JPH07278739A - Alloy steel for muffler of diesel rolling stock excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To produce an alloy sheet improved in the corrosion resisting service life of a muffler exposed to the condensed soln. of a corrosive exhaust gas in a diesel engine with a catalyst by forming an Ni-Mo-Cu composite added steel and specifying its compsn. CONSTITUTION:This alloy steel for the muffler of a diesel rolling stock has a compsn. contg., by weight, 0.5 to 3.0% Ni, 0.5 to 2.0% Mo, 0.2 to 1.0% Cu and 0.05 to 1.5% Mn, contg., as impurities, <=0.02% C, <=0.2% Si, <=0.025% P, <=0.010% S and <=0.015% N, and the balance Fe. Only the Ni-Mo-Cu composite added steel contg. no Cr as the same is excellent in corrosion resistance in an environment of the concentrated soln. of an exhaust gas in which inorganic ions such as sulfuric acid ions and chloride i.ons and organic acids such as formic acid and acetic acid formed in the muffler of a diesel rolling stock are largely present and the value of pH is low of about 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy steel material having excellent corrosion resistance, which is used for a muffler of a diesel engine vehicle which has exhaust gas countermeasures.

[0002]

2. Description of the Related Art Up to now, it has been confirmed that the exhaust gas condensate environment of a gasoline engine vehicle equipped with a three-way system catalyst is a neutral environment mainly composed of ammonium salts. The layer elutes in a short time and the aluminum-iron alloy layer of the inner layer has a noble potential with respect to the iron of the base material, so the anticorrosion effect was small, but the corrosion resistance of the base metal was improved for the purpose of ensuring a long life. As a method to do so, corrosion-resistant steel in which 5 to 10% of Cr is added to iron (JP-A-63-1
No. 43240 and Japanese Patent Laid-Open No. 63-143241), and corrosion-resistant steel in which 10 to 20% of Cr is added to iron and Mo is added in combination (Japanese Patent Application No. 2-328339) have been proposed.

On the other hand, the current exhaust system muffler materials for diesel engine vehicles often use aluminized steel sheets obtained by aluminizing plain steel, and since the exhaust gas purifying catalyst is not mounted, the muffler can be used directly. The exhaust gas reached did not produce a condensate, so there was almost no problem with the corrosion resistance of the muffler material. However, in recent years, exhaust gas regulations for automobiles, especially for diesel engines such as buses and trucks, have been tightened, and oxidation catalysts and heating catalysts have been adopted to reduce the amount of hydrocarbons and carbon particulates in diesel exhaust gas. It has become a direction.
For this reason, exhaust gas from diesel engine vehicles will generate condensed water, and in addition to understanding the corrosive environment, new corrosion resistant materials will be essential in the future.

The diesel condensate environment is an acidic environment of about pH 2 containing sulfuric acid and organic acids, as will be described later, and sufficient corrosion resistance (general corrosion resistance) is ensured with the materials developed for conventional gasoline engine vehicle mufflers. It is a problem because it cannot be done.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above problems and improves the corrosion resistance life of a muffler exposed to a corrosive exhaust gas condensate of an automobile, especially a vehicle equipped with a diesel engine such as a bus or a truck. It is intended to provide a corrosion resistant alloy steel. That is, in the present invention, the actual diesel vehicle muffler material is analyzed in detail, and Cr, Ni, and M, which are the main components of the alloy steel, which affect the corrosion resistance under the exhaust gas condensate environment.
Based on the results of a detailed examination of the effects of o and Cu components, it exhibits excellent corrosion resistance even when applied to actual diesel vehicle muffler materials, ensuring a long service life and safety of the muffler over a long period of time. Internal corrosion of muffler (general corrosion) by diesel vehicle exhaust gas condensate that enables
It is intended to provide an alloy steel capable of withstanding the above.

[0006]

Means for Solving the Problems From the above viewpoints, the present inventors have made various studies to develop a material for a muffler of a diesel vehicle, which has much more excellent corrosion resistance than materials for a conventional muffler. The point became clear. First, in order to clarify the corrosive environmental factors, the liquid composition analysis of the exhaust gas condensate produced in the diesel muffler was performed. As a result, a large amount of inorganic ions such as sulfate ions and chloride ions and organic acids such as formic acid and acetic acid are present in the exhaust gas condensate,
It became clear that the pH was about 2 and was quite low.

Next, a simulated solution was prepared based on this result, and F
The corrosion resistance of alloy steels containing various ratios of Cr, Ni, Mo and Cu in e was examined. That is, among the substances in the exhaust gas condensate, organic acids such as formic acid and acetic acid have high volatility and are mainly present in the gas phase portion when the engine is started and stopped, and the metal surface exposed to the gas phase portion is present. High concentration, low pH
It was found that the organic acid droplets of No. 2 formed to give general corrosion to the alloy steel. It was also found that the exhaust gas condensate also contains chloride ions, and the general corrosion of the alloy steel is increased by the action of the organic acid, chloride ions and high-concentration hydrogen ions. Then, both the vapor phase portion and the liquid phase portion are made of Cr.
It was found that the addition of Al in the alloy deteriorates the corrosion resistance.

Therefore, a new alternative to the stainless steel containing a high concentration of Cr or Cr-Mo, which has been developed in order to secure a long-term corrosion resistance life of the muffler exposed to the exhaust gas exhaust gas condensate of the automobile exhaust system. The need for the design of corrosion resistant alloy materials was found.

The present inventors conducted a detailed investigation of the actual corrosion condition of a diesel vehicle muffler that was actually used, and also showed Cr, Ni, Mo, which are the main components of the alloy steel, which affect the corrosion resistance of the alloy steel in a simulated liquid environment. The effect of the addition amount of Cu, Cu, and Ti was examined in detail, and the following conclusions were reached. That is, the corrosion resistance of the alloy steel in the condensate deteriorates with the addition of Cr. Only the Ni-Mo-Cu composite addition steel that does not contain Cr has excellent corrosion resistance.

The present invention was made on the basis of the above-mentioned new findings, and is 0.5% by weight or more of Ni in Fe by weight%.
0% or less, 0.5% or more and 2.0% or less of Mo, 0.2% or more and 1.0% or less of Cu at the same time, and the balance of C.
02% or less, Si 0.2% or less, Mn
0.05% to 1.5%, P 0.025% or less, S 0.010% or less, N 0.01
It is an alloy steel for diesel vehicle mufflers that is excellent in corrosion resistance and contains 5% or less and other unavoidable impurities.

The reasons for limiting the composition of the steel of the present invention are as follows. Ni: 0.5 to 3.0% Ni coexists with Mo and Cu to suppress general corrosion in an environment where the pH is around 2, but 0.5% or less does not have the effect. If 3.0% or more is added, the structure becomes unstable due to the formation of strong austenite and the toughness of the base material and weld zone deteriorates, so the upper limit was made 3.0%.

Mo: 0.5 to 2.0% Mo is a basic component that greatly improves general corrosion resistance when coexisting with Ni and Cu. Although the general corrosion is suppressed as the amount of Mo added increases, the effect does not occur at 0.5% or less. Although the addition of 2.0% or more improves the corrosion resistance, the material becomes brittle due to the formation of strong ferrite, making industrial production difficult, so the upper limit was made 2.0%.

Cu: 0.2 to 1.0% Cu is a basic component that significantly improves general corrosion resistance when coexisting with Ni and Mo. Although the general corrosion is suppressed as the added amount of Cu is increased, the effect is not obtained at 0.2% or less. In addition, addition of 1.0% or more makes the material brittle,
Since industrial production becomes difficult, the upper limit was made 1.0%.

C: 0.02% or less Since C causes intergranular corrosion and cracking of the alloy steel, it is preferable that C is low. Further, the lower the strength, the workability, and the toughness of the base material, the better, but it takes time to make steel, resulting in an increase in cost.
However, in order to improve the corrosion resistance and workability which are the features of the present invention, the content is limited to a low value of 0.02% or less. 0.0
The effect is further exhibited at 1% or less.

Si: 0.2% or less Si has a deoxidizing action, but if less than 0.01%, no effect can be expected. Further, if it exceeds 0.8%, the workability is significantly deteriorated. Considering the surface treatability and workability, 0.2% or less is preferable.

Mn: 0.05-0.5% Mn has no adverse effect in the exhaust gas muffler exhaust gas condensate environment of a diesel vehicle, but as a normal component content 0.05
% And 0.5% or less.

P: 0.025% or less P is less preferable because it adversely affects the corrosion resistance in the exhaust gas muffler exhaust gas condensate environment of a diesel vehicle. The usual steelmaking conditions were 0.025% or less.

S: 0.01% or less Since S also adversely affects the corrosion resistance in the exhaust gas muffler exhaust gas condensate environment of a diesel vehicle, the smaller the content, the better. The usual steelmaking conditions were 0.01% or less.

N: 0.015% or less N is similar to C to form carbides / nitrides in the heat-affected zone of welding to cause intergranular corrosion, but it is better, but the adverse effect is not so remarkable as C. It was set to 0.015% or less.

[0020]

EXAMPLES The present invention will be described below based on examples.
The inventors adjusted a laboratory evaluation liquid (simulated condensate) set based on the analysis result of the diesel engine vehicle muffler condensate, and evaluated the corrosion resistance of various alloy steels in the environment. Table 1 shows the composition of the laboratory evaluation liquid. That is,
In the evaluation liquid,

[Table 1] As an evaluation of the general corrosion degree due to condensed water on the inner surface of the diesel car muffler material, a dry-wet repeated test incorporating environmental changes due to heating cycles was conducted for 5 cycles, and the average corrosion depth was calculated from the weight reduction. This dry-wet repeated cycle test is performed by injecting 20 ml of the evaluation liquid into a 300 ml glass beaker, inserting the test piece, holding it at a temperature of 80 ° C for 3 hours in a constant temperature air bath, and then injecting 20 ml of the evaluation liquid again. The test was one cycle. The water of the evaluation liquid in the beaker completely evaporates within 3 hours while being kept at a temperature of 80 ° C.

The shape of the test piece used in the dry and wet repeated cycle test is shown in FIG. Table 2 shows the comparison results of the composition and corrosion resistance of the conventional steel and the steel of the present invention. The steel of the present invention was prepared by melting a steel having the composition shown in Table 2 using an ordinary vacuum melting furnace. After casting into an ingot, soaking, heat rolling, and appropriate cold rolling and annealing, the surface was finished by # 400 wet emery polishing and then subjected to the main test.

From the results of Examples and Comparative Examples shown in Table 2, the Ni-Mo-Cu steel of the present invention is a material having extremely excellent corrosion resistance as a diesel engine vehicle exhaust system material as compared with the existing Cr base steel. I know there is.

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

As described above, according to the present invention, the corrosion resistance of the exhaust system material exposed to the environment of condensed water generated in the exhaust system of the diesel engine vehicle is improved, and the service life can be extended.

[Brief description of drawings]

FIG. 1 shows the shape of a test piece used in this evaluation test.

Claims (1)

[Claims] 1. By weight%, Ni: 0.5% or more and 3.0% or less, Mo: 0.5% or more and 2.0% or less, Cu: 0.2% or more and 1.0% or less, Mn: 0. 0.05% or more and 1.5% or less, and as impurities C: 0.02% or less, Si: 0.2% or less, P: 0.025% or less, S: 0.010% or less, N: 0 Alloy steel for mufflers for diesel vehicles, which has excellent corrosion resistance and contains 0.15% or less of balance Fe and other unavoidable impurities.