JP2559916B2 - Automotive exhaust system aluminum plated stainless steel with excellent corrosion resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum-plated stainless steel having excellent corrosion resistance in the environment of condensate used on the outer and inner surfaces of an automobile exhaust system.

[0002]

2. Description of the Related Art Up to now, an aluminum-plated steel sheet obtained by aluminizing plain steel has been often used as an exhaust system for automobile exhaust systems. However, in a condensate environment, it reacts with the iron of the base material in the aluminum-plated layer. Since the aluminum-plated alloy layer produced by the method becomes noble to the base iron in terms of electric potential, the anticorrosion effect was not sufficient. In addition, it was not sufficient for corrosion from the outer surface.

Therefore, conventionally, a chromium-containing steel has been proposed in which the corrosion resistance of the base material is improved more than that of an aluminized steel sheet in a condensate environment. For example, JP-A-63-143240 discloses a method based on a Cr content of 5% to 10%, and JP-A-63-143241 discloses a Cr content of 5%.
% To 10% of the surface of alloy steel is subjected to an oxidation treatment to generate a stable oxide, and a method of preventing it is proposed. Further, the effectiveness of aluminum plating has been proposed from the viewpoint of preventing corrosion from the outer surface of a muffler or the like. From such a viewpoint, as a prior art, a stainless aluminum sheet obtained by applying molten aluminum to stainless steel (11% Cr) has been put into practical use. However, in this case, the anti-corrosion function of the aluminum plating layer (pure aluminum layer and aluminum alloy layer) is that the anti-corrosion potential (usually aluminum and aluminum The alloy layer has a base electric potential with respect to the base steel, which protects the base material), but reverses the corrosion resistance effect. Such a problem is particularly remarkable in the steel containing only chromium.

[0004]

SUMMARY OF THE INVENTION In order to eliminate this drawback, the present invention (1) adds Cr and Mo to a stainless steel material to improve the corrosion resistance of the material in an environment range from neutral to acidic environments. Improving the anticorrosion function of the aluminum plating layer (comprising a pure aluminum layer and an aluminum alloy layer) by contacting different metals by shifting the pH to a lower pH. Further, (2) the corrosion resistance of the aluminized stainless steel is positively utilized by utilizing the alloy layer formed as a result of the reaction between the alloying elements in the material and the molten aluminum, so that Cr and Mo, which are alloy components in the stainless steel material, are intentionally added. By adding Al, molten aluminum reacts with the stainless steel base component to form an alloy layer, and this alloy layer contains the base components Cr and Mo, which itself has extremely good anticorrosion function and corrosion resistance. It was found that

The present invention has been completed based on such findings, and an object of the present invention is to provide an aluminized stainless steel having good corrosion resistance against external corrosion of an automobile exhaust system and internal corrosion due to a condensate. And

[0006]

In order to achieve the above object, the gist of the present invention is that C: 0.0% by weight.
5% or less, Si: 0.2% or less, Mn: 1.0% or less,
Cr: 10% to 20%, Mo: 0.5% to 6.0%,
P: 0.025% or less, S: 0.010% or less, balance F
e and inevitable impurities, or Nb:
0.5% or less, Ti: 0.5% or less , at least 1
A stainless steel material containing seeds is treated by hot dip Al plating to mix Cr and Mo between the material and Al plating.
An automobile exhaust gas condensate containing a sulfate ion and a chloride ion, characterized in that an Al plating layer having a thickness of 80 to 120 μm , which is formed with an Al alloy layer which is sometimes contained, is applied.
In corrosion resistance superior automotive exhaust system aluminum plated stainless steel for.

The reasons for limiting the components of the present invention will be described below. Cr: It is a basic component that secures the corrosion resistance of stainless steel, and is 10% to 20% in combination with Mo. Mo;
From 0.5% or more, the general corrosion rate of the base material is one-fifth or less compared to 10% Cr alone, and the local corrosiveness is required to be 10% due to coexistence with Mo. , At least 10%. The upper limit is straight C
With r-added steel, due to manufacturability restrictions, general corrosion resistance,
From the viewpoint of local corrosion resistance, 20% was made the upper limit.

Like Mo and Cr, it is a basic component for ensuring the corrosion resistance of stainless steel, and when combined with Cr, it is 0.5.
% To 6%. The addition of Mo to the Cr-added steel has an effect of significantly suppressing both general corrosion and local corrosion of stainless steel in an environment containing sulfate ions and chloride ions, and coexistence addition is extremely effective. 0.5%
If it is less than 6%, there is no effect, and if it exceeds 6%, difficulty is involved in terms of manufacturability and economy, so the upper limit was made 6% or less.

C: 0.05% or less in order to prevent intergranular corrosion and cracking of ferritic stainless steel. Si; Si for improving the plating property of the molten Al plating
Since the content needs to be suppressed to 0.2% or less, the upper limit was made 0.2%. Mn: 1.0% as a normal steelmaking condition for stainless steel
Below. P: 0.025 as steelmaking conditions for normal stainless steel
% Or less. S: As normal steelmaking conditions for stainless steel, 0.010
% Or less.

In addition to the above components, the present invention selectively uses Nb
And at least one of Ti is added . Nb; Al-plated stainless steel is sometimes used by welding, and is essential for preventing intergranular corrosion in the heat-affected zone of the welded portion. About 10 times more than C is required,
It was set to 0.5% or less. Similar to Ti; Nb, Al-plated stainless steel is sometimes used by welding, and is essential for preventing intergranular corrosion in the heat-affected zone of the welded portion. Since it is required to be about 10 times as much as C, it is set to 0.5% or less like Nb.

In the present invention, such component steel is aluminized under the following conditions. That is, the steel strip of the above stainless steel material is continuously immersed in a hot dip aluminum plating bath (Al; 88 to 98%, Si; 2 to 12%) to control the proper plating thickness.

Although the thickness of the aluminum plating layer effectively acts as the anticorrosion function of the hot-dip aluminized stainless steel, in the condensate environment as in the present invention, the aluminum produced by the reaction between the aluminum and the base component is generated rather than the aluminum layer. In order to effectively utilize the anticorrosion function of the alloy layer, the minimum aluminum plating thickness was set to 80 μm as a condition for stably producing it. If the aluminum plating thickness exceeds 120 microns, the aluminum plating layer and the alloy layer become too thick and the workability is impaired.

[0013]

EXAMPLES Table 1 shows the results of comparison of the corrosion resistance between the conventional steel and the Al-plated steel of the present invention. Band shape of each material (1.2
mm thickness, width 100 mm) was continuously immersed in an Al plating bath, 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 determined by a dry / wet repeating salt spray test (salt spray 4 hours-dry 2 hours-wet 2 hours / RH 98%; 1 cycle) to determine whether red rust occurred on the sample surface after 300 cycles. And the corrosion depth was determined. (2) Evaluation of corrosion resistance by the condensate from the inner surface of the exhaust system
The corrosion depth was evaluated after 100 cycles of repeated dry and wet in the simulated condensate (the test piece was placed in a semi-immersed state, left in the boiling state for 3 hours and then left for 2 hours as one cycle). In each of the above tests, 50
It was processed into × 70 mm and used for the test. The corrosion depth was evaluated by the maximum corrosion depth observed on the surface of the test piece.

[0014]

[Table 1]

From the evaluation results shown in Table 1, aluminum-plated stainless steel having excellent corrosion resistance could be obtained by Al-plating a stainless steel material based on Cr-Mo. 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.

[0016]

As shown in Table 1, the steel of the present invention is obtained by subjecting steel based on addition of Cr and Mo as alloy components to hot dip aluminizing treatment in order to improve the life of materials used in automobile exhaust gas environment. Is an anticorrosion method that effectively utilizes the aluminum alloy layer formed on the surface layer. The steel of the present invention is
As is clear from Table 1, the red rust properties from the outer surface and the corrosion depth were both superior to those of the comparative steels in corrosion resistance. In addition, the corrosion resistance in the condensate environment, which is a problem, that is, the local corrosion depth of each of the present invention steels was superior to that of the comparative steel. From this, the steel of the present invention has excellent corrosion resistance for a long period of time in a severely corrosive environment such as engine exhaust gas, and is extremely effective in practice for extending the life of automobile parts.

Claims (2)

(57) [Claims] 1. C .: 0.05% or less, Si: 0.2% or less, Mn: 1.0% or less, Cr: 10% to 20%, Mo: 0.5% to 6. 0%, P: 0.025% or less, S: 0.010% or less, the stainless steel material and the balance Fe and unavoidable impurities, the material and the Al coating by dip Al plating
An Al alloy layer containing Cr and Mo simultaneously is formed between
In addition, the aluminum plating layer having a thickness of 80 to 120 μm is applied, and the aluminum plating layer contains sulfate ion and chloride ion.
Automobile exhaust system aluminized stainless steel with excellent corrosion resistance to automobile exhaust gas condensate . 2. A stainless steel material, in % by weight, C: 0.05% or less, Si: 0.2% or less, Mn: 1.0% or less, Cr: 10% to 20%, Mo: 0. 5% to 6.0%, P: 0.025% or less, S: 0.010% or less, Nb: 0.5% or less, Ti: 0.5% or less, at least one kind is contained, and the balance is included. The automobile exhaust system aluminum-plated stainless steel having excellent corrosion resistance according to claim 1, which is composed of Fe and inevitable impurities .