JP2938283B2 - Manufacturing method of steel sheet with good surface quality - 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 producing a steel sheet having a good surface quality, and more particularly to a method for suitably preventing deterioration of the surface quality due to a surface condensate such as Mn generated during annealing of a cold-rolled steel sheet. Is what you do.

[0002]

2. Description of the Related Art In recent years, in manufacturing a cold-rolled sheet, a continuous annealing furnace is used in the annealing step instead of a batch furnace, and a coil-shaped material (steel strip) is continuously introduced into the furnace from the furnace entrance. Continuous annealing method of sending and performing a predetermined heat treatment,
It has been adopted to improve productivity and reduce quality variation. In that case, final cooling is performed on the steel strip immediately after leaving the furnace through the recrystallization process while being mechanically fed through the continuous annealing furnace. This final cooling is generally water cooling, and it is customary to improve the cooling capacity corresponding to the increase in the operating speed and to save energy.

Further, recently, a rolling mill is directly connected after the annealing apparatus, and the steel strip after annealing is subjected to temper rolling or second cold rolling (hereinafter simply referred to as temper rolling), that is, light cold rolling. A method of improving productivity and yield by continuously performing processing is adopted. For example, the roughness, color tone, and shape of the plate surface are extremely important qualities for a temper-rolled tin plate, and it is said that these surface qualities are mostly determined by the temper rolling after annealing.

[0004]

At the time of annealing, components such as Mn, Si, and S in the steel diffuse in the steel structure and gather on the surface to form a concentrated product. These concentrated substances such as Mn are easily peeled off in a mottled state by water cooling performed after annealing.
When the steel strip is temper-rolled while the condensate is peeled off in a mottled state, the condensate remaining on the steel strip surface is unevenly deposited on the work roll during temper rolling, and the deposit is continuously deposited. It is transferred to the sheet surface of the steel strip that is sent. Therefore, there is a problem that a mottled pattern, a so-called two-tone color, is generated on the surface of the steel strip after the temper rolling, and the color tone, the appearance, the plate surface roughness, etc. become non-uniform and the surface quality is impaired. .

Accordingly, an object of the present invention is to provide a method of manufacturing a steel sheet having a good surface quality which solves such conventional problems by improving the cooling method after annealing.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a final cooling step after annealing a cold-rolled steel strip.
In this case, the steel strip is cooled to remove concentrated substances such as Mn formed on the surface of the steel strip during annealing by immersing the steel strip in an organic acid aqueous solution having a concentration of 0.01 % to 1% by weight. Temper rolling or second cold rolling.

[0007]

According to the present invention, an organic acid is added to the final cooling water of the annealed steel strip, and the steel strip is immersed in the final cooling water to reduce the Mn on the steel strip surface.
Since the temper rolling is performed after uniformly removing the concentrate such as, the concentrated material is not unevenly deposited on the work roll of the temper rolling, and when the temper rolling is continuously performed after annealing. The surface roughness and color tone of the steel strip do not change with time. Therefore, a steel sheet having good surface quality can be stably manufactured.

Hereinafter, the present invention will be described in more detail. In view of the fact that it is very difficult to prevent Mn and the like in the steel from diffusing and concentrating on the surface of the steel strip when the steel strip is annealed, the present inventors consider that it is very difficult to prevent the phenomenon itself from being formed on the steel strip surface. Intensive research has been conducted in the direction of uniformly removing the condensate to prevent deterioration in surface quality in the subsequent temper rolling. As a result, it has been found that if the annealed steel strip is immersed in a water-cooling bath containing an organic acid, it is possible to cool the steel strip and at the same time chemically remove the Mn and other condensates uniformly, thereby completing the present invention. Was.

The organic acid used in the present invention includes formic acid,
Suitable are straight-chain aliphatic acids such as acetic acid, oxalic acid, propionic acid and succinic acid, and oxy acids such as citric acid, lactic acid, gluconic acid and tartaric acid. In the present invention, the concentration of the organic acid is limited to 0.01 to 1% by weight for the following reason. That is, as shown in FIG.
When the amount is less than the weight percentage, at least Mn is not sufficiently removed and remains on the steel sheet surface, and a mottle pattern is easily generated. On the other hand, when the concentration of the organic acid exceeds 1% by weight , Mn is sufficiently removed, but rust is easily generated on the surface of the steel strip and the appearance of the steel sheet is significantly impaired. Equipment such as washing with water is required.

In the present invention, as the water cooling device using the aqueous solution of the organic acid, a conventional cooling facility installed on the exit side of the continuous annealing furnace can be used as it is.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows an outline of a process for carrying out the present invention. The steel strip 2 unwound from the cold-rolled coil 1 was sent to an annealing furnace 4 via a degreasing device 3 for annealing. Immediately thereafter
It is immersed and cooled while passing through a water cooling device 5 for final cooling filled with an aqueous solution 5A to which formic acid having a concentration of 0.05% by weight is added. At the same time, Mn generated on the surface of steel strip 2 during annealing
And the like are dissolved in a formic acid solution and uniformly removed.
The treated steel strip 2 was sent through a dryer 6 to a temper rolling mill 7 where it was temper rolled and then wound up on a take-up reel 8 to obtain a tinplate product.

On the other hand, for comparison, a tinplate original plate was manufactured by the conventional method in the same manner as described above by a conventional process using a water-cooling device 5 filled with only cooling water. In the above steps, the steel strip 2 immediately before being sent to the temper rolling mill 7 after the removal treatment of the condensed matter such as Mn in the water cooling device 5 is subjected to the conventional method and the method of the present invention. And the surface concentration state of Mn etc.
It was measured by S (glow discharge optical emission spectrometer). The measurement results are shown in FIGS. The horizontal axis represents the distance in the thickness direction from the surface of the steel strip, and the vertical axis represents the amount of the concentrate.

Compared to the conventional method of FIG.
In the method of the present invention of (b), condensed matter such as Mn was clearly removed, and generation of a so-called two-tone color of a mottled pattern after temper rolling was not observed at all. FIG. 4 shows the results of measuring the relationship between the rolling distance in the temper rolling mill 7 and the plate surface roughness of the original tinplate product in the conventional method and the method of the present invention.
FIG. 5 shows the result of measuring the relationship with the color tone (lightness).
Respectively. From these comparisons, it is clear that according to the production method of the present invention, plate surface roughness and color tone can be stably obtained.

Although the above embodiments are directed to tinplate original sheets, the present invention is not limited to steel sheets for surface treatment such as tinplate original sheets, but may also be applied to automotive steel sheets and general cold rolled steel sheets. Can be.

[0015]

As described above, according to the present invention,
The cold-rolled steel sheet after annealing was immersed in cooling water containing an organic acid in the final cooling step to uniformly remove surface condensates such as Mn generated during annealing. Alternatively, an effect is obtained in which a mottled pattern is not generated on the steel sheet surface after the second cold rolling, and the surface quality of the product is guaranteed. Furthermore, in addition to the above effects, the surface roughness and color tone of the temper-rolled steel strip do not change over time with the cumulative increase in the rolling distance, and a steel sheet having a constant surface quality is always stabilized. The effect that it can be manufactured is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Mn removal rate and the organic acid concentration when an annealed steel strip is immersed in an aqueous solution containing an organic acid.

FIG. 2 is a diagram showing an outline of a manufacturing process according to one embodiment of the present invention.

FIG. 3 shows the results of GDS measurement of the surface concentration state of Mn and the like on a steel strip immediately before being sent to a temper rolling mill, in the case of the conventional method (FIG. 3A) and in the case of the method of the present invention ( (B) of FIG.

FIG. 4 is a graph showing a relationship between a rolling distance after temper rolling and sheet surface roughness in comparison with a conventional method.

FIG. 5 is a graph showing a relationship between a rolling distance and a color tone after temper rolling in comparison with a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cold rolled coil 2 Steel strip 4 Annealing furnace 5 Water cooling device 5A Organic acid aqueous solution 7 Temper rolling mill

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Fumio Kozuno 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works (72) Inventor Hironobu Ohno 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Inside Chiba Works (56) References JP-A-57-149429 (JP, A) JP-B-57-47738 (JP, B2)

Claims (1)

(57) [Claims] In a final cooling step after annealing, a cold-rolled steel strip is immersed in an organic acid aqueous solution having a concentration of 0.01 to 1% by weight and cooled while cooling to form Mn formed on the surface of the steel strip during annealing.
A method for producing a steel sheet having a good surface quality, comprising removing a concentrated product such as a steel sheet and then continuously passivating or second cold rolling the steel strip .