JPH0297617A - Production of grain-oriented permanent magnet alloy - Google Patents

Abstract

PURPOSE:To produce the title grain-oriented permanent magnet alloy with no need for solution treatment by quenching a thin ingot having specified contents of Cr, Co, Mo, and Fe and having a specified thickness from a high temp. to room temp., and then applying in-magnetic-field ageing and ageing. CONSTITUTION:The molten alloy contg. 10-3wt.% Cr, 5-35wt.% Co, 0.1-10.0wt.% Mo, 0.01-5.00wt.% of at least one kind among B, Si, Al, W, Mn, Ti, V, Nb, Zr, Sn, and Zn as required, and the balance Fe is formed into a thin ingot having 3-50mm thickness. The ingot is cooled from >=900 deg.C to room temp. at a rate of >=5 deg.C/s. As a result, only an alpha-single phase region necessary to form a magnet is formed. The alloy is then aged in a magnetic field, and then aged without applying solution treatment. By this method, a grain-oriented permanent magnet alloy having an excellent magnetic characteristic is obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a method for manufacturing a unidirectional permanent magnet alloy,
In particular, in the manufacturing process of Fe-Cr-Co permanent magnets, thin slabs doped with Mo are continuously cast, and the subsequent cooling process is modified to advantageously improve the magnetic properties.

(Prior art) Fe-Cr-Co based alloy magnet is AI-Ni-
Same as Co-based magnets (as it is a spinodal decomposition type magnet, after casting the molten alloy, it is subjected to solution treatment at 1200 to 1350°C to form an α single phase, then water-cooled, and then subjected to aging treatment to undergo spinodal decomposition). Cause α → α.

Ferromagnetic properties are expressed by creating a two-phase separation phase of +α2.

In addition, when imparting anisotropy, a method is adopted in which a magnetic field is applied during the aging treatment, or plastic working such as aging rerolling or wire drawing is performed.

By the way, it is known that when a few percent of Mo is added to a Fe-Cr-Co alloy, crystal anisotropy occurs in the spinodal decomposition described above, and decomposition occurs preferentially in the <001> direction. Therefore, when aging treatment is performed by applying a magnetic field in the <001> direction, the two-phase separated α1 phase is extremely well extended in the <001> direction, and as a result, the magnetic properties are significantly improved.

In alnico magnets, which are spinodally decomposed magnets similar to Fe-Cr-Co magnet alloys, the axis of columnar crystals during solidification coincides with the <001> axis, and the casting method is devised to form columnar crystals. By developing <OO
The cast steel ingot has a high degree of orientation in the b direction, and is subjected to aging treatment in a magnetic field in the <001> direction to improve magnetic properties.

A similar method has been devised for Fe-Cr-Co alloys; for example, in Japanese Patent Publication No. 62-46269, molten alloy is poured into a mold using a chilled metal to create a temperature gradient during solidification. This results in the development of columnar crystals.

(Problem to be solved by the invention) However, in the method of once pouring molten alloy into a mold to form a steel ingot, non-magnetic γ phase and hard and brittle σ phase precipitate during cooling of the steel ingot. Therefore, α due to the materialization process
The problem remained that the single-phase process could not be omitted.

That is, this solution treatment is carried out at 1200 to 1300'C as shown in Japanese Patent Publication No. 62-46269.
Since it is necessary to maintain the temperature at a high temperature, it leads to a significant increase in industrial costs and is also a time-consuming process.

Ta. Moreover, the portion of the steel ingot thus obtained was in the form of columnar crystals at most 75%, and the yield was hardly sufficient.

This invention advantageously solves the above problems, and utilizes a thin slab continuous casting machine (thin slab caster) to achieve a 90% cast rate.
It is an object of the present invention to provide an advantageous method for producing a unidirectional permanent magnet alloy that achieves the above columnar crystal ratio and does not require solution treatment to form an α single phase.

(Means for Solving the Problems) That is, the present invention provides Cr: 10-35-tχ (hereinafter simply expressed as %) Co: 5
~35% and Mo: 0.1-10.0%, and sometimes further contains B+ SI+ ANkai Mn, Ti, V, Nb,
A molten alloy containing Zr + at least one selected from Sn and Zn: 0.01 to 5.00%, and the remainder having a substantially Fe composition,
After forming a thin slab with a thickness of 3 to 50 mm using the thin slab caster method, it is cooled from a temperature of 900°C or higher to room temperature at a cooling rate of 5'C/s or higher, and then subjected to magnetic field aging treatment and aging treatment. This is a method for producing a unidirectional permanent magnet alloy.

This invention will be specifically explained below.

First, the reason why the component composition of the material is limited to the above range in this invention will be described.

Cr: 10-35% Cr is a useful component that forms a non-magnetic matrix, but if its content is less than 10%, the coercive force will be low, while if it exceeds 35%, the residual magnetic flux density (Br) will be low. The Cr content is 10 to 3.
It was limited to a range of 5%.

Co: 5-35% Co is added as a ferromagnetic component along with Fe, but if the amount added is less than 5%, spinodal decomposition is difficult to occur, while if it exceeds 35%, sufficient coercive force is not achieved. Therefore, the Co content was set in the range of 5 to 35%.

Mo: 0.1 to 10.0% Mo promotes crystal anisotropy of spinodal decomposition and has the effect of increasing coercive force. However, 0
．． If it is less than 1%, the effect is poor, and if it exceeds 10.0%, not only the residual magnetic flux density but also the coercive force will actually decrease, so the MO content should be in the range of 0°1 to 10.0%. Limited.

The basic components have been explained above, but other subcomponents include B, St, AI, W, V, Nb+ Ti+
A small amount of one or more selected from Zr+Mnt Sn and Zn can also be added. All of these elements contribute to improving coercive force, but the amount added is
, less than oi%, the addition effect is poor; on the other hand, 5.0θ
%, the residual magnetic flux density decreases, so the amount added should be 0.0% for both single addition and combined addition. O1~5.0
It needs to be within the range of 0%.

Next, the manufacturing method of this invention will be explained.

Now, the molten alloy adjusted to the above-mentioned composition,
The material is continuously supplied between a pair of cooling belts whose cooling surfaces move continuously to form a thin slab with a thickness of 3 to 50 mm. Specifically, a vertical thin slab caster as shown in FIG. 1 or a horizontal one-slab caster as shown in FIG. 2 is used. In the figure, number 1 is a dollar, 2.2' is a tundish, 3.3' is a steel cooling belt, 4.4' is a spray nozzle, 5 is a holding container, and 6.6' is a thin slab.

In this casting process, the thickness of the slab can be adjusted by changing the gap between the cooling belts, the belt material, the belt movement speed, etc.

By rapidly cooling the thus obtained thin slab immediately after casting, it is possible to avoid the (α+γ) phase that occurs in the high temperature region and bring only the α single phase region necessary for magnetization to room temperature.

By the way, when Mo is added to the Fe-Cr-Co alloy, the (α10γ) phase region decreases, but conversely the precipitation of the σ phase is promoted. This situation is shown in FIGS. 3 and 4.

Figure 3 shows Fe -25%Cr -12%Co -3%M
Regarding the alloy with composition o, and Fig. 4 shows Fe-22%C
FIG. 4 shows isothermal transformation diagrams regarding the precipitation of the σ phase for each alloy having a composition of r-15%Co-3%Mo.

As is clear from both figures, the nose of σ phase precipitation is around 800°C, and when the aging time is 100 minutes, the temperature of both sets of acids is around 700°C.
Precipitates in the range of 900"C. For thin slab casters, when cooled to room temperature after casting, the precipitation occurs at 60 to 1
It takes about 20 minutes. Therefore, σ during cooling
In order to avoid phase precipitation, it is necessary to rapidly cool the material from a temperature range of at least 900°C or higher. In addition, the upper limit of the thickness of the slab at this time is set at 50 - because it is necessary to cool the slab uniformly and sufficiently to the center and to sufficiently develop the columnar crystals. The thickness was set at 3 mm to ensure sufficient thickness and to reduce thickness due to surface polishing, grinding, etc. Cooling is achieved by spraying water, and the cooling rate can be adjusted by increasing the amount of water depending on the plate thickness. At this time, it has been confirmed that if the cooling rate is 5°C/S or more, it is possible to avoid the σ phase precipitation in the range of 700 to 900°C.
Cooling was performed at a rate of 5° C./S or more in the temperature range of 00° C. or less.

In this way, when molten metal is poured into a double-belt slab caster, a large temperature gradient occurs during solidification from both surfaces of the slab toward the center, and a columnar shape is formed from the surface toward the center of the thickness. The crystals are greatly developed, and the columnar crystal ratio of the thin slab is almost 100%. FIG. 5 shows a cross section of an example of the solidified structure of the thin slab solidified in this manner.

After casting using the method described above, conventional Fe-Cr-C
It is sufficient to perform the aging treatment in a magnetic field and aging treatment similar to those for o-based magnet alloys, and there is no need for a solution treatment prior to this.

Aging in a magnetic field and aging treatment vary depending on the composition, but
For example, in a magnetic field of about 2 kOe, 600 to TOO
It is sufficient to perform isothermal heat treatment at about 10°C for about 10 minutes to 2 hours, followed by aging at about 600 to 500°C for about several tens of minutes to several tens of hours.

The aging treatment may be either a multi-stage aging treatment in which the temperature is changed during the treatment or a continuous cooling treatment, and the aging treatment in a magnetic field may be slow cooling in a magnetic field.

Aging treatment in a magnetic field is performed by applying a magnetic field in the direction of the columnar crystals.
By performing aging in a magnetic field and aging treatment in this manner, the α and phase separated by spinodal decomposition are extremely well elongated in the columnar crystal direction (direction of the applied magnetic field) in the nonmagnetic α2 phase, resulting in shape anisotropy. It has a structure in which single-domain fine particles are arranged, and thus a magnet with excellent characteristics can be obtained.

(Example) Example 1 Molten steel having the composition shown in Table 1 was cast to a thickness of 30 mm using a vertical thin slab caster as shown in Fig. 1.
,width? Continuous casting into 100 mm thin slabs, temperature:
It was rapidly cooled from 1300°C with spray water at a cooling rate of 10'C/s.

In addition, as a comparison material, 100X10
A steel ingot measuring 0 x 150 mm square was cast (ingot forming method, cooling rate 0.5°C/s). Since this comparative material requires solution treatment, it was subjected to solution treatment in which it was heated to 1300°C for 1 hour and then cooled with water. The as-cast thin slabs obtained as described above and samples cut from the solution-treated steel ingots were subjected to magnetic field aging and aging treatment. These treatments were carried out under the following conditions considered to be optimal depending on the Cr and Co contents of each sample.

■Sample Nal~6: Cr 26%, Co 10%2
After treatment of 640 ”C,Ih in the magnetic field of koe, 62
Hold at 0°C for 1h, then increase to 500”C at 5°C/
After slow cooling at a rate of 15 h, aging treatment was performed by holding at 500°C for 15 h.

■Sample No. 7-12: Cr 22%, Co
After treatment at 650 °C in a magnetic field of 15% 2 kOe for 1 h, it was held at 610 °C for 1 h and then 5 °C to 500 °C.
After slow cooling at a rate of C/h, an aging treatment was performed to maintain the temperature at 500°C.

■Sample N (113-18: Cr 30%, Co
After treatment at 640°C for 940 min in a magnetic field of 20% 2 kOe, it was kept at 600°C for 1 h, and then heated to 500°C for 7
After slow cooling at a rate of °C/h, aging treatment was performed by holding at 500 °C for 5 hours.

■Sample No. 19-24: Cr 35%, Co
After treatment at 670'C for 30 min in a 25% 2 kOe magnetic field, it was held at 620°C for 1 h and then heated to 500°C for 7
After slow cooling at a rate of °C/h, aging treatment was performed by holding at 500 °C for 5 hours.

■25-30 in sample: Cr 25%, Co 12
After treatment at 650°C for 140 minutes in a magnetic field of %2 koe,
620°C for 1h, held at 600°C for 1h, then 5
After slow cooling to 00°C at a rate of 5°C/h,
'C was subjected to aging treatment for 5 hours.

Table 1 shows the results of measuring the magnetic properties of each sample thus obtained. Table 1 also lists the columnar crystal ratios investigated for the cast slabs and steel ingots. The columnar crystal ratio was calculated as the ratio of the area of the columnar crystal portion in the vertical C cross-section of the slab and steel ingot to the total cross-sectional area.

・As is clear from the table, columnar crystals were hardly developed in any sample using the conventional casting method, whereas the samples produced using the thin slab caster method exhibited a high columnar crystal ratio of over 90%. ing.

In addition, regarding the magnetic properties, the value of (BH)wax is significantly lower than that of a thin slab, partly because there are fewer columnar crystal parts in the conventional method. Moreover, in the conventional method, magnetic properties cannot be obtained unless solution treatment is performed.

Example 2 Molten steel having the composition shown in Table 2 was heated to a thickness of 1Off using a horizontal thin slab caster as shown in Figure 2.
It was continuously cast into a thin slab of 1200° C. and quenched with spray water at a cooling rate of 13° C. These samples were then subjected to magnetic field aging and aging treatment. These treatments were carried out under the following conditions considered to be optimal depending on the Cr and Co contents of each sample.

■Sample Nal~3: Cr 30%, Co5%2 kO
After treatment at 600°C for 5 hours in a magnetic field of
Aging treatment was applied.

■Sample Na4-6: Cr 25%, Co 12%
Same treatment as ■ in Example 1 ■ Samples Na7-9: Cr 29%, Co 23% Same treatment as ■ in Example 1 ■ Samples Na1O-12: Cr 34%, Co 3
0% Same treatment as ■ in Example 1 ■ Sample Na13: Cr 12%, Co 17% Sample N
a14: After treatment at 600°C for 30 minutes in a magnetic field of 12% Cr, 18% Co, 2 koe, slowly cooled to 500°C at a rate of 3”C/h, and then cooled to 500”C.

Aging treatment was performed for 50 hours.

■ Sample N (Li2: 20% Cr, 20% Co) Sample NcL16: 20% Cr, 15% Co The results of magnetic measurements for each sample obtained by the same treatment as ■ in Example 1 are shown in Table 2. Also, as in Example 1, the results of investigating the columnar crystal ratio after casting are also listed.

5...Holding container 6.6'...Thin slab (effect of the invention) Thus, according to this invention, a thin slab is produced using a thin slab caster, and the temperature is lowered by 5°C/
By rapidly cooling at a cooling rate of s or more, a unidirectional permanent magnet with excellent magnetic properties can be easily produced at low cost without the need for solution treatment.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a vertical type continuous thin slab casting machine, Figure 2 is a schematic diagram of a horizontal type continuous thin slab casting machine, Figures 3 and 4.
The figure shows Fe-25%Cr-12%Co-3%Mo
Mi composition and Fe-22%Cr-15%C. FIG. 5 is an isothermal transformation diagram showing the σ phase precipitation behavior in an alloy with a 3% Mo composition. 1...Sh-dol 2.2'...Tandish 3.3'...Steel cooling belt 4.4'...Spray nozzle No.1 Figure 4 Time (now)

Claims (1)

[Claims] 1. A molten alloy containing Cr: 10 to 35 wt%, Co: 5 to 35 wt%, and Mo: 0.1 to 10.0 wt%, with the remainder being substantially Fe, is poured into a thin slab caster. It is characterized by forming a thin slab with a thickness of 3 to 50 mm using a method, cooling it from a temperature of 900°C or more to room temperature at a cooling rate of 5°C/s or more, and then subjecting it to aging treatment in a magnetic field and aging treatment. A method for producing a unidirectional permanent magnet alloy. 2. The molten alloy contains Cr: 10 to 35 wt%, Co: 5 to 35 wt%, and Mo: 0.1 to 10.0 wt%, as well as B, Si, Al, W, Mn, Ti, V, Nb, Zr, S
2. The method according to claim 1, wherein the method contains 0.01 to 5.00 wt% of at least one selected from n and Zn, with the remainder being substantially Fe.