JP3170586B2 - Weathering steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to weathering steel. More specifically, the invention of this application relates to a weather-resistant steel which has high corrosion resistance and can withstand use in a beach area having a large amount of flying salt (sea salt).

[0002]

2. Description of the Related Art Since bridges and steel structures have a practical period of several decades, long-term anticorrosion control is required. In the past, painting has been widely used for that purpose, but soaring labor costs and a decrease in construction engineers are expected in the future. On the other hand, various weather-resistant steels have been developed as steels. The weather-resistant steel is a steel exhibiting high corrosion protection by covering the surface with rust having high corrosion resistance, that is, a so-called stable rust in an atmosphere exposed to air. However, stable rust hardly occurs in a beach area with a high amount of flying salt (sea salt), and practical corrosion resistance cannot be expected. For example, JIS-S
MA: 0.3% Cu-0.6% Cr-Fe has a flying salt content of 0.
It is specified by the Ministry of Construction that it cannot be used in areas over 05mdd (mg / dm ² / day).

[0003] In order to improve the corrosion resistance particularly in the seaside area, conventionally known weather-resistant steels such as JIS-SMA and the like are used as corrosion-resistant components such as chromium (Cr), copper (Cu), and phosphorus (P). ) Has been proposed.

[0004]

However, it has been pointed out that the addition of a large amount of Cr and P significantly deteriorates the weldability of steel, and the addition of a large amount of Cu deteriorates the hot workability. Therefore, it is not realistic to use steel containing a large amount of these additional components as a welded structural steel.

[0005] On the other hand, a steel containing a large amount of nickel (Ni) and exhibiting a corrosion resistance effect has recently been proposed. However, in order to ensure corrosion resistance with Ni alone, a large amount is required, which is economically problematic. Therefore, calcium oxide is added to the steel in a complex manner. However, this calcium oxide significantly degrades the low temperature toughness of the steel. This is because calcium oxide becomes a coarse oxide by re-melting / precipitation in a welded portion of steel. Therefore, the Ni-containing steel to which calcium oxide is added in a complex manner cannot exhibit sufficient characteristics as a structural steel.

The invention of this application has been made in view of the circumstances described above, and solves the disadvantages of the conventional weatherable steel, and has stable rust on the surface even in a beach area where there is a lot of flying salt (sea salt). It is an object of the present invention to provide a weather-resistant steel having high corrosion resistance which can be formed and used.

[0007]

Means for Solving the Problems In order to achieve the above object, the inventors of the present invention have determined that the stability of iron-based rust formed on a steel surface in an atmospheric corrosion environment is determined for each single element. Was analyzed by computer analysis of the chemical potential diagram of the compound and evaluating the stability of a plurality of metal species. Then, as a result of analyzing a composite chemical potential diagram of iron and the added element, it was found that extremely stable rust was formed as a composite oxide in an atmospheric corrosion environment.

That is, cobalt (Co) is replaced with iron (Fe)
In the composite oxide formed by adding
As shown in the initial diagram, the spinel (Fe
Co _TwoO_Four) Regions are formed and Fe_ThreeO_FourBecause it covers the area
is there. In this chemical potential diagram, the vertical axis represents the potential E
Shows the oxidizing properties of the environment, and the horizontal axis shows the pH of the environment.
I have. Spinel oxides are stable amorphous phases.
And exhibit high corrosion resistance. Therefore, steel containing Co
Of spinel-based oxides that are stable in atmospheric corrosion environments
It is thought that rust forms on the surface and high corrosion resistance is expressed
You. Maintenance-free is also feasible.

Similarly, when the stability of oxides formed by various elements and iron was analyzed, it was found that tungsten (W), antimony (Sb), nickel (N
i), and the composite addition effect of ruthenium (Ru) was found. W forms FeWO ₄ as a hardly soluble salt, and has an effect of significantly increasing the resistance of chloride ions to permeate iron rust. Both Sb and Ru are stable in a metallic state in iron rust, and have an effect of metal plating active points of iron ingot in iron rust. And Ni is Fe and C
Form a composite spinel with o to form a more stable amorphous phase.

Therefore, in addition to Co, these W and S
It is considered that by further adding at least one of the four elements b, Ni, and Ru, that is, by adding in combination, further improvement in corrosion resistance can be expected. Based on the above technical knowledge, the invention of the present application, in terms of% by weight, shows that cobalt (Co): more than 1.0% and 4.0% or less, carbon (C): 0.15% or less, silicon ( Si): 2.0% or less, manganese (Mn): 2.0% or less, phosphorus (P): 0.03% or less, sulfur (S): 0.04% or less, aluminum (Al): 1.6 % Or less, tungsten (W), antimony (Sb),
At least one element selected from the group consisting of nickel (Ni) and ruthenium (Ru) in a total amount of 0.1 to 2.5% by weight;
Provided is a weatherable steel characterized in that it has a composition in which elements of these groups are added or elements in which these elements are not added, the presence of unavoidable impurities is allowed, and the balance consists of iron (Fe). I do.

[0011]

Hereinafter, the weathering steel of the invention of the present application will be described in more detail with reference to examples.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The weathering steel of the invention of this application contains the above-mentioned elements in predetermined amounts as constituent elements. The effects of these elements and the reasons for limiting the contents (% by weight) are as follows. As described above, cobalt (Co) is a main element that improves corrosion resistance. The effect is 0.1% content
The above effect is exhibited, but if it exceeds 4.0%, the weldability of steel will deteriorate. Therefore, the content of Co is 0.1 to 4.0%
And

Tungsten (W), antimony (S
b), nickel (Ni) and ruthenium (Ru)
It is an important element for improving corrosion resistance, and is added in combination with Co. At the time of addition, one or more kinds can be appropriately selected. The combined effect is exhibited when the blending amount is 0.1% or more, but when it exceeds 2.5%, like Co,
It deteriorates the weldability of steel and is economically disadvantageous.
Therefore, the content of these four elements, W, Sb, Ni, and Ru, is one or more of them in a total of 0.1 to 2.5%.

[0015] Carbon (C) is indispensable as an element for increasing the strength of steel. On the other hand, since it also deteriorates the weldability, the content is set to 0.15% or less. Silicon (Si)
It functions effectively as a deoxidizer in smelting and is also effective in improving corrosion resistance. On the other hand, if the content is too large, the weldability and workability deteriorate, so the content is set to 2.0% or less.

Manganese (Mn) is an important element for adjusting the strength of steel. However, if the content is too large, the weldability deteriorates. Phosphorus (P)
Is an element that is effective in improving corrosion resistance, but as described above, it also significantly deteriorates the weldability of steel.
0.03% or less. Sulfur (S) is an element that degrades corrosion resistance, and is therefore limited to 0.04% or less.

Chromium (Cr) is a corrosion-resistant component of conventional weather-resistant steel. However, as described above, it deteriorates the weldability of steel and may deteriorate the corrosion resistance in an environment containing chloride. 0.1% or less. Aluminum (A
l) improves corrosion resistance. However, if the content is too large, the toughness of the weld is greatly impaired. Therefore,
1.6% or less.

[0018]

EXAMPLES (Examples 1 to 27, Comparative Examples 1 to 10) Alloys having the compositions shown in Tables 1 and 2 below were melted, and steel was produced by hot rolling. Corrosion test specimens include:
One processed to a size of 50 × 60 × 3 tmm (t: thickness) was used.

The corrosion test was performed as follows. That is, 0.5% NaCl solution was applied to each test piece at 40 μm / cm ^2.
1 drop, and a thermo-hygrostat (25 ° C, 60% RH)
Dried in. This is defined as 2 hours, where 1 cycle is 12 hours.
0 cycles were performed. In addition, in order to prevent the salt content from accumulating on the test piece, the test piece was washed with pure water before dropping the reagent. After this corrosion test, rust was peeled off, and the corrosion loss of the metal was evaluated. Specifically, the evaluation was based on the relative corrosion amount (%) with the corrosion amount of general carbon steel (JIS-SM material equivalent material) being 100%. The smaller the relative corrosion amount, the higher the corrosion resistance. Therefore, when the relative corrosion amount was less than 80%, the corrosion resistance was determined to be good, and in the table, 印 was given. On the other hand, 80% or more was regarded as defective, and a cross was given in the table.

Further, a weld crack test was also performed on the produced steel. The oblique Y-type welding crack test defined in JIS was applied, and the presence or absence of cracks was examined at a preheating temperature of 50 ° C.
In the table, ○ marks indicate that no cracks occurred, and X marks indicate that cracks occurred.

[0021]

[Table 1]

[0022]

[Table 2]

As can be seen from the results of Examples 1 to 27, as the content of cobalt (Co) increases, the relative corrosion amount decreases and the corrosion resistance increases. Further, the relative corrosion amount decreases with an increase in the content of silicon (Si) and aluminum (Al), and the corrosion resistance increases.
Further, when at least one of the four elements of tungsten (W), antimony (Sb), nickel (Ni), and ruthenium (Ru) is added together with Co, the relative corrosion amount is further reduced. Improved corrosion resistance is observed.

On the other hand, from Comparative Example 1, the Co content was
It is confirmed that when the content is less than 0.1% by weight, the corrosion resistance becomes insufficient. Further, from Comparative Examples 2 to 10, carbon (C),
When the contents of silicon (Si), manganese (Mn), phosphorus (P), aluminum (Al), Co, tungsten (W), antimony (Sb), and nickel (Ni) each exceed a predetermined content, welding cracks occur. Is generated, and it is confirmed that the weldability of the steel is deteriorated.

Of course, the invention of this application is not limited by the above embodiments. The amount of each element,
It goes without saying that various modes are possible for details such as a method of manufacturing steel.

[0026]

As described in detail above, according to the invention of this application, a stable rust is formed on the surface even in a beach area where a lot of flying salt (sea salt) is present, maintenance-free is achieved, and high corrosion resistance that can withstand use is achieved. A weatherable steel is provided. It is expected to be applied to bridges and steel structures.

[Brief description of the drawings]

FIG. 1 is a chemical potential diagram of an Fe—Co—H ₂ O system.

Claims (2)

(57) [Claims] (1) Cobalt (Co): more than 1.0% and 4.0% or less, carbon (C): 0.15% or less, silicon (Si): 2.0% or less, Manganese (Mn): 2.0% or less Phosphorus (P): 0.03% or less Sulfur (S): 0.04% or less Aluminum (Al): 1.6% or less The presence of typical impurities is allowed,
A weathering steel characterized in that the balance is made of iron (Fe). 2. Cobalt (Co): more than 1.0% and 4.0% or less, carbon (C): 0.15% or less, silicon (Si): 2.0% or less in terms of% by weight. Manganese (Mn): 2.0% or less, Phosphorus (P): 0.03% or less, Sulfur (S): 0.04% or less, Aluminum (Al): 1.6% or less, and tungsten (W) ), Antimony (Sb),
At least one element selected from the group consisting of nickel (Ni) and ruthenium (Ru) in a total amount of 0.1 to 2.5% by weight;
A weather-resistant steel having a composition added thereto, in which the presence of unavoidable impurities is allowed, and the balance is iron (Fe).