JPH07310147A - Ferritic heat resistant cast steel excellent in high temperature corrosion resistance - Google Patents

Abstract

PURPOSE:To develop ferritic heat resistant cast steel excellent in high temp. corrosion resistance by adding and incorporating a specified amt. of Mo to ferritic cast steel as well as Cu and AN. CONSTITUTION:The molten steel of ferritic heat resistant cast steel having a compsn. contg., by weight, 0.1 to 0.2% C, 0.1 to 2% Si, 0.1 to 2% Mn, 16 to 20% Cr, 1.1 to 2.4% Mo, 0.3 to 2.5% Nb, 0.01 to 2.2% Ta, 0.1 to 5% Cu or Al, and the balance Fe is melted by a high-frequency induction electric furnace or the like and is cast into a prescribed mold. Mo contained in the structure is allowed to enter into solid solution in the coexistence of Cu and Al to improve the high temp. corrosion resistance of the cast steel product as well as Cr excellent in high temp. oxidation resistance, and Mo, Nb, Ta or the like form carbides, by which the ferritic heat resistant cast steel product moreover excellent in high temp. strength can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic heat resistant cast steel having excellent high temperature corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, for manufacturing structural members of an internal combustion engine such as a die member located on the combustion gas outlet side of a secondary combustion chamber of a diesel engine, since it is exposed to high temperature combustion gas, high temperature oxidation resistance Various excellent ferritic heat-resistant cast steels, such as JP-A-5-33105, JP-A-5-59498, and JP-A-5-1713.
The ferritic heat-resistant cast steel described in Japanese Patent No. 65 is used.

[0003]

On the other hand, in recent years, the performance and output of internal combustion engines have been remarkably high, and along with this, the environment in which the structural members are used is becoming more severe. Although the conventional ferritic heat-resistant cast steel has excellent high-temperature oxidation resistance, its high-temperature corrosion resistance is insufficient, so under the harsh environment of use, the progress of corrosion accelerates and it is not possible to satisfy it satisfactorily. .

[0004]

Therefore, the present inventors have
From the above viewpoints, as a result of conducting research by paying attention to ferritic heat-resistant cast steel, weight% (hereinafter,% is% by weight)
), C: 0.1 to 0.2%, Si: 0.
1-2%, Mn: 0.1-2%, Cr: 16
.About.20%, Mo: 1.1 to 2.4%, Nb: 0.
Ferritic heat-resistant cast steel having a composition containing 3 to 2.5%, Ta: 0.01 to 2.2%, Cu and / or Al: 0.1 to 5%, and the balance of Fe and inevitable impurities. Obtained the research result that it has excellent high temperature corrosion resistance, and also excellent high temperature oxidation resistance and high temperature strength.

The present invention was made based on the above research results, and the reasons why the composition of the ferritic heat-resistant cast steel is limited as described above will be explained below. (A) C C component has an effect of improving castability and forming a carbide to improve high temperature strength, but if the content thereof is less than 0.1%, a desired effect can be obtained in the above operation. On the other hand, on the other hand, if the content exceeds 0.2%, the formation of carbides becomes excessive and the toughness decreases, so the content was defined as 0.1 to 0.2%.

(B) Si The Si component exerts a strong deoxidizing action on the molten metal and an action of improving castability, but if the content thereof is less than 0.1%, it is desirable for the above action. The effect of
On the other hand, if the content exceeds 2%, the high temperature oxidation resistance will decrease, so the content was defined as 0.1 to 2%. Incidentally, the content of 0.4 to 1.0% is desirable.

(C) Mn The Mn component has the same deoxidizing action as Si and has the action of improving the castability, but its content is 0.1%.
If the content is less than the above, the desired effect cannot be obtained, while if the content exceeds 2%, the high temperature oxidation resistance tends to decrease, so the content is defined as 0.1 to 2%. . Incidentally, the content of 0.3 to 0.9% is desirable.

(D) Cr The Cr component has the effect of improving high temperature oxidation resistance, but if its content is less than 16%, the desired excellent high temperature oxidation resistance cannot be ensured. Content is 20
If the content exceeds%, the material will be rapidly embrittled, so the content was defined as 16 to 20%.

(E) Mo The Mo component, in the coexistence of Cu and Al, both dissolves in the matrix to improve the high temperature corrosion resistance, and at the same time forms carbides to improve the high temperature strength. If the content is less than 1.1%, the desired effect cannot be obtained, while if the content exceeds 2.4%, the toughness decreases, so the content is set to 1.1. ~ 2.4%
I decided. Incidentally, the content of 1.6 to 2.2% is desirable.

(F) Nb The Nb component has the action of forming a solid solution in the matrix and forming carbides to improve the high temperature strength, but if the content is less than 0.3%, the desired high temperature strength improving effect is obtained. Is not obtained,
On the other hand, if the content exceeds 2.5%, the toughness will suddenly decrease, so the content should be 0.3-2.5.
Defined as%. In addition, desirably, the content of 1.2 to 1.9% is preferable.

(G) Ta The Ta component has a function of forming a solid solution with the above Nb in the matrix and forming a carbide to improve the high temperature strength, but if the content is less than 0.01%, it is desirable. The effect of improving the high temperature strength cannot be obtained, and on the other hand, if the content exceeds 2.2%, the toughness decreases, so the content is 0.01%.
It was set to 2.2%. Incidentally, the content of 0.2 to 1% is desirable.

(H) Cu and Al These components have the function of forming a solid solution in the matrix to improve the high temperature corrosion resistance, but if the content is less than 0.1%, the desired improvement effect on the high temperature corrosion resistance is obtained. Not contained, its content is 5%
If it exceeds, the toughness will decrease sharply,
Its content was set to 0.1 to 5%. Incidentally, the content of 0.7 to 2.5% is desirable.

[0013]

EXAMPLES Next, the ferritic heat-resistant cast steel of the present invention will be specifically described by way of examples. Ferrite heat-resistant cast steels of the present invention (hereinafter simply referred to as the cast steels of the present invention) 1 to 18 and comparative ferritic heat-resistant cast steels each having the composition shown in Tables 1 to 3 in the atmosphere using a normal high frequency induction melting furnace (Hereinafter, also referred to as comparative cast steel) 1 to 8 were melted, and this was used in a lost wax precision casting mold to obtain a diameter:
14 mm × length: cast into a rod-shaped casting having dimensions of 200 mm.

In each of the comparative cast steels 1 to 8, the content of the components that affect high temperature corrosion resistance, high temperature oxidation resistance, and high temperature strength among the constituent components (marked with * in Table 3) is within the range of the present invention. It has a composition that deviates from the lower part to.

Then, from this rod-shaped casting, the diameter: 10 mm
× Length: A test piece having a dimension of 120 mm was cut out, and for the purpose of evaluating the high temperature corrosion resistance using the test piece, a temperature of 870 ° C. light oil combustion gas flowing through the test piece at a speed of 1 m / sec. A high temperature corrosion test was carried out under the condition of holding in an atmosphere for 100 hours, and after the test, the weight loss (corrosion weight loss) after removing the scale adhering to the surface of the test piece with a wire brush was measured.

From the above rod-shaped casting, diameter: 10 mm ×
Length: A test piece having a size of 20 mm was carved out, and this test piece was used to evaluate the high temperature oxidation resistance in the atmosphere,
A high temperature oxidation test was performed under the condition of keeping the temperature at 900 ° C. for 100 hours, and after the test, the weight loss (oxidation weight loss) was measured after the scale adhering to the surface of the test piece was removed with a wire brush. Further, a test piece having a diameter of 6 mm and a parallel portion length of 32 mm was carved out from the rod-shaped casting, and the test piece was used to evaluate high temperature strength at 830 ° C.
A tensile test was conducted to measure the tensile strength. The results of these measurements are shown in Table 4.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

From the results shown in Tables 1 to 4, it is clear that the cast steels 1 to 18 of the present invention all have excellent high temperature corrosion resistance, and also excellent high temperature oxidation resistance and high temperature strength. On the other hand, as seen in Comparative Cast Steels 1-8,
If the content of any one of the constituents C, Cr, Mo, Nb, Ta, Cu, and Al deviates from the scope of the present invention, one of the above characteristics becomes inferior. It is clear. As described above, the ferritic heat-resistant cast steel of the present invention has excellent high-temperature corrosion resistance, and also has excellent high-temperature oxidation resistance and high-temperature strength, so that these properties are required, for example, the structure of an internal combustion engine. When used as a member, it exhibits excellent performance for a long period of time even in practical use under severe conditions.

Claims (1)

[Claims] 1. By weight%, C: 0.1 to 0.2%, Si: 0.1 to 2%, Mn: 0.1 to 2%, Cr: 16 to 20%, Mo: 1.1. ~ 2.4%, Nb: 0.3-2.5
%, Ta: 0.01 to 2.2%, Cu and / or Al: 0.1 to 5%, and the balance of Fe and inevitable impurities. Ferritic heat resistant cast steel.