then polishing so that the average roughness Ra in the width direction becomes 0.005 μm. In the conventional example, the die steel is set so that Ra becomes 0.005 μm. A polished roll was used.

  For the surface gloss of the steel strip, the steel strip was cut out from the position of each temper rolling distance, the glossiness was measured by the above method at seven locations in the plate width direction for each of the front and back surfaces, and the average value was taken as the representative value.

  As can be seen from the results obtained in FIG. 2, in the present invention example, even when the temper rolling distance is longer than in the conventional example, a high glossiness of 1100 or more can be stably obtained. Normally, in temper rolling, 20 or more coils (40 km or more in terms of rolling distance) are set as one cycle, and it is desired to perform temper rolling with one set of rolls. However, in the method using the steel roll of the conventional example, it is necessary to frequently change the roll, and high gloss cannot be stably obtained. However, in the method of the present invention, the temper rolling over this long distance is performed. High gloss can be obtained even if the process is performed.

Claims (1)

In the method for producing a stainless steel cold-rolled steel strip, the steel strip that has been subjected to cold rolling, annealing, or further pickling in this order is subjected to surface finishing by temper rolling.
After applying Cr plating to the surface of the steel roll, using a roll whose average roughness Ra in the roll width direction is polished to 0.003 μm or more and 0.010 μm or less, and without lubrication, the elongation becomes 0.8% or more and 2.0% or less. The method for producing a ferritic stainless steel cold-rolled steel strip excellent in surface gloss, wherein the temper rolling is performed as described above.

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