STEEL WITH AN AUSTENITIC STRUCTURE AND USE OF SUCH STEEL FOR APPLICATIONS IN THE ORAL CAVITY OF A HUMAN OR ANIMAL

Description

[0001] The invention relates to a steel with an austenitic structure.

[0002] The invention also relates to the use of a steel, in particular for dental applications.

[0003] The mechanical and corrosion properties specified in this text are determined in accordance with DIN EN ISO 22674:2016-09 (shown here from strength class 3).

[0004] Whenever "%" information is given in this text regarding alloys or steel compositions, these always refer to the mass (indicated in "mass%"), unless expressly stated otherwise.

[0005] The metallic dental alloys commonly used today can be divided into two categories. Precious metal alloys, which include materials based on gold, silver, palladium, or platinum, are considered the first. The other category includes more cost-effective non-precious metal alloys. These can be differentiated based on their main alloy systems: nickel-chromium (NiCr) and cobalt-chromium (CoCr).

[0006] Currently, approximately 1,400 different dental alloys are approved in Germany. They are characterized by excellent corrosion resistance, allowing them to withstand corrosive attack from saliva, stomach acid, and other media found in the oral cavity. In addition, materials for dental applications must possess a certain degree of hardness and mechanical strength to withstand the stresses encountered during chewing.

[0007] In addition, dental alloys must be non-magnetic and biocompatible to avoid rejection reactions, allergic reactions, or other sensitizations in patients. These requirements prove particularly problematic for NiCr-based materials. A nickel allergy is the most common allergic reaction to a metallic material. NiCr alloys can therefore only be used to a limited extent.

[0008] As an alternative to NiCr base materials, CoCr alloys are used for medical dental prostheses, particularly in Europe. However, these are significantly more expensive than nickel alloys. Furthermore, there is suspicion that cobalt could trigger or promote cancer in the body. If this suspicion is confirmed, cobalt alloys will likely no longer be able to be used in the human body in the future.

[0009] Another example of a steel specifically intended for use on the human body is known from EP 0 918 099 A1. This is a chromium-manganese steel alloy consisting of, in mass%, 0.08 - 0.25% C, ≤ 0.015% S, ≤ 0.050% P, 12 - 17% Mn, 0.2 - 1% Si, 1 - 3% Cu, 2 - 6% Co, ≤ 0.01% titanium, 3 - 6% Mo, 17 - 22% Cr, ≤ 1.0% Ni, ≤ 0.01% AI, ≤ 0.01% niobium, ≤ 0.01% B, ≤ 0.2% V, 0.5 - 0.9% N and the remainder being iron and smelting-related impurities, the steel having a nickel equivalent of more than 17, preferably more than 20, and a nickel equivalent according to the formula PREN = %Cr + 3.3 x %Mo + 20 x %N calculated from the Cr content %Cr, the Mo content %Mo and the N content %N, should have a PREN value of at least 37, in particular more than 45, which represents good corrosion resistance.

[0010] In addition to the reactions that nickel and cobalt alloys can trigger in the human body, occupational safety aspects must also be considered when processing these alloys. Dental materials are usually processed manually using machining techniques such as grinding, milling, and the like. This poses the risk that resulting dust can enter the body via the lungs and cause damage.

[0011] In addition to the prior art described above, CN 104 878 316 A describes a conventional austenitic steel consisting of, in mass %, 0.1 - 0.15% C, 0.5 - 0.95% N, 0.5 - 1.5% Si, 13 - 19% Mn, 15 - 21% Cr, 0.5 - 2% Mo, 0.01 - 0.5% Nb, up to 3% Ni, 0.001 - 0.04% B, 0.01 - 0.05% Ti, 0.05 - 0.15% Al, and the remainder Fe and unavoidable impurities. B, Ti, and Al are provided to reduce the Ni content of the steel without compromising strength and ductility.

[0012] JP 2000 239799 A also discloses a steel alloy that also aims to avoid Ni as an alloying element. With N contents of 0.06–0.5 wt.%, the C content is limited to a maximum of 0.06 wt.%.

[0013] CN 105 925 814 A describes a steel alloy suitable for dental applications and the like. It contains, in mass %, up to 0.2% C, 0.7-2% N, ≤ 1% Si, 12-30% Mn, 15-30% Cr, up to 4.5% Mo, up to 4.5% Ni, and the balance Fe and unavoidable impurities. The alloys specified for practical use in this publication each contain C contents of no more than 0.15% by mass.

[0014] JP 2016-102244 A concerns a state of the art in which Ni is explicitly present as an effective mandatory component. This state of the art stipulates, for a C content of 0.05–0.15 mass%, a minimum Ni content of 0.1 mass% in combination with Cr contents of 15–20 mass% and Mn contents of 10–20 mass%, as well as additional V contents of at least 0.005 wt% and Cu contents of at least 0.05 wt%.

[0015] In a comparable manner, in US 2011 / 0008714 A1, a steel for a fuel cell is alloyed with C contents of up to 0.075 wt% and Ni contents of 0.5 - 1.5 wt% in combination with Cr contents of 17 - 20 wt% and Mn contents of 4.0 to 35 wt%.

[0016] Against this background, there has been a need for alloys for oral use that are free of Ni and Co, but have similar properties to the well-known NiCr and CoCr alloys. Dental alloys of the type in question are intended an austenitic and therefore non-magnetic structure, high corrosion resistance, which is characterized by a release of less than 200 µg / cm 2< within 7 days, a yield strength Rp0.2 of at least 270 MPa, an elongation at break A of more than 5%, an elastic modulus of more than 150 GPa (only defined from strength class 5 onwards), good castability, good mechanical workability and good suitability for ceramic veneering.

[0017] Suitability for ceramic veneering requires that no thermally induced stresses occur between the component made of the respective alloy and the ceramic layer with which the component is veneered, either during production or during use. This can be ensured by adapting the thermal expansion coefficient of the component's alloy to the thermal expansion coefficient of the veneering ceramic. Alternatively or additionally, it is also possible to prevent chipping of the veneer by improving the bond between the component's metal material and the veneering ceramic with reactive elements. However, the elements suitable for this purpose generally have a high affinity for oxygen, such as manganese.

[0018] Against the background of the state of the art explained above, the task arose to develop a nickel- and cobalt-free, stainless austenitic steel that reliably meets the requirements in dental technology with regard to its corrosion resistance, its mechanical properties, its castability and its coefficient of thermal expansion.

[0019] The invention has solved this problem by a steel which has the composition specified in claim 1 and, due to its range of properties, is particularly suitable for the production of components for use in the oral cavity of humans or animals.

[0020] Advantageous embodiments of the invention are specified in the dependent claims and, like the general inventive concept, are explained in detail below.

[0021] A steel according to the invention therefore has an austenitic, non-magnetic structure and exhibits a yield strength Rp0.2 of at least 230 MPa, an elongation at break A of more than 5%, and a modulus of elasticity of at least 150 GPa. For this purpose, the steel according to the invention consists of, in mass%, C: >0,2 - 0,8 %, N: 0,3 - 1,3 %, Si: < 2,0 %, Mn: 14 - 30 %, Cr: 17 - 27%, Mon: 0 - 6 %, Note: 0 - 6 %, W: 0 - 6 %, Ga: 0 - 6 %, Ta 0 - 6 %,

[0022] The remainder is iron and unavoidable impurities, whereby the impurity content complies with the requirements for dental materials contained in DIN EN ISO 22674:2016-09 and is limited to less than 0.5%, and the impurities include less than 0.1% Ni and less than 0.1% Co.

[0023] The invention is based on the finding that higher contents of carbon ("C") and nitrogen ("N") reliably produce austenitically solidifying, stainless steel materials, as known, for example, from DE 10146616 A1. Such steel materials contain a total of 0.4–0.7 mass% C and N, with up to 0.7 mass% Si, 17–21 mass% Mn, and 16.5–18.5 mass% Cr, the remainder being iron, and a high proportion of interstitially dissolved C and N atoms. These atoms stabilize the austenitic microstructure and improve the mechanical properties of the alloy through increased solid solution strengthening. Thus, C+N-alloyed, stainless austenites exhibit significantly higher strengths than classic stainless austenitic steels, such as those with material number 1.4404 standardized steel, which consists of, in mass%, up to 0.03% C, up to 1.00% Si, up to 2.00% Mn, 16.5 - 18.5% Cr, 2.0 - 2.5% Mo and 10.0 - 13.0% Ni, the remainder being iron and unavoidable impurities.

[0024] In order to also utilize and expand the beneficial effects of the presence of C and N, the invention provides for a C content of >0.2 mass% to 0.8 mass%, in particular up to 0.7 mass%, and an N content of 0.3 mass% to 1.3 mass%, in particular up to 1.0 mass%, so that the sum of the C and N contents in a steel according to the invention is >0.5 mass% to 2.1 mass%, in particular up to 2.0 mass%, up to 1.8 mass% or up to 1.7 mass%. In practice, C contents of more than 0.2 mass%, in particular more than 0.20 mass%, such as at least 0.25 mass%, at least 0.3 mass%, in particular at least 0.30 mass%, or at least 0.34 mass%, have proven particularly suitable for the purposes of the invention.

[0025] The high C and N contents provided according to the invention result in C and N contributing a further increased share to the solid solution strengthening of the steel according to the invention and thus to its high mechanical properties. Furthermore, the C+N steel according to the invention possesses further increased corrosion resistance, particularly against pitting corrosion, due to its high proportion of interstitially dissolved N. At the same time, the expanded C and N contents provided according to the invention open up a larger melting range and, consequently, facilitate melt-metallurgical processing through improved casting behavior of a melt alloyed according to the invention. The minimum C and N contents prescribed according to the invention ensure that these effects are reliably achieved. In contrast, the C and N content of a steel according to the invention is limited to a maximum of 2.1 mass% in total to avoid increased carbide or nitride formation.This would reduce the corrosion properties. At the same time, higher C and N contents would increase strength and hardness. However, this would make processing and post-processing of the material much more difficult. In addition, if the C and N content is too high, there is a significant drop in toughness. With regard to the optimized effect of C and N, C and N contents of a maximum of 2.0 mass% (with a C content of no more than 0.7 mass% and an N content of no more than 1.3 mass%), a maximum of 1.8 mass% (with a C content of no more than 0.8 mass% and an N content of no more than 1.0 mass%), or a maximum of 1.7 mass% (with a C content of no more than 0.7 mass% and an N content of no more than 1.0 mass%) have proven particularly effective.

[0026] To prevent other alloying elements such as W, Mo and Cr from forming primary carbides when the C supply is too high, the C content can be kept at a low level compared to the N content. Such primary carbides are to be regarded as critical both in the melt-metallurgical production of semi-finished products made from the steel according to the invention and in subsequent processing in the dental laboratory, as they form from the melt and can lead to reduced corrosion resistance and embrittlement. For this reason, it may be advisable to limit the C content to values ​​of no more than 0.7 mass%, in particular no more than 0.6 mass%, and to achieve austenite stability primarily through the elements Mn and N. N contents of at least 0.4 mass%, in particular at least 0.5 mass%, have proven particularly effective for this purpose.

[0027] Silicon ("Si") can be present in the steel according to the invention in amounts of up to 2.0 mass%. Higher Si contents would stabilize too much ferrite in the steel structure, resulting in the material losing its non-magnetic properties. Negative effects of the presence of Si can be avoided by limiting the Si content to a maximum of 1.5 mass%, in particular a maximum of 1.3 mass%.

[0028] As already mentioned, manganese ("Mn") is present in the steel according to the invention in amounts of 14 to 30 mass%, in particular 16 to 28 mass%, to facilitate the alloying of the high nitrogen contents provided for in the invention due to the increased solubility of the melt resulting from the presence of Mn. This enables the production of the steels under atmospheric pressure. Furthermore, Mn, like C and N, is a strong austenite stabilizer.

[0029] The combined presence of the Mn, C, and N contents specified in the invention makes it possible to completely replace nickel ("Ni") as an austenite stabilizer. The positive effects of Mn on the properties of a steel alloyed according to the invention can be utilized particularly effectively at Mn contents of at least 16 mass%, in particular at least 17 mass%. However, at Mn contents above 30 mass%, there is a risk that undesirable ferrite will form in the microstructure of the steel according to the invention, due to its non-magnetic properties. Furthermore, excessively high Mn contents would increase the coefficient of thermal expansion. This effect should also be avoided with a view to the practical use of the material according to the invention. Therefore, Mn contents of < 23 mass%, in particular a maximum of 22.5 mass%, have proven particularly effective in practice.

[0030] The high Mn content of a steel according to the invention, in combination with the also prescribed Cr contents, has the further effect that the steel according to the invention has a high affinity for oxygen. The ceramics used in the dental industry are almost exclusively oxide ceramics, which means that a high proportion of oxygen is present in the veneering ceramics. By varying the manganese content within the scope of the inventive requirement, the adhesion between the alloy and the veneering ceramic can thus be directly influenced. For this purpose, Mn contents of the steel according to the invention of a maximum of 28 mass%, in particular a maximum of 27 mass%, or in particular <23 mass%, such as a maximum of 22.5 mass%, have proven particularly effective.

[0031] As a result of the inventive substitution of Ni with C, N, and Mn, the nickel ("Ni") content in the steel according to the invention can be reduced to such an extent that it is "0 mass%" in the technical sense, but in any case less than 0.1 mass%, and thus ineffective with regard to the properties of the steel according to the invention that are the focus here. At these Ni contents, the steel according to the invention certainly no longer has a potentially allergenic effect. At most, Ni, to the extent that it is present at all, can be classified as unavoidable impurities that are not deliberately added to the steel but can enter it during steel production.

[0032] Likewise, the cobalt ("Co") content in the steel according to the invention is reduced to values ​​of less than 0.1 mass%, at which Co no longer has any effect on the properties of the steel material according to the invention and its presence can pose no health risks. Accordingly, the Co content according to the invention is also preferably reduced to "0 mass%" in the technical sense, but in any case so low that it is present at most in the amounts attributable to unavoidable impurities due to production.

[0033] Chromium ("Cr") is present in the steel according to the invention in contents of 17 mass% to 27 mass% to ensure sufficient corrosion resistance. In this content range, Cr forms a dense chromium oxide layer on components made from the steel according to the invention, which inhibits corrosion reactions. Contents of at least 17 mass% ensure that corrosion resistance is maintained even in the potentially highly aggressive environment that can arise in the oral cavity. By increasing the Cr content to at least 18 mass%, in particular at least 19 mass%, the reliability with which the steel material according to the invention resists corrosive attacks can be further increased. The upper limit of the Cr content of a steel according to the invention is limited to a maximum of 26 mass% to avoid the excessive formation of primary carbides, which would impair the toughness and ductility of the steel.In addition, Cr contents of more than 26 mass% would stabilize the ferritic phase in the microstructure of the steel according to the invention, with the result that the non-magnetic properties of the steel material according to the invention would no longer be guaranteed. The negative effects of the presence of Cr in the steel according to the invention can be counteracted particularly reliably by limiting the Cr content to a maximum of 25 mass%, in particular a maximum of 24 mass%. In the material according to the invention, the impurity contents are adjusted according to the specifications specified in DIN EN ISO 22674:2016-09 for dental materials. The impurity content is limited to less than 0.5 mass%. Less than 0.1 mass% Ni and less than 0.1% Co are considered impurities according to the invention.

[0034] The Pitting Resistance Equivalent Number (PREN) expresses the influence of the alloying elements Cr, Mo, and N on the corrosion resistance of the steel material according to the invention. The invention calculates the PREN value according to the equation PREN = %Cr + 3.3 x %Mo + 20 x %N, where %Cr = the respective Cr content, %Mo = the respective Mo content, and %N = the respective N content of the steel. By adjusting the Cr, Mo, and N contents of the steel according to the invention to achieve PREN values ​​of more than 30%, in particular more than 34%, optimized corrosion resistance can be ensured. PREN values ​​of at least 38%, in particular at least 40%, or at least 45%, prove particularly advantageous in this case.

[0035] In the steel material according to the invention, the melting interval, i.e., the temperature range in which the steel is molten, is shifted to a more favorable temperature range. It typically ranges from Tsol = 1250°C to Tliq = 1350°C. This significantly larger melting interval, which is available even at lower temperatures compared to conventional steels of the type in question, leads to improved mold filling during melting processing (casting) while simultaneously reducing the load on the melting equipment and mold materials.

[0036] The chromium oxide layer formed by Cr on the steel according to the invention can be stabilized by adding up to 6 mass% molybdenum ("Mo"). In particular, the addition of Mo can increase resistance to pitting corrosion. If this is to be utilized, a Mo content of at least 0.5 mass%, in particular at least 0.6 mass%, can be added to the steel according to the invention. The positive effects of Mo can be utilized particularly effectively at Mo contents of up to 5.5 mass%, in particular up to 5.0 mass%.

[0037] Like Mo, tungsten ("W") can also be added to the steel according to the invention in amounts of up to 6 mass% to increase corrosion resistance. If this effect is to be utilized, a W content of at least 0.5 mass%, in particular at least 0.6 mass%, can be provided in the steel according to the invention. The beneficial effects of the presence of W can be utilized particularly effectively at W contents of up to 5.5 mass%, in particular up to 5.0 mass%.

[0038] A further challenge mastered by the invention was to adjust the alloy of the steel according to the invention such that the coefficient of thermal expansion (CTE) is reduced from room temperature ("RT") to 400 °C to a level that ensures the permanent, secure adhesion of a ceramic veneer applied to the steel. Due in particular to their good solubility in Fe, the elements Cr, Mo, and W are suitable for reducing the coefficient of thermal expansion (CTE). However, increasing the contents of Cr, Mo, and W alone for this purpose would have been accompanied by an increased ferrite-stabilizing effect. This effect was counteracted by a simultaneous increase in the contents of the elements C, N, and Mn.As a result, it has been possible to set the coefficient of thermal expansion WAK of a material according to the invention to values ​​which are at most 24 x 10 -6< / K, whereby the coefficient of thermal expansion WAK in practice is typically in the range from 15 x 10 -6< / K to 22 x 10 -6< / K.

[0039] Niobium ("Nb") and / or gallium ("Ga") and / or tantalum ("Ta") in contents of up to 6 mass% each can also be added to the steel to reduce the coefficient of thermal expansion, optionally alternatively to or in combination with the Mo and / or W contents provided for this purpose. This effect can be safely utilized with Nb contents of at least 0.5 mass% and / or Ga contents of at least 0.5 mass% and / or Ta contents of at least 0.5 mass%. Nb, Ta, and Ga can each be added separately or in combination. However, with sufficient Mo contents, the addition of Nb, Ta, and / or Ga can be omitted entirely. Likewise, each of the elements Nb, Ta, and Ga can also be added alone to achieve the improvements made possible by the presence of these elements in the steel according to the invention.The positive effects of the optional presence of Nb, Ta and / or Ga can be used particularly safely with a content of at least 0.6 mass% of Nb, Ta and / or Ga, whereby contents of at least 0.7 mass% of at least one of the elements Nb, Ta, Ga can be particularly useful for this purpose.

[0040] Optional contents of up to 5.0 mass%, in particular up to 1.0 mass%, of Nb, Ta and / or Ga have proven to be particularly practical.

[0041] In the case that more than one element from the group "Nb, Mo, W, Ga, Ta" is present, the effect of these elements can be used with the advantages explained above, in particular if the contents of these elements amount to a total of 0.5 - 10.0 mass%, in particular 0.5 - 6 mass% or 0.5 - 1 mass%.

[0042] The microstructure of a steel according to the invention is completely austenitic in the technical sense due to the steel alloy specified in the invention. Steel according to the invention is therefore also reliably non-magnetic. Accordingly, it is characterized by a relative permeability number µR, determined using a permeability meter based on ASTM A342 and EN 60404-15, for which the following applies: 1.0 ≤ µR ≤ 1.2.

[0043] Steels according to the invention can be made available for processing in dental laboratories or for larger-scale industrial processing as semi-finished products in the form of cast ingots or nuggets, which are remelted during further processing and cast into implants, prostheses, or medical instruments, etc., intended for use in or on the human or animal body. Their particularly good castability makes steels according to the invention particularly suitable for this production method.

[0044] The steels according to the invention can also be processed into steel powders in a conventional manner, which can then be formed into implants, prostheses, or instruments used in the treatment and examination of humans or animals using an additive process, also known as metallic "3D printing." Potential processes for this purpose are described in the VDI Status Report "Additive Manufacturing Processes," September 2014, published by the Association of German Engineers, Department of Production Engineering and Manufacturing Processes, www.vdi.de / statusadditiv, and in VDI Guidelines 3404 and 3405.

[0045] Furthermore, steel according to the invention can be provided in the form of so-called milling discs, from which implants, prostheses or medical instruments and the like are subsequently produced by machining processes, in particular milling, for example by applying known CAD / CAM processes.

[0046] Regardless of the respective processing method, steels according to the invention are particularly suitable for the production of elements that serve as dental prostheses or are required as parts of dental prostheses.

[0047] In this case, semi-finished products, implants, prostheses and the like produced from steels according to the invention can in particular also be subjected to mechanical fine machining, which can of course follow the respective shaping processes explained above.

[0048] The invention is explained in more detail below with reference to a drawing illustrating an exemplary embodiment. Each drawing shows schematically: In a first series of tests, four steels M1_1 to M1_4 were melted, the compositions of which are listed in Table 1.

[0049] In a first series of tests, four steels M2_1 to M2_5 were melted, the compositions of which are given in Table 2.

[0050] All alloying element contents not listed in Tables 1 and 2 were within the impurity range and totaled less than 0.5 mass%. The contents of alloying elements not listed in Tables 1 and 2 were thus so low that they had no influence on the properties of steels M1_1 to M1_4 and M2_1 to M2_5.

[0051] The melts of steels M1_1 to M1_4 and M2_1 to M2_5 were each cast into ingots, which formed the starting material for further processing. Each of the steel melts solidified completely austenitically in the technical sense.

[0052] To evaluate the magnetic properties of the obtained ingots, the relative permeability µR of the ingots made from melts M1_1 to M1_4 was determined. The determined permeability µR values ​​are also listed in Table 1. It was found that all ingots made from steels M1_1 to M1_4 were reliably non-magnetic (µR = 1).

[0053] The ingots made of steels M2_1 to M2_5 also proved to be completely non-magnetic.

[0054] The coefficients of thermal expansion (CTE) have been determined for steels M2_1 to M2_5. The CTE values ​​for ingots made of steels M2_1 to M2_5 are also listed in Table 2.

[0055] The strength of the ingots was also tested in accordance with DIN EN ISO 22674:2016-09. In this case, the ingots made of steel grades M1_1 to M1_4 and M2_1 to M2_5 reliably met the requirements of Class 3.

[0056] In the dental laboratory, the ingots, each consisting of steel grades M1_1 to M1_4 and M2_1 to M2_5, were remelted at temperatures between 1270 and 1350 °C and cast into molds to form implants. Each of the steel grades M1_1 to M1_4 and M2_1 to M2_5 exhibited excellent casting behavior. The casting tests resulted in complete mold filling, even with complex geometries.

[0057] The implants obtained from the casting tests were then provided with a ceramic veneer. The veneering ceramic offered by Wegold Edelmetalle GmbH, 90350 Wendelstein, Germany, under the name "classica• Opaquer Paste • D2 • 6g" was used. This veneering ceramic is based on a leucite glass ceramic (see the "Classica Processing Instructions" published by the manufacturer, printing note QMF 4.5-1277, Rev. b dated December 12, 2019, which is available at the URL https: / / www.wegold.de / ?option= com edocman&task=document.viewdoc&id=738 (Date discovered: December 8, 2020) is available for download).

[0058] The veneering of the implants was easy and reliably reproduced for each of the implants made from steel grades M1_1 to M1_4 and M2_1 to M2_5. No cracks or similar defects occurred, even under load. Table 1 Steel C+N C N Si Mn Cr Mon Ni µ PREN [Mass-%]*) M1_1 1,0 0,4 0,6 <0,1 21 18,0 2,0 <0,1 1,0009 34,2 M1_2 1,35 0,34 1,01 <0,2 18,1 23,3 2,0 <0,1 1,0016 46,6 M1_3 1,32 0,34 0,97 0,2 18,1 24,3 1,95 <0,1 1,0029 46,3 M1_4**) 1,1 0,1 1,0 <0,2 23,5 20,5 1,0 <0,1 1,0009 39,8 *) Remainder iron and unavoidable impurities **) not according to the invention Table 2 Steel C+N C N Si Mn Cr Mon Ni W WAK [Mass-%] *) [10 -6< / K] M2_1 1,0 0,4 0,6 <0,1 21 18,0 2,0 <0,1 - M2_2 1,0 0,4 0,6 <0,1 21 18,0 2,0 <0,1 1,0 17,2 M2_3 1,0 0,4 0,6 <0,1 21 18,0 2,0 <0,1 2,0 16,8 M2_4 1,0 0,4 0,6 <0,1 21 18,0 2,0 <0,1 3,0 16,5 M2_5 1,0 0,4 0,6 <0,1 21 18,0 2,0 <0,1 4,0 16,3 *) Rest iron and unavoidable impurities

Claims

1. Steel having an austenitic structure, an offset yield strength Rp0.2 of at least 230 MPa, a percent elongation A of more than 5%, and a modulus of elasticity of at least 150 GPa, consisting of, in % by mass, C:> 0.2 - 0.8%,N:0.3 - 1.3%,Si:< 2.0%,Mn:14 - 30%,Cr:17 - 27%,Mo:0 - 6%,W:0 - 6%,Nb:0 - 6%,Ga:0 - 6%,Ta:0 - 6%, the remainder being iron and unavoidable impurities, wherein the impurity content complies with the requirements for dental materials in DIN EN ISO 22674:2016-09 and the impurity content is limited to less than 0.5% and the impurities include less than 0.1% Ni and less than 0.1% Co.

2. Steel according to claim 1, characterized in that the content of at least one element of the group "Nb, Mo, W, Ga, Ta" is at least 0.5% by mass.

3. Steel according to any one of the preceding claims, characterized in that the sum of the contents of each optionally present element from the group "Nb, Mo, W, Ga, Ta" is not more than 10% by mass.

4. Steel according to any one of the preceding claims, characterized in that the following applies to the sum of its contents %C of C and %N of N: 0.30 % ≤ % C + % N ≤ 2.0 %5. Steel according to any one of the preceding claims, characterized in that its Mn content is at least 16% by mass.

6. Steel according to any one of the preceding claims, characterized in that its Mn content is not more than 28% by mass.

7. Steel according to any one of the preceding claims, characterized in that its Cr content is at least 17% by mass.

8. Steel according to any one of the preceding claims, characterized in that its Cr content is not more than 27% by mass.

9. Steel according to any one of the preceding claims, characterized in that for its PREN value, which is calculated according to the following equation PREN = % Cr + 3.3 × % Mo + 20 × % N from its Cr content %Cr, its Mo content %Mo and its N content %N, in each case used in % by mass, the following applies: 25 % ≤ PREN ≤ 75 %10. Steel according to any one of the preceding claims, characterized in that the following applies to its coefficient of thermal expansion CTE in the temperature range from room temperature to 400°C: CTE ≤ 25 × 10 − 6 / K11. Steel according to any one of the preceding claims, characterized in that the following applies to its permeability number µR: 1.0 ≤ μR ≤ 1.2 , wherein the permeability number is determined according to ASTM A342 and EN 60404-15.

12. Use of a steel alloyed according to any one of claims 1 - 11 for the production of components for use in the oral cavity of humans or animals.