KR950014351B1 - Method of manufacturing complex chrome carbide system - Google Patents

Abstract

The chromium carbide based composite is prepared by (a) mixing 65-95 wt% chromium carbide powder, 5-35 wt% metallic binder including one or more components of nickel, chromium, cobalt and iron powder, and molding it with the conventional method, (b) sintering the molded body at 1,250-1,600 deg.C, in reduction atmosphere under more than 10 MPa pressure with isotropic pressure sintering method. The another starting materials include nonoxide group such as TiC, TiN, TiCN, WC, Mo2C and TaC, high melting point metal group such as molybdenum and niobium etc.

Description

Method for preparing chromium carbide composite

1 is a photograph of a chromium carbide-based composite prepared by atmospheric sintering

2 is a photograph of a chromium carbide-based composite prepared by pressing and sintering

3 is a photograph of a chromium carbide-based composite prepared according to the present invention

* Explanation of symbols for main parts of the drawings

1: Pre-sintered molded body 2: Atmospheric pressure sintered body

3: crack 4: evaporation site of metal binder

5: pressure sintered body 6: over-aggregation site of the metal binder due to pressure

7: Isotropic pressure sintered cylindrical skid button

8: Isotropic Pressurized Plate Type Hexahedral Skid Button

9: Isotropic Pressure Sintering Guide Roller

The present invention is a variety of engineering parts, ie bearings, pump parts, mechanical seals, cutters, nozzles, guide rollers, steel mill heating furnace skid button, pipe line The present invention relates to a method for producing a chromium carbide-based composite used for a tube, a tube, and the like, and more particularly, to a method for producing a chromium carbide-based composite by hot isostatic pressing and heat treatment. .

In general, there are various methods of sintering (or densifying) powders, and these methods include pressureless sintering (Korean Patent Application No. 92-26487), and hot pressing (Korean Patent Application No. 92-l4097). Methods are known.

In the case of atmospheric sintering, however, mass production is possible, but the productivity decreases due to a relatively slow heating process for sintering difficult sintered materials. As shown in FIG. 5, there is a problem in that defects such as sintering or breaking are high.

On the other hand, in the case of pressurized sintering, the defect rate is small, but it is difficult to mass-produce due to equipment limitations, and as shown in FIG. 2 when pressurized at the sintering temperature, non-homogeneous fine metals are locally bitten or pushed out of the sintered body. There is a problem with organization.

Due to the low mechanical properties of chromium carbide, no commercially available products are known in the world, and the possibility is only suggested by domestic patent applications 92-14097 and 92-26487.

However, there are several academic studies to investigate the effects of properties, sintering properties, and additives [J. of Japan Soc. of Powder ＆ Powder Metall. 37 (7) 121-128, 1987. Solid State Pheneo. (8.9) 383-386, 1989].

Accordingly, the present inventors have conducted research and experiment on the improvement of the above-mentioned domestic patent applications Nos. 92-14097 and 92-26487, and based on the results, the present invention proposes a metal binder and an additive. Isotropically pressurized sintered hard sintered chromium carbide composites lead to uniform microstructures in the sintered composites and additional heat treatment to induce grain growth, especially to improve high-temperature mechanical properties, as well as mass production of products. It is intended to manufacture a chromium carbide-based composite having high economical efficiency due to a low defect rate, a wide application field from room temperature to high temperature.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is a mixed material composed of Cr ₃ C ₂ (chromium carbide) powder: 65-95wt% and one or two or more selected from the group of metal binders consisting of Ni, Cr, Co and Fe powders: 5-35wt%. The present invention relates to a method for producing a chromium carbide-based composite by molding in a conventional manner and isothermally sintering at a temperature of 1250-1600 ° C., a reducing component crisis, and a pressure condition of 10 MPa or more.

In addition, the present invention is Cr ₃ C ₂ (chromium carbide) powder: 65-90wt%, one or two or more selected from the group of metal binders consisting of Ni, Cr, Co and Fe powder: 5-15wt% and TiC, TiN , TiCN, WC, Mo ₂ C, TaC 1 or 2 or more selected from a non-oxide group consisting of: a mixed raw material composed of 5-20wt% by a conventional method, and then the temperature of 1250-1600 ℃, The present invention relates to a method for producing a chromium carbide-based composite by isotropic pressure sintering under a reducing atmosphere and pressure conditions of 100 MPa or more.

In addition, the present invention is Cr ₃ C ₂ powder: 65-90wt%, Ni, Cr, Co and Fe powder selected from the group consisting of metal binder group or two or more: 5-20wt%. And Mo, and Nb selected from the group of high-melting-point metals consisting of one or two: 5-25 wt% of a mixed raw material by molding in a conventional manner, followed by a temperature of 1250-1600 ° C., a reducing atmosphere and a pressure of 10 MPa or more. It relates to a method for producing a chromium carbide-based composite by isostatic pressing sintering.

In addition, the present invention is Cr ₃ C ₂ powder: 55-85wt%, one or two or more selected from the group of metal binders consisting of Ni, Cr, Co and Fe powder: 5-15wt%, TiC, TiN, TiCN, WC One or two or more selected from non-oxide groups consisting of, Mo ₂ C, and TaC: 5-15 wt% and one or two selected from high-melting metal groups consisting of Mo and Nb: 5-15 wt% The present invention relates to a method for preparing a chromium carbide-based composite by molding a mixed raw material in a conventional manner, and then isostatically sintering the same at a temperature of 1250-1600 ° C., a reducing component crisis, and a pressure of 10 MPa or more.

Hereinafter, the present invention will be described in more detail.

If the content of the Cr ₃ C ₂ powder is too large, there is a brittleness problem that the composite is close to the ceramic and easily broken when impact or load is applied, and when too small, the plastic deformation is easily caused by the metal component as a binder at high temperature. As such, the content of the Cr ₃ C ₂ powder is preferably limited to 55-95wt%.

In order to sinter non-sinterable Cr ₃ C ₂ -based ceramic raw materials, a minimum amount of metal binder is required by the liquid phase sintering method. Inappropriate addition amount should be added at least 5% to have uniform microstructure and strength. The higher the amount of the metal binder added, the higher the sintering is at low temperature. However, if the amount of the metal binder is too high, structural deformation of the composite is caused by the fluidity of the metal binder at high temperature, and the wear resistance and chemical stability are low. It is desirable to limit to 35wt%.

The TiC, TlN, WC, TiCN, Mo ₂ C, mid non-oxide powders such as TaC, if to be added to the Cr ₃ C ₂ with excellent Studies Stability to rather than wear resistance, and excellent in thermal shock resistance material system Cr ₃ C ₂ system, the Cr There is an effect that the mechanical properties of the ₃ C ₂ -based composite is improved.

The non-oxide powder should be added 5wt% or more in order to obtain the addition effect, but if 20wt% or more, since the Cr ₃ C ₂ properties, that is, the chemical stability is lost or relatively inferior, the addition amount of the non-oxide powder is 5- It is preferable to limit to 20wt%.

The Mo and Nb is a high melting point metal is added to increase the toughness (break resistance), in order to obtain the effect of the addition should be at least 5wt%, but if more than 25wt% between Cr ₃ C ₂ and the metal binder Since the bonding strength may be lowered to lower the strength value, the amount of the high melting point metal added is preferably limited to 5-52 wt%.

Hereinafter, the sintering conditions and the like will be described.

However, it is difficult to densify the structure of the sintered body with sinterable non-oxide chromium carbide raw material, and even if the densification of the structure, the room temperature curvature is 50-150MPa, which limits the application to mechanical structural parts.

In order to manufacture a chromium carbide-based sintered body, atmospheric pressure sintering or pressure sintering may be used like other ceramics. However, it is difficult to achieve densification of structure due to its sinterability characteristics at atmospheric pressure sintering, and to obtain mechanical properties of parts, it takes long time sintering process and several heat treatments and it is uneconomical. Uniaxial pressure sintering has advantages in densification of structure compared to normal pressure sintering, but low-melting point metal escapes or is concentrated in some areas when pressurized at the highest sintering temperature. Such a sintered body has a high probability of being easily destroyed by external forces when used as a non-uniform microstructure, and there is a disadvantage in that mass production is not possible due to structural limitations of the equipment.

An improvement in the sintering method described above is an isotropic pressure sintering method. The applied pressure can be sintered from 1250 ℃, which is lower than normal pressure sintering in the effect of temperature rise, and the range of pressurization is selected according to the application, but more than 10MPa.

There is no specific limitation because the temperature and pressure are determined according to productivity, economical time such as sintered body manufacturing time, and desired physical properties. However, when isotropic pressure sintering, the sintering temperature is preferably limited to 1600 ° C. or less. That is, when the sintering temperature is 1250 ° C. or less, there is no fluidity of the metal binder, so that uniform liquid phase sintering is not achieved. The powder begins to dissolve, and at high temperatures, the energy and manufacturing costs are increased, and the furnace equipment is limited. Ultimately, when sintering at high temperature [1600 ° C or higher], over sintering occurs, so that the structure is the same as in low temperature sintering. This is not uniform and the evaporation of the metal binder becomes very severe. Therefore, the sintering temperature at the time of the isotropic pressure sintering is preferably limited to 1250-1600 ℃.

At this time, the sintering atmosphere should be a reducing atmosphere, and the atmosphere may include vacuum, nitrogen or argon, and hydrogen atmosphere.

In the present invention, by using the isotropic pressure sintering method described above, it is possible to produce a chromium carbide composite cracked at a low temperature within a short time, and mass production of various industrial products becomes possible.

In addition, a low melting point metal is required for the densification of the structure of the hard sinterable chromium carbide, which requires a large amount of addition at atmospheric pressure sintering, and the metal components must be evaporated by heat treatment for high temperature application or abrasion resistance. The isotropically pressurized sintering method can reduce the amount of metal binder added to 4-5%.

On the other hand, in the present invention, the heat treatment may be performed to induce particle growth in order to improve the mechanical properties (creep resistance, wear resistance) of the sintered body sintered by the above-described method. At this time, the heat treatment temperature is at a temperature higher than the equivalent pressure sintering temperature, there is also the effect of removing residual stress due to grain growth, the preferred heat treatment temperature in the present invention is 1250-1650 ℃.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

To prepare a chromium carbide-based composite by molding a mixed raw material, as shown in Table 1 below, and sintering as shown in Table 2, and then measured mechanical properties, the results are shown in Table 2 below.

On the other hand, photographic observation of the chromium carbide-based composite (application fum) prepared as described above, and the results are shown in Figs.

FIG. 1 shows a case of Comparative Example (a) at atmospheric pressure sintering, FIG. 2 shows a case of Comparative Example (b) sintering under pressure, and FIG. 3 (a) shows a case of Invention Example 2 having isostatic pressure sintering. 3 and (b) show the case of the invention example (4).

In Fig. 1, reference numeral "r represents a sintered wire molded body," 2 "represents an atmospheric pressure sintered body," 3 "represents a crack, and" 4 "represents a metal binder evaporation site.

In Fig. 2, reference numeral 5 denotes a pressurized sintered body, and 6 denotes a metal binder overflocculation due to pressure.

In Fig. 3A, reference numeral 7 denotes an isostatically pressed sintered cylindrical skid button, and 8 denotes an equivalent sintered plate-shaped hexagonal skid button.

In Fig. 3B, reference numeral 9 denotes an equivalent pressure sintering guide roller.

TABLE 1

TABLE 2

* It varies depending on the composition, and it is the result after primary tissue densification process without heat treatment process in the range of lowest and highest values (destructive toughness and hardness measured by indentation method:

As shown in Table 2, it can be seen that the invention example (1-4) of isostatic pressure sintering is superior in mechanical properties than the comparative examples (a, b) of pressurizing and sintering at normal pressure.

In addition, as shown in FIG. 1, in the comparative example (a) of atmospheric pressure sintering, it can be seen that not only the shape change but also the cracks and the structure of the metal binder material aggregated excessively in a specific region are observed.

In addition, as shown in Figure 2, in the case of the comparative example (b) sintered by pressure it can be seen that the metal binder in the molten state is moved to the outside of the composite at the sintering temperature to show an uneven microstructure.

On the other hand, as shown in FIG. 3, in the case of the invention example of equivalent pressure sintering, it can be seen that a uniform microstructure is obtained.

Claims (4)

Cr ₃ C ₂ powder: 65-95 wt%; And one or two or more selected from the group of metal binders consisting of Ni, Cr, Co and Fe powders, and a mixed raw material composed of 5-35 wt% by a conventional method, followed by a temperature of 1250-1600 ° C. And isotropic pressure sintering at a pressure of 10 MPa or more. Cr ₃ C ₂ powder: 65-90 wt%; 1 type or 2 or more types selected from the group of metal binders consisting of Ni, Cr, Co and Fe powders: 5-15 wt% and 1 type selected from the non-oxide group consisting of TiC, TiN, TiCN, WC, Mo ₂ C, and TaC Or at least two kinds: chromium carbide-based composite, characterized in that by molding a mixed raw material composed of 5-20wt% by a conventional method, and isostatic pressure sintering at a temperature of 1250-1600 ℃, reducing atmosphere and pressure of 100MPa or more. Manufacturing method. Cr ₃ C ₂ powder: 65-90wt%, one or more selected from the group of metal binders consisting of Ni, Cr, Co and Fe powders: 5-20wt%: and from a high melting point metal group consisting of Mo, and Nb Selected single or two species: chromium carbide system characterized in that the mixed raw material is composed of 5-25wt% by molding in a conventional manner, and then isostatically sintered at a temperature of 1250-1600 ℃, reducing atmosphere and pressure of 10MPa or more Method for preparing a composite. Cr ₃ C ₂ powder: 55-85wt%, one or more selected from the group of metal binders consisting of Ni, Cr, Co and Fe powders: 5-15wt%, TiC, TiN, TiCN, WC, Mo ₂ C, And a mixed raw material composed of one or two or more selected from the non-oxide group consisting of TaC: 5-15 wt%, and one or two selected from the high melting point metal group consisting of Mo and Nb: 5-15 wt%. After molding in a conventional manner, the method for producing a chromium carbide-based composite, characterized in that the isostatic pressure sintering at a temperature of 1250-1600 ℃, reducing component and pressure conditions of 10Mpa or more.