JP2006037160A - Sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the service life when used for cutting tools, wear resistant tools and components by improving various properties such as strength, hardness and toughness of a sintered compact consisting mainly of tungsten carbide. <P>SOLUTION: The sintered compact with a gradient composition in which the hardness in the vicinity of the surface is high and the toughness of the inside is high by sintering a powdery mixture obtained by mixing 0.1 to 1.0 wt.% iron group metal, 0.1 to 1.0 wt.% of at least one kind of specific element metal selected from Cr, Au, Cu, Sn and Al, and the powder of a hard phase such as tungsten carbide in a controlled atmosphere, and evaporating or scattering the specific element metal(s) from the surface at the time of the sintering, has excellent various properties such as strength, hardness and toughness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a sintered body having high hardness and high toughness and excellent wear resistance. Specifically, non-ferrous metal cutting tools such as aluminum, titanium, and copper, which are easily welded, abrasive or erosion wear resistant members such as blasting nozzles and water jet nozzles, mechanical seals, bearings, etc. The present invention relates to a sintered body optimum for a sliding wear member.

In cemented carbides based on tungsten carbide, it is known that the smaller the amount of the binder phase, the higher the hardness and the better the wear resistance, and the higher the toughness, the better the wear resistance for the same hardness. . However, since the sinterability deteriorates with a decrease in the amount of the binder phase, there is a problem that hardness, toughness, and strength are reduced. In order to improve these, various tungsten carbide-based sintered bodies to which other carbides are added have been proposed.

Mo ₂ C: 2 to 20% by weight, one or more of Cr ₃ C ₂ , VC, NbC, TaC, TiC, ZrC, and HfC: 0.2 to 2% by weight, Co, Ni, Fe Among them, there is a super-hard alloy composed of one or more of them, and 1% by weight or less, and the balance is WC (for example, see Patent Document 1).

The alloy composition after sintering is composed of a hard phase mainly composed of WC having a particle size of 2 μm or less and containing Mo or Mo ₂ C and VC and a binder phase mainly composed of Co. 2 to 1.0 wt% Co, 2.0 to 7.0 wt% Mo or Mo ₂ C, 0.2 to 0.6 wt% VC, balance is high hardness cemented carbide consisting of WC (e.g., (See Patent Document 2).

Further, one or more of Fe, Co and Ni are 0.02 to 0.10% by weight, and one of transition metal carbides, nitrides and carbonitrides of Groups 4a, 5a and 6a of the periodic table Alternatively, two or more kinds are contained in an amount of 0.3 to 3.0% by weight, and the remainder is composed of tungsten carbide having an average particle diameter of 0.5 μm or less, and tungsten carbide has a W ₂ C / (W ₂ C + WC) of 0.01. There is a sintered hard material in a range of ˜0.15 (for example, see Patent Document 3).

Although these sintered bodies have improved sinterability and hardness by adding Mo ₂ C, VC, W ₂ C, etc., they cause abnormal wear under heavy load conditions due to a decrease in toughness. There is a problem to say.

Japanese Patent Laid-Open No. 5-33098 Japanese Patent Laid-Open No. 5-59481 Japanese Patent Laid-Open No. 9-25535

Tungsten carbide-based sintered bodies have high hardness, high toughness, and excellent wear resistance, so they are resistant to abrasive or erosion wear, such as cutting tools, blasting nozzles and water jet nozzles, mechanical seals, and bearings. It is often used for sliding wear-resistant members such as the above, but there is a demand for further improvement in life. Therefore, an object of the present invention is to provide a sintered body in which the hardness near the surface and the internal toughness are simultaneously improved.

The present inventor has studied the simultaneous improvement of the hardness, strength and toughness of the sintered body for many years. At least one specific element metal selected from Cr, Au, Cu, Sn, and Al is used. When added, the sinterability is improved, and by switching the atmosphere at the time of sintering from inert gas to vacuum, the specific element metal is evaporated and scattered from the surface of the sintered body to become a gradient composition material, In order to complete the present invention, the gradient composition material has a high hardness on the surface and a high toughness inside, and as a result, a sintered body excellent in both wear resistance and strength / toughness can be obtained. It has come.

That is, the sintered body of the present invention is a sintered body mainly composed of at least one of carbides, nitrides, and mutual solid solutions of the periodic table 4a, 5a, and 6a group elements. 0.1 to 1.0% by weight, 0.1 to 1.0% by weight of at least one specific element metal among Cr, Au, Cu, Sn, and Al, and in the depth direction from the surface The content of the specific element metal contained in the surface region up to 0.1 mm is expressed as Vi (% by weight), and the content of the specific element metal contained in the internal region of 1 mm or more in the depth direction from the surface is expressed as Vs (% by weight). ), The sintered body satisfies (Vs / Vi) ≦ 0.5.

The sintered body of the present invention comprises a binder phase containing at least one specific element metal and an iron group element among Cr, Au, Cu, Sn, and Al: 0.2 to 2.0% by weight, and the balance Is composed of a hard phase composed of at least one of carbides and nitrides of group 4a, 5a, and 6a elements of the periodic table and their mutual solid solution and inevitable impurities.

The hard phase of the present invention comprises at least one of carbides, nitrides and their mutual solid solutions of the periodic table 4a, 5a and 6a group elements. Specific examples of the hard phase include tungsten carbide such as WC, VC, TaC, NbC, TiN, HfN, (W, Ti) C, (W. Ti. Ta) C, (W, Ti, Ta) (C, N), (Ti, W, Mo) (C, N) and the like, and non-cubic compounds such as Cr ₇ C ₃ and Mo ₂ C. The amount of the cubic compound contained in the hard phase is not particularly limited because it varies depending on the application. VC, TaC, NbC, and Cr ₇ C ₃ improve the hardness by suppressing the grain growth of WC by adding about 0.1 to 3% by weight, and (W, Ti) C, (W.Ti.Ta) Although C and the like reduce the strength, if containing 10 to 80% by weight based on the entire hard phase, the hardness is remarkably improved.

The binder phase of the present invention is a metal containing at least one kind of specific element metal and iron group metal among Cr, Au, Cu, Sn, and Al. , Cr, Mo, etc. may be dissolved. Here, the iron group metal means Co, Ni, and Fe. Since the binder phase is difficult to sinter at less than 0.2 wt., A large amount of pores remain and the hardness, strength and toughness are lowered, and when it exceeds 2.0 wt%, the wear due to the reduced hardness increases. Therefore, the content is determined to be 0.2 to 2.0% by weight.

The amount of iron group metal contained in the sintered body of the present invention is difficult to sinter if it is less than 0.1% by weight, so that a large amount of pores remain and the hardness, strength and toughness are low. When the amount exceeds 5% by weight, wear due to a decrease in hardness increases, so the amount of iron metal was determined to be 0.1 to 1.0% by weight.

The specific element metal of the present invention is at least one selected from Cr, Au, Cu, Sn, and Al, and forms an alloy or intermetallic compound by solid solution in the iron group metal. In some cases, Cr forms a carbide, Al forms an oxide or nitride, and is dispersed as an inevitable impurity in the sintered body. If the amount of the specified elemental metal is less than 0.1% by weight, the effect of improving the sinterability is small. Conversely, if the amount of the specified elemental metal exceeds 1.0% by weight, wear due to a decrease in hardness increases. Of 0.1 to 1.0% by weight. Among the specific element metals, Cu, Cr, and Al are more preferable because they have a great effect of improving hardness and toughness.

The specific element metal of the present invention gradually decreases from the inside of the sintered body toward the surface, and the content of the specific element metal contained in the surface region from the surface to the depth of 0.1 mm in the depth direction is Vi (weight). %), And when the content of the specific element metal contained in the internal region of 1 mm or more in the depth direction from the surface is expressed as Vs (wt%), (Vs / Vi) ≦ 0.5 is satisfied. When (Vs / Vi) exceeds 0.5, the effect of improving the hardness and toughness associated with the reduction of the specific element metal on the surface is small.

The sintered body of the present invention is manufactured by a powder metallurgy method similar to that of cemented carbide, but the following points should be taken into consideration. The particle size of the hard phase powder, which is the main raw material powder, is preferably about 0.5 to 2 μm in view of moldability, sinterability, and structure uniformity. The iron group metal and the specific element metal are also preferably 1 μm or less, and may be added in the form of carbide, oxide, or nitride, and decomposed and reduced during sintering to form fine powder. The sintering atmosphere is a non-oxidizing atmosphere such as argon or nitrogen up to the sintering temperature to prevent evaporation and scattering of the specific element metal. Then, it is necessary to sinter and hold once to obtain a uniform composition, and then to evacuate the specific element metal from the surface. If densification is insufficient, HIP may be applied after sintering.

In the sintered body of the present invention, the added specific element metal has an action of improving the sinterability, and the evaporation and scattering of the specific element metal from the surface of the sintered body at the time of sintering has an action of gradient composition. In the obtained gradient composition material, the high hardness of the surface and the high internal toughness serve to improve both the wear resistance and the strength and toughness.

Since the sintered body of the present invention has higher strength and hardness near the surface and internal toughness than conventional products to which almost the same amount of iron metal is added, the abrasion resistance by blasting is 1.5 times. Titanium alloy cutting has twice the life.

Commercially available WC with an average particle size of 1.0 μm, carbon black with an average particle size of 0.02 μm (abbreviated as C), Co with an average particle size of 0.6 μm, Ni with an average particle size of 1.1 μm, an average particle size of 1.2 μm Fe, Cr ₃ C ₂ with an average particle size of 0.8 μm, Au with an average particle size of 0.5 μm, CuO with an average particle size of 0.9 μm, AlN with an average particle size of 0.2 μm, VC with an average particle size of 0.8 μm , TaC with an average particle size of 1.0 μm, (W, Ti) C with an average particle size of 0.8 μm (weight ratio WC / TiC = 70/30), Mo ₂ C with an average particle size of 1.0 μm, average particle size Using each powder of Sn (stamp powder) that passed through 1.7 μm W ₂ C, # 325 sieve, weighed to the composition shown in Table 1, with acetone solvent and cemented carbide balls in a stainless steel pot It was inserted, mixed and ground for 48 hours, and then dried to obtain a mixed powder. Here, the amount of blended carbon was adjusted by adding C so that free carbon or Co ₃ W ₃ C, Ni ₂ W ₄ C, Fe ₃ W ₃ C or the like would not precipitate after sintering. Then, these powders are filled into a mold, a compacted body of 5.3 × 10.5 × 31 mm is produced with a pressure of 196 MPa, placed on a carbon plate coated with carbon black powder, and then sintered. It inserted in the sintering furnace and heat-sintered and obtained the sintered compact of this invention products 1-9 and comparative products 1-9. Details of the atmospheric conditions in the applied temperature raising, sintering, and cooling steps are collectively shown in Table 2, and the condition number of the atmosphere is shown in Table 1 together with the temperature and time for holding the sintering. All sintered bodies were subjected to HIP treatment in argon at 150 MPa at 1450 ° C. for 1 hour.

注）＊焼結時の雰囲気が前半と後半で異なった場合には、それぞれの時間を示した（例えば２０＋２０と表示）。

Note) * When the atmosphere during sintering is different between the first half and the second half, the respective times are indicated (for example, indicated as 20 + 20).

注）＊所定温度まで雰囲気はすべて５Ｐａの真空であり、また１０００℃以上での昇温速度を１５℃／ｍｉｎとした。
＊＊１０００℃までの冷却速度を１０℃／ｍｉｎとした。

Note) * Up to a predetermined temperature, the atmosphere was all 5 Pa vacuum, and the heating rate at 1000 ° C. or higher was 15 ° C./min.
** The cooling rate to 1000 ° C. was 10 ° C./min.

Specimens (4.3 × 8.5 × 25 mm) of each sintered body thus obtained were wet-grinded with a # 230 diamond grindstone to produce a 4.0 × 8.0 × 25.0 mm shape. . At this time, of two surfaces of 4.0 × 25 mm, one surface (abbreviated as “A surface”) was set to 0.1 mm as a margin for grinding (distance from the surface of the sintered skin). And it set to the jig | tool so that tensile stress might work to A surface, and measured the bending strength by JIS method. The results are shown in Table 3.

Next, about two of the other specimens of each sintered body obtained, one was wet-grinded from the surface (sintered skin) to a depth of 0.05 mm using a 1000 # diamond grindstone, and the other was # Wet grinding was performed to a depth of 1.0 mm from the surface using 400 and # 1000 diamond wheels. Then, after lapping each sample surface with a diamond paste of 1 μm, the load using a Vickers indenter: the hardness at 196 N and the fracture toughness value K1C (IM method) were measured. These results are also shown in Table 3. In addition, when the lapping surface was observed with an optical microscope, all sintered bodies had 0.01 to 0.05% by volume of nest holes of 0.5 to 1 μm, and the particle diameter of WC was 1.5 to It was 3 μm.

According to the results in Table 3, the product of the present invention is about 50 to 400 MPa higher in bending strength than the conventional product and the comparative product obtained by sintering the mixed powder of the same composition by the conventional method, and the surface hardness is 30 in HV. The internal fracture toughness value is about 0.2 to 1.0 high. That is, it can be said that the product of the present invention is excellent in strength, surface hardness and internal toughness.

Next, another specimen of each obtained sintered body was cut, and the cross section was polished and lapped to prepare a sample for composition analysis. Then, using a scanning analytical electron microscope, a line analysis of the composition (through the center of the cross section to the opposite side) was performed from the surface (sintered skin) to the inside. From this line analysis result, for each of the specific element metal and the iron group metal, the average content in the surface region from the surface to the depth direction of 0.1 mm and the average content in the inner region of 1 mm or more from the surface in the depth direction. The amount was determined. The ratio of the content of the surface area to the content of the internal area was calculated. These results are shown in Table 4. From this result, the product of the present invention is about 50 to 400 MPa higher in bending strength than the conventional product and a comparative product obtained by sintering a mixed powder of the same composition by a conventional method, and the surface hardness is about 30 to 120 in HV. The internal fracture toughness value is about 0.2 to 1.0 higher.

Of the 4.0 × 8.0 × 25.0 mm ³ test pieces obtained in Example 1, the present invention products 2, 4, 6, 7 and comparative products 2, 4, 6, 7 were used for sandblasting. A wear test was performed. The blasting conditions are: use surface: 8.0 × 25.0 mm ² abrasive grains: 400 #, spray pressure: 1.1 Mpa, incident angle: 60 °, spray time: 5 minutes. The wear volume by blasting was determined from weight loss / density, and the results are shown in Table 5.

The mixed powder of the present invention products 2, 4, 6, 7 and the comparative products 2, 4, 6, 7 obtained in Example 1 was filled into a die of a chip with a high rake breaker of SNMG120408 in accordance with ISO standards. A chip material was obtained by press molding and sintering under the same conditions as in No. 1. Then, only the boss portion of the rake face is ground with a 270 # diamond grindstone, and then polished with a nylon brush containing 320 # silicon carbide abrasive grains, and the cutting edge portion is subjected to honing with a radius of 0.05 mm. Thus, cutting chips of the present invention products 9 to 12 and comparative products 9 to 12 were obtained.

Using the cutting tip thus obtained, work material: titanium alloy (Ti-6Al-4V), cutting speed: 100 m / min, depth of cut: 1.5 mm, feed: 0.2 mm / rev, outer periphery under wet conditions A continuous turning test was conducted. The time was measured until the cutting edge was chipped or chipped, or the flank wear amount reached 0.20 mm. The results are shown in Table 6.

From the results in Table 6, it can be seen that the product of the present invention has high strength, hardness of the surface, and internal toughness, so that it is difficult to cause chipping and chipping and is excellent in wear resistance.

Claims (2)

Periodic table 4a, 5a, 6a group carbides, nitrides, and sintered bodies mainly composed of at least one of these mutual solid solutions, containing iron group metal in an amount of 0.1 to 1.0% by weight And 0.1 to 1.0% by weight of at least one specific element metal selected from Cr, Au, Cu, Sn, and Al, and included in the surface region from the surface to 0.1 mm in the depth direction. When the content of the specific element metal is expressed as Vi (% by weight) and the content of the specific element metal contained in the inner region of 1 mm or more in the depth direction from the surface is expressed as Vs (% by weight), (Vs / Vi ) Sintered body satisfying ≦ 0.5. The sintered body according to claim 1, wherein the specific element metal is any one of Cr, Cu, and Al.