JP2938207B2 - Manufacturing method of mirror-finished steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a mirror-finished steel sheet made of low carbon steel.

[0002]

2. Description of the Related Art In general, low-rolled steel is used as a cold-rolled steel sheet having a mirror-finished surface used for various fittings such as a stove reflector, a fog lamp reflector, a binder backing, and a battery jacket. It is manufactured through the steps of cold rolling → washing → box annealing → temper rolling. The surface gloss of the cold-rolled steel sheet is provided in the temper rolling step.

Conventional techniques for imparting gloss to a steel sheet in this temper rolling are roughly classified into two methods, one of which is a method of eliminating uneven color tone on the surface of a material steel sheet before a mirror finish (for example, see Japanese Patent Application Laid-Open Another technique is to prevent the work roll surface from fogging during mirror finishing (for example, Japanese Patent Application Laid-Open No. 57-752).
No. 12). That is, the former is rolled with a dull roll having a surface roughness of 1.0 to 2.6 μRa at the final stand of cold rolling, and after annealing, is temper-rolled with a bright roll having a surface roughness of 0.20 μRa or less, thereby obtaining a steel sheet surface. This is a technology to obtain the gloss by flowing the convex part generated by the dull roll into the concave part by the bright roll, and the latter is to reciprocate a brush roll with abrasive particles attached to the work roll entrance side at the time of mirror finishing in temper rolling. This technology maintains the gloss of the work roll surface.

[0004]

However, in the former case, the roughness of the work roll which should keep the surface roughness Ra of 0.20 μm or less becomes large, or the gloss of the mirror finish work roll becomes entirely or partially. , The work roll had to be replaced by a "roll change", and the productivity was hindered by the replacement work in which the line was stopped. In the latter case, when a nylon brush roll or the like is provided to purify the work roll surface, equipment costs are required. In addition, in order to perform uniform polishing in the width direction of the steel sheet, fine equipment maintenance is required, and a mirror finish ( Surface roughness Ra of 0.10 μm or less). Further, there is a problem that a hairline pattern or the like is formed on the steel sheet and the surface appearance quality is impaired.

In view of the above-mentioned conventional problems, the present invention has investigated the case where the gloss of the work roll surface is maintained for a long time during mirror finishing and the case where a part or the whole of the work roll becomes fogged early. From the fact that the Si content of the sodium silicate during the cleaning step, which is the pre-process of temper rolling, adheres to the surface of the steel plate at ^{2 to 5} mg / m ² per side, so that the gloss of the work roll surface is maintained. It is an object of the present invention to solve the above-mentioned problem by causing the Si component to adhere to a steel sheet.

[0006]

According to the present invention, in order to achieve the above object, each step is passed in the order of cold rolling, washing, box annealing, and temper rolling, and the steel sheet surface is subjected to final temper rolling. In the method for producing a cold-rolled steel sheet having a mirror-finished surface, the steel sheet surface is subjected to electrolytic cleaning in an electrolyte solution containing sodium silicate and caustic soda during the cleaning step of the above steps, and the Si content of sodium silicate is applied to the steel sheet surface. Is a method for producing a mirror-finished steel sheet by electrodeposition of ² to 5 mg / m ² .

[0007]

In order to manufacture a mirror-finished steel sheet, it is necessary to maintain the gloss of the work roll surface in the temper rolling, and it is necessary to clarify the mechanism for maintaining the gloss. Hereinafter, the gloss maintenance mechanism discovered by the inventors will be described.

First, the surface of a steel sheet and the surface of a work roll obtained by temper-rolling the steel sheet with a box-annealed material and a continuous-annealed material are mirror-finished. The analysis and adhesion thickness (discharge time) were investigated.

[0009] The results show that the box-annealed material has more surface concentrating elements (Mn, Si, P, S, Al) than the continuous annealed material, but the work roll surface that has been temper rolled is opposite to the steel sheet surface. Almost nothing adheres to the roll surface through which the box annealing material has passed. It was also found that the surface of the work roll through which the continuous annealed material with a small amount of the condensate was passed had a large amount of the above-mentioned deposits.

[0010] This reversal phenomenon is because silica (SiO ₂ ) is electrodeposited on the surface of the steel sheet because the surface of the box annealing material is electrolytically cleaned in an alkaline electrolyte containing sodium silicate in a cleaning step before annealing. is there. In other words, the silica on the surface covers the concentrated substances (Mn, Si, Al) precipitated from the steel, and has the function of shaving off the substance adhering to the work roll surface during temper rolling, and the concentrated substance on the steel sheet surface directly Because of the function of preventing contact with the roll, it has been found that even when the box-annealed material having a thick concentrated layer is temper-rolled, the concentrated material causing clouding does not adhere to the work roll surface.

A technique for adhering sodium silicate to the surface of a steel sheet in the cleaning step is disclosed in Japanese Patent Application Laid-Open No. 57-19429.
No. 6, Japanese Unexamined Patent Publication No. 62-235500, etc., the purpose of which is basically to prevent sticking during box annealing. Further, if the amount of the sodium silicate deposit is too large, a temper color is generated, and the plating characteristics after tin plating are deteriorated.

Further, the present inventors have investigated the range of the amount of SiO ₂ adhered which is suitable for maintaining the gloss of the work roll.
If the amount is less than 1 mg / m ² per one side, the deposits of the concentrate on the surface of the steel sheet on the work rolls start to occur. Also, 5m
When g / m ² was exceeded, it was found that milky tempered color after annealing began to be generated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. As a material for the example, a cold-rolled steel strip was used as a material for Examples and Comparative Examples having different SiO ₂ adhesion amounts as shown in Table 1 by changing a passing speed and an electrolytic current value in a cleaning process. The coil length is
In each case, the distance was 20 km. Box annealing temperature up to 63
0 ° C. The temper rolling for performing mirror finishing after annealing was dry rolling of two stands, and a 1000th work roll was used together with the first stand and the second stand. Further, in order to keep the rolling conditions constant, the rolling load of the first stand was set to a plate width (mm) × 0.9 tons, and the second stand was kept constant at 200 tons, which is the minimum load of the used mill capacity. The elongation rate is 0.8% in each case.

Table 1 shows the results of the above experimental examples. Si0 ₂
In Examples 1 to 3 in which the amount of adhesion was ² to 5 mg / m ² , good mirror-finished surfaces were obtained in all cases.
_{2 (} less than 2 mg / m ² ), the surface of the roll became cloudy at the elongation of 12 km in the temper rolling, and after the completion of the 20 km rolling, both the roll surface and the coil surface lost gloss.
Further, a thickened deposit deposited on the roll surface (discharge time until the intensity of Fe element in GDS is saturated) was deposited for 12 seconds (FIG. 1). FIG. 2 shows that Examples 1-3 are 2.5-3 seconds and Comparative Example 2 is 2.5 seconds. In Comparative Example 2,
Although the gloss of the roll surface was maintained, a milky white temper color was generated on the surface of the steel strip, and the milky white of the edge corresponding to the outer winding during annealing was particularly remarkable.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, by depositing ² to 5 mg / m ² of silica on the surface of the steel sheet in the electrolytic cleaning step, impurities concentrated on the steel sheet surface during annealing are reduced. Prevents deterioration of gloss by adhering to rolls, and can provide high-gloss steel sheets,
Since there is no need to perform "roll change" at a frequency as in the related art, a great effect can be achieved such as a great improvement in productivity.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of GDS analysis of a roll surface deposit after passing through Comparative Example 1.

FIG. 2 is a graph showing the results of GDS analysis of the adhered material on the roll surface after passing through Examples 1 to 3 and Comparative Example 2.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Toshio Akizuki 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside Chiba Works (72) Inventor Kenji Ueda 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside Chiba Works (56) References JP-A-3-243795 (JP, A) JP-A-4-285124 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C25D 9/04 C25D 13/02

Claims (1)

(57) [Claims] 1. A method of manufacturing a cold-rolled steel sheet, wherein each step is passed in the order of cold rolling, washing, box annealing, and temper rolling, and the steel sheet surface is mirror-finished in the final temper rolling. In the washing step, the surface of the steel sheet is subjected to electrolytic cleaning in an electrolytic solution containing sodium silicate and caustic soda, and the Si content of sodium silicate is electrodeposited at ² to 5 mg / m ² on the surface of the steel sheet. Manufacturing method of mirror-finished steel sheet.