EP2914759A1 - Nickel-free stainless steel alloy - Google Patents

Abstract

The invention relates to a cubic austenitic stainless steel alloy with centered surfaces. It comprises, in weight: at least 0.5 % nickel; between 16 % and 20 % chromium; between 30 % and 40 % of a filler metal selected from copper, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum and gold; between 0 % and 2% copper; between 0 % and 2 % gold; between 0 % and 0.03 % carbon; between 0 % and 2 % molybdenum; between 0 % and 2 % manganese; between 0 % and 1 % silicon; between 0 % and 0.1 % nitrogen; between 0 % and 0.5 % tungsten; between 0 % and 0.5 % vanadium; between 0 % and 0.5 % niobium; between 0 % and 0.5 % zirconium; and between 0 % and 0.5 % titanium; the remainder up to 100 % being inevitable iron and impurities.

Description

 Nickel-free stainless steel alloy

Field of the invention

 The invention relates to a stainless steel alloy having a base of iron and chromium.

 The invention also relates to a watch component made of such an alloy.

The invention relates to the fields of watchmaking, jewelery, and jewelery, in particular for structures: watch cases, squares, turntables, bracelets, rings, earrings and others.

Background of the invention

 Stainless steels are commonly used in the fields of watchmaking, jewelery, and jewelery, particularly for structures: watch cases, casebacks, turntables, bracelets, and others.

 The components for external use, intended to be in contact with the skin of the user, must obey certain constraints, in particular because of the allergenic effects of certain metals, especially nickel. Despite the protective and polished qualities of nickel once polished, there is an increasing focus on placing on the market alloys with little or no nickel.

 Nickel is, however, a basic component of most common stainless steels because it improves mechanical properties and ductility, malleability and resilience. By cons nickel is harmful in the field of friction surfaces. Nickel improves the properties of the passive layer, and integrates with the surface layer of oxide. In particular alloy X2CrNiMo17-12 EN (or 316L AISI) comprises between 10.5 and 13% of nickel. Nickel is a metal whose cost is continuously growing, and which, in 2012, is close to 20'00 USD per ton, which increases the cost of alloys containing it.

Nickel-free stainless steel alloys are known which are ferritic steels with a cubic centered structure. However, these ferritic steels are not hardenable by heat treatment, but only by hardening. Their structure is not very fine, and this family of alloys is not very suitable for polishing. The document EP 0 964 071 A1 in the name of ASULAB SA describes the application of such a nickel-free ferritic stainless steel to an outer piece of watch covering, this alloy comprising at least 0.4% by weight of nitrogen, and at most 0.5% by weight of nickel, between 10 and 35% by weight for total chromium and molybdenum, and between 5 and 20% by weight of manganese.

 Other nickel-free stainless steel alloys, which are martensitic steels, which are curable by heat treatment, are on the other hand difficult to machine, particularly maraging grades which comprise precipitates of hardening components. and can not be considered for horological applications.

 Patent EP 0 629 714 B1 in the name of UGINE-SAVOIE IMPHY describes a martensitic stainless steel with improved machinability, with a non-zero nickel content, but between 2 and 6%, a fairly low chromium content of between 1% and 1%. and 19%, and a composition providing many additives, and favorable to the formation of certain inclusions in the matrix, thus improving machinability by localized weakening of the chips. But we see that the nickel rate, although low, remains too high for the application.

 Austenitic steels, of face-centered cubic structure, generally have very good forming properties, which is particularly advantageous for watchmaker or jeweler-type components. They have a very high chemical resistance. They are also non-magnetic because of their face-centered cubic structure. They are also the most suitable for welding. But conventional austenitic stainless steels still contain from 3.5 to 32% of nickel, and more commonly from 8.0 to 15.0% of nickel. Indeed, nickel is a gammagene element which makes it possible to obtain the austenitic structure, and in particular to obtain sheets capable of forming deformations. Certain documents, such as FR 2 534 931 in the name of CABOT CORPORATION, go so far as to state that nickel must be present to favor an austenitic structure in the alloy.

In theory, the gamma loop of the iron-chromium system specific to stainless steels defines an austenitic domain, even with a low or zero nickel content, but the loop is of very limited magnitude compared to that of alloys containing nickel. in higher proportion. In addition, this austenitic domain exists at temperatures much higher than ambient. The effect of the gammagenic alloy elements is twofold since it also makes it possible to widen the austenitic loop in chemical composition (relative to chromium) and to widen the temperature range on which this structure is stable. Austeno-ferritic steels, also called duplex, are weak magnetic, and generally comprise between 3.5% and 8% nickel.

 In sum, if, in the general sense, the nickel-free stainless steels are mainly ferritic steels, the advantages of the austenitic steels, which are generally cataloged as nickel steels, should be available.

 In order to obtain austenitic stainless steel, gammagens such as nickel, manganese or nitrogen are generally used (these are called super-austenitic steels for the last two mentioned), which increase the range of stability of austenite. Theoretically it would therefore be possible to use super-austenitic steel with manganese or nitrogen in place of nickel.

 The patent EP 1 025 273 B1 in the name of SIMA describes such a nickel-free austenitic stainless steel, comprising from 15 to 24% of manganese, from 15 to 20% of chromium, from 2.5 to 4% of molybdenum, from 0, 6 to 0.85% nitrogen, 0.1 to 0.5% vanadium, less than 0.5% copper, less than 0.5% cobalt, less than 0.5% for the total of niobium and tantalum, less than 0.06% carbon, other elements each limited to 0.020% by weight, the balance being iron, and the compositions of certain metals being limited to each other by way of a system of equations and inequalities, which frame the contents of chromium, molybdenum, nitrogen, vanadium, niobium, and manganese.

 But, if these super-austenitic alloys have high mechanical properties, their shaping is very difficult, especially the machining is difficult, the stamping is not possible, and their use is therefore inconvenient.

 Austenitic stainless alloys are known from the documents:

 EP 1 783 240 A1 DAIDO STEEL CO LTD particularly useful in jewelry or jewelry and high nitrogen content;

 EP1 025 273 B1 ADVANCED METALLURGY SIMA nickel-free for biomedical applications;

 DAIDO STEEL CO LTD with a high nitrogen content;

 EP 0 896 072 A1 USINOR UGINE with very low nickel content; - US 2009/060 775 A1 LIU ADVANCED INT MULTITECH medium nitrogen content;

DE 197 16 795 A1 KRUPP high strength and corrosion resistant; US 3,904,401 to MERTZ CARPENTER TECHNOLOGY CO resistant to corrosion.

Summary of the invention

 The invention relates to a stainless steel alloy on a base consisting of iron and chromium, characterized in that it comprises less than 0.5% by weight of nickel, and is arranged according to a cubic austenitic structure with centered faces, and that it consists, in mass values, in:

 chrome: min. value 16%, max. value 20%;

 at least one filler metal, the value of the total of said at least one filler metal or of said filler metals being between: minimum value 30%, maximum value 40%, said at least one filler metal being selected from a first set comprising copper, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, and gold:

 the value of the copper being between: minimum value 0%, maximum value 2%; the value of the gold being between: minimum value 0%, maximum value 2%; carbon: minimum value 0%, maximum value 0.03%;

 molybdenum: minimum value 0%, maximum value 2%;

 manganese: minimum value 0%, maximum value 2%;

 - silicon: minimum value 0%, maximum value 1%;

 nitrogen: minimum value 0%, maximum value 0, 1%;

 tungsten: minimum value 0%, maximum value 0.5%;

 vanadium: minimum value 0%, maximum value 0.5%;

 niobium: minimum value 0%, maximum value 0.5%;

 - zirconium: minimum value 0%, maximum value 0,5%;

 titanium: minimum value 0%, maximum value 0.5%;

 iron and unavoidable impurities: the complement to 100%.

The invention also relates to a watch or jewelery component made of such an alloy. Brief description of the drawings

 Other features and advantages of the invention will appear on reading the detailed description which follows, with reference to the appended drawings, in which:

 FIG. 1 represents, schematically, the gamma loop of an iron-chromium system, as a function of the nickel content in the alloy;

 FIG. 2 schematically represents a Schaeffler diagram, with an equivalent chromium on the abscissa, and an equivalent nickel on the ordinate. This diagram delimits the ferritic, martensitic and austenitic domains, the latter limited by the curve corresponding to the zero ferrite content.

Detailed Description of the Preferred Embodiments

 The invention proposes to produce stainless steels without nickel, which have properties similar to those of austenitic stainless steels with nickel.

 The term "nickel-free alloy" will be referred to below as an alloy comprising less than 0.5% by weight of nickel.

 It is therefore a question of looking for the production of alloys, which, like the super-austenitics, have elements of substitution for nickel, but which harden the steel less than the manganese-nitrogen pair.

 These substitution elements must be soluble in iron, so as to allow the construction of a cubic austenitic structure with centered faces. According to the invention, the alloy comprises, in addition to a base consisting of iron and chromium, at least one filler metal chosen from a first set comprising copper, ruthenium, rhodium, palladium and rhenium. , osmium, iridium, platinum, and gold.

 In a preferred composition, the stainless steel alloy according to the invention, on a base consisting of iron and chromium, has less than 0.5% by weight of nickel, and is arranged in a cubic austenitic structure with centered faces. , and it consists, in mass values, in:

 chrome: min. value 16%, max. value 20%;

at least one filler metal, the value of the total of said at least one filler metal or of said filler metals being between: minimum value 30%, maximum value 40%, said at least one filler metal being chosen from a first set comprising copper, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, and gold:

 the copper value being between: minimum value 0%, maximum value 2%; the value of the gold being between: minimum value 0%, maximum value 2%; - carbon: minimum value 0%, maximum value 0.03%;

 molybdenum: minimum value 0%, maximum value 2%;

 manganese: minimum value 0%, maximum value 2%;

 silicon: minimum value 0%, maximum value 1%;

 nitrogen: minimum value 0%, maximum value 0, 1%;

 - tungsten: minimum value 0%, maximum value 0.5%;

 vanadium: minimum value 0%, maximum value 0.5%;

 niobium: minimum value 0%, maximum value 0.5%;

 zirconium: minimum value 0%, maximum value 0.5%;

 titanium: minimum value 0%, maximum value 0.5%;

 - iron and unavoidable impurities: the complement to 100%.

 In a particular application, the alloy comprises, in addition to a base consisting of iron, carbon and chromium, at least one filler metal chosen from a subset of the first set, called platinoids, this sub-assembly all platinoids comprising ruthenium, rhodium, palladium, rhenium, osmium, iridium, and platinum.

 Indeed, these metals are part of PGM (platinum group metals) or platinoids, that is to say that they are characterized by common and unusual properties for metals. These PGM group metals are also more soluble in iron than copper and gold.

 In a still more particular composition, said at least one filler metal is chosen exclusively from this subset of platinoids.

 A variant of the invention consists in incorporating into the alloy, both on the one hand at least one such filler metal, and on the other hand manganese and nitrogen, to adjust the mechanical properties of the metal. 'alloy. Preferably, in this second variant, the alloy consists, in mass values, of:

chrome: min. value 16%, max. value 20%; manganese: minimum value 0%, maximum value 2%;

 nitrogen: minimum value 0%, maximum value 0, 1%;

 at least one said filler metal of the first set, the value of the total of at least one filler metal or filler metals being between: minimum value 30%, maximum value 40%,

 the copper value being between: minimum value 0%, maximum value 2%; the value of the gold being between: minimum value 0%, maximum value 2%; and the total of, on the one hand, the filler metal or the filler metals of the first set or its subset of the platinoids, and on the other hand the manganese and the nitrogen, being between the values: minimum value 30%, maximum value 40%

 molybdenum: minimum value 0%, maximum value 2%

 silicon: minimum value 0%, maximum value 1%

 carbon: minimum value 0%, maximum value 0.03%.

 silicon: minimum value 0%, maximum value 1%;

 - tungsten: minimum value 0%, maximum value 0.5%;

 vanadium: minimum value 0%, maximum value 0.5%;

 niobium: minimum value 0%, maximum value 0.5%;

 zirconium: minimum value 0%, maximum value 0.5%;

 titanium: minimum value 0%, maximum value 0.5%;

 - iron and unavoidable impurities: the complement to 100%.

 Another variant of the invention consists in incorporating into the alloy, within the limit of 0.5% by weight of the total, at least one carburigenic element taken from a second group comprising tungsten, vanadium, niobium and zirconium. , and titanium, replacing an equivalent mass of iron in the alloy. 5. Thus, in the alloy, at least one carburigenic element taken from a second set comprising tungsten, vanadium, niobium, zirconium and titanium, has a non-zero content, within the limit of 0.5% of the total carburigenic elements of this second set.

This incorporation of one or more carburigenic elements has the effect of forcing the precipitation of specific carbides less harmful to the corrosion resistance than chromium carbides. FIG. 2 is a Schaeffler diagram, which comprises on the abscissa an equivalent chromium, and on the ordinate a nickel equivalent, both in percentage by mass.

 The equivalent chromium Créq corresponds here to the following definition:

 Cr = Cr + Mo + 1, 5 Si.

 This model is similar to the Schaeffler or Delong model:

 Cr = Cr + Mo + 1.5 Si + 0.5 Nb, here simplified for the case of an alloy without niobium.

 The important point is the determination of the filler metal content, replacing the nickel that is outlawed. The notion of equivalent nickel qualifies the proportion by weight of the filler metal, or filler metals if there are several.

 In the particular case of the use of palladium to replace nickel, nickel equivalent Niéq meets the following definition:

 Niq = Ni + 30 (C + N) + 0.5 (Co + Mn + Cu) + 0.3 Pd.

 This model is adapted to the presence of palladium, and derives from known Schaeffler models (for a manganese base alloy):

Niq = Ni + 30 C + 0.5 Mn,

and more precisely Delong (for a manganese base alloy and nitrogen):

 Niq = Ni + 30 (C + N) + 0.5 Mn.

 In a generalization to the set capable of filler metals, the equivalent nickel formula can still be written:

Niq = Ni + 30 (C + N) +0.5 (Co + Mn + Cu) + 0.3 (Pd + Ru + Rh + Re + Os + lr + Pt + Au),

or, preferably in the case where the filler metal is selected from the first set:

Niq = Ni + 30 (C + N) + 0.5 (Co + Mn + Cu) + 0.3 (Pd + Ru + Rh + Re + Os + 1r + Pt).

 This Schaeffler diagram delimits the ferritic, martensitic and austenitic domains, the latter limited by the curve corresponding to the zero ferrite content.

 So-called stainless steels are, according to current standards, those containing more than 10.5% of chromium.

 The curves C1 and C2 delimit the possible presence of austenite A: above C1 and C2 we have austenite A, underneath there is none.

The curve C3 delimits the possible presence of ferrite F: below C3 there is ferrite F, above there is none. The curve C4 delimits the possible presence of martensite M: below C4 there is martensite M, above there is none.

 To best benefit from the properties of austenite, the composition must be such that one is both above the C3 and C4 curves, so as to have only austenite A.

 In order to benefit from the properties specific to stainless steels, it is necessary to respect the minimum chromium content represented by the curve C5, and the domain is then that located to the right of the curve C5. The field D1 hatched in Figure 2 obeys both conditions, and ensures the expected properties. The point P corresponding to the example mentioned above is located in this domain D1.

 According to an approximation, curves are straight lines of equations:

 C1: Neq = - 5/6 (Créq -8) + 21

 C2: Neq = - 13/16 (Creq -8) + 13

 C3: Neq = 13/9 (Creq -8) - 2

 C4: Neq = 7/16 (Creq -8) - 3

 Domain D1 obeys the following three conditions:

Niéq> 13/9 (Créq -8) - 2

Niéq> 7/16 (Créq -8) - 3

Créq> 10.5

 Of course, we can tolerate the presence of a little ferrite or martensite with austenite, and the real area of application can be a little wider than the D1 domain, and in particular to lower the level as much as possible. equivalent nickel, because of the often very high cost of metals chosen as substitutes for nickel; remember that in 2012 the cost of palladium is about half that of gold, and between one quarter and one half that of platinum.

 The rectangular domain D2, defined by the following two inequalities:

16 <Créq <23.5

12 <Nieq <22,

gives a good example of permissible values (in mass) for the use of palladium as the main filler metal:

palladium: minimum value 30%, maximum value 40% chrome: minimum value 16%, maximum value 20%

 molybdenum: minimum value 0%, maximum value 2%

 manganese: minimum value 0%, maximum value 2%

 copper: minimum value 0%, maximum value 2%

 - gold: minimum value 0%, maximum value 2%

 silicon: minimum value 0%, maximum value 1%

 nitrogen: minimum value 0%, maximum value 0, 1%

 carbon: minimum value 0%, maximum value 0.03%

 iron: the 100% supplement.

A more particular alloy consists, in mass values, of:

 palladium: minimum value 30%, maximum value 40%;

 copper: min. value 0%, max. value 2%;

 gold: minimum value 0%, maximum value 2%

 total palladium + copper + gold: minimum value 30%, maximum value 40%;

 - chrome: minimum value 16%, maximum value 20%;

 molybdenum: minimum value 0%, maximum value 2%;

 manganese: minimum value 0%, maximum value 2%;

 silicon: minimum value 0%, maximum value 1%;

 nitrogen: minimum value 0%, maximum value 0, 1%;

 - carbon: minimum value 0%, maximum value 0.03%;

 iron and unavoidable impurities: the complement to 100%.

 In the generalization to at least one filler metal taken from the first set or its subset limited to PGM, the bulk composition becomes:

 total filler metal (s) of the first set or its subset of GMPs: minimum value 30%, maximum value 40%

 chrome: minimum value 16%, maximum value 20%

 molybdenum: minimum value 0%, maximum value 2%

manganese: minimum value 0%, maximum value 2% copper: minimum value 0%, maximum value 2%

 gold: minimum value 0%, maximum value 2%

 silicon: minimum value 0%, maximum value 1%

 nitrogen: minimum value 0%, maximum value 0, 1%

 carbon: minimum value 0%, maximum value 0.03%

 iron: the 100% supplement.

 The choice of palladium as filler metal allows, more particularly, to achieve the desired properties.

 A suitable (mass) composition is 18% chromium, 35% palladium, and 46 to 47% iron. Like all stainless steel, this alloy can contain up to 0.03% carbon. Preferably, its mass composition is 18% chromium, 35% palladium, 0% to 0.03% carbon, and the iron supplement. More particularly, its mass composition is 18% chromium, 35% palladium, and 46.97 to 47% iron, and 0 to 0.03% carbon.

 The invention also relates to a watch or jewelery component made of such an alloy.

Claims

REVE NDI CATI ONS  1. Stainless steel alloy on a base consisting of iron and chromium, characterized in that it comprises less than 0.5% by weight of nickel, and is arranged in a cubic austenitic structure with centered faces, and that it consists, in mass values, in:  - chrome: minimum value 16%, maximum value 20%  at least one filler metal, the value of the total of said at least one filler metal or of said filler metals being between: minimum value 30%, maximum value 40%, said at least one filler metal being selected from a first set comprising copper, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, and gold:  the value of the copper being between: minimum value 0%, maximum value 2%;  the value of the gold being between: minimum value 0%, maximum value 2%;  - carbon: minimum value 0%, maximum value 0.03%;  - molybdenum: minimum value 0%, maximum value 2%; - manganese: minimum value 0%, maximum value 2%;  - silicon: minimum value 0%, maximum value 1%;  - nitrogen: minimum value 0%, maximum value 0, 1%;  - tungsten: minimum value 0%, maximum value 0.5%;  - vanadium: minimum value 0%, maximum value 0.5%; - niobium: minimum value 0%, maximum value 0.5%;  - zirconium: minimum value 0%, maximum value 0,5%;  - titanium: minimum value 0%, maximum value 0.5%;  - iron and unavoidable impurities: the complement to 100%.  2. An alloy according to claim 1, characterized in that at least one said filler metal is selected from a subset, called platinoids, said first set, said subset of platinoids comprising ruthenium, rhodium, palladium, rhenium, osmium, iridium, and platinum.  3. An alloy according to claim 2, characterized in that said at least one filler metal is selected exclusively from said subset of the platinoids. 4. Alloy according to one of claims 1 or 2, characterized in that it consists, in mass values, of: - chrome: minimum value 16%, maximum value 20%;  - manganese: minimum value 0%, maximum value 2%;  - nitrogen: minimum value 0%, maximum value 0, 1%;  at least one said filler metal of said first set, the value of the total of said at least one filler metal or said filler metals being between: minimum value 30%, maximum value 40%,  the value of the copper being between: minimum value 0%, maximum value 2%;  the value of the gold being between: minimum value 0%, maximum value 2%; and the total of, on the one hand, said filler metal or said filler metals of the first set or its subset of the platinoids, and on the other hand the manganese and the nitrogen, being between the values: minimum value 30%, maximum value 40%  - molybdenum: minimum value 0%, maximum value 2%  - silicon: minimum value 0%, maximum value 1%  - carbon: minimum value 0%, maximum value 0.03%. - silicon: minimum value 0%, maximum value 1%;  - tungsten: minimum value 0%, maximum value 0.5%;  - vanadium: minimum value 0%, maximum value 0.5%;  - niobium: minimum value 0%, maximum value 0.5%;  - zirconium: minimum value 0%, maximum value 0,5%; - titanium: minimum value 0%, maximum value 0.5%;  - iron and unavoidable impurities: the complement to 100%.  5. Alloy according to one of the preceding claims, characterized in that at least one carburizing element taken from a second set comprising tungsten, vanadium, niobium, zirconium, and titanium, has a non-zero content, in the limit of 0.5% of the total of said carburigenic elements of said second set.  6. Alloy according to one of claims 1 to 4, characterized in that it consists, in mass values, of:  - palladium: minimum value 30%, maximum value 40%;  - copper: minimum value 0%, maximum value 2%; - gold: minimum value 0%, maximum value 2% - total palladium + copper + gold: minimum value 30%, maximum value 40%;  - chrome: minimum value 16%, maximum value 20%;  - molybdenum: minimum value 0%, maximum value 2%;  - manganese: minimum value 0%, maximum value 2%; - silicon: minimum value 0%, maximum value 1%;  - nitrogen: minimum value 0%, maximum value 0, 1%;  - carbon: minimum value 0%, maximum value 0.03%;  - iron and unavoidable impurities: the complement to 100%.  7. Alloy according to one of claims 1 to 4, or 6, characterized in that it consists, in mass values, of:  - chromium: 18%;  palladium: 35%;  - carbon: 0% to 0.03%;  - iron and unavoidable impurities: the complement to 100%.  8. Watchmaking or jewelery component made of an alloy according to one of the preceding claims.