WO2006109919A1

WO2006109919A1 - High-strength damping alloys and low-noise diamond saw using the same

Info

Publication number: WO2006109919A1
Application number: PCT/KR2005/004231
Authority: WO
Inventors: Kwang Koo Jee; Yoon Bae Kim; Jun Hyun Han
Original assignee: Korea Institute Of Science And Technology
Priority date: 2005-04-11
Filing date: 2005-12-10
Publication date: 2006-10-19

Abstract

High-strength clamping alloys and a low-noise diamond saw using the same are provided. Preferable types of alloys, compositions and processing amounts to be applied to a shank of the diamond saw are suggested. The shank of a welded type diamond saw is increased in hardness by adding 14 to 28% by weight of Mn to Fe and cold-rolling them within the range of 2 to 25%. As a result, the hardness is increased to a standard value (HRC35) and above, and the noise reduction effect has been significantly increased. The shank of a sintered type diamond saw is increased in strength by adding 10 to 28% by weight of Mn to Fe, followed by heat-treating them. The mechanical performance can be further increased by cold-working the shank to by 20% or more prior to sintering.

Description

HIGH-STRENGTH DAMPING ALLOYS AND LOW-NOISE DIAMOND SAW

USING THE SAME

TECHNICAL FIELD

The present invention relates to high-strength damping alloys and a low- noise diamond saw using the same.

BACKGROUND ART As shown in FIG.1 , a diamond saw used for cutting concrete and asphalt at construction sites and road construction sites is prepared by bonding a diamond blade 1 to a shank 20 made of cold-rolled carbon steel.

A diamond saw may be classified into a welded type and a sintered type according to the method of bonding a diamond blade to a shank. Regarding the welded type, a diamond blade is manufactured by mixing metal powder and diamond powder followed by molding and sintering the mixture in a blade form, and the diamond blade is bonded to a shank by laser-welding or brazing, thereby preparing a diamond saw. The welded-type shank is made by quenching carbon steel and then tempering it, and has an excellent strength of about HRC35 of hardness. That is, the sintering of powder and the heat treatment manufacturing of a shank are separately performed, which enables it to manufacture a shank with an excellent strength.

Meanwhile, regarding the sintered type, a shank and a diamond blade are manufactured in an integral form by putting a disk shank into a molding die and charging a mixture of metal powder and diamond powder at the upper and lower sides of the outer periphery of the shank and molding it, and the shank and the diamond blade are bonded by sintering them. The sintered-type diamond saw is manufactured by sintering the shank and the diamond blade for one hour at a temperature of 750 to 850 ⁰C and slowly cooling them. The sintered type has a low strength because of the heating and the slow cooling. When cutting rocks, concrete or the like by using a diamond saw, an immense noise is generated due to the vibration of the shank. In recent years, there is also a growing trend to make it compulsory to use a low-noise diamond saw in Korea. In developed countries, a low-noise diamond saw is already in general use in construction and road construction sites, and thus the demand for the use thereof is increasing. Shank material currently used for a low-noise diamond saw is the so- called sandwich type made by inserting a thin copper plate between two carbon steel plates and spot-welding it, which is configured to reduce noise by absorbing vibration by interference or friction between each metal plate. The low-noise sandwich-type shank is four times higher in price than a general carbon steel shank, but has a lower strength than that of a general carbon steel shank, and thus, it is bent at the time of cutting work, thereby resulting in many restrictions in use.

Meanwhile, representative damping alloys developed until now include the ferromagnetic type such as Fe-Cr-Al, Fe-Al-Si, etc., cast-iron alloys such as Fe-C- Si, the dislocation type such as Mg alloys, and the twin type such as Mn-Cu, Cu- Al-Ni and Ni-Ti alloys. The ferromagnetic alloys with high vibration damping properties are mostly used in a completely annealed state, and therefore, their hardness as low as less than HRC20. If cold working is performed in order to increase the hardness, the magnetic domains are saturated even with a very little deformation of about 1 to 2%, thus the vibration damping properties are lost, thereby eliminating the low-noise effect. Not only that the cast-iron alloys cannot be processed but also they have a low impact value, and therefore, it is difficult to apply them. It is also difficult to utilize the Mg alloys since they also have a low hardness. The twin type is expensive because a nonferrous metal is used and has a low yield strength of 100 to 150 MPa, because it is deformed by movement of twin boundaries, whereby it can easily deformed, and therefore, it is difficult to apply it to be used as a shank.

Therefore, there is a growing demand for alloys that have a high strength and an excellent vibration damping properties such that they can be applied to a diamond saw or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG.1 is a photograph of a diamond saw for cutting rocks; FIG.2 is a phase diagram showing the fraction of each phase produced at an ambient temperature when Fe-Mn alloys are cooled in the air at 1000⁰C ; FIG.3 is an X-ray diffraction patterns caused by a degree of cold-rolling of

FE-13Mn alloys;

FIG.4 is an X-ray diffraction patterns caused by a degree of cold-rolling of FE-18Mn alloys;

FIG.5 is a graph showing changes in hardness caused by an amount of cold-rolling of Fe-13Mn alloys and of Fe-18Mn alloys;

FIG.6 is a graph showing changes in logarithmic decrement caused by an amount of cold-rolling of Fe-13Mn alloys and of Fe-18Mn alloys;

FIG.7 is an optical micrograph of a structure of Fe-19Mn alloys, which is a photograph of a structure obtained when heated for one hour at (a) 700 ^°C , (b) 800⁰C , (c) 900⁰C and (d) 1000⁰C , respectively, after cold-rolling by 30%; FIG.8 shows the specific damping capacity of Fe-19Mn alloys by condition.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to solve the problems with conventional diamond saws of high prices and low efficiency. Another object of the present invention is to provide a new alloy material with an excellent strength and superior noise reduction effect and a method for manufacturing the same.

Yet another object of the present invention is to provide a new diamond saw which has an excellent strength and reduced noise that can be produced at a low cost.

Unlike the high-priced shanks with low-efficiency, low-noise diamond saw which can be manufactured through a simple structural alteration, the present invention uses high-damping alloys that can self-absorb vibration and the so- called material damping, whereby vibration is absorbed by friction between fine phase boundaries of the material.

According to a first embodiment of the present invention, there is provided high-strength damping alloys which are obtained by cold-working iron alloys containing Mn within the range of 14wt% to 28wt% at a reduction rate of 2 to 25%. These iron alloys exhibit only γ -> ε transformation without α phase. The cold working amount is limited to the above range, because the effect is too slight when the amount is 2% or less and the vibration absorption performance is reduced significantly when the amount is 25% or more. In order to improve corrosion resistance, the iron alloys may additionally include at least one material selected from Ni, Cr and Si within the range of more than 0% by weight but not more than 10% by weight. The present invention provides a low-noise diamond saw comprising a shank for a diamond saw manufactured by the use of these iron alloys and a diamond blade welded on the outer periphery of the shank.

According to a second embodiment of the present invention, high-damping alloys that improve strength and reduces noise is provided by heat-treating iron alloys containing Mn within the range of 10wt% to 28wt% and including a ε martensite phase on a γ matrix. The present invention provides a low-noise diamond saw which is made by sintering and bonding a shank of a diamond saw manufactured by using these high-damping iron alloys with a diamond blade that is molded on the outer periphery of the shank. By making crystal grains finer by cold-working the shank by 20% or more prior to sintering the shank, the strength can be further improved.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

In the present invention, Fe-Mn alloys showing a shape memory effect by a nonthermoelastic martensitic transformation were selected and analyzed. In the Fe-Mn alloys, when an external deformation is applied, ε martensite of hep structure is produced on a γ phase of fee structure, and at the time of heating, ε is reversely transformed to γ, thereby exhibiting a shape memory effect. That is, the

Fe-Mn alloys show excellent vibration damping properties by absorbing vibration by the movement of the martensite phase boundary as well as by a change in interatomic distance at the time of elastic deformation.

The transformation behavior of Fe-Mn alloys can be divided into four phases based on the increase of Mn content: γ -> α (Mn: 10% or less), γ -> ε -> α (Mn: 10 to 14%), γ -> ε (Mn: 14 to 27%) and γ (no transformation occurs at a Mn content of 27% or more). As a result, each phase exists at a room temperature as shown in FIG.2. γ is the mother phase of fee structure, α is the martensite phase of bcc structure, and ε is a martensite phase of hep structure. Since the vibration damping properties of Fe-Mn alloys are brought out by γ/ε phase phase boundary, only the compositions causing γ -> ε -> α and γ -> ε transformations show vibration damping properties. The alloys causing the γ -_> ε -> α transformation have a microstructure where ε and α martensites are mixed with γ mother phase at room temperature. The alloys causing the γ -> ε transformation, ε martensite is mixed with γ mother phase at room temperature.

The present invention provides damping alloys, which can be applied to shanks of the welded-type and the sintered-type diamond saws by the use of the transformation behavior of Fe-Mn alloys and a diamond saw using the same. Hereinafter, the present invention is described in more detail through an embodiment.

THE FABRICATION OF SHANK OF A WELDED-TYPE DIAMOND SAW The shank of a welded-type diamond saw requires hardness, an impact value and weldability. The hardness is required to be HRC35 or greater. When the hardness is low, the saw is bent at the time of cutting work, and this deteriorates the cutting performance and causes safety problems. In addition, a toughness with an impact value of 100 J/cm² or greater is required, and there should be no problem in welding a diamond blade. In the present invention, alloy materials and process conditions applicable to a shank were selected by choosing the alloys that cause γ -> ε -> α transformation and the alloys that causes γ -> ε transformation, and thereby analyzing the hardness properties and the vibration absorption performance.

As for the alloys that causes γ -> ε -> α transformation, Fe-13Mn alloys (in one embodiment, it was confirmed that the final Mn component is 13.1 % by weight due to a loss caused by oxidation during melting even after 16% by weight Mn was added in the final manufacturing step) were selected, and as the alloys causing γ -> ε transformation, Fe-18Mn alloys (in the one embodiment, it was confirmed that 22% by weight Mn was added in the final manufacturing step and the final Mn component is 17.8% by weight due to a loss caused by oxidation during melting) were selected.

FIGs.3 and 4 are X-ray diffraction patterns caused by a degree of cold- rolling of Fe-13Mn alloys and of Fe-18Mn alloys, respectively. The Fe-13Mn alloys are composed of ε martensite phase and a small amount of α martensite phase on a mother phase prior to cold-rolling. When cold-working was performed, γ -> ε -> α transformation occurred, and thereby leaving only the α martensite phase. As shown in FIG. 4, in the Fe-18Mn alloys, as γ -> ε transformation occurs by rolling processing, the ε martensite phase increases but no α martensite phase is produced, because the α phase is not stable as shown in the phase diagram of FIG. 2. FIG. 5 shows hardness values based on the amount of cold-rolling of Fe-

13Mn alloys and of Fe-18Mn alloys. The two alloys are both similar in hardness (HRC 28 to HRC 29) and are below a standard value prior to cold-rolling. In the Fe-13Mn alloys, α martensite phase is produced by processing, and excellent in processability. Thus, the strain hardening is not strong. For the hardness to reach a required value, HRC35, as shown in FIG. 5, cold-working of about 40% is required. In contrast, the Fe-18Mn alloys that produce only ε martensitic phase is very rapid in strain hardening, thus the hardness exceeds HRC 35 even with cold- working of about 5%. This is because the ε martensite phase is not capable of plastic deformation unlike the α phase.

FIG. 6 shows a vibration damping performance caused by the amount of cold-rolling of Fe-13Mn alloys and of Fe-18Mn alloys. The vibration damping performance was evaluated in the following method. At the time of free vibration, n-th and n+1-th amplitudes (amount of strain or strain) are denoted by y_n and y_n+i, respectively, the logarithmic decrement becomes ln(y_n/y_n+i). The logarithmic decrement depends on the amplitude. In most cases, when the amplitude becomes larger, the logarithmic decrement increases. In general, it is known that if noise is loud like that of the shank, vibration occurs with a strain amplitude of 2 to 4 x 10^"4. Thus, measurement was performed at 3 x 10^"4, and the result of which is shown in FIG. 6.

Even before rolling or during cold working, it is seen that Fe-13Mn is somewhat more excellent than Fe-18Mn. It can be known that both of the two alloys slightly increase in absorption performance and then gradually decrease during 5% processing. As shown in FIG.5, in order for the hardness to be HRC 35 or greater, cold working of about 40% is required for Fe-13Mn alloys. If the cold working of 40% is performed, the vibration damping performance is greatly decreased. Once the rolling of about 40% is performed, the alloys are mostly comprised of α phase. That is, the alloys causing γ -> ε -> α transformation requires a high cold working in order to increase the hardness, and as a result, the vibration damping performance is greatly decreased and it is difficult to expect a low-noise effect. The Fe-18Mn alloys have a unique property of easily obtaining HRC 35 hardness even at a low level processing of about 5% because they are strain-hardened to a great degree. The processing of about 5% rather increases the vibration damping properties and improves the low-noise effect. Thus, the Fe-18Mn alloys are very suitable for application to products requiring a hardness such as a diamond saw.

Putting the above results together, the Fe-Mn alloys which cause γ -> ε transformation to increase ε martensite phase but produce no α phase are appropriate to be used for the shank of the welded type diamond saw, and the boundary value of the Mn content is 14% by weight.

Meanwhile, in order to evaluate mechanical properties and low-noise effect, three types of samples were prepared. Three types of alloys, including SCM435, an existing material, Fe-13Mn and Fe-18Mn, were prepared to measure hardness, impact value and weldability. The Fe-13Mn and Fe-18Mn alloys were melted and made into an ingot. They were heated for one hour at 1000⁰C , and then hot rolling was performed. After the hot rolling, air cooling was performed at room temperature. Under room temperature (available at a temperature of 200 V or less), the Fe-13Mn alloys were cold-worked by 40%, and the Fe-18Mn alloys were cold-worked by 5%. This is to set the hardness to a required value of HRC 35 or greater. In addition to the purpose of a mechanical testing, this plate material was made into a shank, a diamond blade was welded thereto, and noise was measured at a 1m distance while actually cutting rocks.

[Table 1] Comparison of Mechanical Properties and Low-Noise Effect

According to Table 1 , it can be seen that the hardness, impact value and weldability of the three types of materials conform to the standards. But, it was shown that the low-noise effect of Fe-13Mn was not much but that of Fe-18Mn was very excellent.

SHANK OF SINTERED-TYPE DIAMOND SAW

A shank of sintered type diamond saw is heated at a sintering temperature, so it is difficult to expect a hardening effect caused by cold working, and the cooling speed after sintering is low. Therefore, it is difficult to obtain a quenching effect and the hardness is low. Thus, the shank is bent at the time of cutting work, and this deteriorates the cutting performance and causes a safety hazard. That is, the shank has to be heated for sintering, and it is difficult to perform rapid cooling after sintering, thus a strain hardening effect or martensitic hardening cannot be used. In the present invention, as a novel method for hardening in the alloys for the shank of the sintered type diamond saw, and also as a method not using cold working but available even if the cooling speed is low, ε martensite phase is used. The ε martensite phase is stably produced even if the cooling speed is low, and does not deform by itself. Accordingly, it can contribute to the hardening of metals like composite materials.

The shank of the sintered type diamond saw can be manufactured within the content range of 10 to 28% by weight which is a Mn content range wherein ε martensite phase is produced in FIG. 2.

In an example, Fe-19Mn alloys were induced to melt in the air, and then were homogenized for two hours at 1100⁰C and hot-rolled. As a result of measuring a crystal grain size after the hot rolling, the crystal grains were about 102 μm and no longer increased in size even after they were heated later for one hour at a sintering temperature of 700 to 900⁰C . The yield strength was about 330 MPa.

To increase the yield strength, a hot-rolled plate material was cold rolled by 30%, and thereafter heated for one hour at 700, 800, 900 and 1000⁰C , respectively, and air-cooled at room temperature. At the time of air cooling, ε starts to be produced at 150^°C , and continues to be produced until 90 ^°C . FIG. 7 is a photograph of a structure observed at room temperature, which is obtained when heated for one hour at (a) 700 ^°C, (b) 800 ^°C, (c) 900⁰C and (d) 1000^°C, respectively. The bright plate material is ε martensite phase. The higher the heat treatment temperature, the greater the amount of ε martensite phase is, and as predicted, it was clear that the crystal grains increased in size.

The following Table 2 shows the effect of a heat treatment temperature on crystal grain size and yield strength. The higher the heating temperature, the greater the yield strength is. If the sintering temperature is 750 to 850 ^°C , the yield strength is 430 to 460 MPa, which exceeds three times the yield strength of 140MPa of SK5.

[Table 2] Crystal Grain Size and Yield Strength by Condition

FIG. 8 shows the specific damping capacity(SDC) of a Fe-19Mn alloy sample and of SK5 as a comparative material. The vibration damping performance was evaluated by the following method. At the time of free vibration, n^th and n+1^th amplitudes (amount of strain or strain) are denoted by y_n and y_n+i, respectively, the specific damping capacity (SDC) becomes ((yn)²-(yn+i)²)/(yn)². and indicates the ratio of energy damped in the vibration of one cycle. The specific damping capacity depends on the amplitude. In case of martensitic alloys, if the amplitude becomes larger, the specific damping capacity increases. While SK5 alloys have almost no vibration absorption performance, Fe-Mn alloys show an excellent vibration absorption performance. It is found as a result that the Fe-Mn alloys provide strength and vibration absorption performance by ε in γ matrix. To measure mechanical properties and low-noise effect, a shank with a 1.9mm thickness and a 200mm diameter was prepared by using a plate material obtained by cold-working of the Fe-19Mn alloys by 30% and a SK5 plate material. Copper and bronze metal powder and diamond metal powder were mixed, charged at the outer periphery of the shank, molded, heated for one hour at 850 ^°C , and were sintered. Noise was measured from a 1 m distance while actually cutting rocks by these two types of diamond cutters. Table 3 compares noise and yield strength. [Table 3] Result of Yield Strength and Noise Testing

It can be seen that the diamond saw using high-strength damping alloys according to the present invention have significantly superior strength and low- noise effect.

As described above, in the present invention, high-strength alloys with excellent mechanical performance and low-noise effect are applicable to a shank by controlling the compositions of alloy, the amount of cold-working and so forth. Therefore, it is possible to manufacture a low-priced diamond saw with excellent vibration damping properties and strength.

Claims

1. High-strength damping alloys that cause ε martensitic transformation by cold-working iron alloys containing Mn within the range of 14wt% to 28wt% at a reduction rate of 2 to 25%.

2. The high-strength damping alloys of claim 1 , wherein the iron alloys additionally comprising at least one selected from Ni, Cr and Si within the range of over 0wt% but not more than 10wt%.

3. A low-noise diamond saw comprising a shank for a diamond saw manufactured using iron alloys that cause ε martensitic transformation by cold- working iron alloys containing Mn within the range of 14wt% to 28wt% at a reduction rate of 2 to 25%; and a diamond blade welded on the outer periphery of the shank.

4. High-strength damping alloys that improve strength by heat- treating iron alloys containing Mn within the range of 10wt% to 28wt% and including a ε martensite phase on a γ matrix.

5. A low-noise diamond saw comprising a shank for a diamond saw manufactured from iron alloys that improves strength by heat-treating iron alloys containing Mn within the range of 10wt% to 28wt% and including a ε martensite phase on a γ matrix; and a diamond blade welded on the outer periphery of the shank, wherein the shank and the blade are bonded by sintering.

6. The low-noise diamond saw of claim 5, wherein the strength can be further improved by making crystal grains fine by cold-working the shank by 20% or more prior to sintering the shank.