JPH04301096A - Manufacturing method for mirror-finished steel sheet - Google Patents

Abstract

PURPOSE:To maintains a gloss of a work roll surface of steel plate by electrodepositing Si matter of sodium silicate after electrolyting and washing of the steel plate surface. CONSTITUTION:In a washing process of a manufacture of cold rolled steel plate, an electrolytic cleaning of the steel plate in an electrolyte containing sodium silicate and caustic soda is carried out, the Si matter of sodium silicate is electrodeposited by 2-5mg/m on the surface of the steel plate. By this method, silica(SiO2) on the surface covers a concentrated material (Mn, Si, Al) deposited from the steel which has a function of shaving off attached material on the surface of a work roll when tempering and rolling are carried out, and a function directly not brought into contact with the concentrated material on the surface of the steel plate to the work roll directly, and so the concentrated material causing clowding does not stick and deposit on the work roll.

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 mirror-finished steel sheets made of low carbon steel.

0002

[Prior Art] In general, cold-rolled steel sheets with a mirror finish are used for various metal fittings such as stove reflectors, fog lamp reflectors, binder back fittings, battery jackets, etc., and are made of low carbon steel. Manufactured through the steps of cold rolling → cleaning → box annealing → temper rolling. The surface gloss of this cold-rolled steel sheet is imparted during the temper rolling process.

[0003] Conventional techniques for imparting luster to steel sheets during temper rolling can be roughly divided into two methods, one of which is a method of eliminating uneven color tone on the surface of the raw steel sheet before mirror finishing (for example, the method disclosed in Japanese Patent Application Laid-Open No. The technique disclosed in Japanese Patent Application Laid-Open No. 1983-7521) is mentioned, and another is a method for preventing clouding of the work roll surface during mirror finishing (for example, Japanese Patent Laid-Open No. 57-7521).
No. 2). That is, the former is rolled with dull rolls with a surface roughness of 1.0 to 2.6 μRa in the final stand of cold rolling, and after annealing, temper rolled with bright rolls with a surface roughness of 0.20 μRa or less to improve the surface of the steel sheet. This is a technique to obtain luster by flowing the convex parts created by the dull roll into the concave parts by a bright roll, and the latter involves reciprocating a brush roll with abrasive grains attached to the inlet side of the work roll during mirror finishing in temper rolling. This is a technology that maintains the gloss of the work roll surface.

0004

[Problems to be Solved by the Invention] However, in the former case, the surface roughness of the work roll, which should be kept at a surface roughness Ra of 0.20 μm or less, becomes large, and in the latter case, the gloss of the mirror-finished work roll is reduced entirely or partially. When the work roll is lost, the work roll must be replaced with a "roll change," and the replacement work that stops the line hinders productivity. Furthermore, in the latter case, installing a nylon brush roll or the like to clean the work roll surface requires equipment costs, and in order to uniformly polish the steel plate in the width direction, careful maintenance of the equipment is required, resulting in a mirror finish ( It was unsuitable for surface roughness (Ra: 0.10 μm or less). Furthermore, there was a problem in that a hairline pattern or the like appeared on the steel plate, impairing the quality of the surface appearance.

In view of such conventional problems, the present invention has been developed based on the results of investigating cases in which the gloss of the work roll surface is maintained for a long time during mirror finishing and cases in which a part or the entire surface becomes cloudy at an early stage. It was discovered that the gloss of the work roll surface can be maintained if the Si content of sodium silicate during the cleaning process, which is a pre-rolling process, is attached to the steel plate surface at 2 to 5 mg/m2 per side. The purpose of this invention is to solve the above problem by attaching the Si component to a steel plate.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention passes through each process in the order of cold rolling, cleaning, box annealing, and skin-pass rolling, and the final skin-pass rolling is performed to improve the surface of the steel sheet. In a method for manufacturing a cold rolled steel sheet in which a mirror finish is applied to the steel sheet, the surface of the steel sheet is electrolytically cleaned in an electrolytic 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 surface of the steel sheet. This is a method for producing a mirror-finished steel sheet by electrodepositing 2 to 5 mg/m2.

[0007]

[Operation] In order to produce mirror-finished steel sheets, it is necessary to maintain the gloss of the work roll surface during temper rolling, and for this purpose, it is necessary to elucidate the gloss maintenance mechanism. The gloss maintenance mechanism discovered by the inventors will be explained below.

[0008] First, the surface of the steel plate and the surface of the work roll when it was temper-rolled to a mirror finish were subjected to Grim Glow Discharge Analysis (GDS) to qualitatively characterize the adhering elements of the box-annealed material and the continuously annealed material. Analysis and adhesion thickness (discharge time) were investigated.

The results show that the box-annealed material has more enriched elements (Mn, Si, P, S, Al) on the surface than the continuously annealed material, but the surface of each temper-rolled work roll is opposite to the steel plate surface. , almost nothing adhered to the surface of the roll through which the box-annealed material was passed. In addition, it was found that there were many deposits on the surface of the work roll through which the continuously annealed material with few concentrated substances was passed.

[0010] This reversal phenomenon occurs because silica (SiO2) is electrodeposited on the surface of the steel plate because the surface of the box-annealed material was electrolytically cleaned in an alkaline electrolyte containing sodium silicate in the cleaning process before annealing. . In other words, the silica on the surface covers the concentrated substances (Mn, Si, Al) that precipitate from the steel, and has the function of scraping off the substances that adhere to the work roll surface during temper rolling. It has been found that because of the function of preventing contact with the rolls, concentrates that cause clouding do not adhere to and accumulate on the surface of the work rolls even when box-annealed material with a thick concentrated layer is temper-rolled.

[0011] By the way, a technique for attaching sodium silicate to the surface of a steel plate during the cleaning process is disclosed in Japanese Patent Application Laid-Open No. 57-19429.
No. 6 and Japanese Patent Application Laid-Open No. 62-235500, etc., the purpose of these is basically to prevent sticking during box annealing. Furthermore, if the amount of the sodium silicate deposit is too large, temper color may occur and the plating properties after tin plating may deteriorate, so it is said that it is desirable to keep the amount of the deposit within a certain appropriate range.

[0012] Furthermore, the inventors investigated the range of SiO2 adhesion that is appropriate for the gloss maintenance of the work roll, and found that if it is less than 1 mg/m2 per side, the concentration deposits on the surface of the steel sheet on the work roll will occur. begins to occur. Also,
It was found that when the content exceeds 5 mg/m2, a milky white temper color begins to appear after annealing.

[0013]

EXAMPLES Examples of the present invention will be described below with reference to FIGS. 1, 2, and Table 1. A cold-rolled steel strip was used as an example material, and the strip threading speed and electrolytic current value were changed in the cleaning process to create materials for examples and comparative examples with different amounts of SiO2 adhesion as shown in Table 1, and the total coil of this material was The length was 20 km in each case. The maximum annealing temperature for box annealing is 6
The temperature was 30°C. In addition, the temper rolling for mirror finishing after annealing was carried out using two-stand dry rolling, and a No. 1000 finishing 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 on the first stand was set to 0.9 tons per plate width (mm), and the rolling load on the second stand was kept constant at 200 tons, which is the minimum load of the mill capacity used. Note that the elongation rate is 0.8% in all cases.

The results of the above experimental examples are shown in Table 1. Si02
In Examples 1 to 3, in which the adhesion amount was 2 to 5 mg/m2, good mirror-finished surfaces were obtained, but in Comparative Example 1 (S
When the iO2 adhesion amount is less than 2 mg/m2), the roll surface becomes cloudy at a rolling length of 12 km during temper rolling, and
After km rolling was completed, both the roll surface and the coil surface had lost their luster. Further, the thickness of the concentrate adhering to the roll surface (the discharge time until the Fe element intensity of GDS is saturated) was 12 seconds (FIG. 1). FIG. 2 shows that Examples 1 to 3 take 2.5 to 3 seconds, and Comparative Example 2 takes 2.5 seconds. In addition, in Comparative Example 2,
Although the gloss of the roll surface was maintained, a milky white temper color was generated on the steel strip surface, and the milky white color was particularly noticeable at the edge of the portion corresponding to the outer winding during annealing.

[0015]

[Table 1]

[0016]

As explained above, according to the present invention, by electrodepositing 2 to 5 mg/m2 of silica on the surface of the steel sheet during the electrolytic cleaning process, impurities that concentrate on the surface of the steel sheet during annealing can be removed from the work roll. It is possible to obtain a high-gloss steel plate by preventing it from adhering to the steel sheet and deteriorating its gloss, and it also eliminates the need to change rolls as often as in the past, greatly improving productivity. It has great effects.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of GDS analysis of deposits on the roll surface after passing through the sheet in Comparative Example 1.

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

Claims (1)

[Claims] 1. A method for manufacturing a cold-rolled steel sheet, in which the steel sheet is passed through each step in the order of cold rolling, cleaning, box annealing, and skin-pass rolling, and the surface of the steel sheet is given a mirror finish in the final skin-pass rolling. During the cleaning process, the surface of the steel plate is electrolytically cleaned in an electrolytic solution containing sodium silicate and caustic soda, and 2 to 5 mg/m2 of Si in sodium silicate is electrodeposited on the surface of the steel plate. Manufacturing method of finished steel plate.