WO2000060616A1

WO2000060616A1 - Workable, semi-hard magnetic alloy with small magnetostriction and article made therefrom

Info

Publication number: WO2000060616A1
Application number: PCT/US2000/009347
Authority: WO
Inventors: Bradford A. Dulmaine; David A. Englehart
Original assignee: Crs Holdings, Inc.
Priority date: 1999-04-06
Filing date: 2000-04-06
Publication date: 2000-10-12

Abstract

A semi-hard magnetic alloy having the following weight percent composition is described: C 0.1 max., Mn 2-14, Si 0.5 max., P 0.2 max., S 0.2 max., Cr 0.5 max., Mo 0.5 max., Ni up to 16, Cu up to 7, N 0.05 max., Co 0.3 max., W 0.2 max., Al 0.2 max., Ti 0.2 max., Nb 0.10-1.0. The balance of the alloy is essentially iron and the usual impurities. The alloy provides a unique combination of coercivity, remanence, and low magnetostriction. A magnetically biasable tag or marker employing the semi-hard magnetic alloy is also described.

Description

WORKABLE, SEMI-HARD MAGNETIC ALLOY WITH SMALL MAGNETOSTRICTION AND ARTICLE MADE THEREFROM

Field Of The Invention

The present invention relates to a semi-hard magnetic alloy and an article made therefrom. More particularly, the present invention relates to an Fe-Mn magnetic alloy, and an article made therefrom, that provides a unique combination of coercivity, high remanence, and low magnetostriction.

Background Of The Invention

Certain devices, including the markers or tags used in many theft detection systems, make use of a semi-hard magnetic alloy in the form of foil or strip as the magnetic bias component. For economic reasons, it is desirable for such an alloy to be composed of inexpensive elements and to be easily made in the needed form using common metal-working equipment. In addition, because the amount of magnetic material needed in a device is often inversely related to the material's remanence, a high remanence is desired to minimize the amount of material needed. A very low magnetostriction is also desired because a material having too high a magnetostriction and moderate coercivity can be more easily demagnetized by mechanical stresses. Since the markers used in theft detection systems are often subjected to accidental stresses during manufacturing or when in use, a theft detection marker incorporating a foil having a magnetostriction that is too great may inadvertently become demagnetized and not function properly. In view of the foregoing, a need has arisen for a low cost, semi-hard magnetic alloy, having a low magnetostriction and a high remanence, which is easy to manufacture into strip form. Summary Of The Invention

In accordance with one aspect of the present invention, there is provided an iron-based magnetic alloy having the following broad and preferred weight percent compositions.

Broad Pref'd 1 Pref'd 2 Pref'd 3 Pref'd 4

C up to 0.1 0.02-0.1 0.02-0.1 0.02-0.1 0.02-0.1

Mn 2-14 5-9 5-9 5-9 5-9

Si 0.7 max. 0.1-0.5 0.1-0.5 0.1-0.5 0.1-0.5

P 0.2 max. 0.1 max. 0.1 max. 0.1 max. 0.1 max. s 0.2 max. 0.1 max. 0.1 max. 0.1 max. 0.1 max.

Cr 0.5 max. 0.3 max. 0.3 max. 0.3 max. 0.3 max.

Ni up to 16 0.50 max. 0.50 max. 3-16 3-16

Mo 0.5 max. 0.35 max. 0.35 max. 0.35 max. 0.35 max

Cu up to 7 0.1 max. 1-6 0.1 max. 1-6

N 0.05 max. 0.02 max. 0.02 max. 0.02 max. 0.02 max

Co 0.3 max. 0.2 max. 0.2 max. 0.2 max. 0.2 max.

W 0.2 max. 0.1 max. 0.1 max. 0.1 max. 0.1 max.

Al 0.2 max. 0.1 max. 0.1 max. 0.1 max 0.1 max.

Ti 0.2 max. 0.1 max. 0.1 max. 0.1 max. 0.1 max.

Nb 0.10-1.0 0.15-0.5 0.15-0.5 0.15-0.5 0.15-0.5

The balance of the alloy is iron except for the usual impurities found in commercial grades of such alloys and minor amounts of additional elements which vary from a few thousandths of a percent up to larger amounts that do not objectionally detract from the desired combination of properties provided by this alloy. Within the foregoing weight percent ranges the elements are balanced to provide a unique combination of low magnetostriction and moderate coercivity. The low magnetostriction provided by this alloy is indicated by a magnetostriction value (λ) in the range -6 < λ <+6 for the broad composition and -3 < λ <+3 for the preferred compositions, where λ is in parts per million (ppm). Further, the elements Mn, Ni, and Cu are balanced such that %Ni + %Cu + 2.3(%Mn) is at least about 14.6 to provide a coercivity, H_c, of at least about 17.5 oersteds (Oe) and at least about 20 Oe for the preferred compositions. The alloy according to this invention provides a high remanent induction, B_r, (i.e., at least about 14,000 gauss), in addition to the unique combination of coercivity and low magnetostriction.

The foregoing tabulation is provided as a convenient summary and is not intended to restrict the lower and upper values of the ranges of the individual elements of the alloy of this invention for use in combination with each other, or to restrict the ranges of the elements for use solely in combination with each other. Thus, one or more of the element ranges of the broad composition can be used with one or more of the other ranges for the remaining elements in the preferred composition. In addition, a minimum or maximum for an element of one preferred embodiment can be used with the maximum or minimum for that element from another preferred embodiment. Here and throughout this application percent (%) means percent by weight, unless indicated otherwise.

In accordance with a second aspect of the present invention, there is provided a magnetic article for use in connection with theft detection systems. The magnetic article comprises a magnetic tag having a housing. A first metal strip is disposed in the housing. The first metal strip is formed of a magnetically soft metal or alloy. The magnetic tag also includes a second metal strip disposed in the housing adjacent to said first metal strip. The second metal strip is formed of any of the magnetically semi-hard metal alloys set forth in the foregoing table. Brief Description Of The Drawings

The foregoing summary, as well as the following detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the accompanying drawing which is an exploded view of a magnetic tag or marker for use in a theft detection system.

Detailed Description

The alloy according to the present invention contains at least about 2 % manganese to provide semi-hard levels of coercivity (i.e., at least about 20 oersteds). Preferably the alloy contains at least about 5% manganese. Too much manganese adversely affects the cold workability of the alloy. We have found that above about 14 % manganese, the alloy can no longer be effectively cold rolled. Therefore, manganese is restricted to not more than about 14%, better yet to not more than about 9%, and preferably to not more than about 7%. At least about 1%, better yet, at least about 3% copper may be present in this alloy to increase the coercivity and lower the magnetostriction of the alloy. However, too much copper adversely affects the hot workability of the alloy because it forms a liquid phase at the temperatures typically used to hot work the alloy and causes the alloy to break during hot working. Accordingly, when the alloy must be hot worked, copper is restricted to not more than about 7 %, better yet to not more than about 6% and, preferably, to not more than about 5 %. When the benefits provided by copper in this alloy are not needed, the alloy typically contains not more than about 0.1% copper. When the alloy is made by powder metallurgy or continuous casting techniques, copper may be present substantially up to its solubility limit.

This alloy may contain an amount of nickel that is effective to benefit the magnetostriction property. In the alloy according to the present invention, manganese, and when present, copper shift the magnetostriction to more negative values. Nickel benefits the magnetostriction because it shifts the measured magnetostriction toward more positive values. We have found that at least about 2 or 3% nickel should be present in this alloy to achieve a magnetostriction in the range -3 < λ < +3, where, again, λ is the magnetostriction in parts per million (ppm). By controlling the amount of nickel present in the alloy, relatively low values of magnetostriction can be obtained. On the other hand, too much nickel results in large positive magnetostriction values, especially when manganese is present at the low end of its weight percent range. Therefore, when present, nickel is restricted to not more than about 16 % in this alloy. When the benefit provided by nickel in this alloy is not needed, the alloy typically contains not more than about 0.5% nickel.

A small amount of niobium is present in this alloy to combine with substantially all of the carbon that is present. Niobium combines with carbon to form carbide particles which act to restrict grain growth and, therefore, provide finer grain sizes in this alloy. A fine grain size benefits the coercivity provided by this alloy. An effective amount of niobium is present in the alloy when it reacts with substantially all of the carbon. When too little niobium is present, the excess carbon reacts with other elements to form other, less desirable carbides which adversely affect the basic and novel combination of properties provided by this alloy. Accordingly, at least about 0.15 % niobium is present in the alloy. For best results the alloy contains at least about 8 times the weight percent of carbon (8 x %C). Too much niobium adversely affects the cold workability of the alloy. Therefore, niobium is restricted to not more than about 1.0%, better yet to not more than about 0.8 %, and preferably to not more than about 0.5%.

Up to about 0.3% carbon can be present in this alloy to combine with niobium as described above. Preferably, this alloy contains at least about 0.02 % carbon. The carbon content is preferably restricted to not more than about 0.1 % because more does not provide any benefit and too much carbon adversely affects the workability and formability of the alloy.

A small amount of silicon can be present in this alloy for deoxidation. Accordingly, at least about 0.1% silicon is effective for that purpose. Too much silicon adversely affects the ductility and workability of this alloy, especially cold workability. Therefore, silicon is restricted to not more than about 0.7% and preferably to not more than about 0.50% in this alloy. Up to about 0.5%, preferably up to about 0.3%, chromium and up to about

0.5%, preferably up to about 0.35% molybdenum may be present in this alloy. Also, up to about 0.3%, preferably up to about 0.2% cobalt may be present in this alloy.

The balance of the alloy is essentially iron apart from the usual impurity elements found in commercial grades of alloys intended for similar use or service. The levels of such elements are controlled so as not to adversely affect the desired properties. More particularly, phosphorus, sulfur, tungsten, titanium, and aluminum are each restricted to not more than about 0.2 %, better yet to not more than about 0.1 %, and preferably to not more than about 0.05%. Nitrogen is also restricted to not more than about 0.05 % and, preferably, to not more than about 0.02 %.

No special techniques are required in melting, casting, or working the alloy of the present invention. Vacuum induction melting is the preferred method of melting, but other practices including electric art melting with electroslag remelting can be used. After melting, the alloy is cast into ingots and hot worked to either strip, bar, or rod. The hot worked alloy is cold worked to a final size and shape. At one or more intermediate points during such cold working the alloy is optionally annealed at a temperature between about 700 °C and 1200°C or aged at a temperature between about 350° and 650°C. Annealing improves the cold workability of the alloy, whereas aging helps to develop its magnetic properties. In the cold-worked condition, the alloy has a high remanence, but a relatively low coercivity. The cold-worked alloy is aged at a temperature between about 350 °C and 650 °C to increase its coercivity by causing the precipitation of austenite, copper, and/or MnNi intermetallic compounds in the alloy matrix. Other processes such as powder metallurgy or continuous casting techniques can be used to make this alloy. When using powder metallurgy, the alloy is melted and atomized to form fine powder. The alloy powder is consolidated to a thin slab form by hot isostatic pressing, for example, and then cold worked to form strip of desired width and thickness. Alternatively, the alloy can be continuously cast into a thin slab which is then cold worked to form strip of desired width and thickness.

Referring now to the drawing, there is shown a magnetic article 10, such as a tag or marker, used in connection with a theft detection system. The magnetic tag 10 includes a magnetically soft metal strip 12 which is enclosed within a casing formed by a hat-shaped lid 14 and a rectangular base 16. A magnetically semi-hard metal strip 18 is positioned along a surface of the base 16 facing away from the soft metal strip 12. An optional second base 20 is positioned over the magnetically semi -hard metal strip 18. A pressure sensitive adhesive layer 22 is applied to the external surface of the magnetically semi-hard metal strip 18 or to the external surface of the optional second base 20 to permit the magnetic tag 10 to be secured to an object. The magnetic tag 10 is preferably provided with a peelable cover 24 positioned over the adhesive 22 to protect the adhesive 22 prior to use. When the magnetic tag 10 is activated, the magnetic elements are designed to provide a signal in response to a variable magnetic field produced by a commercial theft detection system. The magnetic article 10 is activated by magnetizing the magnetically semi-hard metal strip 18. The magnetic article 10 is then attached to an object such as a piece of store inventory using the pressure - sensitive adhesive 22. When the object, with the magnetic tag attached thereto, passes through a time- varying magnetic field produced by the commercial theft detection system, the magnetically soft metal strip 12 resonates at a frequency which is detected by the theft detection system. If the detected frequency is within a preset frequency range, the theft detection system produces an alarm signal. The frequency at which the magnetically soft metal strip 12 resonates is a function of the magnetic field produced by the magnetically semi-hard metal strip 18. The magnetic article 10 is deactivated by demagnetizing the magnetically semi-hard metal strip 18. When deactivated, the frequency of the signal produced by the magnetically soft metal strip 12 is altered such that the theft detection system does not detect the signal and, accordingly, does not issue an alarm.

Examples

In order to demonstrate the properties provided by the alloy of the present invention several examples of the alloy of the present invention and comparative heats were prepared. The weight percent compositions of Examples 1-45 and Heats A-X are set forth in Tables 1A to ID below. Tables 1A to ID also include the magnetostriction values (λ) in parts per million (ppm) for each example and comparative heat.

Table 1A

ExJHeat %Mn %Ni %Cu λ

1 5.99 0.01 0.01 -5.5

2 8.97 0.01 0.02 -3.9 A 2.97 0.01 0.03 -7.0

Table IB Ex./Heat %Mn Ni %Cu λ

3 5.97 0.01 2.03 -5.7

4 5.94 0.01 4.05 -5.8

5 8.95 0.01 2.03 -3.8

6 8.92 0.01 3.88 -3.6

B 0.14 0.01 1.96 -8.1 ExJHeat %Mn %Ni %Cu λ

C 0.14 0.01 3.96 -8.5

D 0.14 0.01 5.98 -9.2

E 2.93 0.01 2.10 -1.3

F 2.92 0.01 4.19 -6.8

5

Table 1C

ExJHeat %Mn %Ni %Cu

7 6.06 3.96 0.02 -1.9

8 8.99 3.95 0.03 -2.1

10 9 3.04 7.85 0.02 4.0

10 6.00 7.85 0.02 -0.3

11 8.91 7.87 0.03 -2.2

12 3.05 11.77 0.01 6.0

13 5.99 11.79 0.02 2.8

15 14 8.90 11.83 0.04 -0.1

15 5.95 15.75 0.03 2.5

16 8.90 15.78 0.04 -1.9

G 0.26 3.90 0.03 0.7

H 3.06 3.92 0.02 0.1

20 I 0.29 7.81 0.04 9.5 j 0.30 11.73 0.04 12.3

K 0.34 15.67 0.05 13.7

L 3.02 15.70 0.02 8.8

25 Table ID

ExVHeat %Mn %Ni %Cu λ

17 3.03 3.95 3.98 -2.4

18 6.02 3.94 2.04 -3.6

19 5.99 3.95 4.11 -3.4

20 0.29 7.84 4.04 5.5

21 0.28 7.86 6.04 4.5

22 8.94 3.94 2.02 -2.8

23 8.91 3.95 4.01 -1.8

10 24 3.02 7.89 2.10 2.9

25 3.01 7.90 4.20 1.7

26 5.96 7.87 2.07 -0.6

27 5.96 7.88 4.09 -0.3

28 8.88 7.88 2.01 -1.7

15 29 8.88 7.90 3.89 -1.2

30 3.03 11.79 2.09 5.5

31 3.01 11.81 4.03 5.8

32 3.00 11.85 6.07 3.3

33 5.95 11.79 2.01 1.5

20 34 5.95 11.81 4.03 1.4

35 5.91 11.85 5.99 0.9

36 8.87 11.88 2.02 -0.5

37 8.85 11.90 4.01 -1.3

38 2.99 15.71 4.02 5.5

25 39 2.98 15.76 5.92 4.0

40 5.95 15.79 2.02 1.0

41 5.95 15.86 3.95 -0.1

42 5.93 15.86 5.62 -1.1

43 8.88 15.81 2.06 -1.5

30 44 8.86 15.88 4.02 -2.0 45 8.86 15.92 5.92 -1.3

M 0.26 3.90 2.06 0.7

N 0.26 3.92 4.12 -1.2

O 0.25 3.92 6.22 -1.6

P 3.04 3.93 2.02 -2.4

Q 0.29 7.80 2.02 5.9

R 0.30 11.76 2.08 10.8

S 0.29 11.77 4.03 9.5

T 0.29 11.81 5.85 7.2 u 0.33 15.68 2.12 11.0

V 0.33 15.67 4.17 10.0

W 0.32 15.66 6.16 9.5

X 3.00 15.69 2.03 6.4

The alloys described in Tables 1A to ID also included 0.024-0.040% carbon,

0.23-0.30% silicon, and 0.33-0.34% niobium. The balance in each case was iron and usual impurities.

The examples and comparative heats were induction melted under a cover of argon gas and cast into ingots. The ingots were heated to 2050°C and forged to 1 inch square bars. Portions of the bars were milled to 0.75 inch square, heated to 1121 °C and rolled to 0.25 inch thick strip. Pieces of the strips were annealed at 899 °C for 15 minutes. A portion of each strip was then rolled to 0.020 inch thickness, cut into 2-inch by 0.25-inch coupons, degreased, and then aged at 420 °C for hours. Three (3) coupons of each composition were tested for magnetostriction.

Another portion of each annealed strip was rolled to 0.05 inch thick, annealed for 4 minutes, rolled to 0.004 inch thick, and cut into 0.5 inch wide specimens, some 8 inches long and some 1.6 inches long. One 8-inch and one 1.6-inch specimen from each ingot were aged at temperatures from 400 °C to 650 °C in 50C° increments, each aging taking place for four hours. Other specimens were aged at 420°C. The coercivity of each 1.6-inch specimen was measured with a coercimeter.

Set forth in Tables 2A to 2D are the results of coercivity testing of each of Examples 1-45 and Heats A-X including the coercivity in Oersteds (Oe) in the as-rolled condition (AR) and after aging at each of the aging temperatures utilized.

Table 2A Coercivity (Oe) at indicated aging temperature (°C)

Ex/Ht AR 400 420 450 500 550 600 650

1 16.9 16.6 16.4 17.2 17.8 17.7 17.3 17.6

2 17.8 18.1 19.3 21.2 25.3 27.2 26.4 26.2

15.5 13.1 13.4 13.4 12.4 10.4 8.2 3.1

Table 2B

Coercivity (Oe) at indicated aging temperature (°C)

Ex/Ht AR 400 420 450 500 550 600 650

3 15.0 16.4 16.6 17.7 19.7 21.2 20.4 20.0 4 16.1 20.8 23.2 23.1 25.2 26.4 25.0 21.9

5 16.3 19.3 21.2 23.5 28.6 31.4 28.4 29.5

6 17.6 24.8 26.6 31.0 35.4 36.7 31.1 29.9 B 11.1 6.6 6.4 6.6 6.6 7.1 7.1 6.1 C 13.5 9.3 9.3 9.4 9.6 10.1 10.3 9.0 D 14.7 12.8 13.1 13.1 12.9 13.2 12.7 11.0

E 13.7 13.5 14.2 14.7 14.7 13.7 12.3 10.0

F 15.3 15.3 16.7 17.9 18.2 17.0 15.0 12.2 Table 2C

Coercivity (Oe) at indicated aging temperature (°C)

Ex/Ht AR 400 420 450 51 550 61 650

7 11.9 11.1 12.7 15.3 18.3 24.8 26.8 26.3 8 13.1 23.0 24.4 25.7 36.6 41.6 39.9 30.8

9 10.4 6.7 7.0 8.2 11.3 18.6 20.0 19.6

10 11.2 8.6 9.4 11.4 18.3 32.4 33.8 22.5

11 20.7 18.8 16.5 38.0 41.2 63.0 45.0 37.2

12 12.2 6.5 6.7 7.9 18.4 26.7 28.5 21.0 13 12.5 8.2 9.4 12.7 27.7 46.5 47.9 27.5

14 35.6 41.0 48.3 57.8 56.6 53.4 71.8 53.2

15 25.5 20.7 21.3 28.7 44.6 47.0 57.8 43.5

16 78.4 192 226 208 100 78.1 1400 1400 G 9.2 5.9 5.8 5.7 5.8 5.2 4.6 2.5 H 10.3 7.2 7.5 8.4 9.1 11.2 13.0 15.2

I 10.1 5.6 5.5 5.5 5.8 6.2 7.9 11.4

J 11.3 5.5 5.3 5.3 6.9 13.4 18.3 16.4

K 13.9 5.1 4.7 5.4 7.7 23.0 25.3 23.0

L 11.6 5.9 5.9 6.9 27.2 42.0 42.7 25.0

Table 2D

Coercivity (Oe) at indicated aging temperature (°C)

Ex/Ht AR 400 420 450 500 550 600 650

17 10 8 7 6 9 0 11 3 13 8 15 9 17 8 17 7 18 11 6 10 4 12 1 17 0 20 8 29 0 28 9 29 0

19 11 3 11 5 14 0 21 0 25 5 33 2 31 2 29 9

20 9 7 5 4 5 3 5 5 7 4 10 8 13 4 17 8

21 13 2 6 3 6 3 6 6 9 0 13 2 15 3 20 0 Coercivitv (Oe) at indicated aging temperature (°C) 2 13.2 23.0 27.0 33.4 37.7 38.5 37.1 35.2 3 12.7 26.1 33.4 40.1 43.9 42.8 40.5 35.1 4 10.8 6.6 7.2 8.7 13.5 21.1 21.9 24.7 5 9.9 6.5 7.2 9.6 16.6 24.2 23.7 28.5 6 11.6 8.1 9.6 15.9 26.1 34.3 36.6 29.0 7 11.0 7.7 10.32 19.0 30.1 37.1 38.6 41.3 8 20.5 17.9 25.0 38.3 43.2 40.3 46.0 37.4 9 22.7 23.7 33.8 47.2 46.1 38.4 43.1 41.8 0 11.2 6.2 6.8 8.9 21.1 33.0 33.1 23.8 1 11.0 5.6 6.9 10.3 25.4 38.2 36.4 33.9 2 13.3 6.7 8.5 14.3 35.4 39.5 35.5 39.0 3 13.9 8.6 11.3 21.2 35.2 42.7 51.0 34.7 4 18.4 10.6 15.4 29.1 42.5 43.2 47.7 44.7 5 26.4 21.6 28.6 47.0 48.2 35.5 36.2 49.2 6 38.4 58.5 72.7 85.9 72.1 43.5 59.4 (1) 7 35.3 40.7 49.2 61.0 56.4 56.5 59.7 46.4 8 13.3 5.8 6.5 10.4 32.3 56.3 53.7 39.9

39 18.7 6.9 8.7 14.0 38.4 59.6 54.8 49.9

40 27.4 23.1 28.5 40.7 41.1 39.8 53.2 (1) 41 37.2 38.4 46.6 58.6 51.8 41.0 .4.8 (1)

42 35-3 38.8 49.5 63.1 55.9 44.8 71.2 (1)

43 102 273 392 382 172 86.3 (1) (1)

44 60.8 500 541 486 171 84.6 (1) (1)

45 59.5 529 1400 636 287 (1) (1) (1) M 9.1 6.0 6.1 6.2 6.9 7.3 7.3 6.1

N 9.8 6.3 6.4 7.2 7.8 9.0 9.5 8.2

O 11.5 8.9 8.8 9.1 9.8 11.8 11.5 10.2

P 10.5 7.6 8.3 9.9 11.2 13.7 16.5 17.6

Q 9.6 5.4 5.3 5.5 6.6 8.9 11.2 14.7 Coercivitv (Oe) at indicated aging temperature (°C)

R 11.2 5.0 5.0 5.1 7.5 17.0 19.7 19.3

S 9.9 4.9 5.0 5.1 8.2 19.9 22.2 24.1

T 11.0 5.5 5.4 5.6 9.6 23.1 23.6 28.6 u 13.1 5.0 4.7 4.8 7.7 26.5 32.3 20.6

V 11.7 5.5 6.3 1 100..22 32.1 57.7 54.8 40.6

W 9.4 4.9 4.8 5 5..22 11.7 35.2 38.6 37.2

X 11.4 5.7 6.0 8.0 0 27.4 51.1 48.8 26.7

1 The coercivity exceeded the maximum range of the instrument,

1400Oe.

The data in Tables 1A to ID and Tables 2A to 2D show that the examples of the alloy according to this invention all provide a combination of low magnetostriction (-6 < λ <+6) and good coercivity(H_c >17.5 Oe) in the aged condition, whereas the comparative heats did not. It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims.

Claims

WHAT IS CLAIMED IS:

1. A semi-hard magnetic alloy consisting essentially of, in weight percent, about wt. %

C 0.1 max.

Mn 2-14

Si 0.5 max.

P 0.2 max.

S 0.2 max.

Cr 0.5 max.

Mo 0.5 max.

Ni up to 16

Cu up to 7

N 0.05 max

Co 0.3 max.

W 0.2 max.

Al 0.2 max.

Ti 0.2 max.

Nb 0.10-1.0

The balance is essentially iron and the usual impurities.

2. The alloy set forth in Claim 1 which contains not more than about 9% manganese.

3. The alloy set forth in Claim 1 which contains at least about 0.02% carbon and at least about 0.15% niobium.

4. The alloy set forth in Claim 3 in which the amount of niobium is at least about 8x%C.

5. The alloy set forth in Claim 1 which contains at least about 5% manganese.

6. The alloy set forth m Claim 5 which contains at least about 0.02% carbon and at least about 0.15% niobium.

7. The alloy set forth in Claim 6 m which the amount of niobium is at least about 8x%C.

8. The alloy set forth in any of Claims 1 to 7 which contains not more than about 0.50% nickel and at least about 1% copper.

9. The alloy set forth in Claim 8 which contains not more than about 6% copper.

10. The alloy set forth in Claim 8 which contains not more than about 0.5% niobium.

11. The alloy set forth in any of Claims 1 to 7 which contains at least about 3% nickel and not more than about 0.1% copper.

12. The alloy set forth in Claim 11 which contains not more than about 0.5% niobium.

13 The alloy set forth in any of Claims 1 to 7 which contains at least about 3% nickel and at least about 1 % copper.

14. The alloy set forth in Claim 13 which contains not more than about 6% copper.

15. The alloy set forth in Claim 14 which contains not more than about 0.5% niobium.

16. A magnetic tag comprising: a housing; a first metal strip disposed in said housing, said first metal strip being formed of a magnetically soft metal or alloy and; a second metal strip disposed in said housing adjacent to said first metal strip, said second metal strip being formed of a magnetically semi-hard metal alloy consisting essentially of, in weight percent, about wt. %

C 0.1 max.

Mn 2-14

Si 0.5 max.

P 0.2 max. s 0.2 max.

Cr 0.5 max.

Mo 0.5 max.

Ni up to 16

Cu up to 7

N 0.05 max.

Co 0.3 max.

W 0.2 max.

Al 0.2 max.

Ti 0.2 max. Wt. %

Nb 0.10-1.0

and the balance is essentially iron and the usual impurities.

17. The magnetic tag set forth in Claim 16 in which the semi-hard metal alloy contains not more than about 9% manganese.

18. The magnetic tag set forth in Claim 16 in which the semi-hard metal alloy contains at least about 0.02% carbon and at least about 0.15% niobium.

19. The magnetic tag set forth in Claim 18 in which the semi-hard metal alloy contains at least about 8x%C niobium.

20. The magnetic tag set forth in Claim 16 in which the semi-hard metal alloy contains at least about 5% manganese.

21. The magnetic tag set forth in Claim 20 in which the semi-hard metal alloy contains at least about 0.02% carbon and at least about 0.15% niobium.

22. The magnetic tag set forth in Claim 16 in which the semi-hard metal alloy contains at least about 8x%C niobium.

23. The magnetic tag set forth in any of Claims 16 to 22 in which the semi- hard metal alloy contains not more than about 0.50% nickel and at least about 1% copper.

24. The magnetic tag set forth in Claim 23 in which the semi-hard metal alloy contains not more than about 6% copper.

25. The magnetic tag set forth in Claim 23 in which the semi-hard metal alloy contains not more than about 0.5% niobium.

26. The magnetic tag set forth in any of Claims 16 to 22 in which the semi- hard metal alloy contains at least about 3% nickel and not more than about 0.1% copper.

27. The magnetic tag set forth in Claim 26 in which the semi-hard metal alloy contains not more than about 0.5% niobium.

28. The magnetic tag set forth in any of Claims 16 to 22 in which the semi- hard metal alloy contains at least about 3% nickel and at least about 1 % copper.

29. The magnetic tag set forth in Claim 28 in which the semi-hard metal alloy contains not more than about 6% copper.

30. The magnetic tag set forth in Claim 29 in which the semi-hard metal alloy contains not more than about 0.5% niobium.