JP2997592B2 - Manufacturing method of exterior stainless steel sheet having both anti-glare property and corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel sheet having anti-glare properties and corrosion resistance used for exterior materials such as roofs.

[0002]

2. Description of the Related Art When a stainless steel plate is used for an exterior material such as a roof, in addition to corrosion resistance, antiglare properties and a color tone unique to stainless steel are required. It is effective for the anti-glare property to make large irregularities on the steel sheet surface to reduce the light reflectance. Irregularities on the surface of the steel sheet are formed by transferring the roll surface to the steel sheet by rolling using a dull roll whose surface has been processed.

As a stainless steel having an antiglare property, there is a dull-finished stainless steel disclosed in JP-A-61-227193 and JP-A-1-162779, all of which are colored by chemical coloring. It is a stainless steel plate, which is fundamentally different from the present invention relating to achromatic to white stainless steel.

[0004] As an example of the use of stainless steel plates for roofs, a special dull-satin-finished austenitic stainless steel plate was used for the roof of a shopping center in Paris. Nickel, Volume 6, Number 3, 1991, P .8.

It is known that the color tone (whiteness) of the surface of a stainless steel plate is determined by whether the annealing step is an annealing / pickling (AP) step or a bright annealing (BA) step. In the AP process, the finish is white, and the whiteness tends to increase. On the other hand, in the BA process, unlike the AP process, since there is no pickling (P) process, the whiteness is lower than that in the AP process, and the metal process has a color tone unique to metal. Although this BA steel sheet is finished as an exterior material for roofs and the like, it has a drawback that its corrosion resistance is inferior to that of the AP process material.

[0006]

The steel sheet which has undergone the BA process after dull rolling has a reduced whiteness, and thus has the characteristic of having excellent antiglare properties while maintaining metallic luster. However, there is a problem that the corrosion resistance of the steel sheet that has passed through this step is inferior to that of the steel sheet that has passed through the AP step after dull rolling. An object of the present invention is to provide a method for producing a low-whiteness stainless steel sheet having both anti-glare properties and corrosion resistance, which solves the above problems.

[0007]

The inventors of the present invention have investigated the effects of the production process of dull rolled materials on antiglare properties, corrosion resistance and whiteness, and have obtained the following findings. Although the anti-glare property can be imparted by dulling with an appropriate roughness, the corrosion resistance is reduced if dulling is performed. After dull rolling, normal annealing (combustion gas atmosphere) is performed and immersed in alkali molten salt. The steel sheet pickled with a mixed acid of (nitric acid + hydrofluoric acid) is still corrosion-resistant, but its whiteness is too high, oxide scale is generated during annealing, and the chemical reaction in the molten alkali salt is not uniform. It is extremely difficult to obtain a low-whiteness stainless steel sheet having excellent anti-glare properties and corrosion resistance, such as uneven color tone.

The antiglare property cannot be imparted by the surface roughness of a crystal grain unit, the surface roughness Ra needs to be 0.5 to 10 μm, and the corrosion resistance and color tone under long-term exposure to the atmosphere. Was also found to affect. For this purpose, it is necessary to perform one or more passes of rolling with a dull roll before annealing to adjust the surface roughness to an appropriate value.

Further, in order to clarify the relationship between the dulling and the corrosion resistance, a detailed investigation was made on the steel sheet surface after the dull rolling. As a result, the dulling formed on the steel sheet surface and the convexity of the dull roll surface occurred when the dulling was continued. It was found that there were strongly worked portions that were in contact with the parts and were rolled under a high surface pressure, and that the working structures on these surfaces affected the corrosion resistance.

[0010] As in the present invention, the bright annealed one is maintained in a dull rolling state, and therefore has a color tone unique to stainless steel. After the bright annealed steel sheet is further heated in a specific temperature range to form an oxide scale, electrolysis in a solution according to the present invention, and acid pickling are performed, thereby satisfying both antiglare properties, whiteness, and corrosion resistance. I found that.

That is, in the present invention, C: 0.
020% or less, Cr: 17.0 to 35.0%, Mo:
0.5 to 4.0%, Cr + 3Mo: 26 to 40%, S
i: 0.05 to 1.0%, Mn: 0.05 to 0.5%,
Al: 0.005 to 0.2%, the balance being Fe and other unavoidable impurities, and the surface roughness (Ra) of the steel sheet is 0.1%.
After bright annealing a cold-rolled steel sheet of 5 to 10.0 μm,
Reheat to 0-900 ° C and 1-20A / dm in neutral salt solution
An object of the present invention is to provide a method for producing an exterior stainless steel sheet having both anti-glare properties and corrosion resistance, characterized by performing electrolysis under the conditions of ² , followed by immersion in a mixed acid of nitric acid and hydrofluoric acid or nitric acid.

Further, Nb: 0.1-0.5%, Ti:
When a stainless steel sheet containing one or more elements of 0.1 to 0.5% and V: 0.05 to 0.5% is used, corrosion resistance,
This is advantageous for producing a stainless steel sheet for exterior use such as a roof having excellent anti-glare properties and color tone.

[0013]

The present invention will be described below in more detail. First,
The reasons for limiting the components and surface properties of the stainless steel used in the present invention will be described.

C: If it is more than 0.02%, Cr carbides are formed by heat treatment during production, so that the corrosion resistance is reduced.
Therefore, the amount of C was limited to 0.02% or less.

Cr: An essential component for imparting corrosion resistance, but if less than 17%, it rusts due to long-term exposure to the atmosphere. On the other hand, if it exceeds 35%, ductility and toughness are significantly reduced, and the productivity of a thin plate is significantly impaired. Therefore, the content of Cr is limited to 17 to 35%.

Mo: effective for improving pitting corrosion resistance,
If it is less than 5%, the tendency of pitting corrosion to occur in air exposure increases. On the other hand, when the content exceeds 4.0%, the hot workability is significantly reduced. Therefore, the content of Mo is set to 0.5 to 4.0.
%.

The contents of Cr and Mo are expressed in terms of% by weight (Cr +
The index represented by 3Mo) is preferably 26 to 40.

In order to ensure the effect of improving the corrosion resistance of Cr,
The addition of Nb and Ti is effective.
And the amount of Mo added was limited as follows.

Nb: It is an element that combines with C to form carbides, suppresses the precipitation of Cr carbides at grain boundaries, and is effective in improving corrosion resistance. If it is less than 0.1%, the effect of suppressing the formation of Cr carbide is small, and if it is more than 0.5%, the toughness is reduced. Therefore, the content of Nb is limited to 0.1 to 0.5%.

[0020] Ti: It is an element that combines with C to form carbides, suppresses precipitation of Cr carbides at grain boundaries, and is effective in improving corrosion resistance. If it is less than 0.1%, the effect of suppressing the formation of Cr carbide is small, and if it is more than 0.5%, the toughness is reduced. Therefore, the content of Ti is limited to 0.1 to 0.5%.

V: It is an element that combines with C to form carbides, suppresses precipitation of Cr carbides at grain boundaries, and is effective in improving corrosion resistance. If it is less than 0.1%, the effect of suppressing the formation of Cr carbide is small, and if it is more than 0.5%, the toughness is reduced. Therefore, the content of V is limited to 0.1 to 0.5%.

Si: added as a deoxidizer, 0.05
%, The effect is small, and if it exceeds 1.0%, the mechanical properties are adversely affected. Therefore, the additive amount of Si is 0.1.
It was limited to 05 to 1.0%.

Mn: If it exceeds 0.5%, the corrosion resistance decreases. On the other hand, if it is less than 0.05%, economic efficiency is impaired. Therefore, the addition amount of Mn is limited to 0.05 to 0.5%.

Al: added as a deoxidizer, but 0.00
If it is less than 5%, the effect is small, and if it exceeds 0.2%, the mechanical properties are adversely affected. Therefore, the addition amount of Al is limited to 0.005 to 0.2%.

It is necessary to dull a stainless steel sheet having the above chemical composition to a specific surface roughness in order to impart corrosion resistance and anti-glare properties. Surface roughness by dull processing (Ra)
Is smaller than 0.5 μm, if the incident angle of sunlight is smaller than 60 °, glare is felt. On the other hand, when the surface roughness exceeds 10.0 μm, contaminants floating in the atmosphere during exposure to the atmosphere accumulate, and the corrosion resistance is extremely reduced. Therefore, the surface roughness was limited to 0.5 to 10.0 μm.

In the present invention, the stainless steel having the components and surface properties described above is subjected to the following treatment to produce an exterior stainless steel having both antiglare properties and corrosion resistance.

The stainless steel is first subjected to bright annealing.
Bright annealing is performed to restore the metallic luster and ductility of the dulled surface, and has a dew point of −40 ° C. or less and 950 to 1050 ° C. in an ammonia decomposition gas or pure hydrogen atmosphere.
It is good to do in.

In the present invention, after bright annealing, 400 to 900
By reheating at ℃ and electrodissolving in a neutral salt solution, the collapse formed during the dulling process together with the oxide scale on the steel sheet surface is removed. It should be noted that the term “falling” occurs during dulling and refers to a portion that overhangs over the recess.

Conditions were set so that the metallic luster of the dulled surface secured in bright annealing was not lost even in the reheating / electrolysis step in a neutral salt solution. Reheating temperature is 4
If the temperature is lower than 00 ° C., the generation of oxide scale is small, so that the amount of dissolution is insufficient, and the collapse during dulling cannot be removed. On the other hand, when reheated at a temperature exceeding 900 ° C., the oxide scale becomes thick and cannot be removed by electrolysis in a neutral salt solution. Therefore, the reheating temperature after bright annealing was limited to 400 to 900 ° C.

Next, an electrolytic treatment is performed in a neutral salt solution.
U. This provides a uniform finish of the post-processing on dull surfaces
Do it for As a neutral salt, sodium sulfate or the like is preferably used.
Can be used. Regarding electrolysis conditions, neutral
Electrolysis current value in salt solution is 1A / dm ^Two If less than
Takes time, while 20A / dm^Two Beyond the economy
Is reduced. Therefore, the electrolytic current value is set to 1 to 20 A / dm.
^Two Limited to. The electrolysis time is 10 to 120 sec.
Is good.

The electrolytic treatment alone in the above neutral salt is insufficient in corrosion resistance. Therefore, the stainless steel plate is immersed in an acid to remove smut and passivate the surface. The acid used is preferably a mixed acid of nitric acid and hydrofluoric acid or nitric acid. Mixed acid at a temperature of 40-80 ° C, concentration of 5-25%, nitric acid at a temperature of 30-
The temperature is preferably 70 ° C. and the concentration is 8 to 20%. Note that the immersion time may be appropriately selected.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Example A steel having the chemical composition shown in Table 1 was melted and hot-rolled to obtain a steel plate having a thickness of 4 mm. 1
After a quenching heat treatment at 000 ° C. × 10 min, oxide scale was removed by pickling and polishing. These steel sheets were cold-rolled to 0.8 mm, and the final pass was rolled with dull rolls having a surface roughness Ra of 4 to 20 μm.

The steel sheet dulled in this way was treated as shown in Table 2. In A of Table 2, heat treatment (BA) at 1000 ° C. is performed in an ammonia decomposition gas atmosphere having a dew point of −45 ° C., and after cooling to room temperature, 300 to
Nine kinds of steel sheets heated to 1100 ° C. every 100 ° C. were electrolyzed in a neutral salt solution under the condition of 10 mA / dm ² × 20 seconds. Then, a mixed acid (nitric acid: hydrofluoric acid = 2:
It was pickled in 1). B in Table 2 is obtained only after the above-described bright annealing. C in Table 2 is 1 instead of BA process.
After annealing in an LPG combustion atmosphere of 000 ° C. × 60 seconds, 400
Immersion in alkali molten salt (NaOH + NaNO ₃ )
It was immersed in sulfuric acid at 0% and 80 ° C. and then with nitric hydrofluoric acid (nitric acid: hydrofluoric acid = 2: 1 at a temperature of 60 ° C.) for 60 seconds and 60 seconds, respectively. The gloss, whiteness, and pitting potential of each of the obtained steel sheets were measured. Table 3 shows the results.

As is evident from Table 3, the steel sheet according to the present invention has excellent corrosion resistance and anti-glare properties, and the color tone is almost the same as that of the steel sheet which has been dulled and bright annealed.

The gloss was measured using a gloss meter under the condition of an incident angle of 20 °.

The whiteness can be measured using a colorimeter using a colorimeter L, a,
b was measured and calculated by the Hunter formula W (Lab) = 100 − [(100−L) ² + a ² + b ² ] ^1/2 .

[0038]

[Table 1]

[0039]

[0040]

[Table 2]

[0041]

According to the present invention, the chemical composition of stainless steel is limited to a specific range to secure long-term corrosion resistance during exposure to the atmosphere, and to reduce the reduction in corrosion resistance due to dull processing for imparting antiglare properties. By avoiding annealing and subsequent reheating, and further improving the conditions of electrolysis in neutral salt and acid method, a low whiteness stainless steel sheet excellent in corrosion resistance and anti-glare properties could be obtained.

Continued on the front page (72) Inventor Masaaki Ishikawa 2-88, Wakihama Kaigandori, Chuo-ku, Kobe Kawasaki Steel Works Co., Ltd. Hanshin Works (72) Inventor Masayuki Hino 2-88, Wakihama-kaigandori, Chuo-ku, Kobe-shi No. Kawasaki Steel Corporation Hanshin Works (56) References JP-A-5-163557 (JP, A) JP-A-5-163588 (JP, A) JP-A-5-163587 (JP, A) JP-A-63 -49305 (JP, A) JP-A-60-218498 (JP, A) JP-A-59-6398 (JP, A) JP-A-6-49539 (JP, A) (58) Fields investigated (Int. . ^7, DB name) C21D 8 / 02,9 / 46 C23F 1/28 C22C 38/00 - 38/22 WPI / L (QUESTEL)

Claims (2)

(57) [Claims] (1) In terms of% by weight, C: 0.020% or less, Cr:
17.0 to 35.0%, Mo: 0.5 to 4.0%, Cr
+ 3Mo: 26 to 40%, Si: 0.05 to 1.0%,
Mn: 0.05-0.5%, Al: 0.005-0.2
%, The balance being Fe and other unavoidable impurities, and after bright annealing a cold-rolled steel sheet having a surface roughness (Ra) of 0.5 to 10.0 μm, reheating to 400 to 900 ° C.
Perform electrolysis under the conditions of 1 to 20 A / dm ^{2 in} a neutral salt solution,
A method for producing an exterior stainless steel sheet having both anti-glare properties and corrosion resistance, characterized by thereafter immersing in a mixed acid of nitric acid and hydrofluoric acid or nitric acid. 2. Nb: 0.1-0.5%, Ti: 0.1-
The method for producing an exterior stainless steel sheet having both antiglare properties and corrosion resistance according to claim 1, which contains one or more elements of 0.5% and V: 0.05 to 0.5%.