JPS609579B2 - Anti-vibration flake graphite cast iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvement of the vibration absorption ability (damping ability) of flake graphite cast iron.

Flaky graphite cast iron has better damping ability than steel, and is used in automobile cylinder blocks, etc.
Furthermore, there are cases where a material with excellent damping ability is required.

In such cases, the general method of increasing the damping capacity is to increase the amount of carbon added, since the damping capacity of graphite itself is very large. is to increase the amount of

However, when the carbon content is increased, the strength of cast iron decreases significantly, so it cannot be used where strength is required. In order to improve the strength, Ni, CrFM is generally used.
Although alloying elements such as copper and copper are added, the improvement in strength is small, and when the amount added is increased, the damping capacity is reduced. As mentioned above, if the carbon content is increased to increase the damping capacity, the strength will decrease, and if the carbon content is small, the damping capacity will not be sufficient. Currently, we are having a very difficult time obtaining graphite cast iron.

An object of the present invention is to provide flake graphite cast iron with a low carbon content and excellent damping ability and strength. Increasing the amount of carbon content causes the above-mentioned problems, so in the present invention, we focused on heat treatment to improve the base structure in order to improve the damping ability while keeping the amount of carbon content small. It was successful.

Generally, heat treatments such as quenching, tempering, and austenburizing are performed to improve mechanical strength.
No attention was paid to this from the perspective of improving damping capacity.

However, after conducting various tests, we found that when austempering was applied to special flake graphite cast iron, it not only had superior strength, but also unexpectedly improved damping capacity. This is what was obtained. Generally, austempering treatment is performed to improve bending strength and impact strength, and has nothing to do with improving damping capacity.Incidentally, when the carbon equivalent (C11'3Si) is large, When austempered flake graphite cast iron and untreated flake graphite cast iron were compared, there was no difference in damping capacity. However, C: 3.0-3.7%, Sj: 1.3-2
．． 3%, carbon equivalent: 4.3% or less, Mn: 0.2-1.
Austempering flake graphite cast iron containing 0% by weight or less, P: 0.15% by weight or less, S: 0.15% by weight or less, and the remainder being substantially Fe, and flake graphite with an area ratio of 7 to 7% by weight. 15%, and the base has residual austenite of 10 to 40% in terms of area ratio.
The damping capacity of the bainite structure was dramatically improved compared to the untreated one.

The reason why the damping ability improves contrary to normal predictions is due to energy loss due to crystal sliding within flaky graphite crystals, and viscous friction at the interface between iron and cementite, which is finely dispersed in the bainite structure. This is thought to be due to the addition of energy loss. Next, the reason for limiting each component of flake graphite cast iron will be described. If the carbon content is 3.0% or less, the amount of flake graphite produced is small and a satisfactory damping ability cannot be obtained;
If the carbon content exceeds 3.0%, the strength will decrease significantly.
It is set at 3.7%.

Si is required in an amount of 1.3% or more to graphitize the carbon contained, and is limited to 2.3% from the viewpoint of decreasing strength.

The reason why the carbon equivalent is set to 4.3% or less is not only because if it is more than that, it will lead to a decrease in strength, but also because if it is more than that, the effect of improving the damping capacity by austempering treatment cannot be expected. The chemical composition of flake graphite cast iron generally consists of five main elements: C, Si, Mn, P, and S, with Mn being 0.2 to 1.0% by weight and P being 0.15% by weight.
Hereinafter, it is well known that S is in the range of 0.15% by weight or less.

Furthermore, it is known that trace amounts of alloy components other than the five elements mentioned above may be added to flake graphite cast iron if necessary. The anti-vibration cast iron of the present invention is characterized by the amount of flaky graphite, that is, the amount of carbon, and the structure of the base. It is something to give. Therefore, in determining the amount of flaky graphite, the amount of C and Si, that is, the carbon equivalent, is important, and the amounts of Mn, P, and S have no particular meaning in the present invention, and are generally used as described above. A certain range is fine. Also,
Alloy components other than the above five elements are not necessary, but may be added in amounts that do not impair the graphite shape or the damping ability of the base. The area ratio of flake graphite is required to be 7% or more in order to improve the attenuation hall, and the upper limit is 15% based on the above-mentioned amounts of C and Si.
This is up to.

The area ratio of the bainitic structure and retained austenite is required to be at least 60% and 10%, respectively, from the point of view of damping ability, and the upper limit of the retained austenite is necessarily 40%.

Further, the austempering treatment may be carried out by a normal method, but the temperature is preferably 220 to 360q○.

The reason is that if it is too low, problems such as thermal deformation will occur, and if it is too high, the shape of the precipitated cementite will change from needle-like to feather-like, reducing the damping ability. FIG. 1 shows the change in damping capacity depending on the carbon equivalent of the austempered flake graphite cast iron of the present invention and the untreated cast iron. In addition, the dotted line is C:
3.0-4.3%, Si: 1.5-1.9%, Mn: 0
．． The solid line shows the damping capacity of the untreated cast iron containing 23%, and the solid line shows the damping capacity of the untreated cast iron containing 36,000 ℃ after heating it at 900°C for 1 minute.
This shows the attenuation ability after being maintained in a salt solution for 2 hours.

In both cases, the damping capacity tends to increase as the carbon equivalent increases, but when comparing cast iron with the same carbon equivalent, the cast iron of the present invention shown by the solid line has a better damping capacity than the conventional cast iron shown by the dotted line. , this tendency becomes more pronounced as the carbon equivalent decreases. Note that the value of this damping capacity is the value when the maximum strain amplitude is 1.18×10-7. Figure 2 shows C: 3.38%, Si: 1.86%, Mn: 0
．． 23% (carbon equivalent: 4.0%) of untreated cast iron (dotted line) and austempered cast iron (dotted line) as shown in Figure 1.
(solid line) shows the relationship between the maximum strain amplitude and the damping area. The cast iron of the present invention exhibits better damping ability than untreated cast iron both in the region that does not depend on the maximum strain amplitude and in the region that does depend on it, and especially considering the practical maximum strain amplitude (around 10-4), the cast iron of the present invention More than 300% improvement compared to untreated cast iron. Next, FIG. 3 shows the relationship between Austenbard temperature and damping capacity. C: 3.03%, Sj: 1.41%,
Cast iron containing Mn: 0.21% (carbon equivalent: 3.5%) was austempered under the same conditions as the cast iron indicated by the solid line in Figure 1, and the damping capacity value was 1.18xl when the maximum strain amplitude was 1.18xl.
The value at o-7 is shown. As can be seen from FIG. 3, the lower the austempered temperature, the greater the damping ability, but if it is too low, problems such as thermal deformation may occur, so it is preferable that the austempered temperature is in the range of 220oo to 360q. As described above, by austempering flake graphite cast iron with a low carbon content, the damping capacity can be dramatically improved without increasing the carbon content.

Furthermore, since the amount of carbon is small, the strength is also excellent. In other words,
According to the present invention, flake graphite cast iron having excellent damping ability and strength can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between damping capacity and carbon equivalent in the cast iron of the present invention and conventional cast iron, Figure 2 is a diagram showing the relationship between damping capacity and maximum strain amplitude in both cast irons, and Figure 3 is a diagram showing the relationship between damping capacity and maximum strain amplitude in both cast irons. teeth,
It is a figure showing the relationship between damping capacity and austempered treatment in cast iron of the present invention. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 C: 3.0-3.7% by weight, Si: 1.3-2.3
Weight%, carbon equivalent (C+1/3Si): 4.3% by weight or less, Mn: 0.2 to 1.0% by weight, P: 0.15% by weight
Hereinafter, from a bainitic structure containing S: 0.15% by weight or less, the balance being substantially Fe, containing flake graphite in an area ratio of 7 to 15%, and the base having retained austenite in an area ratio of 10 to 40%. Anti-vibration flaky graphite cast iron characterized by: