JPS5920449A - Sintered structure of iron-base powder - Google Patents

Abstract

PURPOSE:To obtain inexpensively a sintered structure with high denseness by compression-molding iron-base powder surface-treated with a chromic acid soln. and by converting the chromic acid soln. into chromium oxide by calcination. CONSTITUTION:Iron-base powder is dipped in a chromic acid soln. and compression-molded into the required shape in a metallic mold or the like. The molded body is heated to about 200-700 deg.C in steps and treated to convert the chromic acid soln. into chromium oxide by calcination. The particles of the iron-base powder is chemically bonded together by the chromium oxide, and a sintered structure of the iron-base powder is formed. The heat treatment can be carried out at said relatively low temp., and gas, etc. are not required during the heating, so the sintered structure can be manufactured at a reduced cost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to improvements in sintered structures made of iron-based powder that are widely used as components in various machines, equipment, devices, and the like.

Conventional iron-based powder sintered structures, for example, consist mainly of electrolytic iron powder, mixed with a small amount of electrolytic copper powder as a binder, and a small amount of zinc stearate powder as a lubricant, and then compression molded into a desired shape. After that, it was heat-treated at around 1200° C. in an ammonya decomposition gas furnace or a butane decomposition gas furnace, and then the particles were bonded to each other in the molten state of the electrolytic copper powder.

However, due to the appearance of powder trace cavities due to the melting of the electrolytic copper powder mixed in the powder state and the vaporization of the zinc stearate powder, the product state tends to lack compactness (generally the highest density is 7. 0 gr/ryn3), which results in insufficient mechanical strength.In connection with this problem of lack of compactness, when increasing the carbon concentration on the surface by the subsequent gas decarburization method, it is necessary to However, there was a problem in that the charring phenomenon occurred even inside the steel, making it impossible to quench and harden only the surface.

Furthermore, since a high heating temperature is required during sintering, there are problems such as not only a decrease in workability but also an increase in manufacturing costs due to high fuel costs due to combustion gas.

The purpose of the present invention is to provide an iron-based powder sintered structure which extremely effectively solves many of the problems described above.Examples of the present invention will be described in detail below. At least the surface of particles of approximately uniform particle size and grain size is reduced in advance with chromic acid alone, a mixture of chromic acid and chromate, chromic acid and some organic acid, or carbon, with a specific gravity of 1.6 or more. A structure is formed by compression molding iron-based powder impregnated with a chromic acid solution into a desired shape using a mold, etc., and then the structure taken out from the mold is preferably heated in an ordinary electric furnace. 200℃
Heat treatment stepwise over a temperature range of 700°C to 700°C (e.g. 200°C for addition, then 400°C for addition, then 700°C for addition)
A sintered structure formed by chemically bonding the respective particles with each other by chromium oxide converted by firing the chromic acid solution is formed by carrying out a heating process at 00° C.).

As described above, according to the present invention, the powder is simply impregnated with a chromic acid solution in advance, and the particles are chemically bonded to each other by the chromium oxide converted by the chromic acid solution during subsequent sintering and heating. Because of the aspect in which no other powder is used as a binder or lubricant, there is no problem of powder trace cavities caused by melting or vaporized oil as in the conventional products, and the product is highly dense. Since it is possible to form a sintered structure, mechanical strength can be improved, and if necessary, quench hardening can be performed by carburizing only the surface using gas decarburizing method, and at the same time, the mechanical strength is relatively low. Since it is possible to use stepwise heat treatment at different temperatures, work efficiency can be significantly improved. At the same time, gas, etc., as in the conventional method, is not required during heating, so fuel costs can be reduced and manufacturing costs can be reduced. It can be made at low cost.

Patent applicant: Usui Kokusai Sangyo Co., Ltd.

Claims (1)

[Claims] A structure having a desired shape is obtained by compression molding iron-based powder with at least the surface of the particles impregnated with a chromic acid solution, and the particles are chemically bonded to each other by chromium oxide by firing and converting the chromic acid solution. An iron-based powder sintered structure characterized by: