JPH05124862A - Surface-refined chromium compound sintered compact and its production - Google Patents

Abstract

PURPOSE:To produce a surface-reined Cr compd. sintered compact having excellent corrosion resistance, lubricity at high temp., no wettability with glass, etc., and excellent releasability from glass, etc., owing to the refined surface layer as well as enhanced strength and toughness owing to the structure of the refined surface layer and that of the interior of the sintered compact. CONSTITUTION:A refined surface layer is formed in the surface part of a sintered compact contg. >=50wt.% Cr compd. consisting of Cr-contg. oxide and Cr-contg. carbide and the average content of the Cr-contg. oxide in the relevant refined surface layer is made higher than that in the interior of the sintered compact to obtain the objective Cr compd. sintered compact having excellent hardness, corrosion and wear resistances, strength, toughness and chipping resistance in a well-balanced state and such remarkably excellent lubricity at high temp. as a coefft. of friction corresponding to about 26-71% of that of a conventional material and about 3-55% abrasion loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature corrosion resistant material typified by a furnace wall for steelmaking nozzles, skid buttons, glass molding dies, glass melting, etc., or a high temperature sliding typified by a bearing used under high temperature conditions. The present invention relates to a surface-treated chromium compound sintered body suitable for a dynamic material or a wear resistant material represented by a yarn path and a mechanical seal, and a method for producing the same.

[0002]

2. Description of the Related Art Chromium compounds such as chromium carbide and chromium oxide have excellent properties, but on the other hand, it is extremely difficult to form a dense sintered body and the toughness of the sintered body is extremely poor. There's a problem.

Representative examples of solving the above problems and applying various excellent properties of chromium compounds are disclosed in JP-A-60-191059, JP-A-2-74531, and JP-A-2-24531. There is 26841 publication.

[0004]

Problems to be Solved by the Invention JP-A-60-1910
In Japanese Patent Publication No. 59, a chromium carbide-based ceramic composed of one or a mixture of two or more chromium carbides of Cr ₃ C ₂ , Cr ₇ C ₂ and Cr ₄ C, or chromium carbide containing TiC and TiO.
_It describes a chromium carbide-based ceramic containing an additive of ₂ , ZrO ₂ , and Ni-P alloy.

The chromium carbide-based ceramics disclosed in the publication are superior to the conventional chromium carbide-based ceramics in bending strength, thermal shock resistance, hardness, workability, various high temperature characteristics, and acid and alkali corrosion resistance. However, there is a problem that the oxidation resistance, the high-temperature mechanical characteristics, and the wear resistance are not satisfied, and the friction coefficient is high.

Japanese Unexamined Patent Publication (Kokai) No. 2-74531 discloses an optical element molding in which a mold having a coating containing chromium and nitrogen as main components is heated in an oxidizing atmosphere to form Cr ₂ O ₃ on the outermost surface. The type is described.

The optical element molding die of the same publication has a C on the outermost surface.
With r ₂ O ₃ , the wettability with glass is prevented, good releasability is brought out, and corrosion resistance to molten glass is excellent, but the coating is inferior in impact resistance and thermal shock resistance and There is a problem of easy peeling.

JP-A-2-26841 discloses an optical system in which at least the molding surface of a molding die is made of at least one chromium-containing substance selected from chromium oxide, chromium oxycarbide, chromium oxynitride, or chromium oxycarbonitride. A glass molding mold is described.

The optical glass molding mold of the above publication has the same problems as those of the above-mentioned JP-A-2-74531 when the glass-containing material on the molding surface is composed of a coating film, and the chromium-containing material on the molding surface. , Which consists of a sintered body, becomes fragile or has many holes due to the relationship between the layer thickness of the sintered body of the chromium-containing substance and the material and substrate thickness of the molding mold. There is a management problem.

The present invention has solved the above-mentioned problems, and more specifically, the surface portion of a sintered body containing a chromium compound which is a mixture of an oxide containing Cr and a carbide containing Cr. By increasing the average content of Cr-containing oxides in the surface heat-treated layer formed on the surface, corrosion resistance, high temperature lubricity, prevention of wettability to glass, etc., and releasability at the surface of the sintered body can be improved. Provided are a surface-treated chromium compound sintered body and a method for producing the same, in which the strength and toughness are improved by the composition of the whole sintered body, and the quality control in the production is easy. To aim.

[0011]

The present inventors have taken advantage of the greatest advantage of chromium oxide, which is corrosion resistance and high temperature lubricity,
On the contrary, when I was studying to solve the problems of low strength and low toughness, which are the drawbacks of chromium oxide, when a compact sintered body was made by containing chromium oxide and chromium carbide that hardly form mutual solid solution, Grain growth is suppressed to obtain high strength and high toughness, and the advantage of chromium oxide can be utilized by enriching the chromium oxide on the surface of the sintered body, especially the chromium oxide on the surface of the sintered body. It has been found that when the content of is reduced from the surface of the sintered body toward the inside, the above-mentioned advantages are retained and the drawbacks are overcome to obtain more excellent properties.

The present invention has been completed based on this finding.

The surface-conditioned chromium compound sintered body of the present invention is a sintered body containing 50% by weight or more of a chromium compound containing Cr-containing oxide and Cr-containing carbide. A surface refining layer is formed on the surface of the body,
The average content of the oxide containing Cr in the surface-refined layer is C in the inside of the sintered body excluding the surface-refined layer.
It is characterized in that it is larger than the average content of the oxide containing r.

The chromium compound in the sintered body of the present invention is
Specifically, for example, Cr₂O₃, (Cr Al )₂O₃, (C
r Ti)₂O₃Such as chromium oxide or chromium and other metals
Oxide containing one or more of the complex oxides containing Cr
And Cr₃C₂, Cr₇C₂, Cr_{twenty three}C₆Chromium carbide such as
More specifically, one or more of the compound carbides of chromium and other metals
A mixture of Cr and a carbide containing Cr.
You can Contains Cr mixed as a chromium compound
The amount of oxides contained in the surface heat-treated layer of the sintered body and inside the sintered body
It is preferable that there is a difference of 10% by weight or more between
50% by weight or more of oxide containing Cr exists in the surface heat treatment layer.
Preferably exists.

The chromium compound is 50% by weight of the whole sintered body.
When it is contained in the above amount and is less than 50% by weight, it becomes difficult to bring out the various properties of the compound, particularly the advantages of both the oxide containing Cr and the carbide containing Cr.

When the sintered body is made of only a chromium compound, or in addition to the chromium compound, it is contained for the purpose of promoting densification, improving strength and toughness, improving wear resistance or heat resistance, such as Fe, Examples thereof include Ni, Co, Cr, oxides, carbides, nitrides, aluminum oxides and oxides of rare earth metals of 4a, 5a and 6a metals of the periodic table, and mutual solid solutions thereof. Of these, aluminum oxide is a solid solution with chromium oxide and contributes to the improvement of wear resistance, and it is preferable to contain 10 to 40% by weight because the effect is high. Fe, Ni, Co, and Cr have high effects on the strength, toughness, thermal shock resistance, and acceleration of densification of the sintered body, and the effects become remarkable when they are contained in an amount of 5 to 30% by weight. An oxide of a metal of group 4a, 5a, 6a of the periodic table,
Carbides, nitrides, mutual solid solutions thereof (excluding chromium oxide and chromium carbide alone), and oxides of rare earth metals have the effect of improving wear resistance or toughness. Specifically, for example, zirconium oxide partially stabilized with Y ₂ O ₃ , CeO ₂ , MgO or the like is highly effective in improving toughness, and is particularly remarkable when it is contained in an amount of 10 to 40% by weight.
O ₂ and Nb ₂ O ₃ have the effect of improving wear resistance and lubricity at high temperatures, and TiC, TaC, Yb ₂ O ₃ and CeO ₂ have the effect of improving toughness and strength.

In the surface heat-treated layer of the sintered body of the present invention, the average content of Cr-containing oxide in the surface-heat treated layer is present inside the sintered body excluding the surface-heat treated layer. The content of the oxide containing Cr in the surface of the surface heat-treated layer is higher than the average content of the oxide containing Cr. That is, the content is higher than the average content of oxides containing. The constitution of the component composition and the layer thickness of the surface conditioning layer can be selected depending on the application or the shape. Specifically, for example, in the composition of the component composition of the surface heat treatment layer, more metal oxides are present than in the inside of the sintered body, and among them, C
When the amount of oxides containing r is large, and the amount of oxides containing Cr gradually decreases from the surface to the inside, the amount of oxides containing Cr is constant from the surface to the inside. Then, the case where it gradually decreases further inward can be given. Further, the layer thickness of the surface heat treatment layer can be adjusted from submicron to several mm.

In order to enhance the strength and toughness of the sintered body and to maximize the effect of the Cr-containing oxide, the surface-refining layer is an oxidation containing Cr in the surface-refining layer. It is preferable that the material gradually decreases from the surface of the surface heat-treated layer toward the inside of the sintered body.

Further, the oxide containing Cr in the surface tempered layer has a substantially uniform content from the surface of the surface tempered layer toward the inside of the sintered body up to at least 0.05 mm, and then further sintered. At least 0.05m toward the inside of the body
It is particularly preferable that the above-mentioned effect can be enhanced when the content is gradually decreased to m and becomes an average content in the inside of the sintered body. It is particularly preferable that the thickness of the surface refining layer is 0.1 to 2 mm because the above-mentioned effects can be enhanced.

The sintered body of the present invention is produced by the conventional powder metallurgy method, P
VD treatment (physical vapor deposition method) or CVD treatment (chemical vapor deposition method)
However, it is preferable to use the method of the present invention described below because the adjustment and control of the surface refining layer can be easily performed.

The method for producing a surface-modified chromium compound sintered body according to the present invention comprises two or more kinds of powders selected from chromium oxide, metallic chromium, chromium carbide, and carbon (provided that only chromium oxide and metallic chromium are used. (A combination is excluded) as a main component, a powder compact made of a mixed powder is heated and fired in an oxidizing atmosphere, and then heat-sintered in a non-oxidizing atmosphere to obtain a sintered body. A surface-tempered layer is formed toward the inside, and the average content of chromium oxide in the surface-refined layer is higher than the average content of chromium oxide in the interior of the sintered body excluding the surface-refined layer. It is a method characterized by increasing the number.

It is an important feature that the mixed powder in the method for producing a sintered body of the present invention contains carbon or chromium carbide. When carbon is mixed in the mixed powder,
A carbon content of 1 to 30% by weight with respect to metallic chromium and / or chromium oxide is preferred. After forming this powder mixture into a powder compact, it is heated and baked in an oxidizing atmosphere to increase oxides or decrease carbon elements on the surface.

It is necessary to select the heating and firing and the sintering depending on the constitution of the surface conditioning layer of the desired sintered body, but the heating and firing is carried out under the condition of holding at 350 to 450 ° C. for 10 minutes to 5 hours in the atmosphere. Then, in a N ₂ inert gas atmosphere or a non-oxidizing atmosphere in a vacuum, at a temperature of 1300 to 1600 ° C. for 30 minutes to 2
Sinter by holding for a time.

For the sintering, it is preferable to use a hot pressing method because a dense and fine sintered body can be easily obtained, and further hot isostatic treatment after sintering can obtain more excellent mechanical properties.

[0025]

In the surface-modified chromium compound sintered body of the present invention, the surface-conditioned layer functions to enhance corrosion resistance, releasability, wear resistance and lubricity, and the inside of the sintered body has strength and toughness. ， It has the function of increasing the thermal shock resistance, and the function of increasing the thermal shock resistance by the combination of the surface refining layer and the inside of the sintered body.

Further, in the method for producing a surface-modified chromium compound sintered body of the present invention, a mixed powder containing two or more kinds of powder selected from chromium oxide, metallic chromium, chromium carbide and carbon as a main component is used. It has the function of facilitating the formation and control of the surface refining layer.

[0027]

EXAMPLES Commercially available Cr ₃ having an average particle size of 1 to 2 μm
C ₂ , Cr ₂ O ₃ , Carbonyl Ni, TiC, TaC, H
fO ₂ , Nb ₂ O ₅ and Yb ₂ O ₃ , each powder, average particle size of 0.
3 μm high-purity Al ₂ O ₃ powder, ZrO ₂ (3 mol% Y ₂ O ₃ added) powder with an average particle diameter of 0.03 μm, metal Cr of ^# -325, and carbon black powder were used and shown in Table 1. Blended with the composition components to obtain blended powder.

[0028]

[Table 1] To these compounded powders, 6% by weight of a polyethylene glycol-based molding aid was added, placed in an alumina container together with zirconia balls and methanol, mixed for 48 hours, dried and passed through a # 60 sieve to obtain the mixed powder. Obtained. These mixed powders were pressed with a mold at a pressure of 1 ton / cm ² to form a powder compact of 25 (diameter) × 25 (thickness) mm. Then, after degreasing by holding in air at 300 ° C. for 1 hour, the oxidation treatment conditions and the sintering conditions shown in Table 2 were applied to obtain Products 1 to 10 of the present invention.

[0029]

[Table 2] For the sintering, an atmosphere sintering furnace heated by a carbon heater or a hot press furnace heated by a high frequency is used, and a powder compact is embedded in a carbon mold filled with BN powder to obtain 200 kg /
Addition of cm ² pressure, 1 atm N ₂ gas or 10 ^-2 T
Processed in an orr vacuum.

For comparison, Comparative Products 1 to 4 were obtained in the same manner as the above-described product of the present invention except that the oxidation treatment conditions shown in Table 2 were not applied.

The products 1 to 10 of the present invention thus obtained and the comparative product 1
For Nos. 4 to 4, after cutting each into a half with a diamond cutter, polishing the cut surface, diamond lapping, and if necessary, etching treatment and baking with a surface-conditioned layer by an optical microscope, SEM and micro X-ray diffraction. Look inside the union,
The results are shown in Tables 3 and 4.

[0032]

[Table 3]

[0033]

[Table 4] Next, various characteristics of the products 1 to 10 of the present invention and the comparative products 1 to 4 were examined, and the results are shown in Table 5.

[0034]

[Table 5] *, ◎: No reaction trace, no welding, ○: Reaction trace, no welding, Δ: Large reaction trace, welding, ×: Reaction layer, welding

[0035]

INDUSTRIAL APPLICABILITY The surface-treated chromium compound sintered body of the present invention optimally exhibits the respective effects of the surface-conditioned layer and the inside of the sintered body. Hardness, corrosion resistance, wear resistance, strength, and toughness compared to certain chromium carbide-based ceramics sintered bodies, chromium carbide-based cermet sintered bodies, chromium oxide-based ceramics sintered bodies, or chromium oxide-chromium carbide-based ceramics sintered bodies And the fact that each of the fracture resistance is excellent in a well-balanced manner,
Further, the friction coefficient at high temperature is lower than that of the conventional material (26 to 71% of the conventional material), and the amount of wear loss is small (3 to 55% of the conventional material), which is a remarkably excellent effect of high temperature lubricity. ..

Claims (5)

[Claims] 1. A sintered body containing 50% by weight or more of a chromium compound consisting of a Cr-containing oxide and a Cr-containing carbide, wherein a surface heat-treated layer is formed on the surface of the sintered body. And the average content of the oxide containing Cr in the surface refined layer is higher than the average content of the oxide containing Cr in the inside of the sintered body excluding the surface refined layer. A surface-treated chromium compound sintered body characterized by an increasing number. 2. The oxide containing Cr in the surface refining layer gradually decreases from the surface of the surface refining layer toward the inside of the sintered body. Surface-treated chromium compound sintered body. 3. The oxide containing Cr in the surface refining layer has a substantially uniform content up to at least 0.05 mm from the surface of the surface refining layer toward the inside of the sintered body,
Further, at least 0.05 mm toward the inside of the sintered body
2. The surface-treated chromium compound sintered body according to claim 1, wherein the content is gradually reduced to an average content inside the sintered body. 4. The surface conditioning layer has a thickness of 0.1 to 2 m.
The surface-treated chromium compound sintered body according to claim 1, 2, or 3, wherein m is m. 5. Chromium oxide, metallic chromium, chromium carbide,
A powder compact made of a mixed powder containing two or more powders selected from carbon (excluding the combination of chromium oxide and metallic chromium only) as the main component is heated and baked in an oxidizing atmosphere, and then non-oxidizing A sintered body is obtained by heating and sintering in an atmosphere, and a surface-conditioned layer is formed from the surface of the sintered body toward the inside, and the average content of the oxide containing Cr in the surface-conditioned layer is A surface-modified chromium compound sintered body characterized in that the content of Cr-containing oxide in the interior of the sintered body excluding the surface-conditioned layer is higher than the average content thereof. Production method.