KR20000043759A - Method for producing stainless cold rolled steel plate - Google Patents

Abstract

PURPOSE: A method is provided to produce a fine stainless cold rolled steel plate having an excellent corrosion and a fine surface. CONSTITUTION: After an annealing acidification and a surface processing process of a stainless steel used for a roof material and a wall material for construction, a dull rolling is performed to reduce a surface glossiness of the stainless steel used for an interior and an exterior materials of building. A stainless cold rolled steel plate is produced by removing the fat before acidifying. The surface of the steel plate is beautiful and the anticorrosion property is improved by removing a non-acidification with a rolling oil generated on the surface of the cold rolled dull rolling material by additionally performing a removing process of fat before the annealing acidifying process of the dull rolled material. Thereby a fine product is supplied.

Description

Manufacturing method of stainless cold rolled steel sheet

The present invention relates to a method for manufacturing stainless steel cold rolled sheet for annealing pickling and surface treatment of stainless steel used as a building roofing material and a wall material, and in particular, to reduce the surface glossiness of stainless steel used for interior and exterior materials of buildings. The present invention relates to a method for manufacturing a stainless steel cold rolled steel sheet having a beautiful surface and excellent corrosion resistance by degreasing before pickling after rolling.

In general, stainless steel coated steel can be classified into various products according to surface glossiness, pattern tensile, and surface coating method. When used as interior and exterior materials of buildings, appropriate surface treated steel sheet is considered considering usage, environment, and design. Usually, austenitic stainless steel mainly uses 304.316 as interior and exterior material of building.

Conventionally, in order to reduce the glossiness of a surface, less rolling is performed after the first cold rolling annealing and finally annealing and pickling. However, due to the less rolling to reduce the glossiness, the surface roughness is increased, which results in fine pickling at the time of final pickling. In recent years, as the surface roughness of stainless steel is increased according to the high quality and fashion of interior and exterior building materials, the degree of fine pickling is increased, resulting in deterioration of corrosion resistance and design. In order to prevent the pickling generated during the final pickling, there is a method of increasing the acid concentration in the pickling solution. However, the effect of improving pickling is insignificant, and the air pollution problem occurs, thus improving pickling without increasing the acid concentration possible. A new annealing descaling method is required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above request, and an object thereof is to propose a high quality stainless cold rolled steel sheet which can have excellent corrosion resistance and beautiful surface.

In order to achieve the above object, the present invention provides a method for manufacturing a stainless cold rolled steel sheet comprising a first annealing pickling process, a cold rolling process, a second rolling annealing process, and a second annealing pickling process after cold rolling. It is characterized by providing a method for producing a stainless cold rolled steel sheet to improve the pickling properties by adding a degreasing process to wash the cold rolled plate in the degreasing solution.

1 (a), (b) and (c) are diagrams showing changes in pickling properties according to degreasing and mixed pickling conditions.

2 is a view showing a change in pickling properties with annealing temperature and hydrofluoric acid concentration.

FIG. 3 shows an annealed pickled surface (annealed scale observation) after swiping before annealing in situ.

Figure 5 is a view showing the surface annealed pickled after mitigation in the field (edge stain groove, carbon observation).

Figure 6 is a view showing the surface annealed pickled annealed in the field (edge spot groove, carbon observation).

Hereinafter, the present invention will be described in more detail.

The manufacturing process of the stainless steel cold rolled sheet used for interior and exterior materials of a building is manufactured in the following order. Cold Rolling → Annealing → Pickling → Dull Rolling → Annealing → Pickling → Finished Product

However, in the conventional process, since there is no degreasing process of removing the rolling oil used for cold rolling, when the rolling oil is present on the surface of the stainless steel cold rolled steel sheet, it is difficult to penetrate oxygen during annealing and pickling, so that the thickness of the oxide scale is thin and less porous. Porous film is formed, so it is difficult to penetrate the pickling solution, so that less acid pickling is applied. After rolling, a degreasing process is added before the annealing process to remove the stainless cold rolled plate containing the rolled oil (1 ~ 3% NaOH, 70 ~ 80 ℃). ) After immersion for a certain time (1-3 minutes), if washed with water and then passed to the annealing pickling process, the pickling phenomenon disappears completely.

Hereinafter, the present invention will be described in detail through examples.

(Example)

A stainless steel 316 steel less rolled material was used to investigate pickling with or without rolling oil, pickling according to pickling solution, and pickling according to annealing temperature.

According to the pickling test results of rolling oil degreasing, the pickled oil was not pickled after degreasing, but after being immersed in a degreasing solution (1 to 3% NaOH, 70 to 80 ° C) for about 1 to 3 minutes and washed with water Results The annealing scale of the pull roll was removed. Therefore, it is considered that rolling oil degreasing step is essential for improving pickling properties.

From the above results, the deterioration of pickling properties in unrolled rolling oil is considered for the following reasons.

When the rolling oil is present on the surface of the stainless steel sheet, it is difficult to penetrate oxygen in the annealing process, so that the thickness of the oxide scale is thin (when the annealing scale is thin, the steel sheet color is blue after annealing), and a less poresive film is formed. It is difficult with the formation of chromium depleted layer on the over-scale interface and the penetration of pickling solution. Therefore, it is considered that rolling oil degreasing step is essential before annealing in order to improve pickling properties and prevent overpickling of materials. SEM analysis of the surface pickled before annealing at the site (FIG. 3) and the surface after annealing (edge stain groove, carbon observation, FIGS. 4 and 5) were not observed in FIG. 3. The black spots on the surface generated in 4 and 5 consisted of carbides and oxides, and carbon observation shows that rolling oil contaminates the surface of stainless steel sheets during rolling, which is the main cause of micro pickling in the pickling process. The process proved necessary.

However, the effects of annealing temperature and hydrofluoric acid on pickling properties improved the pickling properties as the annealing temperature and the hydrofluoric acid concentration were increased, but the degree was very weak and fine pickling occurred (FIG. 2). The microacid area was less degreasing, which can be seen by the color of the annealing plate (blue). As shown in FIG. 2, as a result of pickling experiments according to the change of annealing conditions, the scale formed by the oil was not removed even when the hydrofluoric acid concentration was increased to 2.0%.

Pickling Investigation with or without Rolling Oil, Pickling Investigation with Pickling Solution Rolled oil Annealing Condition Molten salt Sulfuric acid Mixed acid Remarks Immersion (seconds) Degreasing (seconds) Time in seconds Temperature (℃) Immersion (seconds) Immersion (seconds) density(%) Immersion (seconds / ℃) 4 10 71 66 1100 45 45 0.8 / 8 45/55 5 10 - 66 1100 45 45 0.8 / 8 45/55 6 10 71 66 1100 45 45 1.5 / 8 4555

(Degreasing time: 8mpm, 9.5m (71 seconds)

Degreasing solution: 1.75% NaOH / 75 ℃

Laboratory annealing and pickling conditions assuming sheet steel speed of 20mpm)

Pickling investigation by annealing temperature Pickling investigation by pickling solution Psalm Number Rolled oil Annealing Condition Melting Sulfuric acid Mixed acid Remarks Immersion (seconds) Degreasing (seconds) Time in seconds Temperature (℃) Immersion (seconds) Immersion (seconds) Concentration (%) Immersion (seconds / ℃) 7 10 71 66 1100 45 45 1.5 / 8 45/55 8 10 71 66 1100 45 45 2.0 / 8 45/55 9 10 71 66 1100 45 45 1.5 / 8 45/55 10 10 71 66 1100 45 45 2.0 / 8 45/55 11 10 71 66 1050 45 45 1.5 / 8 45/55 12 10 71 66 1050 45 45 2.0 / 8 45/55 13 10 71 66 1000 45 45 1.5 / 8 45/55 14 10 71 66 1000 45 45 2.0 / 8 45/55 15 10 71 66 950 45 45 1.5 / 8 45/55 16 10 71 66 950 45 45 2.0 / 8 45/55

(Degreasing time: 8mpm, 9.5m (71 seconds)

Degreasing solution: 1.75% NaOH / 75 ℃

Degreasing 7 times is twice (degreasing → washing → degreasing → washing)

Residual oil content on the surface of stainless steel roll Primary measurement Secondary measurement Average Remarks Skim 1185 1215 1200 mg / cm ² 1 time of degreasing 950 980 965 mg / cm ² Degreasing twice 890.5 906 898.25 mg / cm ²

As described above, according to the present invention, before the annealing pickling process of the stainless cold rolled steel sheet less rolled material used for the interior and exterior materials of the building, by additionally inserting a degreasing process that is not conventionally, the fine acid caused by the rolling oil generated on the surface of the cold rolled less rolled material It disappears and the surface of the steel sheet is beautiful, and the corrosion resistance is improved, so that it is possible to supply high-quality products suitable for the trend of high-end and fashioned building interior and exterior materials.

Claims (2)

In the manufacturing method of the stainless cold rolled steel sheet which consists of a 1st annealing pickling process, a cold rolling process, and a 2nd annealing pickling process after cold rolling, Method for producing a stainless cold rolled steel sheet characterized in that the pickling process is improved by adding a degreasing process for washing after immersing the stainless cold rolled plate in the degreasing solution after the less rolling process. The method of claim 1, The degreasing step is a 1 ~ 3% NaOH aqueous solution, a method for producing a stainless cold rolled steel sheet, characterized in that the pickling property is improved, which is carried out for 1-3 minutes at 70 to 80 ℃.