JPS6148505A - Manufacture of metallic mold for extrusion - Google Patents

Abstract

PURPOSE:To manufacture economically an extrusion metallic mold having excellent durability by packing metallic powder into a cavity-shaped groove cut in a metallic mold, sealing the groove tightly under reduced pressure, and compression-molding at high temps. through an inert gas. CONSTITUTION:A cavity-shaped groove 3 is cut in a metallic mold base material 1, and optional metallic powder 2 such as ''Stellite(R)'' is packed into the groove 3. Then the groove 3 is covered with a steel lid 4 and fixed by electro-beam welding 5, etc., and the metallic powder 2-packed part is hermetically sealed under reduced pressure. Then the powder-packed part under said conditions is compression-molded at >=700 deg.C by using an inert gas such as Ar as a pressure medium, the cavity-shaped part is molded with a powdery material, and the mold is worked into a metallic mold of a specified shape. Consequently, an extrusion metallic mold having a high-toughness cavity part and excellent durability can be obtained with a small amt. of expensive metallic powder 2 and without generating oxidation, etc.

Description

[Detailed description of the invention] In metal extrusion processing, a metal piece heated to a high temperature is placed in a container, and then pressure is applied to the metal piece to extrude it through a hole machined into the desired shape to obtain a product. The mold used for extrusion processing is important to ensure stable product quality, but when extruding a high-temperature metal piece through the hole mold, it causes wear, roughness, cracks, etc. Therefore, in order to obtain molded products, there is a need for a mold that has excellent durability against such damage.

Various tool steels are used as materials for this mold,
All of these have excellent abrasion resistance, but the mold parts are exposed to quite high temperatures (1) and are easily abraded or cracked.

For this reason, molds whose holes are welded with a material having high-temperature strength or whose surfaces are treated are used. Although this has slightly improved the life of the mold, damage to the mold still remains a problem, as explained below, and improvements are desired.

FIGS. 1 to 3 are microscopic microstructure photographs showing the various molds described above. SKD-61 is an excellent tool steel for hot working, but the steel ingot that is the workpiece is about 12
Since it is heated to 00°C and extruded through a hole die, the area around the hole die is also heated and plastic flow occurs. Moreover, FIG. 2 shows SKD-61 subjected to nitriding treatment. Although the hardness of the surface of the hole is high, the hardened layer is thin, so when it is actually used, plastic flow occurs from the base material beyond the hardened layer. Furthermore, Fig. 3 shows a case in which asc-16Or-16Mn steel, which has excellent high-temperature strength, is overlay welded to the hole part, but the strength at high temperature is 5KD-6.
1, the rigidity flow was extremely small and the life of the mold was significantly improved. Furthermore, if a high-strength material is overlaid, the life of the mold will be improved, but there are limitations when overlaying a complex-shaped hole with a high-strength material because there is a risk of weld cracking.

Furthermore, the structure of the weld metal is composed of coarse crystal grains, and has low toughness and low resistance to cracking.

As explained above, although many manufacturing methods have been developed for the purpose of improving the durability of molds, mold damage still remains a serious problem.

The present invention aims to improve the current situation and develop an excellent mold.

The features will be explained below using diagrams.

FIG. 4 explains the method of manufacturing the mold according to the present invention, in which a groove (3) is formed in the hole of the mold base material opening for filling the metal powder (2). After the groove (3) is filled with powder (2), it is covered with a steel lid (4), and the powder filling part is welded to the mold base material 11) by electron beam welding (5) or the like. It is fixed in a vacuum sealed state. Further, this container is subjected to pressure molding at 700° C. or higher using an inert gas such as argon as a pressure medium, and after molding the hole portion with the powder material, it is processed into a mold of a predetermined shape.

The mold made in this way has the following features.

In other words, the properties of the hole molded by pressure molding powder are less segregation and have a finer structure than molds manufactured through conventional melting and forging processes, and if they have the same chemical composition, It has excellent toughness and high resistance to cracking.

In addition, since it is possible to fill the desired powder only around the hole rather than the entire mold, expensive powders such as 1-stellite/N1-based self-fluxing alloy, CO-based self-fluxing alloy, high-speed steel, etc. can be used. Furthermore, it is also possible to fill the powder to any thickness according to the usage conditions, and even materials that were previously impossible to weld despite their excellent high-temperature strength can be used around the hole. Furthermore, since the structure has a significantly finer toughness than that of welding, it is highly resistant to cracking during use.Furthermore, using an inert gas as a pressure medium allows molding of high-strength powder. This is because it is easy to obtain high pressure, and this is to prevent oxidation of the metal powder, or to pressure-form the powder filled into a complicated hole from all directions.

In addition, if only the pressure molding of metal powder is required, there is no need to use an inert gas such as argon as a pressure medium, but when molding metal powder as in the present invention, it is possible to form holes with complex shapes facing in all directions. In order to bring the compacted powder into close contact with the surface, it is essential to use an inert gas such as argon as a pressure medium as in the present invention.

The reason why the heating temperature must be 700°C or higher is that metal powder is originally molded by the synergistic effect of temperature and pressure, but for high-strength powder used for this purpose, the heating temperature is 700°C or higher. This is because, even if a large pressure is applied, it is not possible to form the powder sufficiently at a temperature below Fc in close contact with 700℃
This is because the following is not possible.

In addition to sealing the powder-filled portion under reduced pressure, other than sealing by electron beam welding, the entire container may be wrapped in a container, the inside of the container may be sealed under reduced pressure, and the entire container may be press-molded.

As explained above, the method of the present invention is intended to ensure stable quality of the press with excellent durability by disposing high-strength metal powder in the hole portion of the mold.

[Brief explanation of drawings]

Figure 1 is a low magnification micrograph (X
50), Figure 2 is a full-thickness, low-magnification micrograph (X50) of the damaged state of the hole part of the same 8KD-iSI mold that has been subjected to nitriding treatment, and Figure 3 is the 8KD-iSI mold that has been subjected to nitriding treatment. A low-magnification microscopic microstructure photograph (XI
DO), FIG. 4 is an explanatory diagram of the patented invention method. In the figure, (blind) Mold base material (2) Metal powder (3) Groove (4) Lid (5) Electron beam welding part

Claims (1)

[Claims] 1. Fill the grooves drilled in the hole shape of the mold with metal powder, and then press mold at 700°C or higher using inert gas as a pressure medium while the powder-filled part is sealed under reduced pressure. A method for manufacturing an extrusion mold, characterized by: