JP2768173B2 - High weather resistant steel - Google Patents

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 a normal atmosphere but also in a severe atmospheric corrosion environment such as a coastal zone.

[0002]

2. Description of the Related Art Generally, corrosion resistance in the atmosphere can be improved by adding elements such as P, Cu, Cr, and Ni to steel materials. This steel is called weather-resistant steel, but it is rust (
This is a so-called maintenance-free steel which forms weather-resistant rust) and eliminates the need for corrosion-resistant work such as painting. However, in the severely corrosive environment such as coastal areas, it is difficult to form weatherable rust even after several years, and floating rust and flowing rust such as corrosive red rust and yellow rust may occur. This is not only unfavorable in appearance, but also causes pollution of the surrounding environment, and leaves a problem that it is not maintenance-free. As measures against floating rust and flowing rust, for example, Japanese Patent Laid-Open No. 1-1420
As disclosed in JP-A-88-88, a surface treatment method for forming a phosphate film has been proposed.

[0003]

However, the problem of labor shortage in recent years also extends to the technical field of metal surface treatment, and the development of maintenance-free, highly weather-resistant steel that does not require labor or cost of surface treatment and painting is required. It is strongly desired. Therefore, the present invention reduces the occurrence of floating rust and flowing rust, which significantly impairs the appearance, not only in ordinary air, but also in places where sea salt particles fly, and dense weather-resistant rust can be formed early. It is an object of the present invention to provide a required maintenance-free high weather resistance steel material. This is very important in meeting the recently increasing demand for structures used in the atmospheric environment due to the demand for the enhancement of social capital.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that Cr and Mo are contained in steel.
Was added that an appropriate amount of P and / or S or both were added at the same time to form a weather-resistant rust early on the steel material.

The present invention has been developed based on these findings, and the gist 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 to 5%
5.0%, Al: 0.003 to 0.2%, P: 0.15 to
0.30%, balance is iron and unavoidable components.

[0006] 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 highly weather-resistant steel material composed of iron and inevitable components.

[0007] 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
%, Balance is iron and unavoidable components.

[0008]

[Operation] The reasons for limiting the numerical values of the content of the constituent elements of the weatherable steel material of the present invention will be described below. C is an element effective for securing the strength of the steel material, but is also an element that generally reduces the weldability. When the added amount of P and S is large, especially the interaction between them and C greatly deteriorates the weld crack resistance of the steel material. Therefore, the upper limit of the C content is set to 0.15%.

[0009] Si is added for deoxidation of molten steel,
Since the weldability and weather resistance are adversely affected, and particularly if it exceeds 1.0%, the weather resistance is considerably reduced. Therefore, the upper limit of the Si content is set to 1.0%.

Mn does not affect the weather resistance of the steel material, but is generally added to improve strength and toughness. However, if the content 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 having an effect of improving the corrosion resistance of weathering rust of steel, and its effect is particularly large in the presence of Cr. However, if it exceeds 3.0%, the effect of improving weather resistance is saturated, In addition, since the cost is increased, the Cu content is set to 3.0% or less.

[0012] Cr is an element having the effect of improving the corrosion resistance of weathering rust of steel, and if it exceeds 2.0%, it can densify the formed rust and impart sea salt particle resistance. it can. However, even if it is added in an amount of 3.0% or more, the effect of improving weather resistance is saturated and the cost is increased.
The Cr content was less than 3.0%.

Ni is an element having an effect of improving the corrosion resistance of the steel material against weathering rust, and its effect is particularly large in the presence of Cr. However, if it exceeds 5.0%, the effect of improving the weather resistance is saturated. In addition, since the cost is increased, the Ni content is set to 5.0% or less.

Mo is an element having an effect of improving the corrosion resistance of weathering rust of steel, and is 0.05% in the presence of Cr.
The above content is effective, but if it exceeds 5.0%, the effect of improving the weather resistance is saturated and the cost is increased. Therefore, the Mo content is set in the range of 0.05 to 5.0%.

Al is added to deoxidize the steel material, refine the structure and improve the corrosion resistance. Particularly, when the content is 0.003% or more, the effect of Cr can be further enhanced.
Taking into account the saturation of these effects, the upper limit of the Al content is 0.1.
2%.

P has a great effect on weather resistance when coexisting with Cr. For this purpose, the content is made 0.15% or more. However, if the addition exceeds 0.3%, the effect is saturated and the weldability deteriorates. Therefore, the upper limit of the P content is set to 0.3%.

It has been clarified that when S is contained in steel at 0.010% or more, especially when S coexists with Cr, the amount of reduction in the thickness of the steel when exposed to the atmosphere is reduced. That is, by adding 0.010% or more of S together with Cr, a weather-resistant rust having a high anticorrosion ability is formed in a steel material at an early stage. However, in order to lower the weld cracking susceptibility of steel, the upper limit of the S content is 0.020%. In addition, although P and S are effective in weather resistance even if they are added alone, more excellent weather resistance can be obtained by simultaneous addition.

[0018]

Next, the effects of the present invention will be described in detail with reference to examples. Table 1 shows the chemical components of the test steels used in the examples of the present invention. The dimensions of the test piece were 100 mm × 60 mm × 3 mm, and the surface before the treatment was polished with emery paper and buffed to be a mirror surface.

[0019]

[Table 1]

Under the same conditions, each of the test pieces subjected to the above-mentioned treatment was exposed to a coastal area in Kitakyushu City, Fukuoka Prefecture (a severe corrosive environment 5 m from the sea) for 300 days. Collect rainwater flowing down from the test specimen to evaluate the amount of rust,
The total mass of Fe ions and rust that flowed out was measured. After the test, the rust layer on the surface was removed, and the thickness reduction (average of the average corrosion depth 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 each 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 flow rust were extremely small, and the surface tone was uniform black-brown. On the other hand, in Examples 1, 17, 23 to 25 of Comparative Examples, much more reduction in thickness and flow rust were confirmed, and the color of the surface was reddish brown, and red rust was distributed in a dot-like manner.

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 apparent from the 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. Also, when both P and S are added,
It has better weather resistance than the case of adding P and S alone.

[0025]

As is clear from the above description, the steel material of the present invention forms a stable rust layer having high anticorrosion property in an atmospheric corrosion environment with almost no floating rust such as red rust and yellow rust. It is a steel material having excellent weather resistance not only in the atmosphere but also in a severe atmospheric corrosion environment such as a coastal zone, and a steel material having excellent sea salt particle resistance, which has conventionally been a problem, can be provided. Therefore, the weather-resistant steel material of the present invention provides a maintenance-free material suitable as an excellent material for outdoor buildings and structures, and has a great economic effect.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-17060 (JP, A) JP-A-56-9356 (JP, A) JP-A-61-106750 (JP, A) JP-A-6-106750 88127 (JP, A) JP 48-14528 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38/00-38/60

Claims (3)

(57) [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 being a highly weathering steel material 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%, with the balance being a highly weather-resistant steel 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
%, Balance is iron and unavoidable components.