JPH089721B2 - Manufacturing method of powder sintered product - Google Patents

Description

The present invention relates to a method for producing a powder sintered product.

(Prior Art) Attempts have been made to mold powder, heat it at a temperature below the melting point of the material that composes it, and create a strong bond to use it as a component. It is completely in the practical stage as powder metallurgy. According to this powder metallurgy, it is a particularly important technique in the manufacture of parts made of a material that is difficult to manufacture by melting or casting due to its high melting point, or a material that is difficult to forge because of its high hardness.

Further, recently, a metal injection molding method aiming at a more complicated shape and high precision has been developed, and products by this molding method are being supplied to the market.

In order to improve the slippage between powders in these powder moldings, organic substances are usually added, but the amount added is several% of the volume in powder metallurgy, and higher fluidity in injection molding. It reaches 40 to 50% of the volume because it is required.

(Problems to be Solved by the Invention) However, these organic substances have an independent step of degreasing in order to remove the organic substances particularly in the process until the completion of sintering in the injection molding method. It is difficult to completely remove it, and it remains in the sintered product,
This is a cause of deterioration of the characteristics of the sintered product.

That is, for example, in electromagnetic properties such as permalloy and electromagnetic soft iron, the properties decrease as the carbon content increases, and in martensitic stainless steels that require corrosion resistance, the corrosion resistance decreases and becomes magnetic. There was a problem.

Further, the low carbon content metal represented by the above requires the use of low carbon content powder to obtain the sintered product, and as a result, the cost of the powder sintered product increases due to the powder refining cost and the like. It was.

The present invention has been made to solve such a problem, and its object is to reduce the carbon content in a sintered product, thereby providing a high-quality powder excellent in electromagnetic characteristics and corrosion resistance. It is to provide a method for manufacturing a sintered product.

(Means for Solving the Problems) In order to achieve the above object, in the method of the present invention,
As a molding material, a mixture of metal powder, a mixture of metal powder and its oxide, and an organic binder is used, the molding is injection molding, and the organic binder is removed by heating in an oxidizing atmosphere after molding. By degreasing, an oxide film is formed on the powder surface, and by sintering in a reducing atmosphere during sintering, when oxygen dissociates, it dissociates as CO gas or CO ₂ gas, In the method for manufacturing a powder sintered product having a reduced carbon content, the degreasing step is characterized in that most of the degreasing step is performed in a non-oxidizing atmosphere and any part of the step is performed in an oxidizing atmosphere.

(Operation) According to the method of the present invention, the surface of a molded product obtained by forming a metal powder containing carbon such as carbon steel is oxidized by the method of the present invention, and then in a reducing atmosphere (vacuum or H ₂
When heated in an atmosphere, etc., oxygen inside the powder is dissociated from the surface layer in an activated state, and at this time, oxygen is combined with carbon inside the powder and released as CO gas or CO ₂ gas. In addition, the carbon content in the sintered product is reduced.

Therefore, there is an advantage that a high quality powder sintered product having excellent electromagnetic characteristics and corrosion resistance can be obtained.

(Examples) Hereinafter, preferred examples of the method of the present invention will be described with reference to the drawings.

FIG. 1 shows the principle steps of the method of the present invention.

In the figure, a metal-containing powder containing carbon, for example, carbon steel and an organic substance are mixed to obtain a molded product,
When this is heated in an oxidizing atmosphere, most of the organic substances are volatilized, but some are carbonized and remain, and the surface of the metal powder is oxidized.

In this state, when heated to a temperature at which sintering is possible in a reducing atmosphere such as vacuum, oxygen is released from the powder surface in an activated state. At this time, oxygen is combined with carbon inside the powder or carbon content remaining from organic matter to form carbon monoxide (C
O) or carbon dioxide (CO ₂ ) is released from the molded product, and as a result, the carbon content in the sintered product is reduced.

 Hereinafter, more specific examples of the present invention will be described.

In the example, SKH57 containing 1.38% carbon as material powder
Using the water atomized powder of No. 3, the temperature was raised to 450 ° C. in 24 hours in a nitrogen gas (N ₂ ) atmosphere or in a vacuum, and then the temperature was maintained at 450 ° C. for 2 hours in the air atmosphere. This degreased product was heated at 900 ° C. for 3 hours in a vacuum on the order of 10 ⁻⁵ torr, then heated to 1220 ° C. while maintaining the same vacuum degree, and kept at this temperature for 2 hours.

The carbon content of the sintered product obtained in this way was 0.8%, and the hardness after sintering fell to Rock _RC hardness of H _RC 67 to H _RC 64 although the present invention was not applied, but the toughness was large. Improved.

As described above, according to the embodiments of the present invention, there is an advantage that the carbon amount can be arbitrarily controlled according to the required characteristics.

(Effects of the Invention) As described above, the present invention uses, as a molding material, a mixture of a metal powder, a mixture of metal powder and an oxide thereof, and an organic binder, and the molding is performed by injection molding. By heating in an oxidizing atmosphere to remove the organic binder, degreasing is performed to form an oxide film on the powder surface, and by sintering in a reducing atmosphere during sintering, CO gas is generated when oxygen is dissociated. In a method for producing a powder sintered product in which carbon content in the sintered product is reduced by dissociating as carbon dioxide or CO ₂ gas, most of the degreasing process is performed in a non-oxidizing atmosphere, and any part of the process is performed. By performing in an oxidizing atmosphere, it is possible to obtain a high-quality sintered product excellent in electromagnetic characteristics and corrosion resistance without using expensive low-carbon powder as a sintering material. Further, the carbon content of the sintered product can be controlled according to the required characteristics.

[Brief description of drawings]

 FIG. 1 is a diagram showing the principle steps of the method of the present invention.

Claims (1)

[Claims] 1. A molding material comprising a mixture of a metal powder, a mixture of metal powder and an oxide thereof, and an organic binder, the molding is injection molding, and the molding is heated in an oxidizing atmosphere. By degreasing to remove the organic binder, an oxide film is formed on the powder surface, and by sintering in a reducing atmosphere during sintering, when oxygen dissociates, it dissociates as CO gas or CO ₂ gas, In the method for producing a powder sintered product, which reduces the carbon content in the sintered product, most of the degreasing process is performed in a non-oxidizing atmosphere, and any part of the process is performed in an oxidizing atmosphere. A method for producing a powder-sintered product characterized.