COMPOSE STRATIFIE ET UTILISATION DE CE COMPOSE POUR LE MONNEYAGE

COMPOSITE STRATIFIED MATERIAL AND USE THEREOF FOR COINAGE

Abrégé français

L'invention concerne un matériau composite caractérisé en ce qu'il présente une couche centrale en acier au chrome ferritique, qui est revêtue des deux côtés par un acier ayant la composition ci-après (en % en masse): chrome 16,0 à 18,0, nickel 10,0 à 12,0, cuivre 3,5 à 4,5 et d'autres éléments optionnels, le reste étant essentiellement constitué par du fer. L'invention concerne également l'utilisation de ce matériau pour la fabrication de pièces de monnaie, de jetons de valeur, jetons à jouer et objets analogues.

Abrégé anglais

Composite stratified material comprising a core layer of a ferritic chrome
steel that is plated on both sides with a steel consisting of
(mass %): chrome 16.0 to 18.0, nickel 10.0 to 12.0 and copper 3.5 to 4.5, as
well as of selectably other elements, the rest being essentially
iron, and its use for manufacturing coins, chips, tokens and related objects.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A composite stratified material for coins, tokens,
chips, and related objects, comprising a core layer of a
ferritic chromium steel that is plated on both sides with a
layer of steel, characterized in that the steel used to plate
the core layer consists of the following (wt-%)
Chromium 16.0 to 18.0
Nickel 10.0 to 12.0
Copper 3.5 to 4.5
with the remainder being made up of iron and such additives as
may be required by the production process, and additionally
one or more of the following elements (in wt-%):
Manganese max. 1.5
Silicon max. 0.4
Carbon max. 0.02
Nitrogen max. 0.02
Sulphur max. 0.01
Phosphorus max. 0.03
Molybdenum max. 1.0
Titanium max. 0.03
Niobium max. 0.05
Aluminum max. 0.1
Cobalt max. 0.3
Boron max. 0.003.
2. A composite stratified material as defined in Claim
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1, characterized in that the thickness of the layers that are
plated on is 10 to 30% of the total thickness of the composite
stratified material.
3. A composite stratified material as defined in Claim
1 or Claim 2, characterized in that the core layer is of X 6
Cr 17 steel.
4. Use of a stratified composite as defined in Claim 1,
2, or 3, as a material for manufacturing embossed coins,
tokens, chips, or related objects.
8

Description

CA 02271654 1999-09-29
COMPOSITE STRATIFIED MATERIAL AND USE THEREOF FOR COINAGE
The present invention relates to a composite
stratified material for coins, tokens, chips, and related
objects.
JP 04066651 and US 27 75 520 both describe rust-
resistant chromium-nickel-steel alloys as materials used for
coinage manufactured in a single layer; on average, these
alloys contain 17.8 wt-% chromium, 12.8 wt-% nickel, and 3 wt-%
copper.
EP-A 0 343 701 describes a composite stratified
material that is used to manufacture coinage that may contain,
amongst other things, a core layer of a ferritic chromium
steel, plated on both sides with a layer consisting of an
austenitic chromium-nickel steel.
In earlier times, when coins having a face value
equal to the value of the metal they contained were being
minted, it was important that the value of the metal was equal
to the nominal value of the coins, so that this demand governed
the selection of the metal. Gold, silver, and base metals, as
well as alloys of these, were used. In the course of
industrialization, from the middle of the nineteenth century
on, more and more coins having a face value in excess of the
value of the metal they contained were being circulated; the
material for these was selected on the basis of economical
production and, on the other hand, for its physical appearance.
Very frequently, nickel and specific copper alloys
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were used. In more recent times, there have been increasing
demands for better-priced coinage., In the course of this
development, various types of rust: resistant steels were used
to manufacture coinage. Use was made, mainly of X 6 Cr 17
ferritic steel (German Material No. 1.4016) and X 5 Cr Ni 18
12 (German Material No. 1.4303).
The continued proliferation of rust-resistant steel
as material for coinage was hindered by the problems
associated with embossing the metal. Because of hardness
l0 values that remained in practice at approximately 140 to 160
HV30, on average approximately 150 HV30 for the soft-annealed
state, the embossed image was relatively shallow, albeit
highly resistant to abrasion, and the coins remained resistant
to corrosion over very long periods, as is described, for
example, in Coinage Materials, XV:II Mint Directors' Conference
Madrid 1992.
The bluish tinge, in particular of ferritic rust-
resistant steels, prevented these from achieving the same
appeal as coinage materials such as silver or nickel, and
alloys thereof, which were percei~Jed as being whiter.
In contrast to the mech<~nical coin testers that were
usually used in the past, in addii~ion to testing the diameter
and the thickness, the electronic coin testers that are used
today test electrical conductivity inductively at various
frequencies, which is to say at various distances from the
outside surface. This makes it possible to identify composite
stratified materials and distinguish them from foreign coins
and counterfeits.
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This results in an additional, important criterion for
manufacturing materials for coinage, in that material
characteristic such a density, electrical conductivity, and
magnetic behaviour have to be adjusted to fall within a very
narrow acceptance range.
It is an object of the present invention to provide a
rust-resistant material that, compared to the prior art, may be
more easily embossed and is perceived as being white or silvery
and which can be processed to form coins that can be used in
today~s coin testing machines so as to be reliably and
consistently distinguished from other coins and counterfeits.
In one aspect, this invention provides a composite
stratified material for coins, tokens, chips, and related
objects, comprising a core layer of a ferritic chromium steel
that is plated on both sides with a layer of steel,
characterized in that the steel used to plate the core layer
consists of the following (wt-%)
Chromium 16.0 to 18.0
Nickel 10.0 to 12.0
Copper 3.5 to 4.5
with the remainder being made up of iron and such additives as
may be required by the production process, and additionally one
or more of the following elements (in wt-%):
Manganese max. 1.5
Silicon max. 0.4
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Carbon max. 0.02
Nitrogen max. 0.02
Sulphur max. 0.01
Phosphorus max. 0.03
Molybdenum max. 1.0
Titanium max. 0.03
Niobium max. 0.05
Aluminum max. 0.1
Cobalt max. 0.3
Boron max. 0.003.
It is preferable that the thickness of the layer that
is plated on is 10 to 30% of the total thickness of the
composite stratified material.
Surprisingly, it has been found that in the soft-
annealed state, a composite stratified material of a steel of
this type is of the desired colour, which is perceived as white
or silver, and is of a hardness that can be kept well below 140
HV30 and normally even below 120 HV30.
These stainless steels, which on average have hardness
values some 20% lower than those that are used for coin blanks,
in the prior art, produce a much deeper and more plastic
impression. Despite this, the abrasion resistance of these new
coinage materials, as determined in by drum testing of sample
coins, is comparable to that of X 6 Cr 17 and X 5 CrNi 18 12
stainless steels, and about three times greater than that of
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conventional coinage materials such as CuA16Ni2 that are based
on copper.
It is preferable that the core layer of the composite
stratified material of this invention is X 6 Cr 17 steel.
This comparability with other stainless steels is also
demonstrated when testing their resistance to tarnishing in an
aggressive laboratory atmosphere using a 10-% NaCl solution and
when they are subjected to the effects of artificial sweat.
In another aspect this invention provides use of a
l0 stratified composite according to the invention, as a material
for manufacturing embossed coins, tokens, chips, or related
objects.
The present invention will be described in greater
detail below on the basis of one embodiment:
A copper alloyed rust-resistant steel composed as
follows (wt-%) was smelted:
Chromium 17.35
Nickel 10.25
Copper 3.65
Manganese 0.67
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Silicon 0..'30
Carbon 0 . 014
Nitrogen 0.015
Sulphur 0.003
Phosphorus 0.012
Molybdenum 0.49
Titanium <0.010
Niobium 0.010
Aluminum 0 . 02 0
l0 Cobalt 0.01
Boron 0 . 0 0 2
with the remainder being made up of iron and such additives as
may be required by the production process.
The steel was hot-rolled and then cold-rolled to
form a strip 2.07 mm thick. Coin blanks 25.30 mm diameter
were then punched out of the cold strip. These blanks were of
the desired silvery-white colour.
After the edges had been milled, the diameter of the
blanks was 24.85 mm. Each of these blanks weighed 8.10 g, and
their density was 7.98 g/cm3. Their hardness could be adjusted
to 117 HV30 by soft-annealing, which was done without any
coarse-grain formation. As a result, they were easily
embossed, as determined by embossing sample coins.
These coins were comparfsd with coins of X 6 Cr 17
and X 5 CrNi 18 12 rust-resistani~ steels, which are
conventionally used as coinage mai~erials, in a 24-hour drum
test; the weight losses for all three materials was 0.1%.
Coins manufactured from the CuAl6rfi2 copper material usually
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used exhibited losses that were three times as great.
During corrosion testing in an aggressive laboratory
containing 10-% NaCl solution, when acted upon by artificial
sweat, the changes to the new coinage material was
insignificant after three weeks.
Strips of this steel were plated onto both sides of
the X 6 Cr 17, the thickness of the layer being, in each
instance, 20% of the total thickness. The result was the
reliable differentiability from o~~her coins and counterfeits
in the coin-testing machines used today.
One further characteristic of the present invention
is that the new coinage material that is proposed herein is
characterized in that it is easily recycled if today's steel-
making technologies are used; this is so not only when it is
used as a single component, but also if it is used, together
with a ferritic chromium steel, a;s one component of a
composite material.
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