The present invention provides an alloy having excellent corrosion resistance and strength by improving insufficient such properties, which are problems of conventional hard particle-based abrasive wheels comprising a binder alloyed from cobalt and copper.

PRIOR ART Typically, hard particle powders are mixed with cobalt or copper powders, and sintered in a liquid sintering manner at a high temperature of about 1400-1550 °C according to particle sizes and composition of the powder, or in a solid sintering manner or a electro-pressure sintering manner at a low temperature of about 900 °C.

Such liquid reaction of the binder metal and hard particles is effectively used to decrease porosity and improve density, but suffers from the disadvantage of graphitization of diamond particles due to heating at a high temperature.

A cobalt element that is widely used as a binder material, can have, depending on the added elements, a tensile strength of 250-700 MPa which is in a broader range than other metal elements, and has excellent wettability with hard particles, such as carbides or nitrides. Cobalt of HRA 90-92 is added in the amount of 6-12 wt% for sintering, depending on a necessary hardness and toughness.

The cobalt element has the advantage of high hardness but is disadvantageous due to low toughness. Hence, in the case of being subjected to

wear under heavy impact and severe conditions as in the abrasive wheel, cobalt is added in an amount of up to 70-90 %.

As such, there are problems, such as lowering of durability and easy separation of diamond or tungsten carbide particles with a decrease of hardness to HRA 20. Moreover, because cobalt low in corrosion resistance is easily oxidized by friction heat generated during abrasion or cutting and oxygen in the atmosphere, there are problems with durability.

In this regard, U. S. Pat. No. 4,018,576 discloses a diamond abrasive tool by brazing diamond crystals on a thin metal substrate with the use of a nickel-cobalt alloy comprising up to 12 wt% of boron, silicon and chromium. But this patent has the disadvantage of very high material cost due to expensive nickel-cobalt containing more than 60 wt%.

In U. S. Pat. No. 6,056,795, there is provided a technique for adding hardening elements, such as molybdenum, tungsten, rhenium, etc., to a nickel-tin alloy. However, such an alloy is low in hardness and durability, regardless of containing a quantity of expensive elements.

As a basic solution for poor wettability, sintered strength and durability, an alloy composition having excellent corrosion resistance and high strength is used.

However, sintered alloys with more excellent wettability than cobalt are rare, and there are other drawbacks, such as intricate sintering processes and poor wettability.

Therefore, a method for controlling physical properties by improving a sintering process has been practically used. For instance, through a pressurization sintering process, diamond particles are not deteriorated, and their spherical shape is maintained by prevention graphitization of diamond under pressure increased to 5 atm., affecting the energy of the system between a grain boundary and micro porosity. But a device is complicated since heating and pressurization are performed at the same time, and pressure has limitations due to use of a graphite mold. In addition, a forming and sintering process is performed at low temperature by use of high energy sources, such as plasma, laser, microwave. However, there are problems, including a double heating process, and expensive equipment and high

production cost.

DISCLOSURE OF THE INVENTION Therefore, it is an object of the present invention to solve the problems described above and to provide a high strength abrasive wheel blade comprising a binder alloy having a sintering temperature of 1400 °C or lower and hard particles mixed together and sintered, by use of conventional equipment, which is advantageous in terms of durability and wear resistance.

It is another object of the present invention to provide a method for preparing the abrasive wheel.

The present invention is characterized by a binder alloy powder for sintering which can be manufactured from a matrix material comprising a cobalt-belong to late transition metal elements and their alloy, having excellent wettability, high strength and low cost.

BEST MODES FOR CARRYING OUT THE INVENTION In the present invention, a binder alloy comprises 65-97 atomic% of transition metals, and more specifically, a binder alloy consists essentially of 6-35 atomic% of an early transition metal (hereinafter, referred to ETM), 45-90 atomic % of a late transition metal (hereinafter, referred to LTM), and 2-25 atomic % of a precipitation strengthening and stabilizing element selected from among elements of the Groups Ib, Ilb, mb, IVb and mixtures thereof, with inevitable impurities. Preferably, diamond or a hard deposit is added in the range of about 15-35 vol%, in order to obtain a suitable amount of hard deposit.

The ETM elements belong to the Rows ma, IVa, Va and VIa in the periodic table. In particular, chromium of the Group VIa, mainly used in the present invention, is advantageous in terms of high solid solubility for iron, cobalt, nickel among LTM elements of the Groups VIIa and VIM, and low cost. The

chromium solid solution forms borides and carbides, together with boron and carbon, and thus is desirable in terms of processibility and strength. The ETM elements, exclusive of chromium, are used for enhancing the effects of chromium.

Of them, molybdenum is formed to a complete solid solution, along with chromium, to reinforce a matrix structure and to stabilize borides and carbides.

However, because such elements have inferior solid solubility for LTM to chromium at room temperature, they are added in the total amount of up to 5 atomic %. In addition, other ETM elements, such as titanium, vanadium, zirconium, niobium, hafnium, tantalum, tungsten, lanthanide and actinide, are responsible for reinforcing the matrix and forming stable borides and carbides, and thus are highly resistant for fatigue wear, including spalling, pitting, chipping and heat checking. Further, these elements can restrain oxidation of LTM, and the Groups Ib, IIb, Eb and IVb during a sintering process and thus the amount of impurities and the extent of porosity are decreased. Although, if the total amount of ETM elements is less than 6 atomic %, sufficient strength and ductility are not ensured and an alloy with excellent wettability and a low melting point cannot be obtained. Meanwhile, if the amount exceeds 35 atomic %, these elements form excessive deposits, together with the elements of the mb and IVb groups, and thus the abrasive wheel becomes weak to impact.

The LTM elements play a role in strengthening the binder alloy and belong to the Groups VIIa and Vm. In the present invention, inexpensive and abundant iron is mainly used and the other LTM elements such as nickel, cobalt, etc. may be added to improve corrosion resistance and thermal resistance. The element nickel is cheaper than cobalt which is used for a conventional binder, and activates metals of high melting points, such as tungsten and molybdenum, thereby promoting a sintering process. Cobalt has excellent wettability to steel or ceramic, and improves heat resistance. So, if necessary, a small amount of cobalt is used.

Additionally, other LTM elements may be added as matrix elements. But such elements are expensive or low in solid solubility for chromium, and are thus used in small amounts.

In the present invention, when the amount of the LTM elements is less than 45 atomic %, it is difficult to obtain the ductility required for the abrasive wheel. On the other hand, when the amount exceeds 90 atomic %, matrix strength becomes poor and wear resistance is reduced.

The Groups Ib and Ilb are responsible for solid-solution hardening of the matrix of the binder alloy, and the Groups mb and IVb are responsible for forming and reinforcing the hard deposit. As elements of the Groups IIIb and IVb, boron and carbon are mainly used, and silicon and aluminum bear the responsibility of stabilizing boron and carbon compounds. With the total amount of these elements less than 2 atomic %, a matrix hardening effect is poor. Meanwhile, with the total amount more than 25 atomic %, brittleness increases.

A mixing ratio in the binder alloy is determined depending on a required hardness, in which hard particles are added to occupy about 15-35 volume% in the alloy, considering a specific gravity, so as to improve durability of a hard layer in a diamond wheel.

The inventive binder alloy with high surface energy is excellent in wettability with metals or ceramics, and suitable for a binder of hard ceramic particles. Because of such properties, the present binder alloy can be substituted for cobalt widely used as a conventional binder alloy. Thus, the sintered products using the present binder alloy have superior internal compression, heat resistance and corrosion resistance, and are applicable for wear resistant parts for engines, die punch, drawing dice, guides, bearings, processing tools and sintered binder materials for cutters.

In the Example as described below, which uses the binder alloy in a powder form, particle size, particle size distribution, shape, purity and surface condition affect quality of products. Therefore, with a view to obtaining fine particles with very uniform particle size, the binder alloy powder having the composition ratios presented in the present invention is prepared by a gas atomization method. Then, in consideration of compacting with hard particles, the powders for sintering should have a particle size of 45 urn or smaller. Use of

a binder alloy powder which has various particle sizes results in increase of density, strength and elastic limit of the formed products. If the particle size is excessively increased, density of sintered products becomes low. Hence, the particle size should only range up to 45 urn.

Meanwhile, as for the present binder alloy powder, a pre-alloyed powder is separately made and mixed, or a powder in a single metal state is mixed with the pre-alloyed powder on the basis of a composition ratio, to yield a desired alloy composition for a final sintering.

In the case that the hard particles having an average particle size larger than about 25.0, um are present, a crystal plane of a Miller index (001) turns into a cleavage plane and thus cracks parallel to the crystal plane are easily formed.

Moreover, in order to increase formability and density, hard particles are previously mixed with the binder alloy particles to make up to 15 wt%, and are formed. As such, the particles which are formed to a spherical shape with a size of 45-125, um may be used. The hard particle materials comprise diamond particles, tungsten carbide, titanium carbide, zirconium carbide, tantalum carbide, vanadium carbide, silicon carbide, chromium carbide, boron nitride, zirconium nitride, titanium nitride, silicon nitride, hafnium boride, titanium boride, zirconium boride, chromium boride, aluminum boride, cobalt boride, iron boride, aluminum oxide, zirconium oxide and combinations thereof, or other hard ceramic particles.

A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLES 1-12 A binder alloy having an amount (the remainder: hard particles) and a chemical composition shown in the following Table 1 was subjected to gas atomization to prepare a binder alloy powder. The powder for sintering was pulverized to 45 urn or less, considering packing with hard particles. A

composition and an average particle size of hard particles were adjusted as shown in Table 1, after which such materials and an organic binder were uniformly mixed by use of a kneader. As for the organic binder, polymeric elements such as paraffin, polyethylene wax or EBS wax, and a liquid binder, such as stearic acid, glycol, polyvinyl alcohol, are mixed based upon a size and a shape of a final product. In the present invention, paraffin was added in the amount of 0.5 wt% as the organic binder. Other than the organic binder, in order to improve compressibility of the powder and aid a flow of the particles by decreasing friction with a mold, lubricants, such as graphite, resins and metallic soaps are additionally added in the amount of 0.1 wt%. In the present invention, such lubricants were not used.

Although the abrasive wheel having high density would be required, pores necessary for easy removal of abraded particles should be formed on the wheel.

As such, the wheel should also have a lubricating property. As in the examples 6- 12 shown in Table 1 as stated below, pores were artificially formed by sintering only larger particles at the low temperature of 1350 °C or less. Into such pores, a coolant and a lubricant were smeared, thus preventing a seizure between the abrasive wheel and a cutting material due to a friction heat of the abrasive wheel.

During friction, new hard particles were exposed, with removal of the used hard particles. Thus, the hard particles should be removed at a proper time so as to maintain a cutting property. The present abrasive wheel can fulfill such requirements.

By using larger particles with an average 45, um in the alloy powder, formability was lowered with formation of fine segregation. So, in the present invention, iron powders with the size of 1-2 u. m might be mixed with the alloy powder to give a chemical composition for a binder material.

From the tests carried out above, it was found that the binder and the wheel were improved in hardness, while the sintering temperature was relatively lower, compared to a conventional temperature.

COMPARATIVE EXAMPLES 1-5

As shown in Table 1, a comparative example 1 shows a conventional preparation technique by a plating process. As for the comparative examples 2-5, conventional binder alloy powders were mixed with hard particles and sintered.

The binder alloy powder for sintering had an average particle size of 4-45 p, m.

The hard particles of Table 1 were uniformly mixed with 0.5 wt% of paraffin by a kneader. As a result, the binder and the wheel had low hardness, under relatively high sintering temperature.

TABLE 1 Chemical Hard Hardness Metal Binder Sintering Ex. Composition Particle & (HV) Amount Temp. No. of Binder Average (Vol%) (°C) Binder Wheel (at%) size (, um) Ni 15, Co 10, 1 85 Cr 25, Mo 3, W 2, Diamond, 4 1370 703 1280 B 10, Fe bal. Ni 34, Co 10, 2 80 Cr 8, Mo 5, W 5, Diamond, 2 1370 623 1254 B 6, Fe bal. Ni 40, Co 10, Diamond, 4 3 70 Cr 25, Mo 5, 1370 644 1153 CBN, 45 B 10, Fe bal. Ni 45, Co 20, 4 70 Diamond, 2 1380 685 1231 Mol2, B8, Febal. Cr 18, Mo 2, B 9, Si Diamond, 4 5 70 1380 558 1137 1, Fe bal. CBN, 45 Ni 15, Co 10, 6* 70 Diamond, 2 1350 529 964 Mo 12, B 6, Fe bal. Ni 15, Co 10, 7* 65 Cr 25, Mo 3, W 2, Diamond, 4 1350 568 937 B 6, Fe bal. Ni 0.66, Cr 15.8, Mn 0.4, Mo 1.8, 8* 70 Diamond, 2 1350 376 953 Si 0. 39, B 2. 0, C 1. 3, Fe bal. Ni 5. 7, Cr 7. 8, Mn 1. 7, Mo 1. 8, 9* 70 Diamond, 4 1330 608 975 Si 3.3, B 17.25, Fe bal. Ni 16.0, Co 7.8, Cr27. 5, Mo3, 10* 70 W 2, Cu 1. 6, Diamond, 2 1330 789 1012 Si 2.6, B 17.7, Fe bal. Cr 24.8, Mn 1.4, Diamond, 4 11* 85 Si 2. 7, B 16. 1,1250 545 986 Fe bal. Cr21. 8, Mo 2. 1, 12* 85 Ni 8. 1, Si 1. 9, Diamond, 4 1280 518 943 B 13. 7, Fe bal. C. Ex. 1 65 Ni latin Diamond, 4-320 785 C. Ex. 2 65 Ni 97.8, A12. 2 Diamond, 2 1400 380 864 C. Ex. 3 70 Ni 64. 9, Co 35.1 Diamond, 2 1450 260 519 C. Ex. 4 70 Ni 80, Co 20 Diamond, 4 1400 320 906 Ni 95. 1, Co 1. 1, C. Ex. 5 70 Diamond, 4 1380 395 831 Al 1. 4, Si 2. 4

Note.. * : 5-15 % porosity INDUSTRIAL APPLICABILITY The sintered products using the binder materials of the present invention can restrain graphitization of diamond, due to their low melting point, and can substitute for cobalt used in conventional binder material, because of excellent wettability and high strength. When a lead frame having low hardness is cut by use of the abrasive wheel made of the present alloy, a dulling phenomenon easily occurs and thus pores are formed in 10-15 % by area, to readily remove the particles.

Therefore, the abrasive wheel of the present invention is applicable to a variety of fields including wafer dicing wheels, wafer polishing wheels and blades for cutting stone.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.