KR100550797B1 - Method for production of ferritic stainless steel - Google Patents

Abstract

The present invention relates to a method for producing a ferritic stainless steel that can obtain a uniform surface color of stainless steel used as a building exterior material, by weight% C: 0.01% or less, N: 0.02% or less, Si: 0.5% or less, Mn : 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.01% or less, Ti: 0.18% or less, Nb: 0.4% or less, Cu: 1.0% or less, Al: 0.03 to 0.13%, Mo: Slab is prepared by dissolving the usual ferritic stainless steel containing 4% or less, Cr: 20-35%, remaining Fe and other unavoidable impurities, and then hot-rolled and cold-rolled steel sheet by an ordinary method, In the method of annealing through the salt bath and pickling tank, the annealing temperature of the annealing furnace is 975 ~ 1025 ℃, the steel sheet passing through this is 15 to 18 m / min. The composition of the salt bath is 10-20% of sodium chloride, 50-60% of sodium hydroxide, 30% of sodium nitrate, and the temperature is 400-450 ° C. And a ferritic stainless steel manufacturing method, characterized by a base.

Ferritic, stainless steel, pickling solution,

Description

Method for production of ferritic stainless steel

The present invention relates to a ferritic stainless steel production method, in particular to a ferritic stainless steel production method that can obtain a uniform surface color of the stainless steel used as building exterior materials.

In general, stainless steel used for building exterior materials near the coast has high chromium content of 20 to 35% to improve corrosion resistance. When the chromium content is high, pickling is very bad, so it is very difficult to make a product having a uniform surface color. . However, in order for stainless steel to be used as a building exterior material, there must be no surface color difference. If a color difference occurs, it appears to be a stain on the outside, which greatly reduces its commercial value. In Japan, in order to solve this problem, a method of immersion in an acid solution after special bright annealing (JP-A 6-49539), a method of measuring gloss immediately after pickling and reflecting the result (JP-A 6-184774), in the air A method of heat treatment (Japanese Patent Laid-Open No. 10-121276) and the like have been proposed. These methods have problems such as additional installation of new equipment or additional processes, and are disadvantageous in that they cannot be manufactured more economically.

 On the other hand, the present inventors disclose a method of annealing pickling of high chromium stainless steel sheet with a uniform surface color in the Republic of Korea Patent Application No. 2000-80865, the surface color by adjusting the working speed and temperature control of the salt bath during annealing However, the present invention relates to a method for manufacturing stainless steel in which the salt bath composition is adjusted to shorten the time required for dissolving the salt to increase productivity and at the same time, further improve the surface color.

Accordingly, the present inventors conducted research and experiments to solve the above-mentioned conventional problems, and proposed the present invention based on the results. The present invention adjusts the composition of the salts used in the conventional annealing and pickling process. The purpose of the present invention is to provide a method for manufacturing ferritic stainless steel that shortens the dissolution time, implements an appropriate condition of the annealing furnace, improves productivity, and has almost no color difference on the surface.

In the present invention, C: 0.01% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.01% or less, Ti: Ordinary ferritic stainless steel containing 0.18% or less, Nb: 0.4% or less, Cu: 1.0% or less, Al: 0.03 to 0.13%, Mo: 4% or less, Cr: 20 to 35%, remaining Fe and other unavoidable impurities In the method of dissolving steel to produce a slab, and then annealing the hot rolled and cold rolled steel sheet by an annealing furnace, a salt bath and a pickling tank in a conventional manner,
The annealing temperature of the annealing furnace is 975 ~ 1025 ℃, the steel sheet passing through it is mailed at 15 ~ 18 m / min. For 2 mm thickness,
The composition of the salt bath is 10-20% sodium chloride, 50-60% sodium hydroxide, and 30% sodium nitrate, the temperature is 400 ~ 450 ℃ to provide a ferritic stainless steel manufacturing method characterized in that do.

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EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, C: 0.01% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.01% or less, Ti: Ordinary ferritic stainless steel containing 0.18% or less, Nb: 0.4% or less, Cu: 1.0% or less, Al: 0.03 to 0.13%, Mo: 4% or less, Cr: 20 to 35%, remaining Fe and other unavoidable impurities After slab is manufactured by melting the steel, annealing and pickling is performed at a line speed of 15-18 m / min for a 2 mm thickness on a hot rolled and cold rolled steel sheet by a conventional method. It relates to a manufacturing method.

If the working speed is slow to less than 15m / min, the oxidation amount is increased to increase the surface roughness, and if the working speed is too faster than 18m / min does not cause sufficient recrystallization. The annealing temperature is set to 975-1025 ^o C to pass through the cold rolled steel sheet (strip), the surface gloss is too high because the oxidation hardly occurs when the annealing temperature is less than 975 ^o , the annealing temperature is more than 1025 ^o C Oxidation occurs rapidly to form surface irregularities after pickling.

The annealed strip is pickled by passing through a salt bath and a sulfuric acid bath. The composition of the salt bath is 10% to 20% of sodium chloride (NaCl) and 50 to 60% of sodium hydroxide (NaOH). %, And 30% of sodium nitrate (NaNO ₃ ) through a strip at a temperature of 400-450 ^° C. If the temperature of the salt bath is lower than 400 ^o C, the oxidation of + trivalent chromium oxide to +6 is delayed, and it is not sufficiently removed in the subsequent dissolution process with acid. If it is higher than 450 ^o C, the metal of the salt bath Erosion occurs, degrading surface properties. Thereafter, in the sulfuric acid tank, the pickling is carried out in a conventional manner, and the first pickling is performed by adjusting the sulfuric acid temperature and the concentration to 55 to 60 ° C., preferably 55 ^° C. and 6 to 15%. The second pickling degree is also pickled at a temperature of 55 to 60 ° C., preferably at 55 ^° C., 5 to 15% nitric acid, and 0.5 to 1.5% hydrofluoric acid. Through the above annealing pickling method, it is possible to manufacture a high chromium cold rolled stainless steel sheet having an improved surface color difference.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The slab was prepared by dissolving steel having a chemical component as shown in Table 1, followed by hot rolling in a conventional manner, followed by cold rolling. Glossiness was measured according to the composition of Natrium chloride as shown in Table 2 using a strip cold rolled to 2mm. In the case of building exterior materials, the gloss value should be small because the reflection of light should be suppressed. At 5% of the amount of sodium chloride less than 10%, the surface erosion of the strip was very weak and the glossiness was very high as 26.2. However, as the amount of sodium chloride increases, the glossiness of the strips tends to decrease. For 30% of its content, which exceeds 20%, surface erosion occurs rapidly, resulting in surface unevenness of the strip.

Table 3 shows the change in whiteness according to the amount of Natrium chloride using a color system. Where L *, a *, and b *, which represent the color system, are the most common indices of the color of an object, standardized by the International Lighting Commission in 1976, where L * is lightness, a * is red, and b * is yellow. . When the amount of sodium chloride is less than 10%, 5% of the surface glossiness is severe, and at the content of 10-20% of sodium chloride in the range of the present invention, the b * value of yellowness of whiteness decreases and is maintained properly. It shows what happens. If it increases to 30%, staining by surface erosion occurs. When the b * value is more than 1, the gloss of the surface is severe, and when it exceeds 2, the staining starts to be observed. Table 4 shows the heat of dissolution according to the salt bath composition. When the content of sodium chloride is more than 10%, the amount of heat of melting decreases drastically, and when the content of sodium chloride exceeds 20%, the amount of heat of melting does not decrease even if the content of sodium chloride is increased. It can be seen that the time required for dissolution of the salt is significantly reduced at a Natrium content of 10-20%, and thus the working speed is greatly improved.

Composition Cr Mo Nb Ti Al C + N Si Mn P S weight% 26.2 2.0 0.3 0.064 0.065 0.0254 0.29 0.3 0.028 0.0022

Natrium chloride (w%) Glossiness Remarks 5 26.2 Glossy 10 13.4 proper 15 15.2 proper 20 12.8 proper 30 2.4 Surface erosion

Natrium chloride (w%) Colorimeter value Remarks L * a * b * 5 77.09 -0.25 1.24 Glossy 10 73.76 -0.21 0.17 proper 15 72.31 -0.18 0.89 proper 20 71.89 -0.14 0.92 proper 30 68.06 0.10 2.26 Smear

division Salt bath composition Heat of fusion (㎈ / g) Melting time (hours) Natrium hydroxide Nitrate Natrium chloride One 50 30 20 32.02 32 2 55 30 15 34.20 35 3 60 30 10 34.78 36 4 65 30 5 39.08 48 5 70 30 0 45.32 55

As described above, according to the present invention, it is possible to reduce the time required for dissolution of salt by adjusting annealing conditions and salt bath composition without installing additional equipment other than the existing annealing pickling process, thereby improving productivity and workability, and at the same time, surface color. It is possible to manufacture a ferritic cold-rolled stainless steel sheet with improved uniformity.

Claims (1)

By weight% C: 0.01% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.01% or less, Ti: 0.18% or less Nb: 0.4% or less, Cu: 1.0% or less, Al: 0.03 to 0.13%, Mo: 4% or less, Cr: 20 to 35%, and other ferritic stainless steels containing the remaining Fe and other unavoidable impurities In the method of producing a slab, and then annealing pickling through hot-rolled and cold-rolled steel sheet by an annealing furnace, a salt bath and a pickling tank in a conventional manner, The annealing temperature of the annealing furnace is 975 ~ 1025 ℃, the steel sheet passing through it is mailed at 15 ~ 18 m / min. For 2 mm thickness, The composition of the salt bath is 10-20% sodium chloride, 50-60% sodium hydroxide, and 30% sodium nitrate, the temperature is 400 ~ 450 ℃ characterized in that the ferritic stainless steel manufacturing method.