JP2965785B2 - Aluminum plated steel with excellent corrosion resistance in automobile exhaust environment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminized steel having excellent corrosion resistance in a salt damage environment on an outer surface and an exhaust condensate environment on an inner surface used in an automobile exhaust system.

[0002]

2. Description of the Related Art Conventionally, aluminum-plated steel sheets obtained by plating ordinary steel with aluminum have been widely used as materials for mufflers in automobile exhaust systems. The anti-corrosion effect was not sufficient because the plating alloy layer formed by reacting with certain iron was noble in terms of potential with respect to the base iron.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an aluminum-plated steel which exhibits excellent corrosion resistance in a salt damage environment on an outer surface and an exhaust condensate environment on an inner surface as a material for an automobile exhaust system.

[0004]

The features of the present invention are as follows: (1) By weight, C ≦ 0.05%, Si ≦ 0.2%,
P ≦ 0.025%, S ≦ 0.010%, Mn: 1.5 to
25%, balance: Aluminized steel excellent in corrosion resistance in an automobile exhaust environment, characterized by having an 80-120 μm thick Al layer by hot-dip plating on a steel material composed of Fe and unavoidable impurities. (2) By weight, C ≦ 0.05% or less, Si ≦ 0.2%,
P ≦ 0.025%, S ≦ 0.010%, Mn: 1.5 to
25%, Mo: 0.5-6.5%, N
i: 1 to 15% of one or two kinds, and Nb ≦ 0.5
%, One or two of Ti ≦ 0.5%, and the balance: F
An aluminum-plated steel having excellent corrosion resistance in an automobile exhaust environment, characterized by having an Al layer having a thickness of 80 to 120 μm by hot-dip plating on a steel material comprising e and unavoidable impurities.

Hereinafter, the present invention will be described in detail. The present inventors have conducted research on a material capable of exhibiting excellent corrosion resistance in a salt damage environment on an outer surface and an exhaust condensate environment on an inner surface as a material for an automobile exhaust system. As a result, an Al layer formed by a reaction between a steel material and aluminum is obtained. (Outer layer: Al layer, inner layer: alloy layer) was focused on positively utilizing for improving the corrosion resistance of the substrate. That is, by adding Mn, which is an alloy component, to a steel material, and further adding Mo and Ni in a complex manner, molten Al reacts with the base component during aluminum plating to form an Al layer, which is a base component, in the Al layer. , Mn, M
o and the like. Thereby, the steel material of the inner layer and the outer layer can further improve the anticorrosion function and improve the corrosion resistance. Thus, as a material for automobile exhaust systems,
It is possible to obtain an aluminum-plated steel capable of exhibiting excellent corrosion resistance in a salt damage environment on the outer surface and an exhaust condensate environment on the inner surface.

Next, the reasons for limiting the components of the steel material in the present invention will be described. In the present invention, Mn is used alone or N
A generated when Al is plated by complex addition with i
The corrosion resistance of the l layer is improved, and the anticorrosion function for the steel material is further improved. If less than 1.5% of Mn is added, no effect is exhibited, and if more than 25% is added, the effect is saturated. Mo is a basic component for ensuring the corrosion resistance of steel, like Mn. In the present invention, the combined addition of Mn and Ni has an effect of significantly suppressing the overall corrosion and local corrosion of stainless steel in an environment containing sulfate ions and chloride ions. If less than 0.5% of Mo is added, no effect is exhibited. If more than 6.5% of Mo is added, the effect is saturated and, for example, the production of strips becomes difficult, and Increase costs. Mo
Is added to the alloy layer by Al plating.
And the alloy layer together with Mn enhances the effect of improving the corrosion resistance of the steel base.

Ni is the same as A in the plating bath, as in Mn and Mo.
It has the effect of forming an Al alloy layer by reacting with l to improve the corrosion resistance of the alloy layer itself and the corrosion prevention of the steel substrate. Addition of less than 1% does not produce Ni-added steel, and addition of more than 15% not only saturates the effect but also increases the production cost. C causes intergranular corrosion and cracking during welding of Al-plated steel. Therefore, C
The content must be less than 0.05%. Si is
Improves the plating properties of steel base during hot-dip aluminum plating.
The result saturates at 0.2%. P is a harmful element that impairs the corrosion resistance of steel, and is preferably as small as possible. However, the current steel refining technology level is set to 0.025% or less. S is also a harmful element that impairs the corrosion resistance of steel, and is preferably as small as possible. However, it is set to 0.010% or less from the current steel refining technology level.

[0008] Nb improves the aluminum plating property of steel. Further, since aluminum-plated steel is sometimes used by welding, it is necessary to prevent intergranular corrosion of the heat-affected zone of the welded portion. From this point of view, Nb needs to be ten times as large as C, and therefore is set to 0.5% or less. Ti improves the aluminum plating property of steel similarly to Nb. Further, since aluminum-plated steel is sometimes used by welding, it is necessary to prevent intergranular corrosion of the heat-affected zone of the welded portion. From this point of view, Ti needs 10 times the amount of C, and therefore 0.5%
It was as follows.

Next, conditions for aluminum plating will be described. Hot-dip aluminum plating bath (Al: 88-100%, S
i: 0 to 12%), a steel material (strip) having the above-mentioned composition is continuously immersed, and an appropriate plating thickness: 80 to 1
Control to 20 μm. If the plating thickness is less than 80 μm, excellent corrosion resistance will not be exhibited in a salt damage environment on the outer surface of the vehicle exhaust system member and an exhaust gas condensate environment on the inner surface due to plating. Even if the plating thickness exceeds 120 μm, the effect of the hot-dip aluminum plating is saturated.

[0010]

EXAMPLES Tables 1 and 2 show comparison results of the corrosion resistance of the conventional steel and the Al-plated steel of the present invention. Each material was continuously immersed in an Al plating bath in the form of a strip (1.2 mm thick, 100 mm wide), and a sample prepared to a thickness of 120 μm was evaluated by the following test. (1) The corrosion resistance of the exhaust system material from the outer surface was determined by a dry / wet repetition type salt water spray test (salt water spray 4 hours-dry 2 hours-wet 2 hours RH 98%; 1 cycle). The occurrence of red rust and the corrosion depth were determined. (2) Evaluation of corrosion resistance by condensate from the inner surface of the exhaust system was repeated 100 cycles of dry and wet cycles in a simulated condensate (a test piece was placed in a half-immersion state, boiled for 3 hours, and then left for 2 hours as one cycle). ) The corrosion weight loss and corrosion depth after were evaluated. From the evaluation results in Tables 1 and 2, it was possible to obtain an aluminum-plated steel having extremely excellent corrosion resistance by performing Al plating on a steel material based on Mn-added steel. The material of the present invention exhibits its anticorrosion function in a wide range from a neutral to a weakly acidic environment as well as an automobile exhaust system. In each of the above tests, the Al-plated sample was processed to a size of 50 × 70 mm and used for the test. The corrosion depth was evaluated based on the maximum corrosion depth observed on the specimen surface.

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

As described above, according to the present invention, the current A
It has an extremely excellent effect of extending the corrosion life of a 1-plated steel sheet by a factor of 2 to 3 times.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masayuki Amatou 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (56) References JP-A-61-124558 (JP, A) JP-A-60-13053 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. C ≦ 0.05% or less by weight, Si ≦
0.2%, P ≦ 0.025%, S ≦ 0.010%, M
n: 1.5 to 25%, balance: 80 to 120 μm by hot-dip plating on steel material consisting of Fe and unavoidable impurities
An aluminum-plated steel having excellent corrosion resistance in an automobile exhaust environment characterized by having an Al layer having a thickness. 2. C ≦ 0.05% by weight, Si ≦
0.2%, P ≦ 0.025%, S ≦ 0.010%, M
n: 1.5 to 25%, and Mo: 0.5 to
One or two of 6.5% and Ni: 1 to 15%
One or two of Nb ≦ 0.5% and Ti ≦ 0.5%, the balance being: having an 80-120 μm thick Al layer by hot-dip plating on a steel material composed of Fe and unavoidable impurities. Aluminized steel with excellent corrosion resistance in automobile exhaust environments.