JP2000063981A - Atmosphere corrosion resisting steel showing blackish color tone from initial stage of rusting and excellent in external appearance characteristic and stability of color tone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an atmosphere corrosion resisting steel showing a blackish subdued rust color from the initial stage of exposure, that is, from the initial stage of construction of an outdoor steel structure, excellent in corrosion resistance, and capable of withstanding use in an uncoated state. SOLUTION: The steel has a composition consisting of, by weight, 0.01-0.15% C, 0.01-1.0% Si, 0.8-3.0% Mn, 0.05-1.0% Cu, 0.25-5.0% Ni, >0.01-0.2% Al, and the balance iron with inevitable impurities satisfying Mn+Ni >=1.8%, and further containing, if necessary, one or >=2 kinds among 0.25-5.0% Cr, 0.25-1.0% Mo, 0.03-1.0% P, 0.01-0.05% Nb, 0.01-0.1% V, 0.005-0.05% Ti, and 0.01-0.1% Zr, or/and 0.001-0.01%, in total of either or both of rare earth element and Ca.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weather-resistant steel which exhibits a blackish color tone from initial rust and has excellent appearance and stability of color tone and which is used without coating.

[0002]

2. Description of the Related Art Weather-resistant steel typified by Corten steel is a low-carbon steel containing a small amount of Cu, P, Cr, Ni, etc. added in a complex manner. Corrosion is suppressed by forming rust. However, the weather-resistant steel having such a composition is unlikely to cause stable rust in a coastal area where sea salt particles are abundant or in a shaded portion of a structure which is not exposed to rain and wind, and corrosion may not be suppressed. For this reason, weathering steel has been developed that forms stable rust on the surface even in coastal areas and shaded areas.

For example, Japanese Examined Patent Publication (Kokoku) No. 1-42344 discloses a high weather resistance Fe-Cr steel which has a good appearance with a reduced corrosion rusting rate and little red rust outflow.
Japanese Unexamined Patent Publication No. 63-255341 discloses a corrosion resistant steel for welded structures which is used unpainted in coastal areas and has excellent salt corrosion resistance.

[0004]

[Problems to be Solved by the Invention]
The main feature is that it contains 10% of Cr.
It seems that it takes 6 months to several years to produce a good appearance or stable rust. There is also a problem that as the Cr content increases, the initial rust becomes mottled.

Therefore, from the early stage of exposure, that is, from the early stage of construction of an outdoor steel structure, it exhibits a dark tinged rusty color,
Moreover, weather resistant steel that has excellent corrosion resistance and can withstand unpainted use, has a blackish color tone from initial rust, and is excellent in appearance and color stability has not yet been developed.

[0006]

Therefore, the present inventors have
As a result of various studies in order to deal with such a problem, as a result of adjusting the steel components, especially the contents of Mn and Ni contained in the steel, the ratio of Mn and Ni black hydroxide in the rust layer is adjusted. It has been successfully developed by discovering that a dark, dark purple-colored, calm rust layer is formed on the steel surface within a few days to a month after starting exposure to the outdoor air.

The present invention is based on this finding, and the gist thereof is, by weight%, C: 0.01 to 0.15%, Si:
0.01-1.0%, Mn: 0.8-3.0%, Cu:
0.05-1.0%, Ni: 0.25-5.0%, A
1: more than 0.01% to 0.2% under the condition of Mn + Ni ≧ 1.8%, and if necessary, Cr: 0.25 to
5.0%, Mo: 0.25 to 1.0%, P: 0.03 to
1.0%, Nb: 0.01 to 0.05%, V: 0.01
~ 0.1%, Ti: 0.005-0.05%, Zr:
0.01 to 0.1% of one or more, or / and a total of one or two of a rare earth element and Ca of 0.
001 to 0.01% or less, the balance consisting of iron and unavoidable impurities, and a weathering steel exhibiting a blackish color tone from initial rust and having excellent appearance and color tone stability. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The component limitation of the present invention will be described in detail below.

C is contained as a component for imparting the required strength as structural steel, and it is necessary to contain C in an amount of 0.01% or more. However, excessive C adversely affects toughness and weldability, so the upper limit was made 0.15%.

Si must be contained in an amount of 0.01% or more to improve the strength, but if it exceeds 1.00%, the low temperature toughness tends to deteriorate, so the upper limit was made 1.0%.

Mn is an essential element for the initial rust to have a blackish tone, and it is necessary to contain Mn in an amount of 0.8% or more. That is, as the content of Mn + Ni increases, the color tone of the initial rust changes from ocher to reddish brown to dark purple, and when Mn is 0.8% or more and Mn + Ni ≧ 1.8%, the exposure time is from several days to one month. A rust of a dark purple color with a uniform tone is generated on the entire surface. Although the corrosion amount decreases as the Mn content increases, the upper limit is set to 3.0% considering that the toughness also deteriorates. The upper limit of Mn + Ni is 8.0% of the sum of the upper limits of Mn and Ni.

[0012] Cu is a component having an effect of improving corrosion resistance, but its effect is not sufficient if the content is less than 0.05%, and if it exceeds 1.0%, hot workability during production is impaired. May occur. Therefore, 0.05% to 1.0% is contained as a corrosion resistance improving component that does not impair hot workability.

Ni is an essential element for making the initial rust a beautiful dark purple color by synergistic action with Mn, and it is essential to contain 0.25% or more for decreasing the corrosion rate and improving the corrosion resistance. is there. However, if it exceeds 5.0%, the effect is saturated, so the upper limit was made 5.0%.

Al is contained as an effective element for refining the microstructure of steel and improving toughness in an amount of more than 0.01%. If contained too much, alumina clusters are generated and the toughness becomes unstable, so the upper limit is made 0.2%.
The upper limit of the desirable content for obtaining stable toughness is 0.
1%.

The steel composed of such components and contents exhibits a dark and rusty dark color, that is, dark purple from the initial exposure, that is, the early construction of the outdoor steel structure, and is excellent in corrosion resistance and mechanical properties. It is a weather resistant structural steel that can withstand unpainted use.

Further, the present invention provides a steel having the above-mentioned composition with C
R, Mo, P, Nb, V, Ti, Ca and rare earth components are selectively added to further improve the corrosion resistance and mechanical properties of strength and toughness.

Cr is 0.25 mainly for improving the corrosion resistance.
%, But the upper limit is set to 5.0% in consideration of economic efficiency because the effect is saturated even if the content is 5.0% or more.

Mo is also contained in an amount of 0.25% or more from the viewpoint of improving corrosion resistance and ensuring strength, but if too much is contained, the effect is saturated and it is uneconomical, so the upper limit was made 1.0%.

[0019] P is contained because it acts to improve the corrosion resistance, but if it is contained too much, it may impair the weldability, so it was made 0.03% to 0.1%. Therefore,
The corrosion resistance of steel can be improved by containing at least one of Cr, Mo and P.

Ti, Nb, and Zr are contained for the purpose of grain refinement of the austenite structure at the time of heating before rolling during manufacturing of the steel to strengthen the steel, and for improving the toughness of the welded portion, but they are contained too much. Even if it is done, the effect is saturated and it is uneconomical. Therefore, each component is 0.005% to 0.0
5%, 0.01% to 0.05%, 0.01% to 0.1%
It is contained in the range of.

V is contained in an amount of 0.01% or more in order to increase the strength of steel by precipitation strengthening, but the upper limit was made 0.1% so as not to deteriorate the toughness. Therefore, Ti, N
The steel can be strengthened by containing at least one of b, Zr and V.

The addition of rare earth elements such as Ce and Y and / or Ca is 0.00 or a total amount thereof in order to control the morphology of the sulfide inclusions in the steel and improve the toughness.
The content of 1% or more is included, but the content of more than 0.01% tends to contaminate the steel, so 0.001% to 0.0
The range is 1%.

The steel composed of such components and contents, when used unpainted outdoors, has a blackish (blackish) calm color tone on its surface for several days to one month, That is, a beautiful dark purple rust layer is generated.

It should be noted that this beautiful dark purple rust is different from so-called stable rust because it has a high proportion of mainly Mn and Ni black hydroxide in the rust layer, and is therefore said to be produced within 1 to several years of exposure. Although it is different from stable rust accompanied by an amorphous rust layer, the particles are finer and less likely to form flow rust compared to the ocher-colored initial rust generated on ordinary carbon steel. The beautiful dark purple rust layer formed during several days to one month of exposure gradually changes to stable rust, and has a more subdued color tone over time, and has an excellent appearance.

[0025]

EXAMPLES Next, examples of the present invention will be described.

Steel No. 1 in Table 1 1-No. 8 is the steel of the present invention,
No. 9, No. 10 is a comparative steel. Specimens of the present invention steel and comparative steel having such chemical composition (thickness 5 mm ×
Sandblasting is applied to the front and back surfaces (width 50 mm x length 150 mm), and 20, 40 and 60 days after exposure at a slope of 30 ° toward the coastline within 5 meters from the coastline facing the Kanmon Straits. Also, the color tone of rust on the front and back surfaces of the first year (365th day) was observed. In the first year, the rust thickness was also measured.

The steel of the present invention No. 1-No. In each of Nos. 8 and 20, dark purple rust, which was already blackish, was formed on the entire front and back surfaces of the test piece on the 20th day of exposure, and a beautiful dark purple rust color became noticeable every 40 and 60 days. It had an excellent appearance. During this period, there was little outflow rust, and thereafter the color tone remained stable without any major change in color tone. On the other hand, comparative steel No.
9, No. Sample No. 10 remained ocher to reddish brown after 20 days to 1 year of exposure, and the rust did not stop flowing out. The thickness of the rust in the first year of exposure is the same as that of the steel of the invention. 1-No. In each case, the front and back surfaces of the test piece of each of the No. 8 specimens were 200 μm or less, while the comparative steel No. 9, No. 10 is 600 μm or more,
It grew three times thicker and peeled into layers when hit with a mallet. This is because No. 1 of the steel of the present invention. 1-No. Although the initial rust formed on the front and back surfaces of No. 8 suppresses corrosion, it also shows that the initial rust of the comparative steel is rust that does not contribute to corrosion suppression at all.

[0028]

[Table 1]

[0029]

EFFECTS OF THE INVENTION As is clear from the above description, the steel of the present invention exhibits a dark tinged rust color from the early stage of exposure, that is, a beautiful dark purple color, and has little flow rust. Has a remarkable effect on its appearance from the beginning of construction.

Claims (4)

[Claims] 1. C: 0.01 to 0.15% by weight,
Si: 0.01 to 1.0%, Mn: 0.8 to 3.0%,
Cu: 0.05-1.0%, Ni: 0.25-5.0
%, Al: more than 0.01% to 0.2% Mn + Ni ≧ 1.8
% Weathering steel, which has a blackish color tone from initial rust and is excellent in appearance and stability of color tone, which is characterized by containing iron and inevitable impurities in the balance. 2. C: 0.01 to 0.15% by weight,
Si: 0.01 to 1.0%, Mn: 0.8 to 3.0%,
Cu: 0.05-1.0%, Ni: 0.25-5.0
%, Al: more than 0.01% to 0.2% Mn + Ni ≧ 1.8
%, And further contains Cr: 0.25 to 5.0
%, Mo: 0.25 to 1.0%, P: 0.03 to 1.0
%, Nb: 0.01 to 0.05%, V: 0.01 to 0.
1%, Ti: 0.005 to 0.05%, Zr: 0.01
~ 0.1% of one or more kinds, and the balance consisting of iron and inevitable impurities, the initial rust has a blackish color tone and is excellent in appearance and color tone stability. Sex steel. 3. C: 0.01 to 0.15% by weight,
Si: 0.01 to 1.0%, Mn: 0.8 to 3.0%,
Cu: 0.05-1.0%, Ni: 0.25-5.0
%, Al: more than 0.01% to 0.2% Mn + Ni ≧ 1.8
%, And further contains 0.001 to 0.01% or less in total of one or two of rare earth elements and Ca,
Weather-resistant steel with a balance of iron and unavoidable impurities that gives a blackish color tone from initial rust and has excellent appearance and color stability. 4. C: 0.01 to 0.15% by weight,
Si: 0.01 to 1.0%, Mn: 0.8 to 3.0%,
Cu: 0.05-1.0%, Ni: 0.25-5.0
%, Al: more than 0.01% to 0.2% Mn + Ni ≧ 1.8
%, And further contains Cr: 0.25 to 5.0
%, Mo: 0.25 to 1.0%, P: 0.03 to 1.0
%, Nb: 0.01 to 0.05%, V: 0.01 to 0.
1%, Ti: 0.005 to 0.05%, Zr: 0.01
0.1% to 0.1% of one or two or more, and a total of one or two of rare earth element and Ca is 0.001.
~ 0.01% or less, the balance consisting of iron and unavoidable impurities, weathering steel exhibiting a blackish color tone from the initial rust and excellent in appearance and color tone stability.