SU933261A1 - Method of producing rods of sintered refractory metals - Google Patents

Description

(54) METHOD OF MANUFACTURING BARS FROM SINTERED REFINING METALS

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The invention relates to powder metallurgy.

 A known method of manufacturing products from sintered refractory metals, including forming a briquette, preliminary low-temperature sintering at a temperature of 0.3-0.5 melting point with an exposure of 4-8 hours, high-temperature sintering at a temperature of 0.5-O, 8 melting temperature for 12-30 hours; welding of the briquette and its deformation with a percussion tool.

The disadvantages of this method include.

1. Low productivity of the production process products. So, for the manufacture of bars with a diameter of 10 mm

from a briquette with a wall of 35 mm, the total time is 22-45 hours, while the number of passes at the deformation stage varies in the range 4-12.

2. A significant consumption of metal in the form of volatile oxides during heating of semi-finished products before deformation. A distinctive feature of the known method is that, as the length of the semi-finished products increases during the deformation process, it produces with heating up to half of the product, the heated part of which is deformed by strikers. After that, the cold undeformed part of the semi-finished products is placed in the furnace ,. heated and deformed. Thus, the number of heatings and respectively

10 the formation of non-returnable volatile oxides increases with increasing length of the semi-products. The total consumption of metal in the form of irrecoverable waste. Oxides is .10-20%.

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3. Low quality of the products obtained due to the significant anisotropy of the properties resulting from the discrete application of the load and the formation of fragile parts in connection with this

20 cove at the load application boundary.

The closest in technical essence and the achieved result to the invention is the method of preparing bars of sintered refractory metals, in which the formation of a square cross-sectional billet of powder, preliminary sintering and deformation of the billet with a conical matrix 2j. The deformation of the workpiece is carried out by hydraulic extrusion using pressures of the working fluid, which are 1 0 –12 kbar. The disadvantages of this method are as follows: 1. The hydroextrusion process requires complex hardware design of the devices to create significant (1 O-12 kbar) pressure, tanks and pipelines for supplying liquid to the container, seals and similar devices. 2. The well-known method has low productivity due to the length and complexity of the preparatory operations for the hydro-extrusion process. The aim of the invention is to increase productivity, simplify the process and its hardware design. The goal is achieved by the fact that in the method of making rods of sintered refractory metals, including forming a square cross-section of a billet of powder, preliminary sintering and deformation of the billet through a conical matrix, the deformation is carried out by extruding the billet with a punch with a stress elongation 10- 20. The essence of the method lies in the following. The formed briquette made of powder of a low-melting metal is subjected to preliminary low-temperature sintering. then a single deformation of the thus obtained square in cross section of the workpiece is carried out through the matrix on the press, while the corner areas of the workpiece are subjected to the predominant deformation at the entrance section of the sliding tool, which can be done with the help of a matrix . The deformation of the workpiece is carried out with a stretching ratio / J equal to 10-20. The proposed method makes it possible to increase the productivity of the process for the production of rods from sintered fusible metals by reducing the time required for preparatory operations. In addition, the extrusion of the workpiece when // 1 10-20 through a circular conical matrix, which leads to the advantage.-. The deformation of the corner zones of the workpiece, which is substantial at the entrance to the matrix, makes it possible, according to the forging cross principle, to complement the axial zone of the workpiece and the parts adjacent to its side walls, thereby improving the quality of extruded products due to a more uniform density distribution along the length and cross-section of the rods. The density of the finished bars when using the proposed method, as shown by experimental data, is close to theoretical, the density gradient of the peripheral layers and the center of the product do not exceed 2%. In addition, a single extrusion through the matrix eliminates the discreteness of deformation in e; 1 the workpiece, intensifies the development of the original structure by increasing the allowable ultimate deformation. The choice of stretch intervals during deformation is due to the fact that the under-compacted zones of the original blanks are compacted, which results in a non-uniform density distribution in the finished product and a decrease in the quality of the products. With an increase in the draw ratio / C (7–20, as shown by experimental and sequential tests, the destruction of the corner zones and then the surfaces of the products signifies the effective strain hardening of the material, which, with limited ductility of the metal, leads to inertial destruction of the bars. The matrix in the range of stretching / V 1020 allows to obtain high-quality rods with a uniform distribution of density, high surface quality and mechanical properties across the section. Example. a mch grade molybdenum billet with a wall of 20 mm, obtained by molding and using the following {temperature and temperature sintering with a total time of 4 hours, was extruded with a punch on a press with a force of 10,000 kN through a round conical matrix with a draw ratio of 10, 15 and 20. The preheating of the head was made at a temperature of 12 50 s.

Metallographic analysis and the results of studying the density along the length and length of the bars showed that the density was evenly distributed, the structure was completely and uniformly deformed, and no microdefects were found. A visual inspection of the bars did not reveal microdefects on the top of the || The difference in density over sech rods does not exceed 2%.

Subsequent rolling, in multi-roll calibers, was performed with compression per pass JE. 20-23%, while the formation of defects on the surface of the bars and over the cross section was not observed. The material was strengthened by plasticity ((D 46%), and the consumption of metal in the form of volatile carbon monoxide was 3–4%.

The basic variant is based on the method of obtaining rods, carried out by forging square shafts in slips and subsequent rotary forging. The proposed method allows, in comparison with the baseline, to increase the productivity of the process by 3-10 times, to improve the quality of the finished products.

The expected economic effect from its use will be 223.3 thousand rubles. in year.

Claims (2)

1. Zelikman A.N., Nikitina L.S. Vol4man. M., Metallurgists, 1978 s. 221, 2. In the same place 213 (prototype).