JPS5853061B2 - Method for producing Fe-Cr-Co spinodal decomposition type magnetic material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for economically producing Fe-Cr-co based spinodal decomposition type magnetic materials.

In general, ordinary magnetic materials are hard and brittle, so they have the disadvantages of not having plastic workability and poor rigidity, whereas Fe-Cr-C.

Spinodal decomposition type magnetic materials are attracting attention as excellent magnetic materials, as they not only have magnetic properties almost equivalent to those of alnico magnets, but also have the characteristics that plastic processing and cutting are relatively easy. .

The above-mentioned Fe-Cr-co spinodal decomposition type magnetic material contains Fe, Cr' and Co as basic components, and also contains Si to improve magnetic properties and heat treatability.
A7+ Nb+ Ta, 'ri, V, Mo.

and W, and its typical composition, in weight percent, is: Cr: 20-40%, Co: 10-30%, Si: 6% or less, Al: 5φ or less, Nb : 5 coefficient or less, Ta: 5L: fb or less, Ti: 5 coefficient or less, V: 6 coefficient or less, Mo: 15 coefficient or less, W: 15 or less, Fe > and unavoidable impurities: the remainder. ing.

In the spinodal decomposition type magnetic material with the above composition, Cr
The reason for setting the content of 20 to 40 is because if the content is less than 20, the amount of precipitated Cr-rich non-magnetic phase α2 will decrease, resulting in a decrease in coercive force, which is undesirable.
If the content exceeds %, the number of non-magnetic layers increases and the residual magnetic flux density decreases, and the plastic workability deteriorates due to hardening of the material due to alloying with Cr, making it impractical. be.

Similarly, if the Co content is less than 10%, the residual magnetic flux density becomes small due to the small amount of Co-rich magnetic phase α1, which is undesirable. On the other hand, if the Co content exceeds 30%, As the coercive force rapidly decreases, C.

The hardening of the material due to alloying deteriorates the plastic workability and makes it impractical, so it is set at between 10 and 30.

Si is added to slow down the cooling rate during solution treatment, but if the content exceeds 6, the material becomes brittle and plastic workability deteriorates, so the upper limit value is designated as Section 6.

Smaller Al expands the α region and lowers the solution treatment temperature,
Further, it is contained for the purpose of slightly improving the coercive force, but if it is contained in an amount exceeding 5%, the material becomes brittle and plastic workability deteriorates, so the upper limit thereof is set at 5%.

Nb + Ta + Ti, button and V are all α
Expanding the area and lowering the solution treatment temperature, further Nb,
Ta is added to improve plastic workability, Nb: 51 Ta: 5%.

If the content exceeds 6% for Ti and 6% for Ti and V, the coercive force will decrease by 1, so the content is kept below the above upper limit.

More M. Coercive force is improved by adding K and W, but if the content exceeds 15% of each, plastic workability decreases due to hardening of the material due to alloying. The amount is set below the upper limit value.

Conventionally, spinodal decomposition type magnetic materials with the above composition have been melted and cast with a predetermined composition, and then subjected to plastic processing such as rolling and button forging, and machining such as cutting and punching, as necessary. It is manufactured by a process of imparting a desired shape by subjecting it to a desired shape, followed by solution treatment, heat treatment in a magnetic field, and aging treatment to impart magnetic properties.

In particular, when manufacturing spinodal decomposition type magnetic materials with complex shapes and high dimensional accuracy using this conventional melting and casting method, it is necessary to perform machining and hot forging. Large amount (20-40%) of Cr
Although it is possible to machine it, its machinability is considerably poorer than that of carbon steel or low-alloy steel, and even when hot forging is performed. Unless forging and annealing are repeated several times, a button with the desired shape and dimensional accuracy cannot be obtained.

As described above, when manufacturing products with complex shapes or products with high dimensional accuracy using the conventional melting and forging method, there is a problem in that the processing steps become complicated and time-consuming, resulting in high costs.

Therefore, in order to solve the above-mentioned problems with the conventional melting and forging method, it was considered to apply the normal powder metallurgy method to produce spinodal decomposition type magnetic materials, but in this case, the density ratio of the sintered body was In order to make it 95% or more, the raw material powder should be 35%
It is necessary to promote the sinterability of the green compact by pulverizing the powder to a particle size of 0 mesh or less, which results in an extension of the manufacturing process time due to the pulverization process, and also increases the tendency of oxidation of Cr during the pulverization process. A problem has arisen in which .

On the other hand, when a fine powder of 350 mesh or less is generally used as a raw material powder, the fine powder has an apparently low density and the friction between the powder particles during compaction is large. It is difficult to increase the density ratio of the green compact to 80% or more.

95% from such a green compact with a density ratio of 80% or less
Obtaining a sintered body having a density ratio of more than 1% means that the shrinkage during sintering is large, resulting in significant deformation and large dimensional variations in the sintered body.

Therefore, it is difficult to obtain the desired dimensional accuracy with the sintered body 11, and in order to obtain the desired dimensional accuracy, it must be processed.

In this way, even when manufacturing using the normal powder metallurgy method, it is necessary to pulverize the raw material powder and process the sintered body, so high costs cannot be avoided. The drawback is that magnetic properties are impaired by Cr oxidation.

This invention solves the problems of the conventional melt casting method and powder metallurgy method described above, and has magnetic properties almost equivalent to those manufactured by the conventional melt casting method, and has a complex shape with high dimensional accuracy. The present invention provides a method for economically producing a Fe-CrCo spinodal decomposition type magnetic material using a simple process and utilizing the plastic workability of the magnetic material,
It is characterized by consisting of the following main steps a''e.

That is, (a) For example, the above Fe-Cr-C
In order to obtain a mattomized alloy powder with a predetermined composition that has substantially the same composition as a typical composition of an o-based spinodal decomposition type magnetic material, Fe, CrX, and C as basic components are used.
In addition to o, S is added to improve magnetic properties and heat treatability.
i, Al, Nb, Ta+Ti+V+Mo%
After adding Qi, V, etc. and melting in an electric furnace, high frequency furnace, etc., water atomization or gas atomization is applied.

(b) The resulting alloy powder having a predetermined composition is placed in a mold to form a green compact having a simple shape close to or different from the final shape.

In this case, unless the density ratio of the green compact is set to 75% or more, the density ratio of the hot forged body (described later) cannot be increased to 95% or above. A molding pressure of 4 ton/i or more is required to maintain the powder compaction, and on the other hand, even if the pressure exceeds 8 ton/i, it is hardly expected that the density of the green compact will increase, so the molding pressure should be 4 to 8 ton/i. It is preferable to

(c) Next, in order to prevent oxidation, the green compact is preferably exposed to a neutral atmosphere such as nitrogen gas or argon gas, or a reducing atmosphere such as hydrogen gas or decomposed ammonia gas. In order to shorten the heating time as much as possible and increase efficiency, a high-frequency furnace is used to rapidly heat the product.

In this case, if the heating temperature is less than 900°C, the deformation resistance of the rapidly heated green compact that is buttoned during hot die forging in the next step is large, and the hot die with a density ratio of 95% or more is Since it is difficult to obtain a forged body, the temperature must be 900'C or higher.

However, depending on the fractional composition, some materials have a structure in which the σ phase exists, which is hard and brittle even when heated above 900°C. It must be heated above the temperature at which it disappears.

On the other hand, if the heating temperature exceeds 1300°C, the oxidation of the forging die in contact with the heated compact will be significant, the wear of the forging die will become severe, and the dimensional accuracy of the hot forged body will decrease. Do not heat above 130,000 ℃ as this may cause damage to the forging die.

(d) Hot die forging is applied to the powder compact heated to a temperature within the temperature range of 900 to 1300'C, and it has the same final shape and almost the same shape as the old cigarette roll, and
A hot forged body with a density ratio of over 95 is formed.

In this case, the density ratio of the hot forged body was limited to 95% or more because if the density ratio was less than 95%, the magnetic properties, especially the residual magnetic flux density Br, would be inferior to those manufactured by the conventional melt casting method. Because it becomes something.

In addition, when the density ratio is 95% or more, almost no dimensional change occurs during the heat treatment process for imparting magnetic properties in the next process, and the high dimensional accuracy obtained for the hot die forging process is maintained in the final process 1. will be retained.

As mentioned above, the shape of the green compact before hot die forging is either close to the final shape or simpler than the final shape. However, in the former case, the amount of plastic deformation during forging is small, so it is difficult to obtain a hot forged body with a density very close to the true density, but the advantage is that the pressure required for forging is relatively low. There is.

On the other hand, in the latter case, the manufacturing cost of the forging die is low, and since wide plastic deformation is possible during forging, a hot forged body with a true density or a density close to this can be obtained. However, relatively high forging pressure is required;
Therefore, a larger forging press is required.

Which of the above shapes to adopt may be selected appropriately so as to ensure a density ratio corresponding to the required magnetic properties, taking into account that the residual magnetic flux density increases as the density ratio increases.

In the past, as a lubricant for forging, a solid lubricant such as fine graphite or boron nitride dispersed in water or oil may be used.

e) Next, the above-mentioned hot forged body is subjected to solution treatment, heat treatment in a magnetic field, button and aging treatment, etc. in order to impart magnetic properties, but these treatment conditions are not applicable to conventional melt casting methods. The processing conditions are the same as those normally applied to processed materials.

That is, the solution treatment is performed at a temperature of 1100 to 1400°C for 30 minutes.
This is generally carried out by holding for 0 minutes to 3 hours.

In addition, when heating Fe-based powder compacts containing Cr for a long period of time to the above-mentioned high temperatures, in order to prevent oxidation of Cr, it is heated in a high vacuum atmosphere of about 10'' to 10' TorrO, or The above (d) is carried out in a high purity neutral or reducing gas atmosphere with a low dew point of -40°C or less.
Regarding the hot forged body having a density ratio of 95% or more obtained in Section 1, since the bore in the hot forged body is isolated from the outside, it is necessary to perform solution treatment of the hot forged body. For heating, a particularly high vacuum or high purity gas atmosphere is not required, and heating in a vacuum of 10" to 10" Torr, or in an ordinary neutral or reducing gas atmosphere that has not been particularly purified and purified. Even if heating for solution treatment is performed in gas, the inside of the hot forged body will not be oxidized.

Furthermore, this makes it possible to use a continuous furnace when a neutral rich or reducing gas is used as the atmosphere, contributing to a reduction in manufacturing costs.

This invention consists of the main steps shown in sections (a) to (e) above, and will be specifically explained below using Examples.

Example 1 Cr: 28.0%, Co: 16.0%, Si: 1.0%
Al: 0.3φ, Ti: 1. O person, Nb: 0.15 person,
Fe: The remaining alloy was charged into an alumina crucible and heated and melted in an electric furnace until the molten alloy temperature reached 1700℃.
'C, water atomization was applied to this to produce alloy powder having a particle size of 80 mesh or less.

Next, this water atomized alloy powder was put into a mold and 6T
By applying a molding pressure of on/cTL, it has a density ratio of 81 and a dimension close to the final shape, that is, a cylindrical shape in the center.
A green compact having stepped recesses and an outer diameter of 15 mm ψ and a height of 12.1 mm was molded.

Next, the green compact is rapidly heated for 60 seconds at a temperature of 1180°C in a hydrogen atmosphere using a high frequency furnace, and then molded with dimensions slightly larger than the dimensions of the mold used for forming the green compact, that is, the dimensions of the green compact. The density ratio is 98.
%, the final shape and dimensions, i.e., the planar dimensions, were substantially the same as those of the green compact, but the height was 10.0 mm. A hot forged body was formed by applying a forging pressure of 6T/-. .

During the forging, 10% by weight of natural graphite with an average particle size of 0.5 μm dispersed in water was used as a lubricant.

Subsequently, the hot forged body was subjected to solution treatment using an electric furnace at a temperature of 1,250°C for 2 hours in decomposed ammonia gas, and a temperature of 63°C in a magnetic field of 40,000e.
Heat treatment in a magnetic field held at 00C for 25 minutes, and further at a temperature of 61
A spinodal decomposition type magnetic material according to the present invention (hereinafter referred to as the magnetic material of the present invention) was produced by performing aging treatment by holding at 0° C. for 1 hour and holding at a temperature of 560° C. for 5 hours.

Almost no dimensional change was observed in the magnetic material of the present invention, and therefore it had the dimensional accuracy of the final shape.

On the other hand, for the purpose of comparison, an alloy having the same composition as the above-mentioned water atomized alloy powder was heated and melted in an electric furnace, and the molten alloy was tapped at a temperature of 1700°C. A cylindrical casting was produced.

The resulting casting was then machined to have the same dimensions as the hot forged body described above, and then subjected to solution treatment, heat treatment in a magnetic field, button and button under the same conditions as described in Example 1 above. A spinodal decomposition type magnetic material (hereinafter referred to as conventional magnetic material) obtained by aging treatment and conventional melting and casting method.
was manufactured.

A sample having dimensions of 3 mm outer diameter x 6 mm length was cut out from the magnetic material produced in this manner, and its magnetic properties were measured, and the results shown in Table 1 were obtained.

As shown in Table 1, it is clear that the magnetic material of the present invention has almost the same magnetic properties as the conventional magnetic material.

Example 2 Cr: 27.0%, CO: 25.0%, Mo: 3.
0%, Si: 0.5%, Al: o, 3%, Nb: 0
．． An alloy consisting of 25%, V: 0.5%, and Fe: the remainder was charged into an alumina crucible and heated to 1 in an electric furnace at a temperature of 1.
After heating and melting at 7000G, an alloy powder having a particle size of 100 mesh or less was produced by gas atomization using nitrogen gas.

Then, the gas atomized alloy powder was put into a mold and 7T
Adding on/i molding pressure, it has a density ratio of 83%,
Simple shape compared to final shape, i.e. outer diameter 7.8m
A cylindrical green compact having dimensions of mψ x inner diameter 3.0 mm x height 10.9 mm was molded.

Next, the green compact was decomposed using a high frequency furnace at a temperature of 1200°C in an atmosphere of decomposed ammonia gas.

After rapid heating for 30 seconds, hot die forging was carried out by applying a pressure of 10Ton/i to an outer diameter of 12.0+nmψ×
It has dimensions of 3.0 mm ψ inner diameter x 6.2 m height,
A hot forged body was formed in which eight vertical grooves each having an arcuate bottom surface with a radius of 2rIIm were formed at equal intervals along the outer circumferential surface.

The hot forged body had a density ratio of 99.8% and the final geometry.

In addition, during forging, natural graphite with an average particle size of 0.5 μm dispersed in water at a concentration of 15% was used as a lubricant.

Subsequently, the hot forged body was subjected to solution treatment using an electric furnace, in which the temperature was held at 1220°C for 2 hours and then rapidly cooled, and the temperature was held at 600°C for 1 hour and the temperature The magnetic material of the present invention was manufactured by subjecting it to an aging treatment held at 570° C. for 2 hours, but the magnetic material of the present invention almost always experienced dimensional changes due to the heat treatment.
Therefore, it had the desired final shape dimensional accuracy.

On the other hand, for the purpose of comparison, an alloy having the same composition as the above gas atomized alloy powder was heated and melted in an electric furnace at a temperature of 1700°C, and then an outer diameter of 8.6 mmφ x inner diameter of 3.0 mm was prepared.
A cylindrical casting with dimensions of ψ×height 9.0 mm was cast, and this casting was alternately subjected to three hot die forgings and two annealing to obtain the product for Example 2 above. Finished with the same dimensions as the hot forged body.

The above-mentioned hot die forging was performed all three times using a high-frequency furnace by heating to a temperature of 12,000C for 30 seconds in a decomposed ammonia atmosphere, and then applying a pressure of 12T/-, and the annealing was performed in all three cases. Using an electric furnace, the temperature was maintained at 12,000C for 60 minutes in a decomposed ammonia gas atmosphere.

Subsequently, solution treatment and aging treatment were performed under the same conditions as in Example 2 to produce a conventional magnetic material.

The outer diameter of the above-mentioned both magnetic materials obtained as a result is 311 TI.
A sample having dimensions of Iψ x length 6 mm was cut out and its magnetic properties were measured, and the results shown in Table 2 were obtained.

As shown in Table 2, it is clear that the magnetic material of the present invention has almost the same magnetic properties as the conventional magnetic material in this case as well.

As described above, according to the present invention, Fe having magnetic properties comparable to those manufactured by the conventional melting and casting method.
-Cr-Co spinodal decomposition type magnetic materials can be manufactured economically with a high degree of dimensional accuracy and have complex shapes with almost no machining required.

Claims (1)

[Scope of Claims] 1. A material having a shape closer to the final shape than an alloy powder having a composition corresponding to a Fe-Cr-co spinodal decomposition type magnetic material, a shape simpler than a cigarette butt, and a density ratio of 75% or more. A green compact with a temperature of 900 to 1300
After rapidly heating to a predetermined temperature within the range of 0C, hot die forging is performed to obtain a hot die that has the same shape as the final shape, almost the same shape as the residue, and has a density ratio of 95% or more. A Fe-CrCo system characterized by forming a forged body and subsequently subjecting the hot forged body to ordinary solution treatment, heat treatment in a magnetic field, and aging treatment to impart magnetic properties. Dull decomposition type magnetic materials method.