JP2005194556A - Rare-earth-containing sintered alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare-earth-containing sintered alloy containing rare-earth oxides by which remarkable improvement of practical performance and expansion of applications can be attained by improving hardness and wear resistance simultaneously with toughness and chipping resistance. <P>SOLUTION: A compound oxide consisting of chromium oxide and rare earth oxide is added as disperse-phase-forming powder to a starting material for a hard sintered alloy. By this method, the rare-earth-containing sintered alloy consisting of the following phases can be obtained: a binder phase composed mainly of iron-group metals; a disperse phase composed mainly of the compound oxide consisting of an oxide of at least one among scandium, yttrium and lanthanides and chromium oxide; and a hard phase composed mainly of at least one kind among the carbides and nitrides of the group IVa, Va and VIa metals of the periodic table and mutual solid solutions thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a cemented carbide used for various tools typified by cutting tools such as blade-tip-exchangeable tips, drills and end mills, wear-resistant tools such as dies, punches and slitters, and civil engineering tools such as cutter bits. , Cermets, and sintered alloys containing rare earths that are optimal as a base material for coated sintered alloys in which hard films are coated.

Cemented carbides represented by WC-Co, WC- (W, Ti, Ta) C-Co, cermets represented by TiC-Fe, Ti (C, N) -WC-TaC-Ni, etc. The hard sintered alloy has a cutting tool, resistance by adjusting the particle size of the carbide hard phase, the amount of metal binder phase, the amount of other carbides (VC, Cr ₃ C ₂ , Mo ₂ C, ZrC, etc.) added. We have obtained alloy properties and practical performance such as hardness, strength, toughness, wear resistance, fracture resistance, and chipping resistance required for each application such as worn tools and parts. However, hardness and toughness (or wear resistance and fracture resistance) are contradictory alloy properties, and it is very difficult to improve both at the same time. As a measure for improvement, a method of strengthening dispersion by adding a stable oxide such as a rare earth element has been proposed (see, for example, Patent Documents 1 and 2).

JP-A-10-121182 Japanese Patent Laid-Open No. 11-124650

As a prior art for adding a rare earth oxide, JP-A-10-121182 discloses 96 to 88 wt% of spherical and uniform coarse WC having an average particle diameter of 8 to 30 μm together with a binder phase made of Co or Co and Ni. A cemented carbide for rock mining containing a cemented carbide with improved high temperature and thermodynamic properties optionally containing up to 2% rare earth elements such as Ce, Y is described. The cemented carbide described in this publication has poor toughness or hardness due to prevention of transformation of the binder phase due to dispersion of rare earth oxides and strengthening of WC grain boundaries, but poor wettability between the rare earth oxide and binder phase. Therefore, there is a problem that the improvement effect is small.

Japanese Patent Laid-Open No. 11-124650 discloses a binder phase containing iron group metal as a main component and oxides such as Mg, Al and rare earth elements in an amount of 5 to 30% by volume and 0.01% by volume or more. WC-containing cemented carbides are described in which intragranular dispersion strengthening is performed using an oxide composed of WC dispersed in the WC. Although the cemented carbide described in this publication is improved in both hardness and toughness by strengthening WC, there is a problem that the effect is small and it is difficult to disperse uniformly and finely in WC grains.

The present invention solves the above-described problems. Specifically, a rare earth oxide serving as a dispersed phase is added to a raw material powder of cemented carbide or cermet as a composite oxide with chromium. The purpose of the present invention is to provide a rare earth-containing sintered alloy that simultaneously improves the hardness and toughness of the sintered alloy by sintering, and as a result, can achieve a significant improvement in practical performance and expansion of applications.

The present inventor was considering simultaneous improvement of hardness and toughness (or wear resistance and fracture resistance) of a hard sintered alloy to which a rare earth oxide was added, and the rare earth oxide was made into a composite oxide with chromium. What can be achieved by adding and dispersing, because the surface of the dispersed phase is Cr-rich and wettability during sintering is improved, so that both the hard phase of carbide and the bonded phase of metal are firmly bonded. In addition, the present invention has been completed with the knowledge that chromium is dissolved in the dispersed phase and the binder phase to improve the mechanical properties.

That is, the rare earth-containing sintered alloy of the present invention has a binder phase composed mainly of an iron group metal: 3 to 30% by volume, and at least one of scandium, yttrium, and lanthanide elements (atomic number 57 to 71). Dispersed phase mainly composed of composite oxide composed of oxide and chromium oxide: 0.1 to 10% by volume, the remainder being periodic group 4a, 5a, 6a group metal carbide, nitride and their mutual It consists of a hard phase mainly composed of at least one of solid solutions and inevitable impurities.

The dispersed phase in the rare earth-containing sintered alloy of the present invention is mainly composed of a composite oxide comprising at least one oxide of scandium, yttrium, and lanthanide elements (atomic number 57 to 71) and a chromium oxide. Therefore, you may contain 30 volume% or less of rare earth oxides. In the present invention, the rare earth represents scandium, yttrium, or a lanthanide element (atomic number 57 to 71). Specific examples of the composite oxide include YCrO ₃ , LaCrO ₃ , CeCrO ₃ , NdCrO ₃ , SmCrO ₃ , EuCrO ₃ , GdCrO ₃ , DyCrO ₃ , TmCrO ₃ , YbCrO _3, and mutual solid solutions thereof. The inclusion of the rare earth oxide is caused by a component deviation of the composite oxide or a reaction during sintering. If the content of the dispersed phase with respect to the entire rare earth-containing sintered alloy is less than 0.1% by volume, the strengthening by the dispersed phase is insufficient, so the effect of improving the hardness and toughness is small, and conversely exceeds 10% by volume. When the amount is increased, the dispersed phase becomes coarse and aggregates, and the hardness and strength are significantly reduced.

In the rare earth-containing sintered alloy of the present invention, it is preferable to form a surface region (gradient organization) having a smaller dispersed phase content near the surface than inside because the hardness and toughness of the surface region are greatly improved. Specifically, the ratio (Vs / Vi) of the average volume fraction Vs of the dispersed phase from the surface of the rare earth-containing sintered alloy to the inside of 0.1 mm and the average volume fraction Vi of the dispersed phase in the interior of 1 mm or more from the surface. Is preferably 0.5 or less. The volume ratio (Vs / Vi) is more preferably 0.1 or less, and Vs may be substantially 0% by volume.

When the dispersed phase in the rare earth-containing sintered alloy of the present invention contains at least one oxide of samarium, eurobium, thulium, and ytterbium, the above-described gradient organization is promoted, and the hardness and toughness of the surface region are greatly increased. Therefore, it is preferable. That is, if the disperse phase is SmCrO ₃ , EuCrO ₃ , TmCrO ₃ , YbCrO ₃ , these disperse phases are decomposed and reduced during sintering to produce Sm, Eu, Tm, Yb together with Cr, and any metal is vaporized. Since the pressure is high, the dispersed phase in the surface region is significantly reduced by scattering from the surface of the rare earth-containing sintered alloy. It is more preferable that the content of the dispersed phase from the surface to the inside of 0.01 mm is 0.1% by volume or less.

The binder phase in the rare earth-containing sintered alloy of the present invention is mainly composed of at least one of iron group metals Co, Ni, and Fe, and contains 20 wt% or less of Cr and W. Specifically, , Co—W—Cr, Ni—W—Cr, Fe—Ni—Cr—Mo and the like can be mentioned. If the content of the binder phase is less than 3% by volume, the sintering is insufficient and the hardness, strength and toughness are reduced. Conversely, if the content exceeds 30% by volume, the hardness and wear resistance are significantly reduced. The amount of the binder phase was determined to be 3 to 30% by volume.

The hard phase in the rare earth-containing sintered alloy of the present invention is a cubic composed of tungsten carbide or tungsten carbide and carbides, nitrides of the periodic table 4a, 5a, and 6a metals, and at least one of these mutual solid solutions. A crystal compound is preferred in practice. Here, specific examples of the cubic compound include VC, TaC, NbC, TiN, HfN, (W, Ti) C, (W, Ti, Ta) C, (W, Ti, Ta) (C, N). , (Ti, W, Mo) (C, N). Further, some of the hard phases may be Cr ₇ C ₃ , Mo ₂ C, or the like that does not belong to a cubic compound. Here, when the cubic compound contains nitrogen, a surface region enriched with a binder phase not containing the cubic compound is formed on the surface by sintering in vacuum, so that the rare earth oxide according to the present invention is dispersed or textured. You may use together.

Further, the hard phase in the rare earth-containing sintered alloy of the present invention is 30% by weight or more of at least one of titanium carbide, nitride, carbonitride, and the rest of the periodic table 4a, 5a, excluding titanium. It is practically preferable that it is at least one of carbides, nitrides, and carbonitrides of group 6a metals. Specifically, a cored structure in which the core of titanium carbonitride is surrounded by a metal carbonitride solid solution of at least one metal element selected from Mo, V, Ta, Nb, and W and Ti. It has a hard phase.

The rare earth-containing sintered alloy of the present invention can be produced by conventional powder metallurgy by mixing raw material powder, pressure forming, and sintering, but the following points should be noted. First, the composite oxide that is the dispersed phase forming powder needs to be fired at a high temperature in advance to form a stable compound. This is because, when chromium oxide and rare earth oxide are added, almost no complex oxide is formed during the sintering process, and only chromium oxide is preferentially decomposed and only the rare earth oxide remains. Next, in order to promote inclined organization, CO gas may be introduced at the time of raising the temperature of the powder compact to prevent decomposition of the complex oxide, and vacuuming may be performed after the compact has become dense. The complex oxide in the vicinity of the surface that has become unstable in vacuum is decomposed and dissolved in the binder phase, or evaporated and scattered, resulting in a gradient structure.

The rare earth-containing sintered alloy according to the present invention has a function in which chromium dissolved in a rare earth oxide forms a composite oxide to improve the hardness of the dispersed phase and is dispersed in the rare earth-containing sintered alloy. Works to improve the strength and toughness by firmly bonding to the binder phase, and chromium or rare earth elements dissolved in the binder phase strengthens the binder phase. It has the effect of improving.

The rare earth-containing sintered alloy of the present invention is improved in hardness and toughness at the same time as compared with the conventional rare earth-containing sintered alloy in which rare earth oxide is dispersed. And defect resistance are improved.

First, commercially available Cr ₂ O ₃ having an average particle diameter of 0.2 μm and Y ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , 0.02 to 0.3 μm, Using each powder of Gd ₂ O ₃ and Yb ₂ O ₃ , weighed to the composition shown in Table 1 and inserted into a stainless steel pot lined with urethane rubber together with ethanol solvent and alumina ball. After ball milling, it was dried to obtain a mixed powder. These mixed powders are filled into a zirconia crucible, inserted into an atmospheric furnace, subjected to a heat treatment at 1550 ° C. for 1 hour, and then pulverized again for 48 hours by a ball mill to obtain a composite of (A) to (G). An oxide powder was obtained. The particle diameter (by electron microscope observation) and components (by X-ray diffraction) of the obtained composite oxide powder are also shown in Table 1.

Next, the obtained composite oxide powders (A) to (G), the aforementioned Cr ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ and commercially available WC having an average particle size of 0.5 μm (abbreviated as WC / F), 2.3 μm WC (abbreviated as WC / M), 3.5 μm WC (WC / Cb), 0.02 μm carbon black (abbreviated C), 1.0 μm Co, 1.7 μm Ni, 1.5 μm Fe, 2.3 μm Cr ₃ C ₂ , 1.0 μm Using each powder of TaC, 1.2 μm TiN, 1.1 μm (W, Ti, Ta) C (weight ratio WC / TiC / TaC = 50/20/30), the composition shown in Table 2 was obtained. Weighed and inserted into a stainless steel pot together with an acetone solvent and a cemented carbide ball, mixed and ground for 48 hours, and dried to obtain a mixed powder. Here, the amount of blended carbon is such that it becomes a medium carbon alloy (the center of the range of the healthy phase region where free carbon or Co ₃ W ₃ C, Ni ₂ W ₄ C, Fe ₃ W ₃ C or the like does not precipitate) after sintering. , C or W was added. Then, after filling these powders into a mold, producing a 18 × 18 × 7.5 mm powder compact with a pressure of 196 MPa, and placing it on a carbon plate coated with carbon black powder, It inserted in the sintering furnace and heat-sintered, and obtained the cemented carbide of this invention products 1-11 and the comparative products 1-9. Details of the atmospheric conditions in the applied temperature raising, sintering, and cooling steps are collectively shown in Table 3, and the condition number of the atmosphere is shown in Table 2 together with the temperature and time for holding the sintering.

注）＊雰囲気は昇温時の所定温度まですべて５Ｐａ、冷却時では１Ｐａの真空であり、また８００℃以上での昇温速度を１５℃／ｍｉｎとした。

Note) * The atmosphere was all 5 Pa up to the predetermined temperature at the time of temperature rise, 1 Pa at the time of cooling, and the temperature rise rate at 800 ° C. or higher was 15 ° C./min.

After cutting the center of each specimen (14.5 × 14.5 × 6 mm) of each cemented carbide obtained in this way, the section was wet ground with a 1000 # diamond grindstone and then lapped with a 1 μm diamond paste. The sample for cross-sectional structure observation was produced by processing. First, after observing the structure of the entire cross-section with an optical microscope, a structure photograph from the surface (sintered skin) of each sample to the inside is sequentially taken using an electron microscope, and the WC phase, The volume and average particle diameter (excluding the binder phase) of the metal binder phase, the dispersed phase, the cubic compound, and chromium carbide (Cr ₇ C ₃ ) were determined. The volume of each phase within 1 mm or more from the surface (however, the average volume ratio of the dispersed phase is expressed as Vi (volume%)), the average volume ratio Vs (volume%) from the surface of the dispersed phase to the inside of 0.1 mm, and Table 4 shows the volume ratio (Vs / Vi) between the surface and the inside of the dispersed phase. Table 5 shows the average particle diameter of each phase within 1 mm or more from the surface.

From the results shown in Table 4, the composite oxides added and remained in all of the products of the present invention were dispersed, but the comparative products not added as composite oxides (only chromium oxide, rare earth oxide and chromium oxide) , Rare earth oxide only), chromium oxide disappears and only the rare earth oxide is in the dispersed phase. In addition, when the rare earth element in the composite oxide is Sm, Eu, Yb, it can be seen that the gradient structure material has a disperse phase significantly reduced near the surface.

注）＊Ｖｓ／Ｖｉが０／０の場合は―で表す。

Note) When -Vs / Vi is 0/0, it is indicated by-.

Next, about two obtained specimens of each cemented carbide, one side is 0.05 mm deep from the surface (sintered skin) using a 1000 # diamond grindstone on the side (14.5 × 6 mm). The other was wet ground to a depth of 1.0 mm from the surface using 400 # and 1000 # diamond wheels. Then, after lapping each sample surface with a 1 μm diamond paste, a load using a Vickers indenter: a hardness at 294 N and a fracture toughness value K1C (IM method) were measured. These results are shown in Table 6.
According to these results, the product of the present invention in which rare earth oxide is added as a composite carbide with chromium has one of the same hardness and fracture toughness as compared with a comparative product to which only rare earth oxide is added with almost the same composition. And the other is higher. Further, in the products 6, 7, 9, 10, and 11 (containing Sm, Eu, and Yb) of the present invention, which are gradient structures, both hardness and fracture toughness are improved.

The composite oxides (A), (C), (E) used in Example 1, the oxides Y ₂ O ₃ , Ce ₂ O ₃ , Eu ₂ O ₃ , Cr ₂ O ₃ and WC / M, TaC Ni, Co, TiN, 1.3 μm TiC, 1.7 μm Mo ₂ C, 1.3 μm Ti (C, N) (weight ratio TiC / TiN = 50/50), 1.0 μm Each powder of NbC, 1.7 μm of ZrC is weighed to the blending composition shown in Table 7, and mixed, pressure-molded, and sintered in the same manner and conditions as in Example 1 to obtain the inventive products 12-14. Further, cermets of comparative products 10 to 12 were obtained. The atmospheric conditions used during sintering are those in Table 3 of Example 1, and the condition numbers and sintering conditions are also shown in Table 7.

Using the specimens of each cermet thus obtained, the distribution of the dispersed phase, the hardness, and the fracture toughness value were measured in the same manner as in Example 1, and the results are shown in Tables 8 and 9. From these results, it can be seen that the product of the present invention is higher in hardness and toughness because the composite oxide remains and is dispersed than the comparative product in which the dispersed phase is a rare earth oxide.

Using the mixed powders of the present invention products 1, 7 and 9 and comparative products 2, 5 and 9 obtained in Example 1, with a chip die with chip breaker of SNMG120408 according to ISO standard, respectively, similar to Example 1 Chip materials were obtained by press molding and sintering under the conditions described above. The upper and lower boss surfaces are ground with a 270 # diamond grindstone (however, the blade tip and breaker surface are sintered), and then the blade tip portion is polished with a nylon brush containing 320 # silicon carbide abrasive grains. Then, honing with a radius of 0.1 mm was performed to obtain cutting chips of the present invention products 16, 17, 18 and comparative products 12, 13, 14.

The following three types of cutting tests were performed using these cutting tips. These results are summarized in Table 10.
Test (A); Work material: FC250, Cutting type: Dry peripheral continuous turning, Cutting speed: 150 m / min, Cutting: 2.0 mm, Feeding: 0.3 mm / rev, Cutting time: 30 min, Evaluation criteria: Average flank wear amount VB (mm)
Test (B); Workpiece material: S48C with 4 grooves, Cutting mode: Wet outer peripheral intermittent turning, Cutting speed: 100 m / min, Cutting depth: 2.0 mm, Feeding rate: 0.3 mm / rev to 0.1 mm / Up in rev increments (the number of impacts at each feed is 3000 times), evaluation criteria: Maximum feed amount with missing or chipping (average value of 3)
Test (C); work material: SCM440, cutting form: wet peripheral continuous turning, cutting speed: 150 m / min, depth of cut: 2.0 mm, feed: 0.3 mm / rev, cutting time: 20 min, evaluation criteria: clearance Average surface wear VB (mm)

According to the test results in Table 10, it can be seen that the product of the present invention in which the composite oxide with chromium oxide is dispersed has less wear and is less likely to be deficient than the comparative product in which the rare earth oxide is dispersed.

Claims (5)

Bonding phase mainly composed of iron group metal: 3 to 30% by volume, and dispersion mainly composed of composite oxide composed of at least one oxide of scandium, yttrium and lanthanide elements and oxide of chromium Phase: 0.1 to 10% by volume, and the rest is a rare earth-containing material comprising a hard phase mainly composed of at least one of the carbides and nitrides of the periodic table 4a, 5a and 6a metals and their mutual solid solutions Sintered alloy. In the vicinity of the surface of the rare earth-containing sintered alloy, a surface region having a smaller content of the dispersed phase than the inside is formed, and the average volume fraction Vs (volume%) of the dispersed phase from the surface to the inside of 0.1 mm. ) And the average volume fraction Vi (volume%) of the dispersed phase in the interior of 1 mm or more from the surface, the rare earth-containing sintered alloy according to claim 1, wherein the ratio (Vs / Vi) is 0.5 or less. The rare earth-containing sintered alloy according to claim 1 or 2, wherein the dispersed phase contains at least one oxide of samarium, eurobium, thulium, and ytterbium. The hard phase is composed of tungsten carbide or tungsten carbide and at least one cubic compound of carbides, nitrides, oxides and their mutual solid solutions of the periodic table 4a, 5a, and 6a metals. Item 4. The rare earth-containing sintered alloy according to any one of Items 1 to 3. The hard phase is composed of at least one of titanium carbide, nitride, carbonitride of 30 wt% or more, and the remainder of the periodic table 4a, 5a, 6a group metal carbide, nitride, charcoal excluding titanium. The rare earth-containing sintered alloy according to any one of claims 1 to 3, comprising at least one of nitrides.