JPH07118790A - Spheroidal graphite cast iron excellent in high temperature strength - Google Patents

Abstract

PURPOSE:To produce a spheroidal graphite cast iron usable in a high temp. environment. CONSTITUTION:This spheroidal graphite cast iron has a composition consisting of, by weight, 3.3-4.5% C, 2.5-4% Si, 0.03-0.2% P, 0.5-2% Ni, 0.4-2% Mo, 0.02-0.1% Mg, and the balance Fe with inevitable impurities. By this method, high temp. strength and ductility can be improved, and the application of the spheroidal graphite cast iron for use requiring high temp. strength can be made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to spheroidal graphite cast iron excellent in strength and ductility at high temperatures.

[0002]

[Prior Art and Problems to be Solved by the Invention] JIS
Spheroidal graphite cast iron represented by FCD40 and FCD45 has higher strength than ordinary cast iron, and is widely used as an inexpensive industrial material for applications such as crankshafts and low temperature parts of turbine casings. However, it is known that spheroidal graphite cast iron has low strength at high temperatures, and that at high temperatures of 350 to 430 ° C., an embrittlement phenomenon occurs in which tensile strength, elongation at break, and fatigue strength sharply decrease. For this reason, it is difficult to use it in applications requiring high strength at high temperatures, and for example, it cannot be used in high temperature parts of turbine casings.

Therefore, a method is generally used in which a high-temperature strength alloy steel is used in a region where high-temperature strength is required and the steel is welded to obtain a desired shape.
By the way, if cast iron can be used even in the parts where high temperature strength is required, the material cost can be reduced, and the labor such as welding can be saved. Therefore, the manufacturing cost can be significantly reduced. become. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a spheroidal graphite cast iron that has improved strength and ductility at high temperatures and can be used in high temperature environments.

[0004]

That is, in order to solve the above-mentioned problems, the spheroidal graphite cast iron of the present invention is C:
3.3-4.5%, Si: 2.5-4%, P: 0.03
~ 0.2%, Ni: 0.5-2%, Mo: 0.4-2
%, Mg: 0.02 to 0.1%, the balance being Fe and inevitable impurities.

[0005]

According to the present invention, the tensile strength and the elongation at a high temperature are significantly improved by adjusting the components, and the use at a higher temperature becomes possible. The specific actions of the components of the present invention and the reasons for limitation thereof will be described below. C: 3.3 to 4.5% Graphitized by spheroidizing treatment, and is added to secure spheroidized graphite particles. However, if the C content is less than 3.3%, carbides are easily generated, shrinkage cavities occur, and ductility decreases.
Further, if the content exceeds 4.5%, C dross is generated or segregation is generated to lower the strength and ductility, so the C content is limited to the above range.

Si: 2.5-4% Si is contained in order to promote graphitization and generate ferrite surrounding the graphite to increase strength. However, when the Si content is less than 2.5%, these effects are insufficient, and when the matrix is made into ferrite by heat treatment, ductility is obtained but tensile strength is reduced. Further, if the content exceeds 4%, the matrix is strengthened, but it becomes brittle and the toughness decreases, so the Si content is limited to 2.5 to 4%. There is a good correlation between C and Si, and the C / Si ratio is 1.
By setting it to 5 or less, excellent high temperature characteristics can be obtained. Specifically, by setting this ratio to 1.5 or less, it is possible to secure a tensile strength of 375 MPa or more, a proof stress of 235 MPa or more, and an elongation of 15% or more in strength and elongation. Therefore, in addition to the above contents of C and Si, C
It is preferable to regulate the / Si ratio to 1.5 or less.

P: 0.03 to 0.2% P is contained to secure the elongation at high temperature. However, if it is less than 0.03%, the elongation at high temperature is not sufficient,
Further, when the content exceeds 0.2%, steadite is generated and embrittlement occurs, so the P content is limited to 0.03 to 0.2%. Ni: 0.5 to 2% Ni is contained to secure the strength. However, 0.5
If it is less than 2%, the improvement of the strength is insufficient, and if it is added in excess of 2%, the strength is improved but the elongation is lowered. Therefore, the Ni content is limited to 0.5 to 2%.

Mo: 0.4-2% Mo is contained to improve the strength at high temperatures. However, if less than 0.4%, the action is insufficient,
Further, when the content exceeds 2%, Mo carbide is generated and the elongation is reduced, so the Mo content is 0.4 to 2%.
Limited to. Mg: 0.02 to 0.1% Mg is an element necessary for the spheroidization treatment, and 0.02% or more is contained in order to ensure sufficient spheroidization. However,
If it is contained in excess of 0.1%, reverse chills are generated and the elongation decreases, so the content is limited to 0.02-0.1%.

Mn, Cr, V: 0.3% or less for each of these impurities form carbides at the cell boundaries to increase the strength, but on the other hand, reduce the ductility, so each content is limited to 0.3% or less. Is preferred. S: 0.03% or less S inevitably enters from the melted material, but if S is contained in excess of 0.03%, S and Mg react with each other during the spheroidizing treatment to form dross. It is preferable to limit the content to 0.03% or less because defects due to entrainment and a lower spheroidization rate due to a lower yield of Mg occur and elongation and strength are reduced. As other inevitable elements, Al:
0.08% or less, Ca: 0.02% or less, Ce0.02
% Or less, R. A (rare earth): 0.1% or less inevitably enters cast iron from the spheroidizing agent, inoculant, etc. and remains.

[0010]

EXAMPLE A steel ingot of 30 kg was melted in a high frequency melting furnace, and further subjected to a spheroidizing treatment to obtain a 3-inch Y block sand mold 1 (height 210 mm, depth 186 mm, upper width 13) shown in FIG.
0 mm, 82 mm in middle width, 80 mm in lower width), and the invention material and the comparative material having the compositions shown in Table 1 were melted. Next, these test materials were subjected to a two-step ferritic heat treatment in the heat pattern shown in FIG. From this test material, a test piece having a diameter of 12.5 mm and a height of 50 mm was cut out, and a test for measuring mechanical properties at 427 ° C. was performed on the test piece. The test was conducted on proof stress, tensile strength, elongation and drawing, and the results are shown in Table 2.

[0011]

[Table 1]

[0012]

[Table 2]

As is clear from Table 2, the invention material is 42
It has excellent properties in strength, elongation and drawing even at a high temperature of 7 ° C. On the other hand, the comparative material is inferior in terms of strength at high temperature, elongation and drawing.

[0014]

As described above, according to the spheroidal graphite cast iron of the present invention, C: 3.3 to 4.5% by weight, S:
i: 2.5-4%, P: 0.03-0.2%, Ni:
0.5-2%, Mo: 0.4-2%, Mg: 0.02-
Since it contains 0.1% and the balance is Fe and unavoidable impurities, it has high strength and excellent elongation even at high temperature, and spheroidal graphite cast iron is used even in high temperature environment where high temperature strength is required. It will be possible.

[Brief description of drawings]

FIG. 1 is a perspective view of a sand mold used for manufacturing a test material.

FIG. 2 is a heat pattern diagram in heat treatment of a test material.

[Explanation of symbols]

 1 sand mold

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Gohan Miyamoto 4 in Chazu-cho, Muroran-shi, Hokkaido Inside Japan Steel Works, Inc. (72) Inventor Hiroaki Kudo 4 in Chazu-cho, Muroran-shi, Hokkaido Inside Japan Steel Works, Ltd.

Claims (1)

[Claims] 1. C: 3.3-4.5%, S by weight%
i: 2.5-4%, P: 0.03-0.2%, Ni:
0.5-2%, Mo: 0.4-2%, Mg: 0.02-
Spheroidal graphite cast iron containing 0.1% and the balance consisting of Fe and unavoidable impurities and excellent in high temperature strength