JPH073388A - Steel excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a corrosion resistant steel having high resistance to the corrosive environment of seawater by adding a specified amt. each of Cr and Al to a low carbon steel. CONSTITUTION:A low carbon steel contg., by weight, <0.10% C, 0.01-1.20% Si and 0.05-1.70% Mn is prepd. and 0.1-5.5% Cr and 0.3-4.0% Al are incorporated into the steel or one or more among 0.05-0.15% P, 0.05-3.0% Cu, 0.05-2.0% Mo and 0.01-7.0% Ni are further incorporated into the steel to obtain the objective steel having high resistance to corrosion by seawater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel having excellent corrosion resistance, and more particularly to a steel having excellent corrosion resistance in environments used inside and outside a ship or the like.

[0002]

2. Description of the Related Art Conventionally, steel materials used inside and outside a ship or the like have had a problem of corrosion damage due to the environment in which they are used. Since the area of ballast tanks has increased with the use of double hull tankers to control environmental pollution, the demand for steel with excellent corrosion resistance to seawater has increased from the perspective of increasing maintenance and painting work.

The current marine steel has insufficient corrosion resistance,
The increase in area is directly linked to the increase in maintenance work. Further, it is conceivable to use seawater-resistant steel containing about 1% of Cr, but its corrosion resistance is insufficient in an environment where ships are actually used. On the other hand, use of corrosion-resistant steel containing a large amount of Cr is also conceivable, but the material cost increases significantly.

[0004]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a steel having a large resistance to the corrosive environment of seawater and a low cost.

[0005]

In order to achieve the above object, the inventors of the present invention have developed a steel having excellent corrosion resistance in a corrosive environment including an environment where sea water is involved.
Considered from various viewpoints. First, corrosion in an environment where seawater such as a ship is exposed occurs in a wet and dry environment caused by repeated seawater, and the corrosion is 40 to 100 ° C.
It was found that it becomes remarkable in an environment heated to a high temperature.
That is, it is possible to simulate a long-time corrosion phenomenon in an environment exposed to seawater such as a ship in a short time in an environment heated to a high temperature.

[0006] Further, as a result of various studies on means for improving the corrosion resistance in the corrosive environment, Cr was 0.2 to 5.5.
It has been found that the steel containing 0.3 to 4.0% of Al contained in the steel has a very excellent corrosion resistance in repeated wet and dry cycles with seawater and its corrosive environment. In the corrosive environment, a large amount of Al was added on top of the Cr coating on the iron surface.
It was discovered that the corrosion resistance is remarkably improved by forming the coating film of No. 1 and the Al coating significantly strengthens the Cr coating.

The present invention has been made on the basis of the above findings, and the gist of the present invention is that it is% by weight,
C: 0.10% or less, Si: 0.01 to 1.20%, M
n: 0.05 to 1.70%, Cr: 0.1 to 5.5%,
A steel having excellent corrosion resistance, which is characterized by containing Al: 0.3 to 4.0% and the balance being Fe and inevitable impurities. Furthermore, in the present invention, P: 0.05 to 0.
15%, Cu: 0.05 to 3.0%, Mo: 0.05 to
It is a steel excellent in corrosion resistance containing 2.0% and Ni: 0.01 to 7.0% of one kind or two or more kinds.

[0008]

The reason why the range of each component is limited in the present invention will be described below. C: C lowers the workability of the steel sheet, and C forms a carbide with Cr to lower the corrosion resistance. Therefore, it is preferable that the amount be small, but it is necessary to add C to some extent from the viewpoint of strength, so the upper limit is set. It is set to 0.10%. Si: Addition as a deoxidizing agent and a strengthening element is effective, but if the content is less than 0.01%, the deoxidizing effect is not sufficient, and if it is more than 1.2%, the effect is no longer saturated. In addition, since the workability is deteriorated, the content range is limited to 0.01 to 1.20%.

Mn: It is necessary to contain 0.05% or more, which is necessary as a deoxidizing agent, but if it exceeds 1.7%, the workability is deteriorated, so the upper limit content is made 1.7%. . Cr: Since it is an element necessary for ensuring corrosion resistance,
It is necessary to contain 0.1% or more, but 5.5
If it is contained in excess of%, not only the cost is unnecessarily increased, but also the workability is deteriorated, so the upper limit content is made 5.5%.

Al: An element which is important for ensuring corrosion resistance in the present invention, and as described above, when the Al content is less than 0.3%, the effect of forming a passive film and suppressing corrosion is not sufficient. On the other hand, if added in excess of 4.0%, the effect is saturated but the workability is deteriorated. Therefore, the Al content is limited to 0.3 to 4.0%.

Steel containing P, Cu, Mo, and Ni: Al in an amount of 0.3% or more is 0.05%, 0.05%, and 0.1%, respectively.
Addition of more than 05% and 0.01% has the effect of improving the resistance to corrosion, but 0.15% and 3.0% respectively.
%, 2.0%, and 7.0%, the effect is saturated and the hot workability is deteriorated. Therefore, the upper limit contents are 0.15%, 3.0%, and 2%, respectively. 0.0%, 7.
0%

The steel proposed in the present invention is manufactured as a product by first manufacturing it as a steel plate, then forming it into a predetermined shape with a press or the like, and further processing and welding it when used in an environment where seawater such as ships is used. Alternatively, the steel sheet may be formed into a steel pipe with a bending roll and then used in a product by secondary processing, welding, or the like.

Any steel having a composition and a combination of elements limited by the present invention, including other processes, is a subject of the present invention, and is an optimum product production due to the cost and constraints of existing production equipment. The process can be selected and which manufacturing process is selected does not depart from the scope of the invention. Further, the steel proposed in the present invention should be applied to various corrosive environments such as an environment in which an aqueous solution containing chloride is exposed to a high temperature, an environment in which heating and cooling are repeated, in addition to an environment in which seawater such as a ship is exposed. You can

[0014]

[Example] Steel having the composition shown in Table 1 was melted and subjected to a normal manufacturing process such as hot rolling, normalizing heat treatment, etc. to obtain a plate thickness of 10 mm.
Steel plate. Next, from these steel plates, width 50mm, length 7
A 0 mm test piece was sampled and subjected to a corrosion test. The corrosion test is a cycle of immersion in 40 ° C. artificial seawater for 4 minutes and drying at 80 ° C. in the atmosphere for 26 minutes.
20 minutes at 0 ℃ artificial seawater 4 minutes and 40 ℃ humidity 95% 26 minutes
A wet environment corrosion test was conducted for one day, and the amount of reduction in plate thickness before and after immersion was measured.

As is clear from Table 1, in Examples 1 to 9 of the present invention, the amount of reduction in sheet thickness in the corrosion test under repeated dry and wet conditions and a humid environment was small, and good results were obtained. In contrast, Example 10 has a high C, Example 11 has a low Cr, and Example 12
Has a low Al content, has a large amount of reduction in plate thickness in a corrosion test under repeated dry and wet conditions, and has a poor corrosion resistance.

[0016]

[Table 1]

[0017]

INDUSTRIAL APPLICABILITY The present invention makes it possible to provide a steel having excellent corrosion resistance in an environment used inside and outside a ship or the like at a low cost, and greatly contributes to industrial development.

Claims (2)

[Claims] 1. By weight%, C: 0.10% or less, Si: 0.01 to 1.20%, Mn: 0.05 to 1.70%, Cr: 0.1 to 5.5%, Al: 0.3 to 4.0% A steel having excellent corrosion resistance, characterized by comprising the balance Fe and unavoidable impurities. 2. In% by weight, P: 0.05 to 0.15%, Cu: 0.05 to 3.0%, Mo: 0.05 to 2.0%, Ni: 0.01 to 7. The steel having excellent corrosion resistance according to claim 1, containing 0% of one or more of them.