US3769100A

US3769100A - Method for manufacturing semi-hard magnetic material

Info

Publication number: US3769100A
Application number: US00179550A
Authority: US
Inventors: H Watanabe; R Watanabe; H Teramoto
Original assignee: Akai Electric Co Ltd
Current assignee: Akai Electric Co Ltd
Priority date: 1970-09-11
Filing date: 1971-09-10
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30
Also published as: NL173575B; DE2144560C2; NL173575C; CA932992A; GB1369509A; NL7112378A; DE2144560A1; FR2112946A5

Abstract

Semi-hard magnetic Fe-Mn system alloys, prepared by powder metallurgical methods, are subjected to cold working and subsequent heat treatment to obtain a product of superior magnetic properties and relatively constant magnetic characteristics, as compared to those products prepared by conventional casting methods. The properties of these magnetic alloys render them suitable for use in hysteresis motors, mechanical channel elements employed in electrical communication systems and the like.

Description

E] States Patent 1191 1111 3,769,100 Watanabe et al. 1 Oct. 30, 1973 METHOD FOR MANUFACTURING 3,301,720 1/1967 Griest 148/120 SEMLHARD MAGNETIC MATERIAL 3,444,012 5/1969 Shimizu et al.. 148/120 X 2,152,006 3/1939 Welch 75/214 x Inventors: Hisashi Watanabe; Ryuji Watanabe;

Hiroshi Teramoto, all of Tokyo,

Japan Assignee: Altai Electric Company Limited,

Tokyo, Japan Filed: Sept. 10, 1971 Appl. No.: 179,550

Foreign Application Priority Data Sept. 11, 1970 Japan 45179795 Oct. 5, 1970 Japan 45/87272 U.S. Cl 148/126, 29/4205, 75/200, 148/12, 148/120, 148/121 Int. Cl. C2ll 1/00, H01f l/00 Field of Search 148/120, 121, 126, 148/12; 75/200; 29/4205 References Cited UNITED STATES PATENTS 2/1967 Adams et a! 75/200 X OTHER PUBLICATIONS Walker, E. V. et al. The Production of Grain-Oriented 50:50 Nickel-Iron Magnetic Strip By Cold Rolling From Sintered Compacts. ln Powd. Met. No. 4 p. 23-31. (1959) TN 695 p54.

Primary Examiner-Carl D. Quarforth Assistant ExaminerR. E. Schafer Attorney-Norman F. Oblon et al.

[5 7] ABSTRACT Semi-hard magnetic Fe-Mn system alloys, prepared by powder metallurgical methods, are subjected to cold working and subsequent heat treatment to obtain a product of superior magnetic properties and relatively constant magnetic characteristics, as compared to those products prepared by conventional casting methods. The properties of these magnetic alloys render them suitable for use in hysteresis motors, mechanical channel elements employed in electrical communication systems and the like.

6 Claims, No Drawings METHOD FOR MANUFACTURING SEMI-HARD MAGNETIC MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to a method for manufacturing semi-hard magnetic alloys,and more particularly to a method for manufacturing Fe-Mn system magnetic materials of the quench hardening type,which are suitable for hysteresis motors and mechanical channel e1ements,such as are used in electrical communication systems. The term Fe-Mn system magnetic materials refers herein to magnetic materials consisting of less than 20 percent by weight of manganese, less than several percent by weight of additives,such as titanium- ,copper,chromium,vanadium and the like,with the balance being substantially iron. Such magnetic materials may further contain less than 20 percent by weight of cobalt for the purpose of increasing the coercive force and the residual magnetic flux density of the product.

2. Description of the Prior Art Magnetic materials to be useful in hysteresis motors and the like, should have a coercive force of about 50 to 200 Oersteds,and a residual magnetic flux density of about 8,000 to 17,000 Gausses. In the past, Alnico alloy systems have been used in an attempt to satisfy this need. The Alnico system, however,has several inherent drawbacks which have inhibited their full utilization in the art; particularly:

1 the magnet is so hard (more than 600 in Vickers hardness) that machinability is poor,thereby resulting in high manufacturing costs,due to the necessity of abrasive working,

2 they are rather expensive,since they use nickel and cobalt metals,whose yield is very small,in the preparation of the magnet, and

3 it is difficult to obtain a magnet having a high magnetic flux density and a low coercive force.

It has been proposed to use Fe-Mn system magnets instead of Alnico,because of its lower hardness,lower cost and more easily controllable coercive force. Particularly, Fe-Mn systems are characterized by:

1 a hardness of less than 300 Vickers which renders the magnets easily lathe machinable,thereby resulting in significantly greater machining precision,and significantly reduced manufacturing costs,

2 a considerably lower cost for the metals required in producing the magnets,as compared with Alnico systems, and

3 a coercive force which can easily be controlled between the range of 20 and 150 Oe,which renders these alloys especially advantageous for application as rotor magnets in hystersis motors.

Until now,however,Fe-Mn system magnets have been only prepared by casting techniques in which Fe and Mn are co-melted with other additives,such as Co, in vacuum or in an inert atmosphere, cast into a mold and then subjected to hot rolling and cold rolling. The products are then lathe machined,and heat-treated to obtain the desired magnetic characteristics.

The Fe-Mn magnet systems produced by such casting methods, however,have not proven to be entirely satisfactory. For one,it is quite difficult,by casting techniques,to produce a material of constant constituents,- largely because of the high vaporization pressure of Mn at the casting temperature (for example,the vapor pressure of Mn may be as high as mm Hg at l,500

C.,which can cause as much as 10 percent of the Mn to vaporize). Moreover,the cast magnets are frequently subject to blowholes,caused by the casting of molten materials into a mold. As a result,the magnets are frequently characterized by uneven magnetic characteristics.

Another disadvantage of the previously prepared Fe-Mn system magnetics,is that they are difficult to mass produce,especially when smaller magnets are required,since production requires separate casting of each magnet into separate molds. I

Still another disadvantage is that in order to obtain a useable configuratiori,the cast material must be lathed extensively,thereby resulting in wasted material. Of course,lathing is still easier than abrasive machining.

A further disadvantage is the great extent of cold working necessary to obtain the desirable magnetic characteristics.

A need exists,therefore,for an Fe-Mn system magnet which can be produced in a high degree of uniformity and constituent consistency,which is relatively easy to mass produce,and which does not require extensive machining.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel method for manufacturing Fe-Mn system magnets.

It is another object of this invention to provide a novel method for manufacturing Fe-Mn system magnets which are superior in magnetic characteristics,and

which demonstrate less variation in magnetic characteristics,as compared with those magnets prepared by conventional casting techniques.

It is still another object of this invention to provide a novel method for manufacturing Fe-Mn system magnets, which require lower manufacturing costs and permit mass productivity as compared with conventional techniques.

These and other objects have now been attained by admixing Fe and Mn powders optionally, with one or more additive powders, such as Co powder, compacting and sintering the powder mixture, as in conventional powder metallurgical methods, and thereafter subjecting the product to both cold working and heat treatment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS According to the present invention, a mixture of iron and manganese powders is prepared in amounts of 5-14 wt percent Mn, with the balance being Fe. Other additive powders, such as cobalt, titanium, copper, vanadium, chromium, silicon, or the like, may be added to the mixture. When 5-14 wt percent Mn is used, tita nium may be used in amounts of 0.6-6 wt percent and copper, chromium, silicon or the like, may be used in amounts of 0 to 0.3 wt percent with the balance being Fe. When Mn is used, in preferable amounts of 10-13 percent, titanium may be used in amounts of 2-4 wt percent, Cn, Cr, Si or the like may be used in amounts of 0-3 wt percent, with the balance being Fe. Moreover, when Mn is used in amounts of less than 30 wt percent, Ti in amounts of less than 5 wt percent with the balance being Fe, and preferably, when Mn is used amounts of 24 wt percent with the balance being Fe.

The powder mixture is then compacted under high pressure of from -10 ton/cm", and is subjected to sintering temperatures of higher than 1,200" C, but lower than the melting point in an inert atmosphere or in vacuo. Preferably sintering is effected at temperatures of from l,250 C to l,330 C.

The compacted and sintered product is then cold worked by conventional means, at a working ratio of greater than 40 percent, with no upper limit, but preferably at a low cold working ratio of from 40 to 65 percent, to provide sufficient magnetic characteristics of the magnetic materials suitable for hysteresis motors.

If desired, the working processes can be reduced by carrying out sizing" concurrently with cold working. This expedient can lead to reduction in manufacturing costs.

Since the Fe-Mn system magnets are quench hardening type, which is subject to austenite-martensite transformation, the cold working will contribute to improvements in magnetic characteristics by creating strains in the structure of the magnets. The strains promote the transformation to the fullest extent and increases the density of the sintered compact.

Following cold working, the material is subjected to heat treatment of 450 C to 530 C.

The following table compares the residual magnetic flux density Br (Gauss) and coercive force He (Oersted) of (A) Fe-Mn system magnets sintered and subjected to cold working according to the present invention, (B) Fe-Mn system magnets sintered according to the present invention but not cold worked, and (C) Fe-Mn system magnets manufactured according to the conventional casting method. The superiority of the magnets according to the present invention will be clearly understood from this table.

Br (Gauss) Hc (Oersted) (A) more than 9500 lO-l50 (B) less than 3000 -50 (C) 7000-8000 l0-l 50 If the Fe-Mn magnets of the present invention are heat treated, but not cold worked,or are cold worked,- but not heat treated,the superior magnetic characteristics are not obtainable.

The following advantages are obtainable by the present invention:

1 magnets can be prepared which are highly uniform and which are characterized by good component consistency and stable magnetic characteristics,since only a small amount of the Mn will be vaporized during the sintering process as low as 0.1 percent if sintering is conducted at l,300 C. for 5 hours).

2 the process of the present invention provides a high mass productivity,as compared with conventional casting methods,especially where small size magnets,as used in hysteresis motors, are prepared.

3 machining procedures can be eliminated with the resultant reduction in manufacturing costs and lower loss of materials, since the starting materials can be compacted into the desired form in the initial stages of processing.

Having generally described the invention, a more complete understanding can be obtained by reference to certain specific Examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

EXAMPLE 1 A mixture of materials,consisting of 87 wt. percent Fe and 13 wt. percent Mn, was compacted under pressure and then sintered at l,300 C.for 5 hours in an inert atmosphere. The product was then subjected to cold working at a working ratio of 50 percent and heat treated at 500 C.for 10 hours. The magnetic characteristics of the magnets thus prepared were found to have a residual magnetic flux density of 9,500 Gauss and a coercive force of 60 Oersted. By way of comparison, the magnetic characteristics of the magnet prepared without cold working,but under the same treatment conditions werezresidual magnetic flux density of 2,300 and coercive force of 20 Oersted.

The amount of evaporation of Mn in the course of sintering was about 0.1 percent of the prepared amount of Mn and is considerably less than the 10 percent amount for magnets having the same constituents but prepared by conventional casting methods.

EXAMPLE 2 A powder mixture of materials,consisting of 84.5 wt. percent Fe, 12.5 wt. percent Mn,and the balance being additives such as Ti, Cu, V, Cr, Si and the like was compacted and then sintered at l,250 C.for 5 hours in an inert atmosphere. The compact was then subjected to cold working, at a working ratio of 65 percent and heat treated at 500 C.for 8 hours. The magnetic characteristics of the magnets thus prepared were: residual magnetic flux density of 9,700 Gauss,and coercive force of 55 Oersted.

EXAMPLE 3 A powder mixture of materials,consisting of 77 wt. percent Fe, 10 wt. percent Mn,10 wt. percent Co and 3 wt. percent Ti was compacted under pressure and sintered at 1,300 C.for 10 hours in an inert atmosphere. The compact was cold worked at a working ratio of 65 percent,and then subjected to heat treatment at 500 C.for 10 hours. The magnetic characteristics of the magnets thus manufactured were: residual magnetic flux density of 14,000 Gauss,and coercive force of 35 Oersted.

EXAMPLE 4 A powder mixture of materials,consisting of wt. percent Fe, 10 wt. percent Mn, 10 wt. percent Co, 3 wt. percent Ti and 2 wt. percent additives such as Cu, V, Cr and Si,was compacted under pressure and sintered at l,300 C.for 10 hours in an inert atmosphere. The compact was cold worked at a working ratio of 65 percent and heat treated at 550 C.for 8 hours. The magnetic characteristics of the magnets thus prepared were: residual magnetic flux density of 12,000 Gauss- ,and coercive force of 55 Oersted.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention. ACCORDINGLY,

What is claimed as new and intended to be secured by Letters Patent of the United States is:

l. A method of preparing a semi-hard Fe-Mn system magnetic material which comprises:

admixing 75 to 87 wt. percent iron powder and 10 to 13 wt. percent manganese powder,

compacting the powder mixture material,

sintering the compacted mixture material at a temperature of 1200 C. to 1330 C. in an inert atmosphere.

subjecting the sintered material to cold working to cause austenite to martensite transformation, heat treating the material to obtain said semi-hard Fe-Mn magnet.

2. The method of claim 1, wherein said powder mixture contains at least one additive powder selected from the group consisting of: Ti, Cu, V, Cr, Si and Co.

3. The method of claim 2, wherein said additive pow-

Claims

2. The method of claim 1, wherein said powder mixture contains at least one additive powder selected from the group consisting of: Ti, Cu, V, Cr, Si and Co.
3. The method of claim 2, wherein said additive powder is Co.
4. The method of claim 1, wherein said cold working is effected at a working ratio of 40 - 65 percent.
5. The method of claim 1, wherein said heat treatment is effected at temperatures of 500* - 550* C.for 8 to 10 hours.
6. A magnet prepared by the method of claim 1 which is characterized by a residual magnetic flux density of greater than 9,500 Gauss and a coercive force of 10 - 150 Oersted.