RU2334589C2 - Method of fabrication of magnets out of powder material on base of iron-chromium-cobalt system - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes preparation of charge containing powders of iron, chromium, cobalt, ferrosilicon and ferromolybdenum or molybdenum, pressing of prepared charge, sintering, thermo treatment and thermo magnetic treatment. At that the total concentration of ferrosilicon and ferromolybdenum or molybdenum is 0.5-5 mass %.

EFFECT: upgraded density, magnetic properties and reliability of produced magnets.

1 tbl, 1 dwg, 2 ex

Description

The invention relates to powder metallurgy and can be used for the manufacture of structural parts, which require a combination of high mechanical and magnetic properties, for example, magnetic rings of gyroscopes. It will find application in engineering, instrument-making and other industries.

Known methods for producing products from materials of the iron-chromium-cobalt system, including the traditional operations of powder metallurgy, thermal and thermomagnetic processing. To increase the density and improve magnetic characteristics, powders of alloys of the iron-chromium or iron-chromium-cobalt system are additionally introduced into the multicomponent charge (US Patent No. 4601876, 1986). These additives activate sintering, but their content can reach 60%, which negatively affects technological properties, primarily compressibility, and the absence of components used in metallurgy for binding impurities worsens magnetic properties. In addition, it is necessary to specifically melt alloys with a high content of chromium or chromium and cobalt, and then grind them for introduction into the charge, which complicates the production.

The closest technical solution is a method of manufacturing products from powder materials of the iron-chromium-cobalt system, including the preparation of a mixture of powders of chromium, iron, cobalt and powders of ferroalloys of titanium, vanadium and silicon in an amount of 0.7-2.0%, pressing the mixture, sintering, thermal and thermomagnetic processing (RF Patent No. 2038918, 1995, bull. No. 19). This method provides sintering in the presence of a liquid phase and the binding of harmful impurities. However, even small additions of vanadium or titanium to alloys with a high concentration of chromium and cobalt, and these are the best magnetic alloys of this system, leads to the formation of brittle phases (Fig. 1a) located along grain boundaries and sharply lowering the viscosity characteristics. In addition, a further increase in the density, and hence the magnetic properties of alloys based on this system is possible.

The aim of the proposed method is the production of high-density powder magnets based on the iron-chromium-cobalt system with increased density, reliability characteristics and magnetic properties.

This goal was achieved by the fact that, to increase the density, ferrosilicon and molybdenum were introduced into the mixture (ferromolybdenum can be introduced). Molybdenum, along with iron and silicon, is a part of multicomponent eutectics and lowers their melting temperature, which increases the amount of the liquid phase and the temperature intervals of its existence (state diagrams of binary and multicomponent systems based on iron. Reference ed. / Bannykh O.A. et al M.: Metallurgy, 1986, 440 p.). The liquid phase activated sintering and provided a high-density state; in addition, silicon made it possible to bind related impurities. Alloying the best in magnetic properties alloys of the iron-chromium-cobalt system with a high concentration of chromium and cobalt with a relatively small amount of ferrosilicon and molybdenum (ferromolybdenum) eliminates the isolation of brittle phases along the grain boundaries after thermal and thermomagnetic treatments (Fig.1b).

From comparison with the known method of manufacturing products from powder materials of the iron-chromium-cobalt system, it is clear that the claimed method allows to obtain parts in a different way, since molybdenum or ferromolybdenum and ferrosilicon are used to activate sintering. The proposed method allows to obtain parts with a higher density than the prototype method, it eliminates the appearance of brittle phases along grain boundaries, as a result, the most important performance indicators increase. Thus, the proposed method is significantly different from the known, including the prototype method. In addition, it can improve the density, reliability and magnetic properties.

The proposed method includes the preparation of a mixture of a given composition, the manufacture of compacts, sintering, combined with homogenization, thermal and thermomagnetic processing. After heat treatment (before thermomagnetic) calibration is possible.

Example 1. Samples were made using the following technology:

- a mixture containing 31% chromium powder, 23% cobalt powder, 1% ferrosilicon, 1% molybdenum, the rest is iron grade OSCh 6-2, was stirred for 8 hours in a two-cone mixer;

- the samples were pressed at a pressure of 800 MPa in closed steel molds by double-sided molding;

- sintering, combined with impregnation, was carried out in vacuum at a temperature of 1300 ° C, 2 hours

Details were calibrated at a pressure of 800 MPa.

Samples had a density of 7.63 g / cm ³ . The increase in density compared with the prototype method is due to the expansion of the temperature intervals of the existence of the liquid phase and an increase in its quantity, because at the sintering stage, other than in the prototype method, eutectics are formed.

The heat treatment included quenching from a temperature of 1300 ° C, thermomagnetic treatment in a field of 250 kA / m in mode: 640 ° C - 40 min + 620 - 2 h + 610 - 1 h and isothermal tempering in mode: 600 - 2 h + 580 - 3 hours + 560 - 4 hours + 540 - 4 hours + 520 - 2 hours

The samples had a crack resistance (K _IC ) of about 3 MPa · m ^1/2 , impact strength (COP) of at least 100 kJ / m ² , coercive force (Ns) of 65 kA / m and magnetic induction (Br) of 1.35 T.

Example 2. Samples were made using the following technology:

- a mixture containing 31% chromium powder, 23% cobalt powder, 0.5% ferrosilicon, 3% ferromolybdenum, the rest - iron grade OSCh 6-2, was stirred for 8 hours in a double-cone mixer;

- the samples were pressed at a pressure of 800 MPa in closed steel molds by double-sided molding;

- sintering, combined with impregnation, was carried out in vacuum at a temperature of 1300 ° C, 2 hours

The samples had a density of 7, 83 g / cm ³ .

The heat treatment included quenching from a temperature of 1300 ° C, thermomagnetic treatment in a field of 270 kA / m in mode: 640 ° C - 40 min + 620 - 2 h + 610 - 1 h and isothermal tempering in mode: 600 - 2 h + 580 - 3 hours + 560 - 4 hours + 540 - 4 hours + 520 - 2 hours

The samples had crack resistance (K _IC ) 3.1 MPa · m ^1/2 , impact strength (COP) 105 kJ / m ² , coercive force (Ns) 67 kA / m and magnetic induction (Br) 1.31 T.

The increase in reliability (K _IC and KS) and magnetic properties is due to an increase in density and the exclusion of the possibility of the formation of intermetallic phases, which are especially dangerous at grain boundaries.

By varying the composition of the alloys, one can obtain the material characteristics presented in the table.

The proposed method differs significantly from the prototype in that its implementation requires other ingredients in other concentration ranges, it allows to increase the density, reliability characteristics and magnetic properties of the parts compared to the prototype method. Higher than the prototype, the properties reached at a total concentration of ferrosilicon and molybdenum (ferromolybdenum) 0.5-5.0 wt.%.

Table Comparison of the most important performance characteristics of the proposed method and prototype The content of ferrosilicon and molybdenum (ferromolybdenum),% Crack resistance, MPa · m ^1/2 Impact strength, kJ / m ² Coercive force, kA / m Magnetic induction, T Density after sintering, g / cm ³ 0.5 3.2 110 64 1.35 7.55 1,5 3.0 one hundred 65 1.35 7.63 4.0 3,1 105 67 1.31 7.82 5,0 2.9 102 68 1.30 7.83 6.0 2.7 98 68 1.25 7.85 Prototype Less than 0.7 Less than 98 Up to 64 Up to 1.30 Up to 7.50

Claims (1)

A method of manufacturing magnets from powder materials based on the iron-chromium-cobalt system, including the preparation of a mixture containing powders of iron, chromium, cobalt and ferrosilicon, pressing the resulting mixture, sintering, heat treatment and thermomagnetic processing, characterized in that ferromolybdenum is additionally introduced into the mixture or molybdenum, and the total concentration of ferrosilicon and ferromolybdenum or molybdenum is 0.5-5 wt.%.