JP3812925B2 - Compact vermicular graphite cast iron for engine cases - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a compact vermicular graphite cast iron (hereinafter referred to as CV graphite cast iron) that is high in strength and can be reduced in weight and is suitably selected for an engine case.
[0002]
[Prior art]
As an engine case material, gray cast iron which is flake graphite cast iron having a high thermal conductivity, excellent vibration damping ability, good castability, and low cost is known.
[0003]
Gray cast iron has the above-mentioned characteristics (characteristics such as high thermal conductivity, excellent vibration damping ability, good castability, and low cost) due to its flake graphite shape. .
[0004]
However, since the graphite form is flaky, it is easy to crack. For this reason, if the thickness of the engine case is reduced in order to reduce the weight, its strength is limited.
[0005]
As another material, for example, spheroidal graphite cast iron is known as high-strength cast iron. However, spheroidal graphite cast iron has poor castability, and the ratio of the hot water is high in order to ensure the soundness of the product. Also, special measures are required to remove the runway hot water, so the cost is also high. Has the problem.
[0006]
Further, the techniques disclosed in JP-A-9-111393, JP-A-9-202935, and JP-A-5-86437 are not disclosed, but are not related to the problem of the present application to provide a suitable engine case material. .
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a graphite cast iron having high strength, excellent vibration resistance, thinning, and good castability.
[0008]
[Knowledge]
As a result of various experiments conducted by the present inventors to achieve the above-mentioned problems, the intermediate ratio between flake graphite cast iron and spheroidal graphite cast iron is determined based on the amount of Mg and based on the relative mixing ratio with other additives. It was found that a graphite cast iron having the following structure was obtained, and as a result of obtaining the optimum value and continuing the experiment, it was found that the object was achieved by the following composition.
[0009]
[Means for Solving the Problems]
According to the present invention, by weight ratio, C is 3.5 to 4.2%, Si is 1.8 to 2.5%, Mn is 0.25 to 0.5%, and P is 0.1% or less. , S is 0.02% or less, Mg is 0.010 to 0.020%, Cu is 0.3 to 0.8%, Sn is 0.3 to 1.0%, the balance is Fe, It is characterized in that graphite cast iron having compact vermicular graphite in the base is selected as an engine case material.
[0010]
Here, it is preferable that vermicular graphite having a pearlite area ratio of 70 to 90% and a spheroidization ratio of 35 to 50% is deposited.
[0011]
According to the compact vermicular graphite cast iron for engine case of the present invention having such a configuration, by adding each component so as to be within the above range, the vermicular graphite having a rounded tip shape and having a spheroidization rate of 35 to 50%. Is formed, and the notch action is reduced. As a result, the notch effect on the load is reduced and the crack resistance is improved.
[0012]
On the other hand, since the hot metal flowability and the like are maintained in the same manner as flake graphite cast iron, the castability is not impaired even if it is thin.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the composition of the engine case CV graphite cast iron according to the present invention will be described. This engine case CV graphite cast iron has a composition in which C is 3.5 to 4.2% by weight, Si is 1.8 to 2.5% by weight, and Mn is 0.25 to 25% by weight. 0.5%, P is 0.1% or less by weight, S is 0.02% or less by weight, Mg is 0.010 to 0.020% by weight, Cu is 0.3 to 0.3% by weight 0.8%, Sn is contained in 0.3% to 1.0% by weight, the remainder is made of Fe, and the base has compact vermicular graphite. Here, this composition is a composition as CV graphite cast iron, not a material ratio.
[0014]
The component ranges of each additive described above are as follows: C is the influence on the generation amount of graphite and the grain structure; Si is the influence on the grain structure of the material, the graphite morphology and the number of graphite generations; and Mn is the grain structure of the material. And the upper and lower limits determined from the appropriate addition amount in balance with other grain structure affecting elements Cu and Sn, and since P forms a hard material if it enters too much as an impurity, S is It is the upper limit for obtaining stable CV graphite because it affects the shape of graphite entering as an impurity, and Mg is the first factor for forming CV graphite. In addition, the amount of addition necessary to obtain flake graphite and obtain appropriate CV graphite, Cu affects the graphite structure of graphite and makes it pearlite to increase the strength, and Sn affects the texture of graphite. Too much graphite It is determined from the amount added to increase the strength by pearlite becomes law.
[0015]
The operation will be described below.
By adding each component so as to be within the above range as described above, a vermiculite graphite having a rounded tip shape and a spheroidization rate of 35 to 50% is formed like the graphite 1 shown in the structural photograph of FIG. Since the notch action is reduced, the notch effect on the load is reduced and the crack resistance is improved.
[0016]
Moreover, 70-90% of pearlite precipitates and surface pressure strength improves by making Mn, Cu, Sn, etc. into said composition.
[0017]
On the other hand, since the hot metal flowability and the like are maintained in the same manner as flake graphite cast iron, the castability is not impaired even if it is thin.
[0018]
Fig. 2 shows the results of an experimental comparison of tensile strength and Young's modulus. The tensile strength is about 1.75 times that of conventional flake graphite cast iron FC and Young's modulus is about 1.35 times. is doing.
[0019]
FIG. 3 shows a stress fatigue diagram in which the horizontal axis represents the number of load repetitions and the vertical axis represents the load stress, and the fatigue strength is about 1.8 times that of flake graphite cast iron FC (for example, FC250). It shows that.
[0020]
【The invention's effect】
The present invention is configured as described above, and can provide a vermicular graphite cast iron having high heat cracking resistance, high vibration damping capability, good castability, and low cost.
[0021]
Therefore, a thin and lightweight high-strength engine case can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing the distribution and shape of graphite in CV graphite cast iron according to an embodiment of the present invention.
FIG. 2 is a diagram showing tensile strength and Young's modulus between CV graphite cast iron and flake graphite cast iron.
FIG. 3 is a stress fatigue diagram between CV graphite cast iron and flake graphite cast iron.
[Explanation of symbols]
1 ... graphite CV ... compact vermicular graphite cast iron FC ... flaky graphite cast iron

Claims (1)

By weight ratio, C is 3.5 to 4.2%, Si is 1.8 to 2.5%, Mn is 0.25 to 0.5%, P is 0.1% or less, and S is 0.02%. %, Mg is 0.010-0.020%, Cu is 0.3-0.8%, Sn is 0.3-1.0%, and the rest is made of Fe. Compact vermicula graphite cast iron for engine cases characterized by having graphite.

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