RU2834544C1 - Method of forming and activating sintering of powder structural materials - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy. Articles are pressed from a mixture based on pulverized iron powder with the main fraction of 45–160 mcm, containing reduced iron carbonyl powder with particle size of 0.1–8 mcm in amount of 0.1–4.9 wt.%.

EFFECT: improved physical and mechanical properties of sintered powder material and strength characteristics of thin-walled elements included in composition of complex parts from powder structural steels.

1 cl, 1 dwg, 1 tbl

Description

A method for producing powder materials is known (Patent RU 243227C2, B22F 3/12, 2006.01/Method for forming powder articles or materials / A.G. Ermilov, V.Yu. Lopatin, Zh.V. Eremeeva), in which the sintering process is intensified by introducing highly dispersed (nanosized or nanocrystalline) particles into the reaction space, consisting of the elements of the article base or alloying the main matrix. The powder is blended with an organometallic plasticizer based on triethanolamine, and the resulting blend is formed. Sintering is carried out under conditions that ensure the formation of highly active nonequilibrium nanocrystalline structures that activate the sintering process. The method allows lowering the sintering temperature without disturbing the elemental composition of the final material, and ensures uniform shrinkage during sintering due to the uniform distribution of highly active nanocrystalline phases.

The disadvantage of the method is the complex process of obtaining the mixture, which includes mixing the powders with an ammonia solution of a molybdenum- or tungsten-containing organometallic compound and drying the mixture to remove the solvent and form a film of the molybdenum- or tungsten-containing organometallic compound on the surface of the particles of the base material.

In the work adopted as a prototype (Lopatin V.Yu., Eremeeva Zh.V., Nguyen N.D. Study of the influence of carbonyl iron powder VK on the compactibility and strength characteristics of sintered atomized iron powder PZhRV 2.200.26. Perspective materials, 2019, No. 7, pp. 51-58. https://doi.org/10.30791/1028-978X-2019-7-51-58), the influence of additives of carbonyl powder of the VK brand on the technological characteristics of the mixture and the properties of the sintered material made of PZhRV 2.200.26 powder was investigated. It was found that the addition of carbonyl powder VK to the atomized one in an amount of 5-15% by weight. increases the strength of sintered materials due to the formation of an additional framework of carbonyl iron particles sintered to each other between the particles of the sprayed powder. The optimal content of carbonyl powder in the prototype is a mixture of PZhRV 2.200.26 and VK 15% by weight.

The transition to industrial application in the ratios of carbonyl and atomized powder proposed by the prototype for the production of traditional structural materials seems unlikely due to the uncompetitiveness of the technology with a significant increase in its cost.

The fundamental difference of the invention is the reduction of the mass fraction of the dispersed fraction in the mixture to 0.1÷4.9%, the most optimal amount of which is selected individually for each composition.

It is proposed to add dispersed powder with a particle size of 0.1÷8 μm in an amount of 0.1 to 4.9% by weight to the molding mixture based on sprayed iron powder, the main fraction of 45÷160 μm. The content of dispersed powder is selected individually depending on the composition of the charge based on the principle of filling the interparticle space of the molded part with particles of the dispersed fraction. During sintering, the dispersed powder acts as an activator of sintering of the powder material, contributing to increased shrinkage, increased density and strength of the material. Pressing of products is carried out on standard equipment on automatic presses and sintered in conveyor furnaces according to standard modes.

Technical result: the invention solves the problem of manufacturing critical products of complex shape with thin-walled elements by increasing the degree of filling during pressing of narrow channels of the press mold and reducing the effect of density differences between the main body of the part and its individual thin-walled elements.

The method allows to improve the characteristics of powder materials without significant increase in cost and changes in the technological process scheme.

Traditionally, the composition of the charge for pressing powder blanks consists of a base iron powder with a particle size of 45-200 μm, powders of alloying elements such as copper, nickel, molybdenum, graphite powders and lubricant in the form of zinc stearate powder. The chemical composition and physical and mechanical properties of the main structural materials are regulated by GOST 28378-89 "Iron-based structural powder materials".

The technical result is achieved due to the fact that for each composition of the material, the optimal content of the activating additive of dispersed iron powder is selected, quantitatively determined by the densest packing of the mixture particles during pressing.

To assess the achieved effect, mixtures were prepared based on sprayed iron powder according to the compositions of the most typical structural materials of GOST 28378-89 with the addition of dispersed iron powder in an amount of 0 to 4.9%. Samples were manufactured according to the scheme of pressing on an automatic press and sintering in a conveyor furnace in an endogas environment according to standard temperature conditions. In the process of technological processing, the bulk density of mixtures, the density of compacts and the properties of sintered materials were determined depending on the content of the dispersed fraction. The optimal content was determined according to the graphs of the dependence of the determined indicators on the mass fraction of the dispersed powder.

An example of determining the optimal content of the dispersed fraction for the powder structural material PK10 (GOST 28378-89) is shown in Fig. 1, which shows graphs of the dependence of bulk density, density of sintered samples, shrinkage during sintering and strength of samples on the mass fraction of dispersed powder.

When adding dispersed powder to the mixture for PK10 in an amount of up to 4.9% by weight, due to filling the gaps between the particles of large sprayed powder with particles of the dispersed fraction, the bulk density of the mixtures increases, the density of the compacts increases, and shrinkage during sintering is activated. The greatest technical result is achieved with an additive content of 3% by weight.

Table 1 shows the achieved technical result of adding the optimal content of the dispersed fraction using the example of sintered materials PK10D3-68 and PK40N4D2M-68

Table 1

Example of the material used Content of dispersed fraction, % by weight. Tensile strength, MPa Relative elongation, % Hardness, MPa Achieved technical result PK10D3-68 density after sintering 6.83-6.84 - 263 3.8 770 Increase in strength 10.6%, increase in ductility 13.1% 2 291 4.3 790 PK40N4D2M-68,
density after sintering 6.8-6.82 - 630 2.1 1850 Increase in strength 16%, increase in ductility 30% 1 731 3 2030

Claims (1)

A method for producing a charge for pressing complex-shaped articles with thin-walled elements, including preparing a charge based on atomized iron powder, characterized in that reduced carbonyl iron powder with a particle size of 0.1-8 μm is additionally introduced into the charge in an amount of 0.1-4.9 wt.%, and powder with a main fraction of 45-160 μm is used as the atomized iron powder.