JP3597211B2 - Spheroidal graphite cast iron with excellent high-temperature strength - Google Patents

Description

【００１２】
【表２】

【００１３】
表２から明らかなように、発明材は、４２７℃の高温においても、強度、伸び、絞りについて優れた特性を有している。これに対し比較材は、高温における強度、伸び、絞りのいずれの点においても劣っている。
【００１４】
【発明の効果】
以上説明したように、本発明の球状黒鉛鋳鉄によれば、重量％で、Ｃ：３．３〜４．５％、Ｓｉ：２．５〜４％、Ｐ：０．０３〜０．２％、Ｎｉ：０．５〜２％、Ｍｏ：０．４〜２％、Ｍｇ：０．０２〜０．１％を含有し、残部がＦｅおよび不可避不純物からなるとともに、不可避不純物中のＭｎ含有量を０．２％未満に規制したので、高温においても高い強度と優れた伸びを有しており、高温強度が必要とされる高温環境においても球状黒鉛鋳鉄を使用することが可能になる。
【図面の簡単な説明】
【図１】図１は、試験材の製造に用いる砂型の斜視図である。
【図２】図２は、試験材の熱処理におけるヒートパターン図である。
【符号の説明】
１ 砂型[0001]
[Industrial applications]
The present invention relates to a spheroidal graphite cast iron having excellent strength and ductility at high temperatures.
[0002]
Problems to be solved by the prior art and the invention
Spheroidal graphite cast iron represented by JIS FCD40, FCD45 and the like 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 at high temperatures of 350 to 430 ° C., an embrittlement phenomenon occurs in which tensile strength, elongation at break, and fatigue strength rapidly decrease. For this reason, it is difficult to use it for applications requiring high strength at high temperatures, and for example, it cannot be used for a high temperature portion of a turbine casing.
[0003]
Therefore, a method is generally adopted in which alloy steel having high high-temperature strength is used in a portion where high-temperature strength is required, and a desired shape is obtained by welding the alloy steel.
By the way, if cast iron can be used in such places where high-temperature strength is required, material costs can be reduced, and labor such as welding can be reduced, so that manufacturing costs 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 which can be used in a high temperature environment by improving strength and ductility at a high temperature.
[0004]
[Means for Solving the Problems]
That is, in order to solve the above-mentioned problems, the spheroidal graphite cast iron of the present invention is, in terms of% by weight, C: 3.3 to 4.5%, Si: 2.5 to 4%, and P: 0.03 to 0.2%. , Ni: 0.5 to 2%, Mo: 0.4 to 2%, Mg: 0.02 to 0.1%, the balance being Fe and inevitable impurities, and the Mn content in inevitable impurities. Is regulated to less than 0.2% .
[0005]
[Action]
ADVANTAGE OF THE INVENTION According to this invention, tensile strength and elongation at high temperature are improved significantly by adjustment of a component, and use at higher temperature is attained.
Hereinafter, the specific actions of the components of the present invention and the reasons for limiting them will be described.
C: 3.3 to 4.5%
It is added to secure graphitized and spheroidized graphite particles by spheroidizing treatment. However, when the C content is less than 3.3%, carbides are easily formed, and shrinkage cavities are generated, and ductility is reduced. Further, when the content exceeds 4.5%, C dross is generated or segregation is generated, and strength and ductility are reduced. Therefore, the C content is limited to the above range.
[0006]
Si: 2.5-4%
Si is contained in order to promote graphitization and generate ferrite surrounding graphite to increase the strength. However, if the Si content is less than 2.5%, these effects are insufficient, and when the base is ferritized by heat treatment, ductility is obtained but tensile strength is reduced. If the content exceeds 4%, the matrix is strengthened, but the material becomes brittle and the toughness is reduced. Therefore, the Si content is limited to 2.5 to 4%.
Note that there is a good correlation between C and Si, and excellent high-temperature characteristics can be obtained by setting the ratio of C / Si to 1.5 or less. Specifically, by setting the 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, it is preferable to control the C / Si ratio to 1.5 or less in addition to the above contents of C and Si.
[0007]
P: 0.03 to 0.2%
P is contained to secure elongation at high temperatures. However, if it is less than 0.03%, elongation at a high temperature is not sufficient, and if it is contained more than 0.2%, steroidite is formed and becomes brittle, so that the P content is 0.03-0. Limited to 2%.
Ni: 0.5 to 2%
Ni is contained to secure the strength. However, if it is less than 0.5%, the strength is not sufficiently improved, and if it exceeds 2%, the strength is improved, but the elongation is reduced. Therefore, the Ni content is reduced to 0.5 to 2%. Limited.
[0008]
Mo: 0.4 to 2%
Mo is contained to improve the strength at high temperatures. However, if the content is less than 0.4%, the effect is insufficient. If the content is more than 2%, Mo carbide is generated and the elongation is reduced, so the Mo content is reduced to 0.4 to 2%. Limited.
Mg: 0.02-0.1%
Mg is an element necessary for the spheroidizing treatment, and is contained at 0.02% or more to secure sufficient spheroidizing. However, if the content exceeds 0.1%, reverse chill is generated and elongation is reduced. Therefore, the content is limited to 0.02 to 0.1%.
[0009]
Mn, Cr, V
These impurities intensity generates carbides cell boundary increases, while as it reduces the ductility, Cr, V is rather is preferably to limited to 0.3%, respectively, Mn are 0. It shall be less than 2% .
S: 0.03% or less S inevitably enters the dissolved material, but if it exceeds 0.03%, during spheroidization, S and Mg react to generate dross, and this dross is generated. It is preferable to limit the content to 0.03% or less because defects due to entrainment and a reduction in the spheroidization rate due to a decrease in the yield of Mg cause a reduction in elongation and strength.
Other unavoidable elements include Al: 0.08% or less, Ca: 0.02% or less, Ce 0.02% or less, A (rare earth): 0.1% or less inevitably enters and remains in cast iron from a spheroidizing agent and an inoculant.
[0010]
【Example】
A 30 kg steel ingot is melted in a high-frequency melting furnace and further subjected to spheroidizing treatment to form a 3-inch Y block sand mold 1 (height 210 mm, depth 186 mm, upper width 130 mm, middle width 82 mm, lower width 80 mm) shown in FIG. The invention material and the comparative material having the compositions shown in Table 1 were respectively produced by casting.
Next, these test materials were subjected to a two-stage heat treatment for ferrite formation with 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 performed for proof stress, tensile strength, elongation, and drawing, and the results are shown in Table 2.
[0011]
[Table 1]

[0012]
[Table 2]

[0013]
As is clear from Table 2, the inventive material has excellent properties in strength, elongation, and drawing even at a high temperature of 427 ° C. In contrast, the comparative material is inferior in strength, elongation, and drawing at high temperatures.
[0014]
【The invention's effect】
As described above, according to the spheroidal graphite cast iron of the present invention, C: 3.3 to 4.5%, Si: 2.5 to 4%, and P: 0.03 to 0.2% by weight. , Ni: 0.5 to 2%, Mo: 0.4 to 2%, Mg: 0.02 to 0.1%, the balance being Fe and inevitable impurities, and the Mn content in inevitable impurities. Is regulated to less than 0.2%, so that it has high strength and excellent elongation even at high temperatures, and it is possible to use spheroidal graphite cast iron even in a high-temperature environment where high-temperature strength is required.
[Brief description of the 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 a heat treatment of a test material.
[Explanation of symbols]
1 sand mold

Claims (1)

By weight%, 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, and Mn content in inevitable impurities is regulated to less than 0.2%. Excellent spheroidal graphite cast iron.

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