JPH06220582A - Corrosion resisting multilayer steel for structural use - Google Patents

Abstract

(57) [Summary] [Purpose] Structural multi-layer steel with excellent corrosion resistance used for bridges and revetments. [Structure] The surface layer is austenitic or ferritic stainless steel, and the inner layer is an extremely low C of C: ≤ 0.01 and V = 0.
Corrosion resistant multi-layer steel for structural use, which is a steel containing alloy elements based on 03 to 0.20% and N = 0.08 to 0.025%. [Effect] When stainless steel and ordinary structural steel are multilayered, the mechanical properties as structural steel can be secured, but martensite occurs at the multilayer interface, causing cracking and reduced ductility. on the other hand,
If the inner layer is made to have an extremely low C in order to prevent this, the mechanical properties will be poor. The invention steel eliminates both drawbacks and provides a structural steel with excellent corrosion resistance. Characteristic is extremely low C due to V (CN) precipitate
It is to improve the strength below and prevent the formation of martensite by fixing C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet pile, a thick plate, an H-section steel, a steel pipe, and other corrosion-resistant structural multi-layer steel used for bridges and revetments.

[0002]

2. Description of the Related Art Structural steel such as steel sheet pile is widely used for construction of bridges and seawalls, and is an essential steel material for industrial development. Moreover, once these structures are built, they are shared for 50 to 100 years due to the peculiarities of the structures.

On the other hand, the atmospheres around them are in a corrosive environment, that is, they are in contact with water, seawater, earth and sand, etc., and if ordinary steel materials are applied as they are, it is difficult to share them with the service life mentioned above. As a countermeasure for this, use of corrosion resistant steel such as stainless steel is considered, but that method is not a good idea from the viewpoint of construction cost. Therefore, at present, a method of covering the steel material with a corrosion-resistant material such as urethane or resin and a method of surrounding the steel material with concrete as a part of the structural material are used. However, in the former case, the coating layer is locally peeled off and local corrosion is likely to occur, and in the latter case, there are problems such as an increase in construction cost.

[0004]

In recent years, steel materials having different characteristics have been produced by various methods such as a welding method, a cast-in-girth casting method, a thermal spray overlay method, an explosive deposition method, a laminated dispersion casting method, and a multi-layer continuous casting method. As a result of the development of technology, it has become possible to combine a material having corrosion resistance in the surface layer of steel and a material having the inherent properties of structural steel such as mechanical properties in the inner layer. When using these methods to produce a multi-layer steel product by combining stainless steel having corrosion resistance in the surface layer and structural steel in the inner layer, if ordinary carbon steel plate or low alloy high-strength steel is used in the inner layer, There is a problem in that layer components are mixed with each other and mutual diffusion occurs, martensite is generated at a multi-layer interface during manufacturing or in a product, and hydrogen cold cracking at the interface or ductility of a steel material is deteriorated.

The present invention does not generate martensite at the multi-layer interface, which is a problem in the multi-layer material of stainless steel and structural ordinary steel, or has low hardness even when it is formed, and thus cracks and ductility are reduced. It is an object of the present invention to provide a corrosion-resistant multi-layer steel for structural use which has a tensile strength of 400 to 600 MPa, which is not present and is left to cool after rolling or water-cooled or solution-cooled after solution heat treatment.

[0006]

The gist of the present invention is that the surface layer is austenitic or ferritic stainless steel, the inner layer is C: 0.01% or less, Si;
1.0%, Mn; 0.1 to 2.0%, V; 0.03 to
0.2%, N; 0.008 to 0.025%, or Cr: 0.05 to 2.0%, Mo;
05-0.5%, Nb; 0.01-0.05%, Cu;
0.1-1.0%, Ni; 0.1-1.0%, Ca;
The present invention is a corrosion-resistant structural multi-layer steel containing 0.0010 to 0.0050% of one type or two or more types, and the balance being low alloy steel containing Fe and unavoidable impurities.

The present invention will be described in detail below. To suppress the formation of martensite at the multi-layer interface, it is effective to reduce the amount of C that greatly contributes to the formation. Further, even if martensite is produced, the solid solution C in martensite is low, and if the hardness is low, the susceptibility to cold cracking and ductility reduction can be reduced. Therefore, it is also effective to reduce the amount of C and fix C as a precipitate before the martensitic transformation during cooling. As a result of various investigations, the inventors have found that in achieving extremely low C,
It has been found that V is more likely to precipitate as V carbide than other carbide forming elements, and that solid solution C is easily fixed.

On the other hand, it is well known that the reduction of C hinders the improvement of strength, and it is necessary to introduce means for ensuring the strength as structural steel. As a result of investigating a method for improving strength under the extremely low C, the inventors have found that nitride is effective and V nitride is large in effect. C is 0.05
Although the effect of V nitride on the strength at a content of 0.1% or more is also introduced in the literature (iron and steel), it was found that the effect of improving the strength is great even if C is 0.01% or less.

As described above, V has a large effect of reducing the solid solution C as a carbide and an effect of improving the strength as a nitride in the extremely low carbon content, and normally acts as a carbonitride of V. To occur. The inventors have utilized this effect to invent a corrosion resistant structural steel.

The reasons for limiting each component will be described below.
C of the low alloy steel used for the inner layer machine is required to be 0.01% or less in order to suppress the formation of martensite at the multi-layer interface. Si is necessary for improving the strength, and if it is 0.1% or less, its effect is small, and if it is 1.0% or more, martensite is likely to be generated, and toughness is lowered. Mn improves the toughness of steel, but its effect is small at 0.1% or less,
If it is 2.0% or more, the effect is saturated. V is a main element of the present invention, forms carbonitrides, lowers the solid solution C at the multi-layer interface, and further improves the strength of the structural body. 0.0
If it is 3% or less, the effect is small, and if it is 0.2% or more, the effect is saturated. N combines with V to improve strength,
If less than 0.008%, the effect is small, 0.025%
Above the above range, bubbles are likely to be generated, which is not preferable.

Further, in the present invention, in addition to the steel having the above composition, Cr, Mo and N are used as strengthening elements for the steel.
b, Cu and Ni are selectively contained. Further, Ni has the effect of improving the toughness as well as the strength. Below the lower limit of each component range, the effect of that component is small, and above the upper limit, the effect is saturated. Ca has an effect of reducing strain-age embrittlement when strain-age embrittlement in a high nitrogen content steel becomes a problem, and the effect is required to be contained at least 0.001% or more. Moreover, addition of 0.0050% or more impairs the soundness of the steel as oxide inclusions.

As shown in FIG. 1, when the steel 1 having the above-described composition is applied to the inner layer, the formation of martensite at the multi-layer interface with the austenitic or ferritic stainless steel 2 in the surface layer is prevented, Even if it is formed, it becomes an extremely low C martensite, so there is no cold cracking at the multi-layer interface or reduction in ductility, and tensile strength is 500 MPa.
It is possible to provide the above corrosion-resistant structural steel such as a steel sheet pile, a thick plate, an H-shaped steel plate, and a steel pipe. Next, examples will be described.

[0013]

[Examples] Table 1 shows example steels of the present invention and conventional steels. Steel plates A to G are ultra-low C steels with V and N added to the inner layer, with alloying elements added as necessary, and austenitic or ferritic stainless steels and developed steels with multiple layers. No cracks occur at the interface, and the mechanical properties of the structural steel having a tensile strength of 500 MPa or more are satisfied. On the other hand, Steels H to L represent conventional steels, and when mechanical properties are satisfied, cracks occur at the multi-layer interface, and when cracks are minimal, mechanical properties are unsuitable as structural steel.

[0014]

[Table 1]

[0015]

[Table 2]

[Brief description of drawings]

FIG. 1 is an explanatory view of steel of the present invention.

[Explanation of Codes] 1 ... Austenitic or ferritic stainless steel 2 ... Extra low C-VN high tensile steel

Claims (2)

[Claims] 1. The surface layer is austenitic or ferritic stainless steel, the inner layer is C; 0.01% or less, Si;
0.1-1.0%, Mn; 0.1-2.0%, V;
03-0.2%, N; 0.008-0.025%, the balance being Fe and inevitable impurities low alloy steel, characterized in that it is a corrosion-resistant structural multilayer steel. 2. The surface layer is austenitic or ferritic stainless steel, the inner layer is C; 0.01% or less, Si;
0.1-1.0%, Mn; 0.1-2.0%, V;
03-0.2%, N: 0.008-0.025%, Cr: 0.05-2.0%, Mo: 0.05
.About.0.5%, Nb; 0.01 to 0.05%, Cu;
1-1.0%, Ni; 0.1-1.0%, Ca; 0.0
A corrosion-resistant multi-layer steel for structural use, characterized by containing 010 to 0.0050% of one or more kinds, and the balance being Fe and a low alloy steel of inevitable impurities.