JP2007008776A - Chromium-containing sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium-containing sintered compact capable of attaining the improvement of the finish profile irregularity or the life in metal processing because of the excellent melt sticking resistance and strength/toughness. <P>SOLUTION: The chromium-containing sintered compact comprises 1-20 volume% 1st dispersion phase comprising at least one kind of oxides of Zr, Hf and Zr-Hf, 1-30 volume% 2nd dispersion phase comprising at least one kind of carbide, nitride and carbonitride of Zr, Hf and Zr-Hf and the balance being a composite compound expressed by a compositional formula; (Cr<SB>1-x</SB>M<SB>x</SB>)(N<SB>1-y</SB>C<SB>y</SB>)<SB>z</SB>(in the formula, M expresses at least one kind of Ti, V, Nb and Ta, (x) expresses an atomic ratio of M to the total of Cr and M, (y) expresses an atomic ratio of C to the total of N and C and (z) expresses an atomic ratio of the total of N and C to the total of Cr and M) where each of (x), (y) and (z) satisfies 0.3≤x≤0.9, 0≤y≤0.3 and 0.7≤z≤1.0. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a chromium-containing sintered body used for a cutting tool such as a blade-tip-exchangeable tip, a wear-resistant tool such as a die or a cutting blade, and a bearing part used in a high temperature or corrosive atmosphere.

Since chromium nitride is excellent in welding resistance, oxidation resistance, corrosion resistance and the like, it is frequently used for non-metal cutting and various molds as a coating by the PVD method. Examples of the coating include CrN, (Cr, Ti) N, and (Cr, Al) N. On the other hand, the ceramic sintered body is added to improve the characteristics. The reason is that chromium nitride is easily decomposed, difficult to be densified, inferior in hardness and wear resistance, and the like.

As prior art of ceramics containing chromium nitride, by weight percent, ZrO ₂ and / or stabilized ZrO ₂ : 10 to 40%, one or more of Cr ₃ C ₂ , CrN, Cr: 0 There are ceramics having a composition consisting of 0.01 to 2%, Ni and / or Co: 0.2 to 8%, TiCN and / or TiCNO: the balance (see, for example, Patent Document 1). In addition, there is a particle-dispersed silicon nitride sintered body in which chromium nitride (Cr ₂ N) particles are dispersed within a range of a volume fraction of 1 to 8% (see, for example, Patent Document 2). Further, there is a refractory for casting containing 3 to 25% by weight of chromium nitride, and chromium nitride forms a matrix connective structure (for example, see Patent Document 3). These chromium nitride-containing ceramics have insufficient improvement in welding resistance and oxidation resistance due to low chromium nitride, and inferior in strength and wear resistance because chromium nitride is not uniformly distributed. There is a problem to say.

Japanese Patent Laid-Open No. 5-221724 Japanese Patent Laid-Open No. 9-278529 JP-A-10-139530

Stainless steel and non-ferrous metal cutting and wear-resistant tools are required to improve finish surface accuracy and life by improving welding resistance. The conventional sintered body added with chromium nitride having the above-mentioned problems cannot meet such demands. Accordingly, an object of the present invention is to provide a chromium-containing sintered body mainly composed of a Cr-containing composite compound having improved welding resistance and oxidation resistance and improved strength and toughness.

The present inventor has been studying improvement in characteristics and performance of a sintered body containing chromium nitride. Chromium nitride and at least one nitride of Ti, V, Nb, and Ta are in a wide range. Forming a solid solution of the mold, the composite compound that is a solid solution has a uniform composition and high hardness, suppresses the decomposition of chromium nitride and improves the sinterability, and also sinters the composite compound When Zr, Hf, Zr—Hf metal, nitride, or carbide is added to Zr, Hf, Zr—Hf, an oxide of Zr, Hf, Zr—Hf is preferentially removed to remove oxygen in the composite compound. The oxides of Hf and Zr—Hf are uniformly dispersed in the sintered body as a dispersed phase, and the resulting chromium-containing sintered body is excellent in hardness, toughness, strength, wear resistance, Improves flaw resistance, welding resistance, and oxidation resistance To obtain the knowledge to say which has led to the completion of the present invention.

That is, the chromium-containing sintered body of the present invention includes a first dispersed phase composed of at least one of oxides of Zr, Hf, and Zr—Hf: 1 to 20% by volume, and Zr, Hf, and Zr—Hf. Second dispersed phase composed of at least one of carbide, nitride and carbonitride: 1 to 30% by volume, and the remainder is composition formula: (Cr _1−x M _x ) (N _1−y C _y ) _z ( Where M represents at least one of Ti, V, Nb, and Ta, x represents the atomic ratio of M to the sum of Cr and M, and y represents the atomic ratio of C to the total of N and C. Z represents the atomic ratio of the sum of N and C with respect to the sum of Cr and M.), and x, y, z are 0.3 ≦ x ≦ 0.9, 0 ≦ y ≦ 0. 3, a composite compound satisfying 0.7 ≦ z ≦ 1.0.

The composite compound in the chromium-containing sintered body of the present invention has a composition formula: (Cr _1−x M _x ) (N _1−y C _y ) _z (where M is at least one of Ti, V, Nb, and Ta). X represents the atomic ratio of M to the sum of Cr and M, y represents the atomic ratio of C to the sum of N and C, and z represents the ratio of N and C to the sum of Cr and M. X, y, z is a B1 type satisfying 0.3 ≦ x ≦ 0.9, 0 ≦ y ≦ 0.3, and 0.7 ≦ z ≦ 1.0. It is a cubic compound. Among them, it is more preferable that M is Ti and / or Nb because of excellent hardness and wear resistance.

X in the composite compound of the present invention represents the atomic ratio of M to the total of Cr and M, and is in the range of 0.3 ≦ x ≦ 0.9. This is because when x is less than 0.3, the Cr content is excessive and the hardness is significantly reduced. Conversely, when it exceeds 0.9, the Cr content is too low and the welding resistance is reduced. At the same time, since the sinterability decreases, a fine and dense sintered body cannot be obtained. Among these, it is more preferable that x is in the range of 0.4 ≦ x ≦ 0.7 because a uniform composite compound can be easily formed, which is excellent in strength and toughness and easy to manufacture.

In the composite compound of the present invention, y represents the atomic ratio of C to the total of N and C, and is in the range of 0 ≦ y ≦ 0.3. This is because when y exceeds 0.3, a complex compound is not formed, and a large amount of chromium carbide and chromium carbonitride is precipitated to reduce strength and toughness.

Z in the composite compound of the present invention represents the atomic ratio of the total of N and C to the total of Cr and M, and is in the range of 0.7 ≦ z ≦ 1.0. This is because when the z is less than 0.7, the hardness of the composite compound is decreased, and a large amount of intermetallic compounds such as Cr or Cr ₂ Ti and Cr ₂ Nb are precipitated to decrease strength and toughness. It is because it becomes difficult on manufacture to enlarge exceeding 1.0. z is preferably as close to 1.0 as it is excellent in hardness, wear resistance and welding resistance. In addition, although the composite compound in this invention contains oxygen as an inevitable impurity, since the fall of toughness will be remarkable when oxygen is included, 1 weight% or less is preferable.

When Zr, Hf, Mo, W, or the like is added to the chromium-containing sintered body of the present invention, these metal elements are difficult to dissolve in the composite compound, so Zr, Hf is a first material such as nitride or oxide. A dispersed phase and a second dispersed phase are formed, and Mo and W remain as metals.

The first dispersed phase in the chromium-containing sintered body of the present invention comprises at least one of oxides of Zr, Hf, and Zr—Hf. Specifically, ZrO ₂ , HfO ₂ , (Zr, Hf) O _{2 and the} like can be mentioned. If the content of the first dispersed phase is less than 1% by volume, the residual oxygen in the composite compound is relatively increased, and since the dispersion effect is small, the strength and toughness are significantly reduced. Since hardness and abrasion resistance will fall when it becomes large, it was set as 1-20 volume%.

The second dispersed phase in the chromium-containing sintered body of the present invention comprises at least one of Zr, Hf, Zr—Hf carbides, nitrides, and carbonitrides. Specific examples include ZrN, HfN, ZrC, HfC, (Zr, Hf) (C, N), and the like. If the content of the second dispersed phase is less than 1% by volume, the residual oxygen in the composite compound will increase relatively, so the strength and toughness will decrease significantly. Since the compound is decreased and the welding resistance and oxidation resistance are lowered, the content is determined to be 1 to 30% by volume.

In addition to the first dispersed phase, the second dispersed phase, and the composite compound, the chromium-containing sintered body of the present invention includes at least one of Cr, V, Mo, and W metals, nitrides, carbonitrides, and their mutual solid solutions. One kind may be contained in an amount of 30% by volume or less. Specifically, Cr, Mo—Cr alloy, W—Cr alloy, etc. are used as metals, and Cr ₂ N, (Cr, V) ₂ N, (Mo, Cr) ₂ N, etc. are used as carbonitrides as nitrides. Examples thereof include Cr ₂ (C, N), (Cr, V) ₂ (C, N) and the like. When these contents exceed 30% by volume, the hardness and wear resistance are rapidly lowered.

The method for producing a chromium-containing sintered body of the present invention is a method in which a raw material powder is sintered by hot pressing or cold pressing. However, when the following starting materials and sintering conditions are applied, a dense powder having excellent mechanical properties is obtained. Thus, a sintered body having a fine structure can be obtained.

As a starting material for the composite compound, for example, for (Cr, Ti) N, a mixture of Cr ₂ N or metal Cr and TiN may be used. It is preferable to synthesize and use. Specifically, a mixed powder of Cr and Ti or TiH ₂ is heat-treated in a high vacuum to once form a uniform alloy, and then nitrided at a temperature of 1000 to 1200 ° C. to obtain a composite compound. It is. Here, when Zr, Hf and Mo, W are added in advance at the time of preparation of the composite compound, they hardly dissolve in the composite compound and are separated as nitrides and metals, respectively, but are uniformly dispersed to have hardness, strength, This is preferable because toughness is enhanced and sinterability is improved.

The starting materials for the first dispersed phase and the second dispersed phase are Zr, Hf, Zr—Hf metals, carbides, nitrides, carbonitrides, and the like. Among them, the metal absorbs oxygen during sintering to form a first dispersed phase of oxide, and reacts with nitrogen in the atmosphere to form a second dispersed phase of nitride. Carbides, nitrides, and carbonitrides all absorb oxygen to form a first dispersed phase of oxide, and a part remains as it is. Therefore, the first dispersed phase is generated from the starting material of the second dispersed phase and oxygen contained in the mixed powder, and it is preferable not to add a large amount as the starting material.

The chromium-containing sintered body of the present invention is obtained at a low cost and with a low oxygen content by a cold press method in which the pressure-formed powder is sintered without pressure. At this time, it is necessary to switch to a nitrogen atmosphere from 1100 ° C. at which the heating temperature is raised in a high vacuum to sufficiently deoxidize and the composite compound decomposes rapidly. Moreover, when it is desired to further improve the composition, hardness and strength with insufficient sinterability, it is preferable to perform HIP (hot isostatic pressure) treatment.

In the chromium-containing sintered body of the present invention, the Cr component ensures the welding resistance, and the Ti, V, Nb, and Ta components act to improve the hardness and wear resistance. The compound acts to improve strength and toughness, the added Zr and Hf components remove oxygen in the composite compound, and the dispersion of the generated oxide further improves the hardness, strength and toughness. It is what you are doing.

The chromium-containing sintered body of the present invention is superior in strength, toughness, and welding resistance compared to conventional chromium nitride-containing ceramics, so that it is difficult to cause chipping, chipping, and welding in stainless steel cutting and sliding friction at high temperatures. , Long life.

Using the commercially available # 325 Cr, V, Ti, Nb, Ta, Zr, and Hf metal powders and carbon black having an average particle size of 0.02 μm (denoted as C), the composition shown in Table 1 was obtained. Weighed, 0.2% by weight paraffin wax and hexane solvent were inserted together with a cemented carbide ball on a stainless steel pot, and after 24 hours of ball milling, dried to obtain a mixed powder. These mixed powders were lightly filled into a zirconia crucible and inserted into a heating furnace, and then heated in a vacuum of 1 Pa and subjected to a heat treatment at 1150 ° C. for 1 hour. Subsequently, the pressure was increased to 0.5 MPa while gradually introducing nitrogen gas, and then nitriding treatment was performed at 1150 ° C. for 1 hour. Then, the treated powder was crushed and pulverized for 24 hours by the ball mill, and then inserted again into a heating furnace, and subjected to renitriding treatment at 1150 ° C. in 0.5 MPa nitrogen for 1 hour ( A composite compound powder of A) to (I) was obtained. Table 1 shows the average particle diameter (FSSS) of the obtained composite compound powder and the results of identification by X-ray diffraction.

The obtained composite compound powders (A) to (I), 2.5 μm HfC, # 325 metal Zr, 1.7 μm ZrN, 2.1 μm metal Mo, 1.5 μm metal W, 3 mol % Y ₂ O ₃ in a solid solution of 0.2 μm ZrO ₂ , 4.5 μm Cr ₂ N, 1.3 μm TiN, 4.3 μm NbN, 1.5 μm Ti (C _0.5 N _0.5 ), 1 Each powder of 7 μm Ni was weighed to the composition shown in Table 2, and 1.0 wt% paraffin wax and hexane solvent were inserted into a stainless steel pot with a cemented carbide ball on the outside. After 48 hours of ball milling, it was dried to obtain a mixed powder. And after filling each mold, producing a green compact of 5.5 × 4.5 × 43 mm with a pressure of 200 Mpa, setting it on a boron nitride setter and inserting it into a sintering furnace, Heating and heating were performed in a vacuum with an atmospheric pressure of 10 Pa or less. Then, after introducing nitrogen gas at the pressure shown in Table 3 at 1100 ° C., the mixture was heated and held at the temperature shown in Table 3 for 1 hour. Furthermore, the sintered body of this invention products 1-11 and comparative products 1-7 was obtained by performing the HIP process for 1 hour in 100 MPa Ar at the temperature written together in Table 2.

Each 4.5 × 3.5 × 35 mm sintered body thus obtained was subjected to wet grinding with a # 400 diamond grindstone to obtain a JIS test piece of 3.0 × 4.0 × 35.0 mm, and then bent. The strength was measured. The results are shown in Table 4. Further, after lapping one surface of the sample with 1.0 μm diamond paste, Vickers hardness: HV and fracture toughness value: K1C (IF method using a Vickers indenter with a test load of 98 N) were measured. The results are also shown in Table 3.

Next, after identifying the lap surface of each sample by X-ray diffraction, a structure photograph is taken with an electron microscope, and a composite compound phase, a first dispersed phase, a second dispersed phase, and other components are taken using an image processing apparatus. The content volume% of the dispersed phase was determined. Furthermore, each sample was pulverized and the contents of carbon, nitrogen, and oxygen were measured. And the composition formula of the composite compound phase in each sintered compact was calculated | required by calculation from these measurement results and the compounding composition in Table 1. The results of X-ray diffraction, the contents of carbon, nitrogen and oxygen are shown in Table 4, and the composition formula and contents of the composite compound phase and the types and contents of each dispersed phase are shown in Table 5.

＊ 複合化合物を含まない。

* Does not include complex compounds.

Using the mixed powders of the present invention products 2, 3, 4, 9, 10 and the comparative products 1, 3, 5, 7 obtained in Example 1, with a mold for ISO standard SPGN120408 shape, Example 1 The present invention products 12 to 16 and the comparative products 8 to 11 are subjected to press molding, sintering, HIP treatment, and wet grinding under the same method and conditions as above, and a round honing process with a radius of 0.07 mm is applied to the cutting edge. Each cutting tip was obtained. Using this SPGN120408 chip, a wet continuous turning test was performed under the conditions of a work material: SUS304, a cutting speed: 200 m / min, a cutting depth: 1.0 mm, and a feed rate: 0.2 mm / rev. The time was measured until the cutting edge was chipped or chipped, or the average flank wear amount reached 0.20 mm. The results are shown in Table 6.

It can be seen from Table 6 that the inventive products 12-16 have a longer life than the comparative products 8-11.

Using the mixed powders of the present invention products 1, 4, 7, 10 and comparative products 2, 3, 4, 7 obtained in Example 1, 13 × 13 × 5 mm in the same manner and conditions as in Example 1. After the sintered body was prepared and the upper and lower surfaces were wet ground, the friction test pieces of the present invention products 17 to 20 and the comparative products 12 to 15 were obtained by lapping on one surface. Then, set in a ball-on-disk friction tester, mating material: φ6 mm SUJ2 ball, temperature and atmosphere: 400 ° C. air, load: 19.6 N, sliding speed: 10 m / mim, high temperature A friction test was performed. The friction test was performed while measuring the friction torque, and the friction time until the friction coefficient exceeded 1.0 (but stopped at the maximum of 5 hours) and the average friction coefficient were measured. For samples for which the friction test was successfully completed, the wear volume was calculated from the cross-sectional area of the friction marks by a surface roughness meter. These results are shown in Table 7.

＊焼結体の摩擦痕にクラックと微少剥離が観察される。

* Cracks and minute delamination are observed in the friction marks of the sintered body.

It can be seen from Table 7 that the inventive products 17 to 20 have a smaller wear volume than the comparative products 12 to 15 and are excellent in wear resistance.

Claims (3)

First dispersed phase composed of at least one of oxides of Zr, Hf, Zr—Hf: 1 to 20% by volume, and at least of carbides, nitrides, carbonitrides of Zr, Hf, Zr—Hf Second disperse phase consisting of one kind: 1 to 30% by volume, and the rest is composition formula: (Cr _1−x M _x ) (N _1−y C _y ) _z (where M is Ti, V, Nb, Ta X represents the atomic ratio of M to the sum of Cr and M, y represents the atomic ratio of C to the sum of N and C, and z represents the sum of Cr and M. X, y, z are 0.3 ≦ x ≦ 0.9, 0 ≦ y ≦ 0.3, 0.7 ≦ z ≦ 1.0. A chromium-containing sintered body comprising a composite compound satisfying the requirements. Substituting a part of the composite compound, at least one of Cr, V, Mo, W metal, nitride, carbonitride, and their mutual solid solution is added to the entire chromium-containing sintered body. The chromium containing sintered compact of Claim 1 containing 30 volume% or less. The chromium-containing sintered body according to claim 1 or 2, wherein M in the composition formula is Ti and / or Nb.