Method for additively manufacturing a component by means of arc build-up welding

Abstract

The invention relates to a method for additively manufacturing a component, in particular a chromium-nickel steel component, in which method a plurality of material layers are deposited on top of one another by means of arc build-up welding by melting a welding filler material, in particular a wire-shaped welding filler material, under shielding gas. The aim of the invention is to improve the practicability of manufacture and the usability of the component. This aim is achieved in that the material layers are formed by an austenite-containing steel, wherein the shielding gas is formed predominantly by argon and, with a volume fraction of 1-15%, preferably of 3-10%, nitrogen in order to form a nitrogen fraction of the steel alloy using the nitrogen of the shielding gas.

Description

[0001] Method for the additive manufacturing of a component using arc cladding welding

[0002] The invention relates to a method for the additive manufacturing of a component, in particular a chromium-nickel steel component, wherein several layers of material are applied one on top of the other by arc welding with melts of a welding filler, in particular a wire-shaped one, under a protective gas.

[0003] The invention further relates to a component, in particular a semi-finished product, which is formed with several layers of material applied one above the other, wherein the material layers are formed with an austenite-containing steel.

[0004] Additive manufacturing of steel components using arc welding, also known as wire-arc additive manufacturing (WAAM), typically enables the production of steel components with complex geometries and high material efficiency. To form the steel component, a filler wire is usually melted successively using an electric arc, and the molten material from the filler wire is deposited in layers of material. These material layers are typically made of steel, the...

[0005] The alloying element composition corresponds to the alloying element composition of the welding filler wire. This is usually carried out under a protective gas, typically argon, for oxidation reduction.

[0006] Austenitic chromium-nickel steel typically exhibits good ductility, weldability, and high corrosion resistance, which is why structural components made from these alloys are used in various industrial applications. A disadvantage of these alloys is often a low yield strength and low abrasion resistance. The strength of this alloy can frequently be improved by interstitial alloying with nitrogen.

[0007] The use of chromium-nickel steel for the additive manufacturing of a chromium-nickel steel component by arc cladding, where the welding filler wire has an alloying element composition corresponding to that of the chromium-nickel steel, including a nitrogen component for interstitial alloying, often proves difficult due to degassing effects, and in particular the associated porosities and / or nitride formation. Chromium, which typically stabilizes ferrite, generally increases nitrogen solubility. Nickel, which typically stabilizes austenite, generally reduces nitrogen solubility in the chromium-nickel steel or in the material layers formed with the chromium-nickel steel.

[0008] This is where the invention comes in. The object of the invention is to provide a method of the type mentioned above which exhibits a high degree of practicality for the additive manufacturing of the component using arc cladding, in order to produce the component with high serviceability, in particular high strength.

[0009] Furthermore, it is an objective of the invention to provide a component, in particular a semi-finished product, of the type mentioned above, formed with several superimposed layers, which has a high service life, in particular high strength.

[0010] The object of the invention is achieved by forming the material layers with an austenite-containing steel in a process of the type mentioned at the outset, wherein the protective gas (in vol%) consists predominantly of argon and nitrogen with a volume fraction of 1% to 15%, preferably 3% to 10%, in order to form a nitrogen fraction of the steel with the nitrogen of the protective gas.

[0011] In this way, nitrogen from the protective gas can be practically introduced into the steel of the material layers. The nitrogen from the protective gas can contribute to the formation of a nitrogen content in the steel, particularly in its alloying element composition. Generally, there is essentially a linear relationship between the nitrogen content of the protective gas and the nitrogen content of the steel. Steel typically has a solubility limit for nitrogen. This linear relationship can hold true within a range of applications limited by the nitrogen solubility limit of the steel. Once the nitrogen solubility limit is reached, a further increase in the nitrogen content of the protective gas usually does not lead to a further increase in the nitrogen content of the steel.In particular, a further increase can lead to the formation of porosity and / or nitrides in the steel, which is generally undesirable. It is therefore advantageous if the nitrogen content of the shielding gas is adjusted so that the solubility limit for nitrogen in the steel is not exceeded. The shielding gas typically has a nitrogen content (by volume) of 1% to 15%, preferably 3% to 10%, and most preferably 4% to 8%. Specifically, the welding filler metal can also contain nitrogen, particularly in addition to the shielding gas. The nitrogen content of the steel can then be formed by, or be formed from, nitrogen in the welding filler metal and nitrogen in the shielding gas. Increasing the nitrogen content of the shielding gas can increase the nitrogen content of the steel.In particular, it is possible to adjust, and especially increase, the strength of the component in the protective gas, depending on the nitrogen content and especially the additional helium content.

[0012] Typically, the welding filler material is successively melted using an electric arc to form the component. The material layers, or the steel itself, are usually formed with, and especially from, molten material of the welding filler material and, in particular, nitrogen from the shielding gas. This can be implemented as described above. The component is usually formed by depositing the material layers one on top of the other. Generally, several material layers are arranged on top of each other, usually in a normal direction. The material layers are typically made of austenitic steel. Usually, each material layer is deposited onto a preceding or underlying material layer, and the layers are welded together. This arc welding process can be referred to as Wire Arc Additive Manufacturing, often abbreviated as WAAM.The welding filler material is usually a welding filler wire.

[0013] It is advantageous if the steel is interstitially alloyed with the nitrogen from the protective gas. This generally improves the steel's strength, particularly its yield strength. The nitrogen can stabilize the steel's austenite. Interstitial alloying is typically achieved by distributing the nitrogen interstitially within the steel. It is beneficial if the steel, and especially its alloying element composition, contains, in addition to iron as the largest alloying elements (by mass %), chromium, nickel, and, in particular, molybdenum. Experience has shown that this results in high strength, as described in this document, which can be adjusted via the nitrogen content. Specifically, the steel can contain, in addition to iron (by mass %)...The steel may contain chromium as the largest alloying element after iron, followed by nickel as the second largest. Molybdenum may also be present as the third largest alloying element (in mass percent).

[0014] Experimental investigations have shown that, as a rule, the alloying proportions of chromium, nickel, and molybdenum in the steel of the material layers are essentially independent of the gas composition, particularly the nitrogen content, of the shielding gas. A chromium, nickel, and / or molybdenum content in the welding filler material typically corresponds to a corresponding content in the steel. However, the manganese content of the steel has proven problematic. It has been shown that, as a rule, the manganese content of the steel is lower relative to the manganese content of the welding filler material the higher the nitrogen content and, if applicable, the helium content (described below) of the shielding gas. This can be explained by an increase in the thermal conductivity of the shielding gas and the evaporation of manganese, particularly during the melting of the welding filler material.This problem is generally exacerbated by the fact that the proportions of nitrogen and / or helium in the protective gas, compared to a protective gas formed from argon, increase the thermal conductivity of the protective gas, thereby further intensifying manganese evaporation processes. A reduction in the manganese content in the steel is also generally associated with a reduced, especially maximum, solubility of nitrogen in the steel. At a high...

[0015] The manganese content of the steel or the welding filler metal has been shown to increase the formation of undesirable porosity, which can be explained by degassing effects, and / or the formation of undesirable nitrides. The aforementioned problems can occur particularly when the steel, in addition to iron, contains chromium and nickel as its largest alloying elements (by mass percent), and especially molybdenum, specifically as described in this document. It is advantageous if the steel has a manganese content (by mass percent) of less than 2%. This allows the benefits of manganese, such as stabilizing the austenite content in the steel and promoting high nitrogen solubility, to be utilized while simultaneously minimizing the disadvantages of a high manganese content.In particular, this approach achieves a favorable balance between the advantages and disadvantages of the manganese content with regard to practical application. Typically, the manganese content (in wt%) is between 0.1% and 2%, particularly between 0.5% and 1.8%, and preferably between 1% and 1.5%. Specifically, it is advantageous if the steel, in addition to iron, contains chromium and nickel as its largest alloying elements (in wt%), and especially a molybdenum content, specifically as described in this document, wherein the manganese content of the steel is as described above.

[0016] It is advantageous if the shielding gas contains 1% to 15%, preferably 3% to 10%, and particularly 4% to 6% helium by volume. This allows for a refinement of the steel's microstructure. In particular, it further increases the steel's strength, especially its yield strength. This can be explained by the higher thermal conductivity of helium, resulting in an improved arc penetration profile. Argon and helium typically do not require a change in dissociation energy, especially since they exist in atomic form in the shielding gas, but they exhibit different ionization energies and thermal conductivities. The helium in the shielding gas usually leads to a reduced current density in the arc. Specifically, the shielding gas can contain, in addition to argon, a volume fraction of 3% to 10% nitrogen and a volume fraction of 3% to 10% helium.

[0017] It has proven effective when the nitrogen content of the steel is predominantly, and especially primarily, derived from nitrogen in the shielding gas. This allows the advantages of introducing nitrogen into the steel via the shielding gas to be efficiently utilized, particularly during interstitial alloying of the steel. For practical application, it is recommended that the welding filler material have a nitrogen content (in mass %) of less than 0.070%, particularly less than 0.050%, and preferably less than 0.020%. It is standard practice in the industry to determine or specify the microstructure of a steel using a so-called Schaeffler diagram. For this purpose, a chromium equivalent, denoted as Cr, can be calculated from the mass fractions of the alloying elements in the steel that have a ferrite-stabilizing effect. eq , calculated and from the mass fractions of the steel which have an austenite-stabilizing effect, a nickel equivalent, designated as Ni eq, can be calculated. The following usually applies (in mass %):

[0018] Cr eq = Cr + Mo + 0.7 Nb and Ni eq = Ni + 35 C + 20 N + 0.25 Cu. An abscissa of the Schaeffler diagram usually represents the chromium equivalent and an ordinate the nickel equivalent, with the Schaeffler diagram indicating different microstructure regions for the steel. The calculated chromium equivalent and calculated nickel equivalent of the steel usually denote a point in the Schaeffler diagram. In particular, the Schaeffler diagram indicates regions for austenitic primary solidification, austenitic-ferritic primary solidification, ferritic-austenitic primary solidification, and ferritic primary solidification of the steel. One type of primary solidification of the steel can usually be indicated by a ratio of the chromium equivalent to the nickel equivalent, — — . Typically,

[0019] Nieq defines a ratio of chromium equivalent to nickel equivalent greater than 1.95 as entirely ferritic primary solidification, between 1.95 and 1.48 as ferritic-austenitic primary solidification, between 1.48 and 1.25 as austenitic-ferritic primary solidification, and less than 1.25 as entirely austenitic primary solidification.

[0020] By varying the nitrogen content in the protective gas, the nickel equivalent or the ratio of the chromium equivalent to the nickel equivalent of the steel can be changed. Increasing the nitrogen content in the protective gas typically increases the nickel equivalent or decreases the ratio of the chromium equivalent to the nickel equivalent. This is advantageous if the steel is formed with an austenitic-ferritic or austenitic primary solidification. The ratio of the chromium equivalent (Cr) eq ) and the nickel equivalent (Ni eqThe ρ of the steel is typically less than 1.48. It is preferred that the steel has an austenitic-ferritic primary solidification, in particular with a ratio of one chromium equivalent (Cr) eq ) and a nickel equivalent (Ni eqThe primary solidification of the steel is between 1.25 and 1.48. The chromium and nickel equivalents of the steel can be converted as described in this document and / or, using a Schaeffler diagram, particularly as described in this document, describe a microstructure, specifically a primary solidification, of the steel. It is advantageous if the nitrogen content is chosen such that the steel is formed with such a primary solidification. In particular, a primary solidification that would be ferritic under a protective gas formed from argon can be changed to an austenitic primary solidification of the steel under a protective gas described in this document. In this way, a primary solidification advantageous for high steel strength can be achieved.

[0021] It is advantageous if the steel has an austenite phase fraction of more than 95.0%, particularly more than 99.0%, preferably more than 99.3%, especially more preferably more than 99.5%, and most specifically more preferably more than 99.9%. It can be practical for the steel to be composed entirely of austenite. This allows the material layers to be robust and exhibit high strength.

[0022] High strength of the material layers can be achieved if the steel microstructure consists predominantly of γ-austenite dendrites and β-ferrite arranged in interdendritic zones, or essentially of γ-austenite dendrites, with the microstructure optionally including an intermetallic γ-phase. The formation of γ-austenite dendrites can be varied by fine-tuning the nitrogen content in the protective gas. It is advantageous to select the nitrogen content such that the steel is formed with this microstructure. γ-austenite dendrites can be referred to as gamma-austenite dendrites. β-ferrite can be referred to as delta-ferrite. The γ-phase can be referred to as a sigma-phase. The interdendritic zones typically refer to the γ-austenite dendrites.

[0023] For particularly high robustness, it is advantageous if o-ferrite is present in the microstructure of the steel in the form of platelets oriented with a preferred direction, where preferably the preferred direction is substantially orthogonal to a stacking direction of the material layers. This applies particularly in an electron micrograph, especially a BSE electron micrograph, of a cross-section of the respective material layer. In particular, a predominant majority of the platelets, preferably substantially all of the platelets, can be oriented in this way. The preferred direction is usually an ND direction of the deposition of the material layers by arc welding. This can be achieved by varying the nitrogen content, especially if the steel, besides iron, has chromium and nickel as its largest alloying elements (by mass%), and the manganese content of the steel (by mass%) is less than 2%.The stacking direction of material layers is typically the direction in which the material layers are arranged or will be arranged on top of each other. The stacking direction is usually the ND direction. In industry practice, ND stands for Normal Direction, TD for Transverse Direction, and WD for Welding Direction.

[0024] It has proven effective to apply successive material layers continuously, particularly without waiting for a predetermined interpass temperature to be reached. Typically, the application of each subsequent material layer onto a preceding one is carried out only after the preceding layer reaches its interpass temperature. However, it has been shown that the implementation described in this document can be carried out continuously, especially without waiting for the interpass temperature to be reached. This allows for highly efficient component production. The interpass temperature can be characterized by a minimum and a maximum temperature. These temperatures usually refer to the temperature of the respective preceding material layer.

[0025] It is particularly advantageous if the steel contains or consists of (in mass-%) iron:

[0026] Cr from 16.5% to 18.5%, in particular from 17.5% to 18.5%, Ni from 10.0% to 13.0%, in particular from 11.5% to 12.5%, Mo from 2.0% to 3.0%, in particular from 2.3% to 2.7%, N up to 0.21%, in particular from 0.08% to 0.21%, preferably from 0.10% to 0.20%, optionally Mn less than 2%, in particular between 0.1% and 2%, preferably between 0.5% and 1.8%, in particular preferably between 1% and 1.5%, optionally C up to 0.03%, in particular from 0.005% to 0.02%, preferably from 0.01% to 0.02%, optionally Si up to 1%, in particular from 0.1% to 0.6%, preferably from 0.2% to 0.5%, optionally P up to 0.05%, optionally S up to 0.02%. The component can then be produced particularly practically using the additive manufacturing process and exhibits high usability, especially the steel exhibits high strength.In particular, it has been shown that with such an alloy composition of steel, a particularly pronounced increase in strength, especially in yield strength, of the steel or the material layers can be achieved, and in particular, adjusted, through the interstitial alloying of nitrogen. Specifically, the microstructure of the steel described in this document can be implemented with high stability. The steel typically contains iron as a residue. It may usually contain manufacturing-related impurities and trace elements (in wt%), particularly of less than 0.1%, preferably less than 0.01%.

[0027] The term "steel" typically refers to the steel or steel alloy of the material layers in a solid state, particularly at room temperature. The alloying element composition or proportions of the steel are usually expressed in mass percent (wt%). The gas composition or proportions of the protective gas, particularly the argon, nitrogen, and / or helium content, are usually expressed in volume percent (vt%). The material layers may be composed of a material. The material is typically composed of, and especially made of, steel. The microstructure of the steel may be predominantly, preferably substantially, implemented according to a microstructure described in this document.

[0028] The further objective of the invention is achieved by providing that, in a component, particularly a semi-finished product, of the type mentioned above, the steel is interstitially alloyed with nitrogen, wherein the microstructure of the steel is predominantly formed with γ-austenite dendrites and β-ferrite arranged in interdendritic zones, or essentially with γ-austenite dendrites, and, in particular, optionally, the microstructure includes an intermetallic β-phase. The component can be manufactured using additive manufacturing. The component, and in particular the steel, can be designed according to the features and effects described in this document, specifically above, within the context of the additive manufacturing process. The same applies to the process with regard to the component, and in particular its steel.

[0029] It is advantageous if, in addition to iron, the steel contains chromium and nickel as its largest alloying elements (by mass%), with a manganese content of less than 2% (by mass%). Specifically, the steel can be produced as described above in this document, and in particular, it can have a corresponding alloying element composition.

[0030] It is advantageous if the ferrite in the steel microstructure is present in the form of platelets oriented with a preferred direction, the preferred direction being substantially orthogonal to a stacking direction of the material layers. This applies particularly to an electron micrograph, especially a BSE electron micrograph, of a cross-section of the respective material layer. The preferred direction is typically a standard arc direction used for applying the material layers by arc cladding.

[0031] Further features, advantages, and effects of the invention will become apparent from the following description of an exemplary embodiment. The drawings referred to therein show:

[0032] Fig. 1 shows a graph which shows a nitrogen content of a chromium-nickel steel of a component additively manufactured by arc cladding welding as a function of a nitrogen content in the shielding gas;

[0033] Fig. 2 shows an exemplary image of a component designed as a hollow profile made of chromium-nickel steel, which was manufactured by additive manufacturing using arc welding under a protective gas containing nitrogen;

[0034] Fig. 3 shows a table which, starting from the same welding filler, shows a chemical composition of chromium-nickel steels of additively manufactured components depending on a gas composition of the shielding gas;

[0035] Fig. 4 a Schaeffler diagram showing primary solidification zones and Fig. 5 an enlarged view of a section of the Schaeffler diagram showing the positions of the chromium-nickel steels formed in the additively manufactured components, corresponding to different nitrogen fractions of the protective gas; Fig. 6 a diagram showing a 0.2% yield strength of the chromium-nickel steels of Fig. 3;

[0036] Fig. 7 shows a diagram of the tensile strength of the chromium-nickel steels of Fig. 3; Fig. 8 shows microscopic images of cross-sections of the chromium-nickel steels corresponding to different protective gas compositions;

[0037] Figs. 9 to 11 are electron microscopic BSE images of cross-sections of chromium-nickel steels corresponding to different protective gas compositions.

[0038] In a process for the additive manufacturing of a component, wherein several material layers are deposited one on top of the other by arc welding using melts of a, in particular, wire-shaped welding filler material under a shielding gas, and wherein the material layers are made of austenitic steel, the shielding gas (in vol.%) can advantageously consist of, in particular, predominantly argon and also nitrogen, and especially helium. The nitrogen content of the shielding gas can be adjusted (in vol.%) from 1% to 15%. In addition to argon and nitrogen, the shielding gas can contain 1% to 15% helium (in vol.%). In this way, a nitrogen content of the steel can be formed with the nitrogen from the shielding gas, with the nitrogen typically being interstitially incorporated into the steel. The steel can advantageously have (in wt.%): Cr from 16.5% to 18.5%, Ni from 10.0% to 13.0%, Mo from 2.0% to 3.0%.

[0039] The steel contains nitrogen up to 0.21%, particularly from 0.08% to 0.21%, optionally manganese less than 2%, preferably less than 1.6%, optionally carbon up to 0.03%, optionally silicon up to 1%, optionally phosphorus up to 0.05%, optionally sulfur up to 0.02%, balance Fe, as well as manufacturing-related impurities and accompanying elements of less than 0.1%, preferably less than 0.01%. Figure 1 shows a graph illustrating the nitrogen content (in mass %) of the steel as a function of the nitrogen content (in volume %) of the protective gas. The graph shows a linear relationship between the nitrogen content of the protective gas and the nitrogen content of the steel in the material layers. The graph shows linear curves, 1, 2, 3 for a protective gas of argon and nitrogen, with reference numeral 1, as well as for an additional admixture (in vol.%) of 5% helium with reference numeral 2 and an additional admixture (in vol.%).-%) of 10% helium with reference numeral 3, shown, wherein the linear curves for shielding gas formed with admixtures of helium lie slightly above the linear curve for shielding gas formed from argon and nitrogen. Fig. 2 shows an exemplary image of a component designed as a hollow profile, which is additively manufactured using the process, wherein the material layers are formed with a steel according to the above composition.

[0040] The fabrication of such a component is illustrated below by way of example, where the material composition of the wire-shaped welding filler (in mass %) is: C: 0.0099%, N: 0.042%, Si: 0.46%, Mn: 1.58%, Cr: 18.32%, Mo: 2.57%, Ni: 11.94%, balance iron. Fig. 3 shows a table in which the composition of the welding filler and the chemical compositions of steels resulting from different shielding gas compositions are given, based on the material layers of components formed under the shielding gas during the additive process. Fig. 3 shows steels formed when using a shielding gas consisting of 5% nitrogen and balance argon, 10% nitrogen and balance argon, and with the additional addition of either 5% or 10% helium. For comparison, Fig. 3 also shows a steel formed using a protective gas of 100% argon.

[0041] By increasing the nitrogen content of the protective gas, the nitrogen content of the steel, which is typically present mainly interstitially within the steel, can be increased directly proportionally from approximately 0.07% by mass to approximately 0.14% and further to approximately 0.19%. Increasing the nitrogen content in the protective gas (by volume) to 15% by volume allows the nitrogen content (by mass) of the steel to be increased to approximately 0.25% by mass. This represents the solubility limit of nitrogen in steel. Further increases in the nitrogen content beyond this solubility limit can lead to porosity and nitride formation in the steel. No effect of helium admixture on the chemical composition of the steel has been observed. The protective gas has no significant effect on the proportion of the main alloying elements: chromium, nickel, and molybdenum in the steel. The table in Fig. 3 lists the chromium equivalent, denoted as Cr, for each element. eq, a nickel equivalent, designated as Ni eq as well as

[0042] Cr is a ratio of the chromium equivalent and nickel equivalent, calculated from the Niq of the respective steel composition. The chromium equivalent can be calculated from the mass fractions of the steel's alloying elements that stabilize ferrite. The nickel equivalent can be calculated from the mass fractions of the steel that stabilize austenite. The respective calculated chromium and nickel equivalents can be used to assign a point in a Schaeffler diagram, where the point may lie in one of several regions indicated by the Schaeffler diagram, each representing a type of primary solidification of the steel.

[0043] Cr is expressed as a ratio of chromium equivalent to nickel equivalent, Nieq. In the table in Fig. 3, the chromium equivalent is essentially the same for the different steels. Due to an austenite-stabilizing effect of nitrogen in the steel, the nickel equivalent (in mass %) increases from approximately 13.9% to approximately 15.3% and further to approximately 16.5% with increasing nitrogen content. Correspondingly, the ratio of chromium equivalent to nickel also changes.

[0044] nickel equivalent, from approximately 1.50 to 1.36 and further to 1.26 with increasing

[0045] Nitrogen content.

[0046] Fig. 4 shows a standard Schaeffler diagram with areas for different types of steel microstructure. Fig. 5 shows an enlarged section of the Schaeffler diagram. The Schaeffler diagram has separate areas for austenitic primary solidification (A), austenitic-ferritic primary solidification (AF), ferritic-austenitic primary solidification (FA), and ferritic primary solidification (F). In Fig. 5, the corresponding positions of the steels corresponding to a shielding gas of argon (P1), a shielding gas of 95% argon and 5% nitrogen (P2), and a shielding gas of 90% argon and 10% nitrogen (P3) are shown in the section of the Schaeffler diagram, as well as a position PO indicating the material composition of the welding filler metal. The material composition of the welding filler results in a ferritic-austenitic primary solidification (FA) and a ferrite number of approximately 8.By changing the nitrogen content in the protective gas, or correspondingly in the steel layers formed during the process, the type of primary crystallization of the steel can be altered. An increase in the nitrogen content increases the nickel equivalent and decreases the nitrogen content.

[0047] Cr corresponds to the ratio of chromium equivalent to nickel equivalent, — — , with Nleq to which a type of primary solidification can be specified. For steels formed under a protective gas consisting of argon, a ferritic-austenitic primary solidification results, exhibiting the formation of β-ferrite dendrites and γ-austenite arranged between the β-ferrite dendrites. For steels formed under a protective gas consisting of nitrogen, an austenitic-ferritic primary solidification results, exhibiting the formation of γ-austenite dendrites and β-ferrite arranged between the γ-austenite dendrites, or, for high nitrogen contents, an essentially entirely γ-austenite microstructure of the steels.

[0048] Fig. 6 shows a diagram representation of a 0.2% proof stress R p Figure 0.2 of the chromium-nickel steels of Fig. 3 and Fig. 7 shows a diagram representation of a tensile strength R. mThe steels shown in Fig. 3. The interstitial nitrogen content in the steel increases its strength and enables a high yield strength. Helium content in the protective gas leads to a refinement of the steel's microstructure and supports the development of high strength.

[0049] Fig. 8 shows microscopic images of cross-sections in an ND-TD plane of a layered material, corresponding to different shielding gas compositions of steels. In image a), the shielding gas is entirely argon. The shielding gas (in vol%) in image b) consists of 5% nitrogen, in image c) of 5% nitrogen and 5% helium, in image d) of 5% nitrogen and 10% helium, in image e) of 10% helium, in image f) of 10% nitrogen and 5% helium, and in image g) of 10% nitrogen and 10% helium. In each case, the remainder of the shielding gas is argon. The microstructure of the steel changes with the change in shielding gas composition. Images taken with a 5% nitrogen content of the shielding gas show a cellular to columnar-dendritic structure. Images taken with a 10% nitrogen content of the protective gas show a fine columnar structure.Images taken with additional helium content in the protective gas show a refinement of the respective microstructure. Figures 9 to 11 show electron micrographs in BSE mode of cross-sections in the ND-TD plane of the material layer deposition, corresponding to different protective gas compositions of the steels. The image in Figure 9 shows a steel with a protective gas formed from argon. The image shows a vermicular β-ferrite network embedded in a γ-austenite matrix. An intermetallic β-phase is visible at interfaces. The image in Figure 10 shows a steel with a protective gas formed with 5% nitrogen and the remainder argon. Due to a change towards an austenitic-ferritic primary solidification, the image shows columnar γ-austenite dendrites, with β-ferrite present between them in the form of platelets.The platelets are no longer randomly oriented, but exhibit a preferred orientation in an ND direction of the applied material layers. The image in Fig. 11 shows a steel coated with a protective gas consisting of 10% nitrogen and the remainder argon. The image shows an increasing dissolution of the o-ferrite and o-phases towards a dispersed distribution.

[0050] In the additive manufacturing process using arc welding, the microstructure and / or primary solidification of the steel can be modified or adjusted by mixing the shielding gas with nitrogen, and especially helium, in addition to argon, depending on the nitrogen and helium content. This allows for highly practical manufacturing of the component. The component can be manufactured with a customized microstructure and / or high strength, particularly yield strength, of the steel.

Claims

Patent claims 1. A method for the additive manufacturing of a component, in particular a chromium-nickel steel component, wherein several material layers are applied one above the other by arc welding with melts of a welding filler, in particular a wire-shaped, under a protective gas, characterized in that the material layers are formed with an austenitic steel, wherein the protective gas is formed with predominantly argon and with a volume fraction of 1% to 15%, preferably 3% to 10%, nitrogen, in order to form a nitrogen content of the steel with the nitrogen of the protective gas.

2. Method according to claim 1, characterized in that the steel is interstitially alloyed with the nitrogen of the protective gas.

3. Method according to claim 1 or 2, characterized in that the steel, in addition to iron, has a chromium content and a nickel content as the largest alloying elements (in mass %).

4. Method according to one of claims 1 to 3, characterized in that the steel has a manganese content (in mass %) of less than 2%.

5. Method according to one of claims 1 to 4, characterized in that the protective gas has a volume fraction of 1% to 15%, preferably 3% to 10%, of helium.

6. Method according to one of claims 1 to 5, characterized in that the welding additive has a nitrogen content (in mass %) of less than 0.070%, in particular less than 0.050%, preferably less than 0.020%.

7. Method according to any one of claims 1 to 6, characterized in that the steel has an austenitic-ferritic primary solidification or an austenitic primary solidification, in particular with a ratio of one chromium equivalent (Cr) eq ) and a nickel equivalent (Ni eq ) of the steel less than 1.48, is formed.

8. Method according to one of claims 1 to 7, characterized in that the steel has austenite with a phase fraction of more than 95.0%, in particular more than 99.0%.

9. Method according to one of claims 1 to 8, characterized in that a microstructure of the steel is formed predominantly with y-austenite dendrites and o-ferrite arranged in interdendritic zones, or substantially with y-austenite dendrites, wherein in particular the microstructure may optionally have an intermetallic o-phase.

10. Method according to one of claims 1 to 9, characterized in that the application of successive material layers is carried out continuously, in particular without waiting time to reach a predetermined interpass temperature.

11. Method according to any one of claims 1 to 10, characterized in that the steel comprises or consists of (in mass-%) in addition to iron: Cr from 16.5% to 18.5%, Ni from 10.0% to 13.0%, Mo from 2.0% to 3.0%, N up to 0.21%, in particular from 0.08% to 0.21%, optionally Mn less than 2%, preferably less than 1.6%, optionally C up to 0.03%, optionally Si up to 1%, optionally P up to 0.05%, optionally S up to 0.02%, as well as manufacturing-related impurities and accompanying elements.

12. Component, in particular semi-finished product, which is formed with several superimposed layers of material, in particular according to a method according to one of claims 1 to 11, wherein the layers of material are formed with an austenitic steel, characterized in that the steel is interstitially alloyed with nitrogen, wherein a microstructure of the steel predominantly consists of γ-austenite dendrites and β-ferrite arranged in interdendritic zones, or substantially formed with Y-austenite dendrites, with the steel optionally exhibiting an intermetallic o-phase.

13. Component according to claim 12, characterized in that the steel, in addition to iron, has chromium and nickel as the largest alloying elements (in mass %), wherein the manganese content of the steel (in mass %) is less than 2%.

14. Component according to one of claims 12 or 13, characterized in that o-ferrite is present in the microstructure of the steel in the form of platelets oriented with a preferred direction, wherein the preferred direction is preferably essentially orthogonal to a stacking direction of the material layers.

Images