JP2005320559A - Automotive exhaust system parts with excellent initial rust resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automobile exhaust system part satisfying resistance to initial rust at as low cost as possible in an automobile exhaust system part made of SUS409L level steel.
In an automobile exhaust system part molded from steel containing Cr: 10.0 to 13.5% by mass, an alkali metal or an alkali is formed on the surface of the part exposed to the external environment. A film made of an earth metal silicate is formed. The coating contains one or more of sodium silicate, potassium silicate, calcium silicate, or further contains corrosion products of basic zinc carbonate, zinc oxide, zinc hydroxide, or metal zinc.
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Description

  The present invention relates to exhaust system parts such as an exhaust manifold and a muffler for automobiles, and more particularly to an exhaust system part having excellent resistance to initial rust on the outer surface.

  Since automobile exhaust system parts are exposed to high temperatures for a long time, high temperature strength, resistance to scale peeling, formability for processing into complex shapes, corrosion resistance to flue gas condensed water, corrosion resistance to salt damage environment, and low price Therefore, various properties are required, and various stainless steels have been frequently used. Many proposals have been made so far in order to satisfy each or all of these requirements.

  For example, in Patent Document 1, Si: 0.01 to 0.50%, Mn: 0.01 to 0.50%, Cr: 11.0 to 14.0%, P: ≦ 0.030%, S: ≦ 0.0050%, C, N, Nb, Ti content is 0.01% ≦ C + N ≦ 0.020%, 0.4% ≦ Ti + Nb ≦ 0.6%, (Ti + Nb) / (C + N ) Ferritic stainless steel for automobile exhaust system equipment that improves the intergranular corrosion resistance of welds and has excellent mechanical properties by making the composition satisfying ≧ 30 is disclosed.

  In Patent Document 2, C: 0.001 to 0.015%, N: 0.001 to 0.015%, Si: 0.50 to 2.0%, Mn: 0.01 to 1.00% , P: 0.010 to 0.030%, S: ≦ 0.003%, Cr: 10.0 to 14.0%, one or two of Nb and Ti: 20 × (C + N) ≦ Nb + Ti ≦ 0 A ferritic stainless steel for automobile exhaust system that is excellent in high temperature salt damage corrosion resistance and contains 0.3% to 2.0% in total of at least one of Ni and Mo as required. It is disclosed.

  Alternatively, in Patent Document 3, C: less than 0.02%, Si: less than 0.5 to 1.5%, Mn: less than 0.2%, Cr: less than 10-14%, Ni: 0.05-1 Less than 0.0%, Ni: less than 0.05 to 1.0%, Ti: less than 0.05 to 0.3%, Nb: less than 0.3 to 0.6%, P: less than 0.06%, S : Ferritic stainless steel for engine exhaust members containing less than 0.01% and excellent in heat resistance and weld corrosion resistance is disclosed.

However, in recent years, in addition to the conventional characteristics as described above, initial rust resistance on the outer surface of the member has been required.
The problem of initial rust here refers to the problem of red rust that occurs in a short period of time from the shipment of the vehicle to before use or immediately after use, such as an exhaust manifold or a muffler, that can be easily observed by the vehicle user. It is.
Although this initial rust does not affect the life of the member, it is not desirable from the viewpoint of appearance, so it is necessary to prevent it.

Conventionally, 11% Cr-based SUS409L has been widely used for the end plate of a muffler, a tail pipe, or an outer pipe of a double pipe exhaust manifold, and SUS409L is used to satisfy only the conventionally required characteristics. Even when it is sufficient, since importance is attached to the countermeasure against initial rust, there are many cases in which a material with excessive quality is applied to the conventional function such as higher grade 14Cr-0.5Mo steel.
Although this initial rust is a kind of problem related to corrosion resistance in a broad sense, it differs from the problem related to corrosion progress represented by hole corrosion, which has been handled in the past, and is a problem related to a very short-time corrosion form. For this reason, the solution is naturally different from that taken in the prior art.
In other words, the idea of simply optimizing the steel composition to improve rust resistance increases the content of alloy elements such as Cr and Mo, which inevitably increases costs, and is inexpensive and simple without changing the material. The idea of trying to solve the problem by combining temporary rust prevention treatment should be taken. However, such a solution is not presented in the prior art as described above.
JP-A-6-184705 JP-A-6-248394 Japanese Patent Laid-Open No. 10-204590

  An object of the present invention is to provide a technology for overcoming this initial rust problem. Exhaust system parts such as high temperature strength, scale peel resistance, moldability, corrosion resistance against flue gas condensation water, corrosion resistance against salt damage environment, etc. It is an object of the present invention to provide an automobile exhaust system part that uses steel of SUS409L level, which has a sufficient original function as a raw material, and further satisfies the resistance to initial rust at as low a cost as possible.

Since the present inventors have a problem that the initial rust problem is limited to a very short period from the shipment of the automobile to the time before use or just after use, a temporary rust prevention treatment is performed rather than improving the corrosion resistance of the material itself. Considering that it is a realistic method, various rust prevention treatment methods were examined.
The main factors considered in the study are 1) high rust prevention capability, 2) low cost, 3) no environmental impact, and 4) impact on oxidation and corrosion of exhaust system parts after automobile use. There is no such thing.

  As a result of various investigations, by forming a coating mainly composed of alkali metal or alkaline earth metal silicate on the surface of exhaust system parts, it promotes deterioration of parts after use at low cost and without environmental impact. It has been found that initial rust can be prevented very effectively. The present invention is configured based on the above findings, and the gist thereof is as follows.

(1) In an automobile exhaust system part molded from steel containing Cr: 10.0 to 13.5% by mass, the surface of the part exposed to the external environment is alkali metal or alkaline earth. Automotive exhaust system parts with excellent initial rust resistance, characterized by forming a coating of a silicate of a similar metal.

(2) The automobile exhaust system part having excellent initial rust resistance according to (1), wherein the material of the automobile exhaust system part is SUS409L.

(3) The vehicle exhaust having excellent initial rust resistance according to (1) or (2), wherein the film contains one or more of sodium silicate, potassium silicate, and calcium silicate. System parts.

(4) Any one of (1) to (3), wherein the film further contains one or more corrosion products of basic zinc carbonate, zinc oxide, zinc hydroxide, and metal zinc. Auto exhaust system parts with excellent initial rust resistance as described in the section.

  According to the present invention, the problem of initial rust of automobile exhaust system parts manufactured with existing SUS409L level steel is solved at as low a cost as possible, so that the industrial effect is extremely large.

Hereinafter, the present invention will be described in detail.
First, the material of an automobile exhaust system part that is the subject of the present invention is steel having an initial rust resistance equivalent to SUS409L (Cr: 11.0 to 13.5%), and a Cr content of 10.0% to 13 The steel is in the range of 5%.
Note that steel containing alloy elements other than Cr may be used as long as it does not hinder cost and other characteristics.

  From the steel plate or steel pipe of the material, the outer surface where the initial rust of exhaust system parts such as mufflers and exhaust manifolds assembled by processing such as molding and welding is given is subjected to rust prevention treatment, It is not an object of the present invention to apply a rust prevention treatment to a steel plate or a steel pipe before assembly. This is because the rust preventive film is damaged in the process of molding, welding, and the like, and the initial rust prevention effect is reduced.

As the rust prevention treatment, a film made of an alkali metal or alkaline earth metal silicate is formed on the surface of the component. Alkali metal or alkaline earth metal silicates have the advantage of being water-soluble in addition to being inexpensive and non-environmental.
For this reason, as a method for forming a film, it is a common practice to apply an aqueous solution of these silicates dissolved in water to the part, and then heat the part to dry and bake the coating. Yes, it can be processed without using organic solvents.

The alkali metal or alkaline earth metal silicate coatings thus formed not only isolate the steel surface from corrosive substances such as water, oxygen and chloride ions, but still remain after drying and baking. Since it is water-soluble and generates alkali when dissolved in water, even if corrosive substances such as water reach the steel surface, the pH of the water adhering to the steel surface is maintained alkaline, and the passive state is stabilized and ignited. It is suppressed.
Typical examples of such alkaline earth metal silicates include sodium silicate, potassium silicate, and calcium silicate. In the present invention, a coating containing one or more of these is applied.

Furthermore, in addition to the silicate, one or more of corrosion products of basic zinc carbonate, zinc oxide, zinc hydroxide, and metal zinc may be included in the film.
Although corrosion products of basic zinc carbonate, zinc oxide, zinc hydroxide or metallic zinc have low water solubility, they have an action of buffering pH to alkalinity. When it is desired to maintain it, it should be included as necessary.

The invention is explained in more detail on the basis of examples.
A 70 × 150 mm size test piece for initial rust reproduction test was collected from a cold rolled steel sheet of SUS409L, and subjected to various rust prevention treatments described in Table 1, followed by a combined cycle test (5% NaCl spray, 35 C. × 2 Hr → forced drying 70 ° C. × 4 Hr → wet 95% RH, 50 ° C. × 2 Hr), and the wrinkling situation after 1 week was evaluated.
The degree of rusting was determined by referring to a SARN standard photograph established by the Stainless Steel Association, giving a SARN score, rating 4 or lower as bad, and rating 5 or higher as good.

As shown in Table 1, no. In the present invention of Nos. 1 to 5, Comparative Example No. It was confirmed that satisfactory initial rust resistance comparable to 102 14Cr-0.5Mo steel (SUS429) was obtained. On the other hand, Comparative Example No. For 101, 103, and 104, the initial rust resistance was insufficient.
In addition, the present invention No. About 1-5, it evaluated together about the oxidation resistance after film formation, and salt corrosion resistance, and has confirmed that there is no performance degradation by film formation.

Claims (4)

  In an automobile exhaust system part formed from steel containing Cr: 10.0 to 13.5% by mass, the surface of the part exposed to the external environment is made of alkali metal or alkaline earth metal. Automotive exhaust system parts with excellent initial rust resistance, characterized by forming a silicate coating.   The automobile exhaust system part excellent in initial rust resistance according to claim 1, wherein the material of the automobile exhaust system part is SUS409L.   The automotive exhaust system part having excellent initial rust resistance according to claim 1 or 2, wherein the coating contains one or more of sodium silicate, potassium silicate, and calcium silicate. The film according to any one of claims 1 to 3, wherein the coating further contains one or more of corrosion products of basic zinc carbonate, zinc oxide, zinc hydroxide, and metal zinc. Automotive exhaust system parts with excellent initial rustability.