JP5618466B2 - High rigidity high damping capacity cast iron - Google Patents

Description

  The present invention relates to a high-rigidity and high-damping capacity cast iron excellent in Young's modulus and vibration damping properties. The cast iron of the present invention is used as a structural material for machine tools and high precision machine tools that require rigidity, or precision measuring instruments in which Young's modulus and vibration are a problem. Accuracy and precision can be increased.

  Conventionally, flake graphite lead cast iron having relatively excellent vibration damping ability has been mainly used as a structural material for machine tools. The flake graphite cast iron has a combined vibration isolation mechanism that contains a large amount of flake graphite, so it has a high damping capacity compared to steel, etc., and the formability and cost for producing large structural materials. This has advantageous features. In consideration of application to machine tool structural materials in place of flake graphite cast iron, research has been conducted on materials having excellent damping ability such as concrete materials, natural granite, and CFRP. However, none has been put into practical use due to problems such as low rigidity, workability, and cost.

  Currently, flake graphite cast iron, which is excellent in terms of damping performance, castability, and cost, is widely used in structural materials such as machine tool beds, tables, and columns. However, a machine tool that processes difficult-to-work materials with severe work hardening requires high rigidity for stably maintaining a large depth of cut and high vibration damping ability for suppressing generation of harmful vibrations. As described above, when the vibration damping capability is further sought, the current flake graphite cast iron may not be able to obtain sufficient processing efficiency and accuracy of the processed product due to the influence of vibration.

  Conventionally, flake graphite cast iron such as FC300 used for machine tools and the like contains a large amount of flake graphite that expresses a composite damping mechanism, so it is a structural material with excellent vibration damping ability among conventional materials. is there. In order to improve the vibration damping capacity of the flake graphite cast iron, the amount of flake graphite may be increased. However, there is a problem that the dynamic Young's modulus (hereinafter simply referred to as Young's modulus) decreases as the amount of flake graphite cast iron increases. Adjustment of the graphite amount of flake graphite cast iron can be controlled by the amount of C and Si. As a structural material of a machine tool, when the Young's modulus decreases, it becomes necessary to increase the thickness of the structural material in order to maintain rigidity. Therefore, not only a problem in structural design occurs, but also the cost increases, which is not preferable.

  As a method for improving the vibration damping capacity, a method of forming bainite or martensite in the base structure of flake graphite cast iron has been proposed (casting engineering 68 (1996) 876). However, in these methods, the Young's modulus decreases as the vibration damping capacity is improved, so it is difficult to achieve both. Further, methods for improving the vibration damping ability are disclosed in Patent Documents 1, 2, and 3, for example. Any of Patent Documents 1 to 3 describes a method for improving the logarithmic attenuation ability.

  In these Patent Documents 1 to 3, measurement results of vibration damping ability are shown. However, since there is no description regarding the Young's modulus, the value is unknown. Specifically, since Patent Documents 1 and 2 relate to brake materials, it is presumed that Young's modulus is not indispensable but rather strength is emphasized. In particular, Patent Document 1 describes that it is an object of the present invention to provide a brake material having excellent strength comparable to that of gray cast iron and having a damping capacity superior to that of gray cast iron. Patent Document 3 describes that an aluminum-containing vibration-damping cast iron was invented in order to improve the vibration-damping performance from the viewpoint of improving the vibration-damping performance of machine tools and precision machining equipment. However, in order to maintain the mechanical accuracy, it is indispensable to maintain the rigidity of the structural material, but this is not shown.

From these Patent Documents 1 to 3, it can be seen that the vibration damping ability can be improved by adding aluminum, but the method differs in detail. Specifically, Patent Document 1, a cast iron with the addition of aluminum was heated at A ₁ transformation point or above (910-1000 ° C.), and the perlite to 70% in the subsequent cooling rate and adjust the area ratio vibrations Brake material with excellent damping capacity and strength has been obtained. Presumed Patent Document 2, have been achieved improvements in the vibration damping capacity by in the effects and hypereutectic compositions of A ₁ added to form a bulking and fine pores of the graphite, the method Young's modulus is significantly reduced Is done. Patent Document 3 is an example in which aluminum is added to improve vibration damping performance, but the Young's modulus is not mentioned. In other words, the methods described in Patent Documents 1 to 3 cannot necessarily achieve both Young's modulus and vibration damping ability, and therefore need to further improve the vibration damping ability.
JP 63-140064 A JP 2001-200330 A JP 2002-348634 A

  The present invention has been made in consideration of such circumstances, and has both a Young's modulus and a vibration damping capability, both of which have been problems of the prior art, while being able to further improve the vibration damping capability and excellent in a high Young's modulus and vibration damping capability. An object is to provide cast iron with high rigidity and high damping capacity. Specifically, the present invention provides a high-rigidity and high-damping capacity cast iron having a Young's modulus comparable to that of conventionally used flake graphite cast iron having an excellent vibration-damping capacity and significantly superior vibration-damping capacity. The purpose is to do.

The high-rigidity and high-damping capacity cast iron according to the present invention (first invention) is cast iron containing Al: 3 to 7%, and is obtained by heating at 280 to 630 ° C. after casting and further cooling treatment. Features. More specifically, the first invention includes Al: 3-7%, Mn: 0.25-1.0%, P: 0.04% or less, S: 0.03% or less, Ri Do the balance C, Si, Fe and unavoidable impurities, is cast iron is from 3.30 to 3.95 carbon equivalent represented by the following formula (1), and heated at 280 to 630 ° C. after casting, cooled further processing It is characterized by being obtained.
Carbon equivalent (%) = C amount (%) + (1/3) × Si amount (%) (1)

Moreover, the highly rigid high damping capacity cast iron which concerns on this invention (2nd invention) is cast iron containing Al: 3-7% and Sn: 0.03-0.20%, 280-630 after casting It is obtained by heating at 0 ° C. and further cooling treatment. More specifically, the second invention includes Al: 3-7%, Mn: 0.25-1.0%, P: 0.04% or less, S: 0.03% or less, Sn: 0.03 to 0.20%, balance C, Fe, and cast iron composed of unavoidable impurities, characterized by being obtained by heating at 280 to 630 ° C. and further cooling.

Furthermore, the high-rigidity and high-damping capacity cast iron according to the present invention (the third invention) includes C and Si having a carbon equivalent of 3.30 to 3.95 shown in the following formula (1), and Al: 3 to 7%. It is characterized by being obtained by heating at 280 to 630 ° C. after casting and further cooling treatment.
Carbon equivalent (%) = C amount (%) + (1/3) × Si amount (%) (1)
More specifically, the third invention relates to C and Si in which the carbon equivalent shown in the above formula (1) is 3.30 to 3.95, Al: 3 to 7%, and Mn: 0.25. -1.0%, P: 0.04% or less, S: 0.03% or less, Sn: 0.03-0.20%, balance iron and inevitable impurities cast iron, It is characterized by being obtained by heating at 280 to 630 ° C. and further cooling.

  According to the present invention, it is possible to obtain a high-rigidity and high-damping capacity cast iron excellent in Young's modulus and vibration damping ability that can further improve the vibration damping capacity while making the Young's modulus and vibration damping capacity compatible. Specifically, it is possible to obtain a high-rigidity, high-damping capacity cast iron having a Young's modulus comparable to that of conventionally used flake graphite cast iron having excellent vibration-damping capacity and significantly superior vibration-damping capacity.

Hereinafter, the present invention will be described in more detail.
In order to solve the above-described problems of Patent Documents 1 to 3, the present inventors have proposed a high-rigidity steel damping capacity cast iron that previously disclosed the relationship between the carbon equivalent, the C content, and the Si content (Japanese Patent Application No. 2007- 33894). However, in the case of this patent, it has been found that sufficient attenuation performance cannot be obtained.

For these reasons, the present inventors have made further improvements to find out the present invention.
In flake graphite cast iron (high rigidity and high damping capacity cast iron), the vibration damping capacity is improved with the addition amount of Al (aluminum), but the limit appears. For example, when the addition amount of Al is sequentially increased and the vibration damping ability and Young's modulus are measured, the improvement is seen from the addition of 3% Al, but when it exceeds 7%, the vibration damping ability is rather lowered. However, the present inventors have found out that Young's modulus and vibration damping ability are improved by adding an appropriate amount of tin (Sn) to flake graphite cast iron to which Al is added. Furthermore, the present inventors have also clarified that the vibration damping capacity and Young's modulus vary greatly depending on the adjustment of the addition amount of carbon equivalent (CE) , Al, and Sn in flake graphite cast iron. In order to improve the vibration damping capacity while maintaining the Young's modulus, C.I. E. , Al, and Sn need to be properly adjusted.

  In the present invention, Al is defined as 3 to 7% for the following reason. That is, in flake graphite cast iron to which Al and Sn are added, the addition amount of Al has a favorable effect on the vibration damping capacity from 3%, and when it is less than 3%, almost no improvement effect is recognized. Moreover, when it becomes 6% or more, the vibration damping capacity gradually decreases, and when it exceeds 7%, the vibration damping capacity further decreases. And if the addition amount of Al exceeds 7%, the iron Al carbide formed by the addition of Al becomes hard and brittle, so that it becomes easy to crack and the workability deteriorates. For these reasons, the appropriate addition amount of Al is set to 3 to 7%.

  Regarding the mechanism for improving the vibration damping capacity of flake graphite cast iron by the addition of Al, there are two theories (the former) that are based on the formation of iron alloys in which Al is dissolved, and the latter (the latter) that is based on the formation of iron Al carbides. There is, however, the latter theory in our study. Both theories are the same in that they are presumed to be due to the ferromagnetic damping mechanism of these formed substances.

  In the present invention, Sn is defined as 0.03 to 0.2% for the following reason. That is, if the amount of Sn added is too small, the effect of improving the Young's modulus and vibration damping ability is not recognized. The effect is shown to improve the Young's modulus and vibration damping capacity from about 0.03%, and the most remarkable effect is shown at around 0.08%. When the amount of Sn added is increased, the effect is gradually reduced, and when it is 0.2% or more, the effect is greatly reduced and the improvement effect cannot be obtained. Therefore, 0.03 to 0.2% is an appropriate value for the addition amount of Sn. Sn is an important additive element because it improves not only the Young's modulus and vibration damping capacity but also the tensile strength.

  Although there are various theories about the mechanism of the improvement effect by adding Sn, it can be considered as follows. That is, when Al is added to flake graphite cast iron, iron Al carbide is said to be formed by the reaction of iron, Al and carbon. Further, iron Al carbide is a ferromagnetic material, and is said to exhibit a ferromagnetic vibration damping mechanism. According to the study by the present inventors, if the amount of Al added is increased, the iron Al carbide increases, but the iron Al carbide does not increase at about 6%. However, it is considered that when Sn is added, more iron Al carbides are always formed as compared with the addition of Al alone, and as a result, the improvement effect due to the addition of Sn appears.

In the present invention, the high-rigidity and high-damping capacity cast iron of the present invention contains C, Si, Mn, P, S and the like in addition to the above Al and Sn. Here, the amounts of C and Si are as described in detail later.
Mn is 0.25 to 1.0% as in the case of ordinary flake graphite cast iron. The reason is that if Mn is 0.25% or more, the strength and hardness of cast iron increase, but if it exceeds 1.0%, cast iron is chilled and hardened and brittle.

P is set to 0.04% or less as in the case of ordinary flake graphite cast iron. The reason for this is that when P exceeds 0.04%, it reacts with iron to form a steadite, which is a hard compound, and makes cast iron brittle.
S is 0.03% or less as in the case of ordinary flake graphite cast iron. The reason for this is that if S exceeds 0.03%, the fluidity of the molten metal is deteriorated and the cast iron is chilled to be hard and brittle.

  In the third invention, the carbon equivalent shown in the formula (1) is 3.30 to 3.95% as described above. When the carbon equivalent is increased, the vibration damping ability is improved and the Young's modulus is lowered. The increase or decrease of the carbon equivalent cannot achieve both, but the influence on vibration damping capacity and Young's modulus is large, so an appropriate value is required. When Al is added, the eutectic composition at which the eutectic reaction between austenite and graphite changes as compared with conventional flake graphite cast iron. Conventional flake graphite cast iron causes a eutectic reaction when the carbon equivalent represented by the above formula 1 is 4.3%, but when Al is added, the eutectic reaction occurs at a value smaller than this value. . A carbon equivalent larger than the eutectic composition is not preferable because it becomes hypereutectic and the Young's modulus is greatly reduced.

In the case of the present invention, if the carbon equivalent (CE) exceeds 3.95%, the vibration damping ability is greatly improved, but the Young's modulus is greatly reduced. This is thought to be because the carbon equivalent exceeds the eutectic composition and becomes hypereutectic. On the other hand, when the carbon equivalent is small, the Young's modulus is improved because the amount of graphite formed is reduced. However, since the vibration damping ability is reduced, a carbon equivalent of 3.3% or more is required. Therefore, the carbon equivalent was 3.30-3.90.
In the present invention, the heat treatment temperature after casting is 280 to 630 ° C. The performance improvement by the heating / cooling process varies greatly depending on the heating temperature. The effect of this heat treatment is shown in FIG. In addition, although FIG. 1 showed the case of the invention material which added Al and Sn, the same tendency was shown also when only Al was added. If the heat treatment temperature is less than 280 ° C., the effect is small, and if it exceeds 630 ° C., the effect is similarly small.

  That is, it is preferable to cool after heat treatment at a temperature range of 280 to 630 ° C. in which the improvement rate of the damping performance is 5% or more. The temperature range in which the effect is improved to 20% or more is 360 to 580 ° C. Although a high effect appears in these temperature ranges, the most effective case is when heated to 500 ° C. and cooled. The cooling method may be either furnace cooling or air cooling. The reason why the damping performance is improved by the heat treatment is unknown.

  The process of heat-treatment changes with processes after the casting of the cast product according to the present invention. For example, when using as it is after casting, it heat-processes after casting. Further, for example, when used after being machined after casting and finished to a predetermined size, it is most preferable to perform heat treatment after machining. However, if there is a reason why heat treatment cannot be performed after machining, heat treatment may be performed before machining.

Next, specific examples of the present invention will be described together with comparative examples.
(Examples 1-8 and Comparative Examples 1-8)
First, the composition of cast iron was adjusted using a high-frequency melting furnace. Next, cast iron ingot, carburized material, ferromanganese, and silicon carbide produced with FC300 are put into a graphite crucible and dissolved, and then the amount of carbon and silicon are adjusted with ferrosilicon and the carburized material, and the dissolved amount is about 20 kg. It was. However, the Al amount of the obtained casting was adjusted by adding ferroaluminum and the tin amount by adding pure tin. The dissolution temperature was about 1450 ° C. After adding the Ca-Si-Ba-based inoculant before pouring, it was cast into a furan self-hardening mold of φ30 × 300 mm.

The obtained casting was processed to 4 × 20 × 200 mm, and the logarithmic damping factor and dynamic Young's modulus were obtained as evaluation values of vibration damping ability. At this time, a comparison was made with one that was not heat-treated. That is, in Examples 1-8, Al-added cast iron was heat-treated, and in Comparative Examples 1-8, Al-added cast iron was not heat-treated. The test method was based on JISG0602. That is, the test piece was hung at two points to give a strain amplitude of 1 × 10 ⁻⁴ with an electromagnetic vibrator, and thereafter the vibration was stopped and free attenuation was performed to obtain a logarithmic attenuation factor and a dynamic Young's modulus. The properties of the cast product thus obtained are shown in Table 1 below. However, the logarithmic attenuation rate showed a value when the strain amplitude of vibration was 1 × 10 ⁻⁴ . Although P and S were not shown in Table 1, both P <0.025 and S <0.020. Moreover, although there exists the thing of the same composition in an Example, these mean that melt | dissolution is the same and a cast sample differs.

  Of the data shown in Table 1, a graph showing the relationship between the Young's modulus and the logarithmic decay rate of each sample is shown in FIG. When the Young's modulus and the logarithmic decay rate are evaluated at the same time, it is easy to understand when compared in FIG. The values of Young's modulus and logarithmic decay rate of each sample vary, but the average value is represented by a straight line. In FIG. 2, line a represents data of Examples 1 to 8, and line b represents data of Comparative Examples 1 to 8. The Young's modulus of the above data is in the range of 115 to 130 GPa because the Young's modulus is about 120 GPa when the vibration damping performance is emphasized in FC250 and FC300 of current cast iron. The data of the range was published in.

From FIG. 2, the performance improvement of about 40% is recognized in the present invention in which the heat treatment is performed with respect to the Young's modulus-logarithmic decay characteristics of Comparative Examples 1 to 8 (when heat treatment is not performed). This value shows a performance of about 2.5 to 3.0 times or more as compared with the characteristics of the cast irons FC250 and FC300 (the logarithmic decay rate when the Young's modulus is 120 PGa is about 100 × 10 ⁻⁴ ).

(Examples 9-16 and Comparative Examples 9-16)
The same operations as in Examples 1 to 8 and Comparative Examples 1 to 8 were used to cast a furan self-hardening mold of φ30 × 300 mm.
The obtained casting was processed to 4 × 20 × 200 mm, and the logarithmic damping factor and dynamic Young's modulus were obtained as evaluation values of vibration damping ability. At this time, a comparison was made with one that was not heat-treated. That is, in Examples 9 to 16, Al and Sn-added cast iron was heat-treated, and in Comparative Examples 9 to 16 Al and Sn-added cast iron were not heat-treated. The test method was based on JISG0602. That is, the test piece was hung at two points to give a strain amplitude of 1 × 10 ⁻⁴ with an electromagnetic vibrator, and thereafter the vibration was stopped and free attenuation was performed to obtain a logarithmic attenuation factor and a dynamic Young's modulus. The properties of the cast product thus obtained are shown in Table 2 below. However, the logarithmic attenuation rate showed a value when the strain amplitude of vibration was 1 × 10 ⁻⁴ . Although P and S were not shown in Table 2, both P <0.025 and S <0.020. Moreover, although there exists the thing of the same composition in an Example, these mean that melt | dissolution is the same and a cast sample differs.

  Of the data shown in Table 2, a graph showing the relationship between the Young's modulus and the logarithmic decay rate of each sample is shown in FIG. When the Young's modulus and the logarithmic decay rate are evaluated at the same time, it is easier to understand when compared in FIG. The values of Young's modulus and logarithmic decay rate of each sample vary, but the average value is represented by a straight line. In FIG. 3, line a represents data of Examples 9 to 16, and line b represents data of Comparative Examples 8 to 16. The Young's modulus of the above data is in the range of 115 to 130 GPa because the Young's modulus is about 120 GPa when the vibration damping performance is emphasized in FC250 and FC300 of current cast iron. The data of the range was published in.

From FIG. 3, the performance improvement of about 30% is recognized in the present invention in which the heat treatment is applied to the Young's modulus-logarithmic decay characteristics of Comparative Examples 9 to 16 (in the case where heat treatment is not performed). This value shows about 3.5 times the performance compared with the characteristics of the cast irons FC250 and FC300 (the logarithmic decay rate when the Young's modulus is 120 PGa is about 100 × 10 ⁻⁴ ).

  The present invention is not limited to the above-described embodiment as it is, and is embodied by appropriately changing the composition of Al, Sn, C, Si, Mn, P, S, etc. within the scope not departing from the gist of the invention. it can. Moreover, various inventions can be formed by appropriately combining a plurality of compositions disclosed in the embodiment.

FIG. 1 is a characteristic diagram showing the relationship between the heat treatment temperature and the improvement rate of the damping performance. FIG. 2 is a characteristic diagram showing the relationship between the Young's modulus and logarithmic decay rate of Al-added flake graphite cast iron. FIG. 3 is a characteristic diagram showing the relationship between the Young's modulus and the logarithmic decay rate of Al, Sn-added flake graphite cast iron.

Claims (2)

Al: 3-7%, Mn: 0.25-1.0%, P: 0.04% or less, S: 0.03% or less, balance C, Si, Fe and unavoidable impurities In addition, it is cast iron having a carbon equivalent of 3.30 to 3.95 shown in the following formula (1), and is obtained by heating at 280 to 630 ° C. after casting and further cooling treatment. Damping capacity cast iron.
Carbon equivalent (%) = C amount (%) + (1/3) × Si amount (%) (1) C and Si in which the carbon equivalent shown in the following formula (1) is 3.30 to 3.95, Al: 3 to 7%, Mn: 0.25 to 1.0%, and P: 0.04% Below, S: 0.03% or less, Sn: 0.03 to 0.20%, cast iron composed of the balance Fe and inevitable impurities, heated at 280-630 ° C. after casting, and further subjected to cooling treatment High rigidity, high damping capacity cast iron
Carbon equivalent (%) = C amount (%) + (1/3) × Si amount (%) (1)

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