JPH06108160A - Production of steel plate good in surface quality - Google Patents

Abstract

PURPOSE:To provide a method for producing a steel plate free from deterioration in surface quality caused by concentrated substance such as Mn formed on the surface of a steel strip in the process of annealing. CONSTITUTION:A steel strip after being annealed in an annealing furnace 4 is immersed in aq. soln. of an organic acid 5A with 0.01 to 1% concn. in a water-cooled device 5 and is subjected to final cooling to uniformly remove surface concentrated substance such as Mn formed in the process of the annealing, and then, it is subjected to skinpass rolling by a skinpass rolling mill 7 or is subjected to secondary cold rolling. In this way, the steel plate such as a tin original plate good in surface quality can be obtd.

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 in particular, suitably prevents deterioration of the surface quality due to a surface concentrate such as Mn produced during annealing of a cold rolled steel sheet. To do.

[0002]

2. Description of the Related Art In recent years, in the production of cold rolled thin plates, a continuous annealing furnace is used in the annealing process in place of a batch furnace, and a coiled material (steel strip) is continuously introduced into the furnace from the inlet of the furnace. The continuous annealing method of sending in and performing a predetermined heat treatment is
It has been adopted to improve productivity and reduce quality variation. In that case, final cooling is performed on the steel strip immediately after it has gone out of the furnace through the recrystallization process while being mechanically fed in the continuous annealing furnace. This final cooling is generally water cooling, and it is customary to improve the cooling capacity corresponding to the higher operating speed and save energy.

Further, recently, a rolling mill is directly connected after the above-mentioned annealing device, and the steel strip after annealing is temper-rolled or second cold-rolled (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, for a temper-rolled tin plate, the roughness, color tone and shape of the plate surface are extremely important qualities, and the surface quality of these is said to be almost determined by the temper rolling after annealing.

[0004]

During annealing, Mn, Si, S, etc., which are components in the steel, diffuse in the steel structure and gather on the surface to form a concentrate. Concentrates such as Mn are easily mottled by water cooling performed after annealing.
When the steel strip is temper-rolled while the concentrate is peeled off in a mottled manner, the concentrate remaining on the steel strip surface is unevenly deposited on the work roll during temper rolling, and the deposit is continuously formed. It is transferred to the plate surface of the steel strip that is sent. Therefore, a mottled pattern, so-called two-tone color, occurs on the surface of the steel strip after temper rolling, and there is a problem that the color tone, appearance, plate surface roughness, etc. become uneven and the surface quality is impaired. .

Therefore, an object of the present invention is to provide a method for producing a steel sheet having a good surface quality by solving such a conventional problem by improving the cooling method after annealing.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention cools a cold rolled steel strip by immersing it in a 0.01 to 1% organic acid aqueous solution after annealing. Concentrates such as Mn generated on the surface of the steel strip during the annealing are removed, and then temper rolling or second cold rolling is continuously performed.

[0007]

According to the present invention, the organic acid is added to the final cooling water of the steel strip after annealing, and the steel strip is dipped in this to add Mn on the surface of the steel strip.
Since the temper rolling is performed after uniformly removing the concentrates, etc., the concentrate does not accumulate unevenly on the work rolls 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 over time. Therefore, a steel sheet having a good surface quality can be stably manufactured.

The present invention will be described in more detail below. In view of the fact that it is very difficult to prevent the phenomenon itself in which Mn or the like in the steel diffuses and concentrates on the surface of the steel strip during annealing of the steel strip, the present inventors formed it on the surface of the steel strip. Further, the inventors have earnestly conducted research to prevent the deterioration of the surface quality in the subsequent temper rolling by uniformly removing the concentrate. As a result, the inventors have found that by immersing the annealed steel strip in a water cooling bath containing an organic acid, it is possible to chemically and uniformly remove concentrates such as Mn while cooling the steel strip. It was

As the organic acid used in the present invention, formic acid,
Suitable are straight-chain aliphatics such as acetic acid, oxalic acid, propionic acid and succinic acid, and oxyacids 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% for the following reason. That is, as shown in FIG. 1, when the concentration of the organic acid is less than 0.01%, at least Mn is not sufficiently removed, and Mn remains on the surface of the steel sheet to easily cause a mottled pattern. On the other hand, when the concentration of the organic acid exceeds 1%, Mn is sufficiently removed, but since the rust is likely to occur on the surface of the steel strip and the appearance of the steel sheet is significantly impaired, the organic acid on the steel sheet surface is washed with water. Then, equipment such as removal is required.

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

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 2 shows an outline of steps for carrying out the present invention. The steel strip 2 unwound from the cold rolled coil 1 was sent to the annealing furnace 4 via the degreasing device 3 and annealed. Immediately thereafter, 0.
A final cooling water-cooling device 5 filled with an aqueous solution 5A to which 05% formic acid is added is soaked and cooled. At the same time, the concentrated substance such as Mn generated on the surface of the steel strip 2 during annealing is dissolved in the formic acid solution and uniformly removed. The treated steel strip 2 was sent to a temper rolling mill 7 via a dryer 6, was temper rolled, and then wound on a take-up reel 8 to obtain a tin plate product.

On the other hand, for comparison, a tin plate according to the conventional method was manufactured in the same manner as 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 fed to the temper rolling mill 7 after the removal treatment of the concentrated matter such as Mn by the water cooling device 5 is performed by the conventional method and the method of the present invention. Sampled for each of the
It was measured by S (glow discharge emission spectrometer). The measurement results are shown in FIGS. 3 (a) and 3 (b). The horizontal axis represents the distance in the thickness direction from the steel strip surface, and the vertical axis represents the amount of concentrate.

As compared with the conventional method of FIG.
In the method of the present invention of (b), the concentrated substances such as Mn were obviously removed, and no mottled so-called two-tone color was observed after temper rolling. In addition, the results of measuring the relationship between the rolling distance in the temper rolling mill 7 and the plate surface roughness of the product tin plate in the conventional method and the method of the present invention are shown in FIG.
Fig. 5 shows the result of measuring the relationship with the color tone (brightness).
Respectively shown. From these comparisons, it is clear that according to the manufacturing method of the present invention, the plate surface roughness and the color tone can be stably obtained.

Although the above-mentioned embodiment is applied to the tin plate, the present invention is not limited to the surface-treating steel plate such as the tin plate, and may be applied to other automobile steel plates and general cold-rolled steel plates. You can

[0015]

As described above, according to the present invention,
Since the cold-rolled steel sheet after annealing was immersed in cooling water containing an organic acid to uniformly remove surface concentrates such as Mn generated during annealing, the subsequent temper rolling or second cooling No mottled pattern occurs on the steel plate surface after hot rolling,
The effect is that the surface quality of the product is guaranteed. Furthermore, in addition to the above effects, the plate surface roughness and color tone of the temper-rolled steel strip do not change with time as the rolling distance increases, and a steel plate having a constant surface quality is always stabilized. The effect that it can be manufactured is obtained.

[Brief description of drawings]

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

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

FIG. 3 shows the results of measuring the surface enrichment state of Mn and the like in a steel strip immediately before being fed into a temper rolling mill by GDS, in the case of the conventional method (FIG. (A)) and the method of the present invention (FIG. It is a graph separately shown in FIG.

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

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

[Explanation 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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fumio Furukaku, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside the Chiba Works, Kawasaki Steel (72) Hironobu Ohno 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Chiba Steel Works, Ltd.

Claims (1)

[Claims] 1. A cold-rolled steel strip is annealed and immersed in an aqueous solution of 0.01 to 1% of an organic acid to cool the strip, and then Mn and other concentrates formed on the surface of the strip during annealing are removed. A method for producing a steel sheet having good surface quality, which comprises temper-rolling or second cold rolling the steel sheet.