JPH0693372A - Steel material with high weather resistance - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a steel material having excellent weather resistance not only in normal air but also in severe atmospheric corrosion environments such as coastal areas. [Structure] C: 0.15% or less, Si: 1.0% or less, M
n: 2.0% or less, Cu: 3.0% or less, Cr: more than 2.0% and less than 3.0%, Ni: 5.0% or less, Mo: 0.05 to 5.
0%, Al: 0.003 to 0.2%, and P: 0.0.
A high weather resistance steel material comprising 15 to 0.30%, S: 0.010 to 0.020% of one or two kinds, and the balance iron and unavoidable components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material having excellent weather resistance not only in ordinary air but also in severe atmospheric corrosion environments such as coastal areas.

[0002]

2. Description of the Related Art Generally, by adding an element such as P, Cu, Cr or Ni to a steel material, corrosion resistance in the atmosphere can be improved. This steel material is called weather resistant steel, but it can be protected from corrosion in a few years outdoors by rust (
It is a so-called maintenance-free steel that forms corrosion resistant rust (hereinafter referred to as "weather-resistant rust") and does not require subsequent corrosion-resistant treatment such as painting. However, in an atmosphere with a severe corrosive environment such as the coastal area, weather-resistant rust is hard to form even after several years, and floating rust and flow rust such as corrosive red rust and yellow rust are generated. This is not only unfavorable in appearance, but also causes pollution of the surrounding environment, which leaves the problem of not being maintenance-free. As measures against floating rust and flow rust, for example, Japanese Patent Laid-Open No. 1-1420
As disclosed in JP-A-88, a surface treatment method for forming a phosphate film has been proposed.

[0003]

However, the recent problem of labor shortage extends to the technical field of metal surface treatment, and the development of maintenance-free high weather-resistant steel that does not require the labor and cost of surface treatment or coating. Strongly desired. Therefore, the present invention can reduce the occurrence of floating rust and flow rust that significantly impair the appearance and form a dense weather-resistant rust at an early stage, not only in the normal atmosphere but also in the place where sea salt particles fly. The problem to be solved is to provide the required maintenance-free high weather resistance steel material. This is very important to meet the increasing demand for structures used in the atmospheric environment due to the demand for improvement of social capital.

[0004]

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have earnestly studied, and as a result, in the steel material, Cr and Mo were added.
It was found that weathering rust is formed in the steel material early by adding P in an appropriate amount and simultaneously adding P or S or both of them.

The present invention has been developed on the basis of these findings, and the summary thereof is as follows. 1. C: 0.15% or less, Si: 1.0% or less, Mn:
2.0% or less, Cu: 3.0% or less, Cr: more than 2.0% and less than 3.0%, Ni: 5.0% or less, Mo: 0.05-
5.0%, Al: 0.003 to 0.2%, P: 0.15 to
High weather resistance steel with 0.30% and the balance iron and unavoidable components.

2. C: 0.15% or less, Si: 1.0% or less, Mn: 2.0% or less, Cu: 3.0% or less, Cr:
More than 2.0% and less than 3.0%, Ni: 5.0% or less, M
o: 0.05 to 5.0%, Al: 0.003 to 0.2%,
S: 0.010 to 0.020%, the balance being a steel having high weather resistance composed of iron and unavoidable components.

3. C: 0.15% or less, Si: 1.0% or less, Mn: 2.0% or less, Cu: 3.0% or less, Cr:
More than 2.0% and less than 3.0%, Ni: 5.0% or less, M
o: 0.05 to 5.0%, Al: 0.003 to 0.2%,
P: 0.15 to 0.30%, S: 0.010 to 0.020
%, The balance is high weather resistant steel consisting of iron and unavoidable components.

[0008]

[Operation] The reason for the numerical limitation of the content of the constituent elements of the weather-resistant steel material of the present invention will be described below. C is an element effective for ensuring the strength of the steel material, but it is also an element that generally decreases the weldability. When the addition amount of P and S is large, the weld crack resistance of the steel material is greatly deteriorated due to the interaction between them and C. Therefore, the upper limit of the C content is set to 0.15%.

Si is added for deoxidation of molten steel,
Since the weldability and the weather resistance are adversely affected, and particularly when the content exceeds 1.0%, the weather resistance is considerably deteriorated, the upper limit of the Si content is set to 1.0%.

Although Mn does not affect the weather resistance of steel, it is generally added to improve strength and toughness. However, if it exceeds 2.0%, the weldability of the steel material is significantly deteriorated, so the Mn content is set to 2.0% or less.

Cu is an element which has the effect of improving the corrosion resistance of the steel material against weathering rust, and its effect is particularly great when it coexists with Cr, but when it exceeds 3.0%, the effect of improving weather resistance is saturated, And since it raises cost, Cu content was made into 3.0% or less.

[0012] Cr is an element having the effect of improving the corrosion resistance of the weather resistant rust of the steel material, and if it exceeds 2.0%, the rust formed is made dense and the sea salt particle resistance is imparted. it can. However, even if added in an amount of 3.0% or more, the effect of improving the weather resistance saturates and the cost increases, so
The Cr content is less than 3.0%.

Ni is an element having an effect of improving the corrosion resistance of steel materials against weathering rust, and its effect is particularly great when coexisting with Cr. However, when it exceeds 5.0%, the effect of improving weather resistance is saturated. Moreover, since the cost is increased, the Ni content is set to 5.0% or less.

Mo is an element which has the effect of improving the corrosion resistance of steel materials against weathering and rust, and when it coexists with Cr, it is 0.05%.
The above content is effective, but if it exceeds 5.0%, the weather resistance improving effect is saturated and the cost is increased. Therefore, the Mo content is set to the range of 0.05 to 5.0%.

Al is added for the purpose of deoxidizing the steel material, refining the structure, and improving the corrosion resistance. Particularly, the content of 0.003% or more can further enhance the effect of Cr.
Considering the saturation of those effects, the upper limit of Al content is 0.
It was set to 2%.

Coexisting with Cr has a great effect on weather resistance. Therefore, 0.15% or more is contained. However, when the content exceeds 0.3%, the effect is saturated and the weldability deteriorates, so the upper limit of the P content was made 0.3%.

It has been revealed that when S is contained in the steel material in an amount of 0.010% or more, especially when S is present together with Cr, the reduction of the plate thickness of the steel material upon exposure to the air becomes small. That is, by containing S in an amount of 0.010% or more together with Cr, weather resistant rust having a high anticorrosive ability is formed in the steel material at an early stage. However, S lowers the weld crack susceptibility of the steel material, so the upper limit of the S content is 0.020%. It should be noted that although P and S are effective in weather resistance even if added alone, more excellent weather resistance can be obtained by simultaneous addition.

[0018]

EXAMPLES Next, the effects of the present invention will be described in detail based on examples. Table 1 shows the chemical composition of the test steel used in the examples of the present invention. The size of the test piece was 100 mm × 60 mm × 3 mm, and the surface before the treatment was mirror-finished by emery paper polishing and buffing.

[0019]

[Table 1]

Under the same conditions, each test piece subjected to the above treatment was exposed to the coastal area of Kitakyushu City, Fukuoka Prefecture (a severe atmospheric corrosive environment at a position of 5 m from the sea) for 300 days. Collect the rainwater that runs down from the test piece to evaluate the amount of rust flowing,
The total mass of Fe ions and rust that flowed out was measured. After the test was completed, the rust layer on the surface was removed, and the amount of reduction in plate thickness (average of average corrosion depths on both front and back surfaces) was measured. The test results are shown in Tables 2 and 3.

[0021]

[Table 2]

[0022]

[Table 3]

As a result, in any of the tests, the steels of the present invention 2, 3, 5, 6, 8, 9, 11, 12, 14, 1
In Nos. 5, 18 to 22, the amount of reduction in plate thickness and the flow rust were very small, and the surface color tone was blackish brown. On the other hand, in Comparative Examples 1, 17, 23 to 25, much more reduction in plate thickness and flow rust were confirmed, the surface color tone was reddish brown, and the red rust was distributed in dots.

The results of Comparative Examples 4, 7, 10, 13, and 16 were the same as those of the steel of the present invention, but as is clear from comparison with the results of 5, 6, 9, 12, and 15, respectively. The effect of the element added in excess of the component range of the present invention is saturated. When both P and S are added,
It has better weather resistance than the case of adding P and S alone.

[0025]

As is apparent from the above description, the steel material of the present invention forms a stable rust layer with high anticorrosiveness in an atmospheric corrosive environment with almost no floating rust such as red rust or yellow rust. It is possible to provide a steel material which has excellent weather resistance not only in the atmosphere but also in severe atmospheric corrosion environments such as coastal areas, and which has excellent sea salt particle resistance, which has been a problem in the past. Therefore, the weather-resistant steel material of the present invention provides a material that is suitable as an excellent material for outdoor buildings and structures and is maintenance-free, and has a great economic effect.

Claims (3)

[Claims] 1. C: 0.15% or less, Si: 1.0% or less, Mn: 2.0% or less, Cu: 3.0% or less, Cr:
More than 2.0% and less than 3.0%, Ni: 5.0% or less, M
o: 0.05 to 5.0%, Al: 0.003 to 0.2%,
P: 0.15 to 0.30%, the balance is a steel having high weather resistance composed of iron and unavoidable components. 2. C: 0.15% or less, Si: 1.0% or less, Mn: 2.0% or less, Cu: 3.0% or less, Cr:
More than 2.0% and less than 3.0%, Ni: 5.0% or less, M
o: 0.05 to 5.0%, Al: 0.003 to 0.2%,
S: 0.010% to 0.020%, the balance being a high weather resistance steel material composed of iron and inevitable components. 3. C: 0.15% or less, Si: 1.0% or less, Mn: 2.0% or less, Cu: 3.0% or less, Cr:
More than 2.0% and less than 3.0%, Ni: 5.0% or less, M
o: 0.05 to 5.0%, Al: 0.003 to 0.2%,
P: 0.15 to 0.30%, S: 0.010 to 0.020
%, The balance is high weather resistant steel consisting of iron and unavoidable components.