JP2906179B2 - Clad steel pipe for structures - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a clad steel pipe for a structure used, for example, as a pillar of a building.

[Conventional technology]

A cylindrical steel pipe is one of the typical pillar materials used for buildings such as buildings. The pillars are often provided with a fire-resistant coating according to the provisions of the Fire Service Law, and are often coated with various panel materials for design effects.

When a steel pipe is used as it is, such as a structure such as a steel tower or a pillar material of a building in a wholesale market, a steel pipe that has been subjected to rust-preventive treatment with galvanized or weather-resistant material is used.

[Problems to be solved by the invention]

Of the pillars for buildings, for example, pillars in a stage room do not require a fire-resistant coating, and can be provided as pillars by imparting the required design effect and corrosion resistance to the surface of a cylindrical steel pipe. In addition, there is a wide variety of uses for steel pipe columns that do not require a fire-resistant coating and can be used as column materials by satisfying the design effect and corrosion resistance. As a pillar material for such applications,
A column material in which a thin stainless steel plate is wound around the circumference of a cylindrical steel pipe to have the corrosion protection of the stainless steel plate and the design effect of the beautiful metallic gloss surface is considered.

However, the welding and assembling work for winding a thin stainless steel plate is extremely troublesome and difficult, and there is a problem of deterioration of the corrosion protection of the welded portion. Moreover, the wound plate has deformation such as distortion and irregularities. The design effect of the plate is significantly impaired by the deformation even when the deformation is very slight.

The present invention has been made to solve the above problems.

[Means and actions for solving the problem]

The clad steel pipe for a structure according to the present invention has an inner layer made of carbon steel or low alloy steel having a carbon content of 0.2% or less and a carbon equivalent (Ceq) calculated by the following formula [I] of 0.48 (%) or less. And an outer layer made of austenitic stainless steel, a nickel alloy, or a nickel-copper alloy, and the outer layer and the inner layer are metallurgically bonded to each other by 50% or more (area ratio) of the layer interface. And a centrifugally cast tube having an outer layer thickness of 3 mm or more.

 Ceq = C (%) + Si (%) / 24 + Mn (%) / 6 + Ni (%) / 40 + Cr (%) / 5 + Mo (%) / 4 + V (%) / 14) [I] Hereinafter, the present invention is described in detail. explain.

The clad steel pipe of the present invention has a corrosion-resistant property and a beautiful metallic glossy surface provided by an outer layer surrounding the inner layer, while securing mechanical properties such as strength required as a column material or the like in the inner layer made of carbon steel or low alloy steel. This is a centrifugal casting tube having a two-layer structure with a design effect.

The carbon steel or low alloy steel forming the inner layer of the clad steel pipe of the present invention has a C content of 0.20% or less and a carbon equivalent Ceq represented by the above formula (I) of 0.48 (%) or less. The purpose is to ensure good weldability, prevent hard embrittlement and cracking in the heat affected zone, and ensure the formation of sound welds required for structures such as buildings. is there. There are no specific restrictions on the selection of the specific material of the carbon steel and the low alloy steel except for the above-mentioned C content and the provisions of Ceq.Examples of carbon steel include JIS G5201 SCW50CF, and examples of low alloy steel Is JIS G5201 SCW53-C
F, SCW58CF and the like.

On the other hand, the outer layer forming material is defined as austenitic stainless steel, a nickel alloy, or a nickel-copper alloy, by applying these metal materials, the necessary anticorrosion as a pillar or the like is secured, This is because the beautiful metallic luster on the surface is stably maintained and the design effect is exhibited over a long period.

As the austenitic stainless steel as the outer layer forming material, for example, various stainless steels specified in JIS G 5121 can be arbitrarily applied.

Examples of nickel alloys include Incoloy 825 (Ni: 38.0
~ 46.0%, Cr: 19.5 ~ 23.5%, Mo: 2.5 ~ 3.5%, Cu: 1.5 ~ 3.0
%, Nb: 0.6-1.2%, Si: 1.0% or less, Mn: 1.0% or less, Fe: Ba
l), Inconel 625 (Ni: 58.0% or more, Cr: 20.0-23.0%,
Mo: 8.0 to 10.0%, Nb + Ta: 3.15 to 4.15%, Al: 0.4% or less, T
i: 0.4% or less, Co: 1.0% or less, Si: 0.5% or less, Mn: 0.5% or less, Fe: 5.0% or less, Hastelloy C276 (Cr: 14.5-16.5)
%, Mo: 15.0 ~ 17.0%, W: 3.0 ~ 4.5%, Fe: 4.0 ~ 7.0%, Co:
2.5% or less, Si: 0.08% or less, Mn: 1.0% or less, V: 0.35% or less,
Ni: Bal). P and S accompanying impurities in these alloys may be about 0.04% or less, respectively, and C is preferably 0.05% or less from the viewpoint of corrosion protection.

Examples of nickel-copper alloys include Monel metal (Ni: 6
4 to 69%, Cu: 26 to 32%, Fe: 1.75 to 2.5%, Si: 1 to 2.5%, C:
0.15 to 0.25%, S: 0.01 to 0.25%, Mn: 0.25 to 1.0%). C accompanying the nickel-copper alloy as an impurity is preferably 0.2% or less.

In addition to the above metals, ferritic stainless steel and austenitic / ferritic duplex stainless steel can be used as the outer layer forming material in addition to the above metals in view of corrosion resistance, weather resistance, and design effect. The formation of a martensitic phase during the process causes a failure in the metallurgical bonding of the interface between the two layers. Therefore, the present invention excludes these uses.

The inner layer made of carbon steel of the clad steel pipe of the present invention is given a layer thickness (for example, 10 to 100 mm) necessary to secure the mechanical strength required as a column material.

On the other hand, the outer layer has no role to bear the mechanical strength.
It is a layer for imparting weather resistance and a design effect to the column material, so that it does not require a thick wall such as an inner layer. The outer layers are more advantageous as the outer layers are thinner from the viewpoint of material cost economy. However, the corrosion resistance inherent in the outer layer metal is impaired, and the design effect cannot be ensured. Also, it is not easy to cast an extremely thin layer thickness uniformly over the entire length of the entire circumference, and the thickness tends to be uneven. In order to prevent these problems, the outer layer preferably has a thickness of 3 mm or more.

The clad steel pipe of the present invention is manufactured by double centrifugal casting. According to the double centrifugal casting method, a first stage casting in which an outer layer metal melt is poured into a mold under a rotational movement of a mold horizontally supported on a turning roller and an outer layer is cast along the inner peripheral surface thereof. The casting of the clad steel pipe is formed by the process and the second-stage casting process of injecting the inner layer metal melt onto the inner peripheral surface of the outer layer and laminating and casting the inner layer. The casting amount of the molten metal for casting each layer is appropriately determined in consideration of the layer thickness of each layer of the target clad steel pipe and the machining allowance applied to the inner and outer surfaces of the cast body. In order to prevent problems caused by insufficient heat of the molten metal (for example, poor hot water running, occurrence of hot water wrinkles, etc.),
It is preferable to cast the molten metal in an amount slightly larger than that, for example, in a layer thickness of about 6 mm or more. Excess wall thickness can be removed by machining after casting to finish to a design layer thickness.

Also, the formation of a metallurgical bond at the interface between the outer and inner layers
It depends on the timing of casting of the inner layer molten metal after casting the outer layer, the inner surface properties of the outer layer at the time of casting the inner layer molten metal (existence of oxidation contamination, nonmetallic inclusions, etc.), the casting temperature of the inner layer molten metal, and other factors. You. For example, casting the inner layer molten metal at a stage where the unsolidified molten metal remains in a thin layer immediately before solidification of the outer layer is completed is effective in facilitating the formation of a metallurgical bond at the interface between both layers. It is a way. In addition, using a flux, the surface of the outer layer molten metal is coated with a molten flux to prevent oxidation of the molten metal and to adsorb and remove nonmetallic inclusions. is there. In addition, when casting the inner layer molten metal after the outer layer molten metal is completely solidified, the casting temperature of the inner layer molten metal is set to a higher value, and the inner surface of the outer layer is re-melted by the retained heat of the inner layer molten metal, whereby the metal at the interface is melted. It is also possible to achieve a logical connection.

At the interface between the outer layer and the inner layer, there is no partial unevenness in the metallurgical bond, and the metallurgical bond is formed uniformly over the entire circumference (the entire area of the interface) (area ratio 100%). This is ideal, but when used as a pillar or the like, it is not always necessary, and it is sufficient if at least 50% (area ratio) of the entire area of the layer interface is metallurgically bonded.

〔The invention's effect〕

The clad steel pipe of the present invention, which has both anticorrosion properties and design effects, is useful as a pillar material for buildings and the like, and since the clad steel pipe is a laminate of an outer layer and an inner layer formed by centrifugal casting, a corrosion-resistant metal plate is used. Unlike a steel pipe column wound on a steel pipe, corrosion resistance and design effects are stably maintained over a long period of time.

The clad steel pipe of the present invention is not limited to applications such as pillars of buildings, but is also useful for applications requiring an anticorrosion function, for example, construction members of marine structures.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-65057 (JP, A) JP-A-2-296090 (JP, A) JP-A-1-180720 (JP, A) 5217 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 13/02 C22C 38/00 301 B32B 1 / 08,15 / 01

Claims (1)

(57) [Claims] 1. A carbon equivalent (Ceq) with a carbon content of 0.2% or less.
An inner layer made of carbon steel or low alloy steel of 0.48 (%) or less, austenitic stainless steel, nickel alloy,
Alternatively, it has a two-layer structure with an outer layer made of a nickel-copper alloy, and the outer layer and the inner layer are metallurgically bonded at 50% by area or more of the interface, and the outer layers have a thickness of 3 mm or more. A clad steel pipe for a structure, which is a pipe.