CN114045445A

CN114045445A - Nickel-free austenitic stainless steel

Info

Publication number: CN114045445A
Application number: CN202111366891.9A
Authority: CN
Inventors: J·布雷; G·普兰克尔特; T·卡罗扎尼
Original assignee: Swatch Group Research and Development SA
Current assignee: Swatch Group Research and Development SA
Priority date: 2015-09-25
Filing date: 2016-09-23
Publication date: 2022-02-15
Also published as: JP6435297B2; CN106987785A; JP2017061741A; EP3147380B1; EP3147378A1; EP3147380A1; US20170088923A1

Abstract

The invention relates to a nickel-free austenitic stainless steel comprising, expressed in mass%: chromium in an amount of 10< Cr < 21%; manganese in an amount of 10< Mn < 20%; molybdenum in an amount of 0< Mo < 2.5%; 0.5 or more Cu < 4%; carbon in an amount of 0.15< C < 1%; nitrogen in an amount of 0< N < 1%, nickel in an amount of 0< Ni < 0.5%, when the nickel-free austenitic stainless steel comprises manganese in an amount of 15< Mn < 20%, the steel comprises carbon in an amount of 0.25< C < 1%, expressed in mass%, the remainder being formed by iron and any impurities from the melt.

Description

Nickel-free austenitic stainless steel

The application is a divisional application of an invention patent application with the application number of 201610847224.5, the application date of the original application is 2016, 9 and 23 days, and the name of the original application is 'nickel-free austenitic stainless steel'.

Technical Field

The present invention relates to a nickel-free austenitic stainless steel composition. More particularly, the invention relates to a nickel-free austenitic stainless steel which is particularly well suited for use in watchmaking and jewelry fields.

Background

Nickel-free austenitic stainless steel compositions are advantageous for applications in the field of watchmaking and jewelry, because they are non-magnetic and hypoallergenic.

Over the past 50 years, a number of nickel-free austenitic stainless steel compositions have been proposed. In fact, the removal of nickel from austenitic stainless steel compositions is rapidly sought, firstly for cost reasons and then, more recently, for public health reasons, since nickel is known to cause allergic reactions.

These nickel-free austenitic stainless steels are based mainly on the elements Fe-Cr-Mn-Mo-C-N. In fact, in order to replace nickel, which ensures an austenitic structure, it has been proposed to use elements such as manganese, nitrogen and carbon. However, these elements have the effect of improving some of the mechanical properties of the resulting alloy, such as hardness, elastic limit and strength, which makes it very difficult to shape the parts by machining and forging, which are operations commonly used in the manufacture of components for watch and jewelry.

An example of a nickel-free austenitic stainless steel is disclosed by EP patent 1786941B 1. In this document, the compositions proposed by Berns and Gavriljuk can be obtained by melting and solidifying the alloying elements at atmospheric pressure, but they contain high concentrations of manganese, carbon and nitrogen, intended to maximize the mechanical properties. This results in great difficulty in forming by machining and forging. Further, a high concentration of manganese is disadvantageous from the viewpoint of corrosion resistance.

Some of the compositions proposed recently are intended in particular for the production of parts which may come into contact with the human body (watches, jewellery, medical prostheses). Examples of nickel-free austenitic stainless steels that can be used to produce parts in contact with the human body are disclosed in

EP patent 875591B1 to Edelstahl GmbH. Group disclosed in this documentThe compounds have in particular a high concentration of molybdenum to obtain corrosion resistance, allowing the use of such alloys in the medical field. However, in order to obtain low concentrations of manganese, carbon and nitrogen, while exhibiting high concentrations of molybdenum, these alloys must undergo a step of melting and solidification with a nitrogen overpressure, i.e. a nitrogen pressure higher than atmospheric pressure, thereby drastically increasing the cost of the resulting alloys.

In order to avoid the use of special devices for overpressure melting and solidification of the alloy with nitrogen, compositions are disclosed in particular in EP patent application 2455508a 1. However, despite their low concentration of manganese, these compositions exhibit high concentrations of carbon and nitrogen, also resulting in difficulties in forming by machining and forging. By removing molybdenum, the concentration of carbon and nitrogen can be reduced by producing the alloy at atmospheric pressure, as disclosed in US patent application US2013/0149188a1, but the corrosion resistance is not sufficient for applications in the field of watchmaking and jewelry.

In the watchmaking and jewelry fields, if it is necessary to manufacture a large series of parts, usually with complex shapes, a compromise must therefore be made between formability (machinability and forgeability) and corrosion resistance. Furthermore, for cost reasons, alloys obtained at atmospheric pressure must be preferred.

To obtain an austenitic (and therefore non-magnetic) stainless steel suitable for contact with the human body, the absence of nickel must be compensated by other gamma-source (gamma-genic) elements that reinforce the austenitic structure. The gamma source elements for which this choice is limited and the most common are nitrogen, carbon and manganese.

Nitrogen and carbon are the only elements that can completely compensate for the absence of nickel. However, these gamma-source elements have the effect of significantly increasing the hardness of the resulting austenitic steels by interstitial solid solutions, making the forming operations of such steels, such as machining and stamping, very difficult, in particular in the watchmaking and jewellery fields. Nitrogen acts even more than carbon in the hardness of the resulting austenitic steel. Therefore, the nitrogen concentration must be as low as possible. However, a minimum nitrogen content is required to obtain a fully austenitic structure, since unlike nitrogen, carbon alone cannot provide an austenitic structure without precipitates. Such precipitates are detrimental in terms of the grindability and corrosion resistance of austenitic steels.

Manganese promotes the austenitic structure only slightly. However, its presence is indispensable to increase the solubility of nitrogen and thus to ensure the production of a nickel-free fully austenitic structure. In fact, the more manganese added, the higher the solubility of nitrogen. However, manganese impairs the corrosion resistance of austenitic steels and is also responsible for the increased hardness of austenitic steels. Therefore, manganese is detrimental in the machinability and forgeability of the resulting steel.

The presence of a small amount of molybdenum is indispensable because it provides sufficient corrosion resistance, as defined by the salt spray test specified in ISO standard 9277. In fact, chromium alone, as shown by alloys 1.3816 and 1.3815, produces insufficient corrosion resistance for external timepiece components. Therefore, there is also a need to have a small amount of molybdenum, which improves the corrosion resistance of the resulting austenitic steel, as demonstrated by many studies. Furthermore, corrosion resistance increases with nitrogen content, provided that the nitrogen is in solid solution. However, the molybdenum and chromium concentrations in the alloy must be limited because these elements promote the damage of the ferritic structure to the austenitic structure. Therefore, to compensate for the effects of molybdenum and chromium, the concentration of elements such as nitrogen or carbon in the alloy has to be increased, which in turn is contrary to the machinability and forgeability properties of the alloy.

There are two possible ways to produce nickel-free austenitic steels.

The traditional approach consists in obtaining a semifinished product by casting, followed by remelting to refine the composition of the alloy, followed by various thermomechanical treatments. The solidification of the nickel-free austenitic stainless steel is therefore particularly critical, since nitrogen is introduced here into the liquid alloy. In practice, ferrite may form from a liquid state and may lead to porosity in the solidified alloy, depending in particular on the composition of the alloy and the nitrogen partial pressure. Since the solubility of nitrogen is much greater in ferrite than in austenite, nitrogen can "salt out" of the liquid in gaseous form, thereby creating unwanted porosity.

There are two main possibilities for preventing or at least limiting the formation of the above mentioned porosity. A first possibility consists in requiring a nitrogen overpressure during casting or remelting, for example by using a technique called forced induction melting or pressurized electric slag remelting. This allows the amount of nitrogen in the liquid alloy to be increased beyond solubility at ambient atmospheric pressure, thereby limiting or preventing the formation of ferrite during solidification. Furthermore, the formation of the holes is made more difficult by the overpressure applied to the solidified alloy. However, the use of these techniques greatly increases the price of the resulting alloy, particularly because the production equipment is expensive.

A second possibility to prevent or limit the formation of porosity during solidification of the alloy is to carefully select the elements comprised in the alloy composition, for example by increasing the concentration of gamma-source elements (C, Mn, Cu) and/or by decreasing the concentration of alpha-source elements (Cr, Mo) and/or by increasing the concentration of elements (Mn, Cr, Mo) that increase the solubility of nitrogen. Some elements have opposite effects, but not necessarily in the same proportions. Therefore, complete austenite solidification avoiding salting out of nitrogen by ferrite formation is possible at ambient atmospheric pressure or lower.

The solution involving casting and remelting of steel at ambient atmospheric pressure is therefore less expensive than the solution involving working with nitrogen overpressure and is therefore preferred. However, there is a constraint that affects the composition of alloys that can be cast at ambient atmospheric pressure.

Other techniques that can be used to manufacture nickel-free austenitic steel components use powder metallurgy, for example by metal injection molding, a technique also known as MIM. In that case, it is not necessary to use 100% austenite powder, since nitrogen may also be added during sintering, thereby converting the remaining ferrite to austenite.

Disclosure of Invention

The object of the present invention is to overcome the above-mentioned problems, as well as others, by providing a nickel-free austenitic stainless steel composition, for which the forming operation is facilitated, which has sufficient corrosion resistance, and which can be obtained by conventional metallurgy (casting), in particular at ambient atmospheric pressure, or by powder metallurgy. By "sufficient corrosion resistance" is meant a resistance sufficient for the field of external horological parts and the field of jewellery, in particular as defined by the salt spray test (ISO standard 9227).

To this end, the invention relates to a nickel-free austenitic stainless steel comprising, in mass%:

chromium in an amount of 10< Cr < 21%;

manganese in an amount of 10< Mn < 20%;

molybdenum in an amount of 0< Mo < 2.5%;

0.5 or more Cu < 4%;

carbon in an amount of 0.15< C < 1%;

nitrogen in an amount of 0< N.ltoreq.1%;

ni of 0-0.5%, and

when the nickel-free austenitic stainless steel contains manganese in an amount of 15. ltoreq. Mn < 20%, the steel contains carbon in an amount of 0.25< C < 1% in mass%,

the remainder being formed by iron and any impurities from the melt.

According to another characteristic of the invention, the nickel-free austenitic stainless steel comprises, in mass%:

chromium in an amount of 15< Cr < 21%;

manganese in an amount of 10< Mn < 20%;

molybdenum in an amount of 0< Mo < 2.5%;

0.5 or more Cu < 4%;

carbon in an amount of 0.15% < C < 1%;

nitrogen in an amount of 0< N.ltoreq.1%;

si in an amount of 0. ltoreq. Si < 2%,

0 or more and Ni < 0.5%,

w is more than or equal to 0 and less than 4 percent,

0 or more and Al < 3%, and

the remainder being formed by iron and any impurities from the melt.

According to a further feature of the present invention, the nickel-free stainless steel comprises at least one element selected from the group consisting of S, Pb, B, Bi, P, Te, Se, Nb, V, Ti, Zr, Hf, Ce, Ca, Co, Mg, each of which may be present in a mass concentration of at most 1%.

Within the meaning of the present invention, "nickel-free austenitic stainless steel" means an alloy comprising not more than 0.5 mass% nickel.

By "any impurities" is meant elements that are not used to improve one (or more) property(s) of the alloy, but are inevitably present as a result of the melting process. In particular, in the fields of watchmaking and jewelry, the presence of these impurities must be limited as much as possible, since such impurities may significantly form non-metallic inclusions in the alloy, such as oxides, sulfides and silicates, which may have detrimental consequences for the corrosion resistance and the burnish properties of the resulting alloy.

In the nickel-free austenitic stainless steel composition according to the invention, the molybdenum concentration by mass must be lower than 2.5%. In fact, the presence of molybdenum is necessary because it enhances the corrosion resistance, in particular the pitting corrosion resistance (resistance to pitting corrosion), of the resulting steel. However, the concentration of molybdenum should be limited to a small amount because molybdenum has a disadvantage of promoting a ferrite structure. Thus, the higher the concentration of molybdenum, the greater the need for the addition of elements such as nitrogen, carbon and manganese which promote the austenitic structure, but with the disadvantage of making the resulting alloy harder and therefore more difficult to machine and forge.

In addition, in the nickel-free austenitic stainless steel composition of the present invention, the copper mass concentration must be higher than 0.5% and lower than 4%. Copper, which is considered as an impurity in the prior art, is intentionally added to the composition of the invention, in particular because copper promotes the austenitic structure and therefore makes it possible to limit the concentration of nitrogen and carbon. In addition, the presence of copper improves the general corrosion resistance of the alloy and inherently enhances the machinability and forgeability of the alloy of the present invention. However, the concentration of copper must be limited to 4% because copper tends to make the steel brittle at high temperatures, which makes thermomechanical processing difficult.

Also, the manganese concentration in the alloy of the invention must be higher than 10% and lower than 20%. Manganese is known to enhance the solubility of nitrogen in nickel-free austenitic stainless steel compositions. However, the higher the concentration of manganese, the harder the alloys will be and the lower their machinability and forgeability. In addition, their corrosion resistance is reduced. Thus, by teaching that the concentration of manganese must be limited in nickel-free stainless steel alloys, the present invention makes it possible to enhance the corrosion resistance of such alloys as well as their machinability and forgeability. However, a minimum concentration of manganese is necessary to ensure sufficient solubility of nitrogen, particularly so that the alloy solidifies at ambient atmospheric pressure.

According to a further feature of the present invention, the nickel-free austenitic stainless steel contains carbon in an amount of 0.2. ltoreq. C < 1% by mass.

According to a further feature of the present invention, the nickel-free austenitic stainless steel contains molybdenum in an amount of 1. ltoreq. Mo.ltoreq.2% by mass.

Preferred examples of compositions are given by the following formula:

-Fe-17Cr-17Mn-2Mo-1Cu-0.3C-0.5N

-Fe-17Cr-12Mn-2Mo-2Cu-0.33C-0.4N

-Fe-17Cr-11Mn-2Mo-1Cu-0.25C-0.4N

-Fe-17Cr-14.5Mn-2Mo-2Cu-0.22C-0.35N

the first two compositions are particularly advantageous when the corresponding nickel-free austenitic steels are obtained by conventional metallurgical processes (casting, remelting and thermomechanical treatment). In fact, at ambient atmospheric pressure, without overpressure, solidification is completely austenitic, thereby avoiding the formation of undesirable porosity in the alloy. Furthermore, optimizing these compositions allows the temperature at which precipitates such as carbides or nitrides occur to be as low as possible. The austenite temperature range is thus the largest, thereby facilitating any thermomechanical processing.

The advantage of the first composition comprising 1% copper is that the austenite temperature range is higher than the second composition comprising 2% copper. However, the second composition containing 2% copper is easier to machine and stamp. In fact, copper naturally enhances the machinability and forgeability of the alloy. Furthermore, the use of more copper means that the nitrogen and carbon content can be reduced while ensuring the austenitic structure.

In addition to the fact that they are obtainable by conventional metallurgical methods, the first two compositions can also be advantageous in the case of powder metallurgical shaping. In fact, these compositions make it possible to obtain particularly dense assemblies after sintering, in particular after the technique known as supersolidus liquid phase sintering.

The third and fourth compositions are particularly suitable for powder metallurgy forming. They offer in particular the possibility of solid-phase sintering in an atmosphere comprising a reduced partial pressure of nitrogen. This allows the atmosphere to be supplemented with, for example, hydrogen, which is known to improve the densification of stainless steel during sintering. Since these alloys also have a low content of interstitial elements after sintering, any shaping operations after sintering, such as machining or forging, are also facilitated. Also, optimizing both compositions allows the temperature at which precipitates such as carbides or nitrides occur to be as low as possible. It should be noted, however, that although the third and fourth compositions are particularly well suited for powder metallurgical shaping, these compositions may also be obtained by conventional methods, for example by using a nitrogen overpressure during melting and solidification.

In the prior art, in most cases, the aim is sought to maximize the corrosion resistance and hardness of austenitic steels by favouring high contents of nitrogen and molybdenum in the alloy.

However, in the case of the present invention, the specifications for the external parts used in the watchmaking and jewelry fields are different. The proposed alloys therefore have optimised properties, making them particularly well suited for use in the watchmaking and jewellery fields.

First, the machinability of the alloys of the invention is improved, mainly because the amount of nitrogen present in these alloys is low. In fact, by limiting the molybdenum content to a value less than 2.5% by weight and by adding other gamma-source elements such as carbon and copper, the amount of nitrogen can be reduced while ensuring the austenitic structure. The addition of small amounts of sulfur (up to 0.015 wt.%) may also improve machinability due to the formation of manganese sulfide, but care must be taken because this has an effect on the corrosion resistance of the resulting alloy. "machinability" means any type of machining operation, such as piercing, grinding, perforating or other operation.

Secondly, the forgeability of the alloy of the present invention is also improved.

Since nitrogen is the main element in such alloys that improves the mechanical properties, the limited concentration of nitrogen makes shaping by deformation easier.

Another important more element, copper, may reduce the strain hardening level of the alloy, which thus facilitates shaping by deformation. Finally, due to the copper, an improved general corrosion resistance is observed.

The invention also relates to the use of the nickel-free austenitic stainless steel as described above for producing external elements for horology and jewelry.

Drawings

Further characteristics and advantages of the invention appear more clearly from the following detailed description of an embodiment of the nickel-free austenitic stainless steel of the invention, which example is given by way of non-limiting illustration only with reference to the accompanying drawings, in which:

FIG. 1 is a phase diagram illustrating a first example of a nickel-free austenitic stainless steel according to the invention, having the composition Fe-17Cr-17Mn-2Mo-1 Cu-0.3C-0.5N.

FIG. 2 is a phase diagram illustrating a second example of a nickel-free austenitic stainless steel according to the invention, having the composition Fe-17Cr-12Mn-2Mo-2 Cu-0.33C-0.4N.

FIG. 3 is a phase diagram illustrating a third example of a nickel-free austenitic stainless steel according to the invention, having the composition Fe-17Cr-11Mn-2Mo-1 Cu-0.25C-0.4N.

FIG. 4 is a phase diagram illustrating a fourth example of a nickel-free austenitic stainless steel according to the invention, having the composition Fe-17Cr-14,5Mn-2Mo-2 Cu-0.22C-0.35N.

Figure 5 is a table describing the composition of a nickel-free austenitic stainless steel, expressed in mass percentages.

Fig. 6 is a Schaeffler diagram as defined by Gavriljuk and Berns in "High Nitrogen Steels", 2010, Springer edition, which predicts the structure of the alloy after hardening according to the composition.

Detailed Description

The invention starts from the general inventive concept that consists in proposing a nickel-free austenitic stainless steel exhibiting a very good compromise between machinability and forgeability and corrosion resistance, taking into account the problems specific to the field of external horological parts. In addition, the proposed composition can be obtained by means of conventional metallurgical processes (casting), in particular at ambient atmospheric pressure, which is very advantageous from the standpoint of production costs, or by powder metallurgy with very high densities after sintering. The concentration of alpha source elements such as chromium and molybdenum is defined to obtain sufficient corrosion resistance. The concentrations of manganese, carbon and nitrogen are low enough to enhance the machinability and forgeability of the resulting alloy, but high enough to obtain an alloy by melting and solidification at atmospheric pressure or a very dense part by powder metallurgy. In addition, the concentration is optimized to obtain the maximum austenite temperature range. Finally, copper makes it possible to reduce the concentration of the above-mentioned γ source element to facilitate shaping by machining or deformation and improve general corrosion resistance. However, the concentration of copper must be limited because copper reduces the austenite temperature range and tends to make the austenitic steel brittle at high temperatures, making any thermomechanical processing (forging/lamination, annealing, etc.) more difficult.

For the first composition example, whose phase diagram is shown in FIG. 1 (Fe-17Cr-17Mn-2Mo-1Cu-0.3C-0.5N), it is seen that complete austenite solidification at atmospheric pressure can be obtained and that the temperature at which precipitates appear is as low as possible for the nitrogen concentration obtained after solidification (cross-over point between line 1 and line 3). The austenite temperature range is therefore the widest possible. The composition is also advantageous for obtaining very dense parts by powder metallurgy. In fact, the presence of a wide "austenite-liquid" phase (between

lines

4,5 and 6) at 900 mbar of nitrogen allows liquid phase sintering to be carried out without loss of nitrogen. In that case the sintering temperature is defined to be about 30% liquid during sintering.

For the second composition example shown in FIG. 2 (Fe-17Cr-12Mn-2Mo-2Cu-0.33C-0,4N), the increase in copper concentration makes it possible to shift the boundaries of the austenite range (line 6) to lower nitrogen concentrations. Thus, the manganese concentration may be reduced and the resulting alloy after solidification contains less nitrogen. Due to the higher concentration of copper and the reduced concentration of nitrogen and manganese, the machinability and deformability of the alloy is promoted compared to the first composition. Although higher copper concentrations reduce the austenite temperature range, this range is the largest for the intended nitrogen concentration (1300 ℃ to 1050 ℃).

For the third composition example shown in FIG. 3 (Fe-17Cr-11Mn-2Mo-1Cu-0.25C-0.4N), ferrite is formed upon solidification at atmospheric pressure, which may result in porosity in the solidified alloy. However, the composition is optimized for powder metallurgy forming. In fact, for this composition, sintering can be carried out at high temperature (1300 ℃) with a reduced partial pressure of nitrogen (about 600 mbar). The sintering atmosphere can thus be supplemented with hydrogen, which improves the densification of the resulting component after sintering, due to its strong reducing power.

The fourth composition example shown in FIG. 4 (Fe-17Cr-14,5Mn-2Mo-2Cu-0.22C-0.35N) is also advantageous for powder metallurgy forming. Sintering can be carried out at high temperature (1300 c) with even lower partial pressure of nitrogen (about 400 mbar) compared to the previous examples. Finally, the alloy has a very low concentration of interstitial elements, thus facilitating any machining or forging operations after sintering.

The table shown in fig. 5 compares the values of MARC (alloy corrosion resistance measure) index of the above composition examples with standard austenitic stainless steels comprising nickel and commercially available nickel-free austenitic stainless steels. The MARC index is an excellent measure of corrosion resistance of comparative austenitic steels, particularly nickel-free austenitic steels. The higher the MARC index, the greater the corrosion resistance of the alloy. The table includes two nickel-containing standard austenitic stainless steels, 6 commercial nickel-free austenitic stainless steels and 4 examples of the preferred compositions described above, commonly used in watchmaking and jewelry. In addition, the last row in the table gives the MARC index for each alloy as defined in Speidel, M.O. in "Nitrogen consistent austenitic stainless steel", materials wissenschaft und Werkstofftechnik, 37(2006), page 875-. This is the sum of the elemental concentrations in the austenitic stainless steel composition involved:

MARC＝Cr(％)+3.3Mo(％)+20C(％)+20N(％)-0.5Mn(％)-0.25Ni(％)

examples of compositions of the invention have a higher MARC index value than austenitic stainless steel 1.4435, austenitic stainless steel 1.4435 being the most commonly used steel in watchmaking and jewelry. 3 of the 4 examples of the composition of the invention even had a higher value for the MARC index than steel 1.4539, the latter being known to have excellent corrosion resistance.

The present invention seeks to improve the machinability and deformability of nickel-free austenitic stainless steels by teaching a reduction of the carbon and nitrogen content in these alloys and the addition of copper. Thus, while the proposed alloys have lower index values than alloys 1.4456, 1.4452, UNS S29225, and UNS S29108, they have higher index values than alloys 1.3816 and 1.3815, which is sufficient to enable them to pass the salt spray corrosion test. Furthermore, in contrast to alloys 1.4456, 1.4452, UNS S29225 and UNS S29108, which were subjected to a melting and solidification step under a nitrogen overpressure, the first, second and fourth examples of the composition of the present invention showed austenite solidification at atmospheric pressure, thus avoiding the use of special equipment. This therefore reduces the cost of the resulting alloy.

Finally, the position of these different alloys on the Schaeffler diagram is shown in fig. 6. As with the other alloys shown, 4 preferred examples of compositions are in the austenite range of the figure. This demonstrates the stability of the austenitic structure of the compositions of the invention, if desired. It is also seen that examples of compositions lie between alloy 1.3816/1.3815 (which is too low in corrosion resistance) and alloy 1.4456/1.4452/UNS 29225/UNS 29108 (which are very difficult to form by machining and forging, and which are expensive to cost because they are produced under nitrogen overpressure).

The invention is of course not limited to the embodiment just described and a person skilled in the art will expect numerous and simple modifications and variations without departing from the scope of the invention as defined by the appended claims. In particular, it should be noted that the proposed alloy provides an excellent compromise between corrosion resistance, formability (machinability and forgeability) and density of the part after sintering. In fact, the part can be sintered at low nitrogen pressure and compensated with hydrogen. Furthermore, in the case of composite materials with a metal matrix, the metal matrix can be realized by means of the steel composition according to the invention. Sintered parts may also be treated under high isostatic pressures. Parts formed by pressing or by metal injection molding can also be sintered at high isostatic pressures. Semi-finished products can also be produced under high isostatic pressure. Finally, the part after sintering may be forged.

Claims

1. A nickel-free austenitic stainless steel comprising, in mass%:

chromium in an amount of 10< Cr < 21%;

manganese in an amount of 10< Mn < 20%;

molybdenum in an amount of 0< Mo < 2.5%;

0.5 or more Cu < 4%;

carbon in an amount of 0.15< C < 1%;

nitrogen in an amount of 0< N.ltoreq.1%, and

0 or more and Ni < 0.5%,

the remainder being formed by iron and any impurities from the melt.

2. Nickel-free austenitic stainless steel according to claim 1, characterized in that the steel comprises, in mass%:

chromium in an amount of 15< Cr < 21%;

manganese in an amount of 10< Mn < 20%;

molybdenum in an amount of 0< Mo < 2.5%;

0.5 or more Cu < 4%;

carbon in an amount of 0.15% < C < 1%;

nitrogen in an amount of 0< N.ltoreq.1%;

si in an amount of 0. ltoreq. Si < 2%,

0 or more and Ni < 0.5%,

w is more than or equal to 0 and less than 4 percent,

0 or more and Al < 3%, and

the remainder being formed by iron and any impurities from the melt.

3. Nickel-free austenitic stainless steel according to claim 1, characterized in that the composition is given by the formula Fe-17Cr-11Mn-2Mo-1Cu-0.25C-0.4N, expressed in mass%.

4. Nickel-free austenitic stainless steel according to claim 2, characterized in that the composition is given by the formula Fe-17Cr-11Mn-2Mo-1Cu-0.25C-0.4N, expressed in mass%.

5. Nickel-free austenitic stainless steel according to claim 1, characterized in that the composition is given by the formula Fe-17Cr-12Mn-2Mo-2Cu-0.33C-0.4N, expressed in mass%.

6. Nickel-free austenitic stainless steel according to claim 2, characterized in that the composition is given by the formula Fe-17Cr-12Mn-2Mo-2Cu-0.33C-0.4N, expressed in mass%.

7. Nickel-free austenitic stainless steel according to claim 1, characterized in that the composition is given by the formula Fe-17Cr-14.5Mn-2Mo-2Cu-0.22C-0.35N, expressed in mass%.

8. Nickel-free austenitic stainless steel according to claim 2, characterized in that the composition is given by the formula Fe-17Cr-14.5Mn-2Mo-2Cu-0.22C-0.35N, expressed in mass%.

9. Nickel-free austenitic stainless steel according to claim 1, characterized in that the composition is given by the formula Fe-17Cr-17Mn-2Mo-1Cu-0.3C-0.5N, expressed in mass%.

10. Nickel-free austenitic stainless steel according to claim 2, characterized in that the composition is given by the formula Fe-17Cr-17Mn-2Mo-1Cu-0.3C-0.5N, expressed in mass%.

11. Nickel-free austenitic stainless steel according to any of the claims 1-10, characterized in that the steel comprises copper in an amount with a mass percentage 0.5< Cu < 4%.

12. Nickel-free austenitic stainless steel according to any of the claims 1-10, characterized in that the steel comprises carbon in an amount of 0.2 ≦ C < 1% in mass percentage.

13. Nickel-free austenitic stainless steel according to claim 11, characterized in that the steel comprises carbon in an amount of 0.2 ≦ C < 1% in mass percentage.

14. Nickel-free austenitic stainless steel according to any of the claims 1-10, characterized in that the steel comprises molybdenum in an amount of 1 mass-% Mo 2.

15. The nickel-free austenitic stainless steel according to claim 11, characterized in that the steel comprises molybdenum in an amount of 1% by mass or less Mo 2% by mass.

16. The nickel-free austenitic stainless steel according to claim 12, characterized in that the steel comprises molybdenum in an amount of 1% by mass or less Mo 2% by mass.

17. The nickel-free austenitic stainless steel according to claim 13, characterized in that the steel comprises molybdenum in an amount of 1% by mass or less Mo 2% by mass.

18. Nickel-free stainless steel according to claim 1, characterized in that the steel comprises at least one element selected from the group consisting of S, Pb, B, Bi, P, Te, Se, Nb, V, Ti, Zr, Hf, Ce, Ca, Co, Mg, each of which may be present in a mass concentration of at most 1%.

19. Nickel-free stainless steel according to claim 2, characterized in that the steel comprises at least one element selected from the group consisting of S, Pb, B, Bi, P, Te, Se, Nb, V, Ti, Zr, Hf, Ce, Ca, Co, Mg, each of which may be present in a mass concentration of at most 1%.

20. Timepieces and jewelry made of the nickel-free austenitic stainless steel according to claim 1.

21. Timepieces and jewelry made of the nickel-free austenitic stainless steel according to claim 2.