JPH05287489A - Aluminum plated steel excellent in corrosion resistance in automotive exhausting environment - Google Patents

Abstract

PURPOSE:To prolong the service life in corrosion resistance of a steel sheet by forming an Al layer having specified thickness by hot dip plating on the stock of steel contg. specified wt.% C, Si, Mn or the like. CONSTITUTION:Steel stock is constituted of, by weight, <=0.05% C, <=0.2% Si, <=0.025% P, <=0.010% S and 1.5 to 25% Mn, and the balance Fe with inevitable impurities. On the steel stock, an Al layer having 80 to 120mum thickness is formed by hot dip plating. Moreover, one or two kinds of 0.5 to 6.5% Mo and 1 to 15% Ni as well as one or two kinds of <=0.5% Nb and <=0.5% Ti are incorporated therein. In this way, the aluminum plated steel having excellent corrosion resistance in the external salt damage environment and inside exhausting concentrated liq. environment used in an automotive exhausting system can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum-plated steel used in an automobile exhaust system, which has excellent corrosion resistance in an external salt damage environment and an internal exhaust condensate environment.

[0002]

2. Description of the Related Art Conventionally, an aluminized steel sheet obtained by aluminizing ordinary steel has been widely used as a material for mufflers in automobile exhaust systems. The plating alloy layer formed by reacting with certain iron becomes noble to the base iron in terms of electric potential, so the anticorrosion effect was not sufficient.

[0003]

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

[0004]

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

The present invention will be described in detail below. The inventors of the present invention have conducted research on materials capable of exhibiting excellent corrosion resistance in the environment of salt damage on the outer surface and the environment of exhaust gas condensate of the inner surface as materials for automobile exhaust systems, and as a result, an Al layer formed by a reaction between a steel material and aluminum. We focused on positively utilizing the (outer layer: Al layer, inner layer: alloy layer) to improve the corrosion resistance of the substrate. That is, by adding Mn which is an alloy component to the steel material and further adding Mo and Ni in combination, molten Al reacts with the base component during aluminum plating to form Fe which is a base component in the Al layer. , Mn, M
etc. are included. As a result, the steel materials of the inner layer and the outer layer can further improve the anticorrosion function and the corrosion resistance. Thus, as a material for automobile exhaust system,
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 gas condensate environment on the inner surface.

Next, the reasons for limiting the components of the steel material in the present invention will be explained. In the present invention, Mn may be either alone or N
Formed when Al-plated by combined addition with i
It improves the corrosion resistance of the 1-layer and further improves the anticorrosion function for the steel material. Addition of Mn less than 1.5% does not exhibit the effect, and addition of more than 25% saturates the effect. Mo, like Mn, is a basic component for ensuring the corrosion resistance of steel. In the present invention, the combined addition of Mn and Ni has the effect of significantly suppressing general corrosion and local corrosion of stainless steel in an environment containing sulfate ions and chloride ions. Addition of Mo less than 0.5% does not exhibit the effect of addition, and addition of more than 6.5% saturates the effect and makes not only manufacturing into strips difficult, but also Increase the cost. Mo
The steel with addition of
Is included together with Mn to enhance the effect of improving the corrosion resistance of the steel substrate by the alloy layer.

Like Mn and Mo, Ni is A of the plating bath.
It has the effect of reacting with 1 to form an Al alloy layer to improve the corrosion resistance of the alloy layer itself and enhance the corrosion resistance of the steel base material. If the addition amount is less than 1%, Ni-added steel does not appear, and if the addition amount exceeds 15%, the effect is saturated and the manufacturing cost is increased. C causes intergranular corrosion and cracking during welding of Al-plated steel. Therefore, C
The content should be less than 0.05%. Si is
Improves the plating property of the steel substrate during hot dip aluminum plating.
The result is saturated at 0.2%. P is a harmful element that impairs the corrosion resistance of steel, and it is better that it is as small as possible. However, from the current steel refining technology level, it was set to 0.025% or less. S is also a harmful element that impairs the corrosion resistance of steel, and the smaller the content, the better. However, it was set to 0.010% or less from the current steel refining technology level.

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 in the heat-affected zone of the welded portion. From this point of view, Nb needs to be 10 times as much as C, and is therefore 0.5% or less. Ti, like 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 in the heat-affected zone of the welded portion. From this viewpoint, Ti needs to be 10 times as much as C, and therefore 0.5%.
Below.

Next, the aluminum plating conditions will be described. Hot-dip aluminum plating bath (Al: 88-100%, S
i: 0 to 12%), a steel material (strip) having the above component system is continuously dipped, 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 the salt damage environment on the outer surface of the automobile exhaust system member due to plating and the exhaust condensate environment on the inner surface. Even if the plating thickness exceeds 120 μm, the effect of hot-dip aluminum coating is saturated.

[0010]

EXAMPLES Tables 1 and 2 show the results of comparison of corrosion resistance between conventional steel and Al-plated steel of the present invention. Each material was continuously dipped into an Al plating bath as a strip (1.2 mm thickness, 100 mm width), and a sample prepared to have 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 evaluated by a dry-wet repeating salt spray test (salt spray 4 hours-dry 2 hours-wet 2 hours, RH 98%; 1 cycle). The presence or absence of red rust and the corrosion depth were judged. (2) Evaluation of corrosion resistance by the condensate from the inner surface of the exhaust system was repeated 100 cycles of dry and wet in the simulated condensate (the test piece was left in the semi-immersed state for 3 hours in the boiling state, and then left for 2 hours as 1 cycle). After that, the corrosion weight loss and the corrosion depth were evaluated. From the evaluation results in Tables 1 and 2, by aluminum-plating a steel material based on Mn-added steel, it was possible to obtain an aluminum-plated steel having extremely excellent corrosion resistance. The material of the present invention exhibits its anticorrosion function not only in the exhaust system of automobiles but also in a wide range from neutral to weakly acidic environments. In each of the above tests, an Al plated sample was processed into 50 × 70 mm and subjected to the test. The corrosion depth was evaluated by the maximum corrosion depth observed on the surface of the test piece.

[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 resistance life of the 1-plated steel sheet by 2-3 times.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Tento 20-1 Shintomi, Futtsu City, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (2)

[Claims] 1. By weight, C ≦ 0.05% or less, 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, which is characterized by having a thick Al layer. 2. By weight, C ≦ 0.05% or less, Si ≦
0.2%, P ≦ 0.025%, S ≦ 0.010%, M
n: 1.5 to 25% and further Mo: 0.5 to
6.5%, Ni: 1 to 15%, one or two, and
Having an Al layer having a thickness of 80 to 120 μm by hot dipping on a steel material containing one or two of Nb ≦ 0.5% and Ti ≦ 0.5%, and the balance: Fe and unavoidable impurities. Aluminized steel with excellent corrosion resistance in the characteristic automobile exhaust environment.