JPS6283403A - Production of high-hardness sintered alloy - Google Patents

Abstract

PURPOSE:To develop a high-hardness sintered alloy consisting of extremely fine crystal grains and having excellent wear resistance in a high-temp. corrosive environment by adding and mixing an oxide to and with a Cr-Ni-Co alloy powder having a specific compsn., subjecting the powder to a ball mill treatment to apply work strain thereto, then subjecting the powder to pressure molding and sintering. CONSTITUTION:The alloy powder having the compsn. consisting of 35-60% Cn, <=10% total of Al and Ti, <10% oxide such as Y2O3 and the balance Ni and Co is mixed and ground in a high-energy ball mill in the atm. atmosphere to apply the large work strain thereto. Such alloy powder 5 is packed between the inside surface of a steel pipe 4 and a cylindrical vessel 6 disposed therein and is sealed by a cap 7. The alloy powder is then subjected to pressure sintering by a high-temp. hydrostatic press. The sintered alloy layer of the ultrafine structure having <=1mum crystal grain is formed on the inside surface of the pipe 4 and the inside surface sintered layer having the excellent wear resistance even in the high-temp. corrosive environment is formed.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention is a high-temperature corrosion-resistant alloy with high wear resistance, in other words, suitable as a material for mechanical equipment parts that require wear resistance in high-temperature corrosive environments. This invention relates to a method for producing a sintered alloy.

(Prior art) A method in which a weld metal made of a high-temperature corrosion-resistant alloy with a composition in which carbides and borides are precipitated is overlay-welded onto the metal surface, and these precipitates form a hardened layer on the metal surface. It is used for surface treatment of mechanical equipment parts that require wear resistance in corrosive environments.

Examples of such alloys include stellite alloys, and it seems possible to increase the C content in order to improve high-temperature corrosion resistance, but the increase in Cr reduces the ductility of the material and increases the hardness. Precipitating carbides and borides to increase the ductility further reduces the ductility, making it difficult to put it to practical use.

(Problems to be Solved by the Invention) In order to solve the above-mentioned problems, the present invention does not rely on the hardening effect caused by the precipitation of carbides or borides, but by creating an ultra-fine structure with crystal grains of 1 μm or less. The purpose is to obtain a sintered alloy with hardness.

(Means for Solving the Problems) This invention processes a mixed powder of metal powder and oxide powder in a ball mill to give processing strain, and press-molds the powder to form a molded body at a crystal grain growth temperature. The present invention relates to a method for producing a high-hardness sintered alloy, which is characterized in that it is sintered at the following temperature to form a sintered body with a fine grain structure.

In the present invention, a highly hard sintered body without precipitation of carbides or borides is obtained because large processing strains are imparted to the powder by a ball mill, which recrystallizes during sintering to form an ultrafine grain structure of 1 μm or less. Primarily based on becoming.

The sintering temperature is set to be below the crystal grain growth temperature; if the temperature is too high, the metal structure will become coarse, which is not preferable.

Since the raw material powder is subjected to large processing strains, the compact is easily sintered by heating below the grain growth temperature, and
It recrystallizes and becomes an ultra-fine grain structure.

Even if 35% or more of Cr is added to obtain sufficient high-temperature corrosion resistance, a sufficiently hardened sintered body can be obtained according to the method of the present invention. High-temperature corrosion resistance increases as the crystal grains become finer (i.e., due to the early formation of a protective film by promoting grain boundary diffusion of atoms); from this point of view, the high-temperature corrosion resistance is higher than that of conventional hardening methods such as overlay welding and plasma spraying. You can get excellent results.

If the Cr content is 60% or more -F, the hardened layer becomes brittle, so the upper limit is preferably 60%.

The addition of oxides is effective as an inhibitor against grain growth during sintering. Oxides are also generated by oxidation during processing in a ball mill, but it is better to add them in advance from the standpoint of quality control. It is better to do so.

A1 and Ti are effective for high-temperature corrosion resistance and hardening, but if added in a large amount, embrittlement occurs, so it is best to limit the amount to 10%.

The present invention is characterized by subjecting the metal powder to a large processing strain before sintering, and a high-energy ball mill is suitable for this purpose. A high-energy ball mill is a normal ball mill equipped with an impeller for stirring the balls, and can shorten processing time. As the balls collide with each other during operation, the powder sandwiched between them undergoes significant deformation, but an example of the conditions for effective treatment is as follows.

Ball-to-powder weight ratio: 20 Impeller rotation speed: 20 rpm Processing time: 30 hours In order to obtain the same processing effect in a normal ball mill, several times longer time is required.

In order to create a compact before sintering, the alloy powder to which large processing strains of the present invention have been applied is conventionally filled into a mold and press-molded. In addition, as shown in FIG. 1, a treated powder 2 has been strained on the surface of a metal part 1 whose hardness is desired to be increased in a part of the surface.
is placed and sintered using the press jig 3 at a temperature below the recrystallization temperature while pressurizing in vacuum or inert gas.

If the high-temperature strength of the component 1 whose surface hardness is to be increased is low and deformation occurs during pressure sintering, the strain imparting powder of the present invention is shaped and sintered into the desired shape in advance, and this sintered body is waxed. With?
If it is bonded to the surface of a metal part using JI412 or diffusion brazing 4, it will be L.

Further, as shown in FIG. 2, the hardened powder 5 of the present invention is filled between the inner surface of the tube 4 whose inner surface hardness is desired to be increased and the cylindrical container 6, sealed with a lid 7, and pressed with a tooth temperature isostatic press (not shown). It is also possible to form a hard inner layer by pressure sintering.

(Example) Next, an example will be described.

605 grams of N+ powder with a particle size of 5 pm, 350 grams of Cr powder with -325 methane, A1 and Ti with -325 methane powder.
A mixed powder of 20 grams of each powder and 5 grams of 0.02 μm Y2O3 powder was processed in a high-energy ball mill in an air atmosphere, and the powder was molded at a pressure of 200 kir/-, and the molded body was sintered at 1050°C for 1 hour. did. 35
The Vickers hardness 11ν of this sintered body containing % Cr was about 500. For comparison, the hardness of a sintered body obtained by sintering the mixed powder in the same manner without applying strain was 11ν200.

(Effects) As described above, according to the method of the present invention, metal powder is processed using a high-energy ball mill, etc., and a large processing strain of 1j,
Therefore, when a compact formed from this metal powder is sintered by heating at a temperature below the crystal grain growth temperature, it becomes a fine crystal structure and exhibits high hardness.

Therefore, since the hardness can be increased without the presence of precipitates such as carbides and borides, there is an advantage that the hardness does not deteriorate due to the precipitates.

In addition, since the crystal grains are fine, it exhibits excellent high-temperature corrosion resistance, which is extremely effective in practical applications.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the method of the present invention applied to a metal surface, and FIG. 2 is a cross-sectional view showing an example of the method applied to the inner surface of a cylinder. 1... Metal to be hardened, 2... Strain imparting powder,
3...Press, 4...Cylinder, 5...Strain imparting powder,
6...Cylindrical container, 7...Lid Applicant's agent Patent attorney Kamoshi 1) Second son 17th 2nd ward

Claims (1)

[Claims] 1. Processing a mixed powder of metal powder and oxide powder in a ball mill to give processing strain, and sintering the molded body obtained by press-molding the powder at a temperature below the crystal grain growth temperature. 1. A method for producing a high-hardness sintered alloy, characterized in that a sintered body having a fine grain structure is obtained. 2. The method for producing a high hardness sintered alloy according to claim 1, wherein the mixed powder is 35 to 60% Cr, 10% or less AL+Ti, 10% or less oxide, and the balance Ni+Co. 3. A method for producing a high-hardness sintered alloy according to claim 1 or 2, which comprises pressurizing and sintering ball-milled powder on a metal surface to form a sintered body.