DE102016215812A1 - Process for processing a case hardening steel to form a component - Google Patents

Abstract

The present invention relates to methods of processing a case hardening steel to form a component, comprising the steps of: a) providing a powder of a metallic material; and b) forming a component from the powder provided by an additive manufacturing process; wherein the metallic material comprises a case hardening steel, and wherein the method comprises the further step of: c) carrying out a low pressure carburizing with subsequent hardening of the molded component.

Description

The present invention relates to a method of processing a case hardening steel to form a component. The present invention relates in particular to a method for producing a component from a case hardening steel, in particular from a M50NiL steel, by means of additive manufacturing.

Tools or components with complex geometry and hard surface are currently being carried out by machining tool steels, case hardening or tempering steels, and optionally subsequent finishing. The cutting of such tools is usually very time-consuming and costly and also just in case of steels often not easily feasible.

It is also known to produce components by means of so-called additive or generative method. This is how the document describes DE 10 2014 214 957 A1 a method for producing a bearing ring, are introduced in the cooling channels in the immediate vicinity of the contact zone or the tread. To produce such a structure, according to this document, the bearing ring is produced by a generative manufacturing process. However, this document makes no statement about the specific type of hardening of the bearing ring or any after-treatment processes carried out after curing.

The solutions known from the prior art can offer even further potential for improvement.

It is the object of the present invention to at least partially overcome the disadvantages known from the prior art. It is in particular the object of the present invention to provide a solution by which even heavy-duty components can be manufactured from case-hardened steels in a simple manner.

The object is achieved by a method having the features of claim 1 and by a component having the features of claim 10. Preferred embodiments of the invention are described in the subclaims, in the description or the figures, wherein further in the subclaims or in The features described or shown in the description or the figures, individually or in any combination, may constitute an object of the invention, unless the context clearly indicates otherwise.

• a) Bereitstellen eines Pulvers aus einem metallischen Werkstoff; und
• b) Formen eines Bauteils mittels eines additiven Fertigungsverfahrens aus dem bereitgestellten Pulver;

wobei
der metallische Werkstoff einen Einsatzstahl umfasst, und wobei
das Verfahren den weiteren Verfahrensschritt aufweist:

• c) Durchführen eines Niederdruckaufkohlens mit anschließendem Härten des geformten Bauteils.

It is proposed a method for processing a case hardening steel to form a component, comprising the method steps:

• a) providing a powder of a metallic material; and
• b) forming a component by means of an additive manufacturing process from the powder provided;

in which
the metallic material comprises a case hardening steel, and wherein
the method comprises the further method step:

• c) carrying out a low-pressure carburizing with subsequent hardening of the molded component.

By the method described above, a highly stressed component made of a case-hardening steel can also be produced with complicated geometry in a simple manner.

In the context of the present invention, a case hardening steel can be understood in particular to mean a steel having a carbon content of ≥ 0.10% by weight to ≦ 0.20% by weight. In particular, a case steel can be defined according to DIN EN 10084 , Particularly advantageously, the case steel can be a M50NiL steel.

The method described above thus describes the processing of a case-hardened steel in order to produce a component from this.

For this purpose, according to method step a), a powder of the metallic material is provided, from which according to method step b) a component is formed by means of an additive manufacturing method.

The provided powder of the metallic material may have a particle size which is adapted to the component to be formed and the additive manufacturing process used. In principle, a finer particle size allows a higher resolution of the components to be produced.

With regard to the additive or generative production method, this can be understood in particular to mean a process in which a component is built up in layers on the basis of digital 3D design data by the depositing or building up of material. Examples of such processes include, for example, 3D printing, which is often also understood to mean laser sintering or laser melting. An additive manufacturing process differs significantly from conventional, erosive manufacturing methods. Instead of, for example, milling a workpiece out of a solid block, as known in abrasive processes, the components in additive manufacturing processes become layer by layer Layer composed of materials that are present as a starting material as a particular fine powder. Such methods find application in so-called rapid prototyping or in mass production.

Thus, the additive manufacturing process can be based in a conventional manner on in particular digital shape data, which define the mold to be produced and based on which, for example, a laser or electron beam source for layered melting of the powdery raw material can be controlled, so as to build the component in layers.

In most cases, a laser such as a CO ₂ laser, an Nd: YAG laser or a fiber laser or an electron beam source is used for processing, such as melting of the raw material, with a selection in particular on the powder used as a raw material to meet, such as in particular the melting point of the powder.

By using an additive or additive manufacturing process, components of any shape or geometry can be generated.

The metallic material used is a case hardening steel. Since a case steel often has a low hardness due to a comparatively low content of carbon, it should be hardened. A hardened steel should be enriched with carbon before the actual hardening in the edge area. Thus, according to method step c), the carrying out of a low-pressure carburizing with subsequent hardening of the molded component takes place. In this method step, the component produced is thus enriched only in the edge region with carbon and then cured. In detail, an enrichment with carbon in the above-described process is carried out by low-pressure carburizing. In particular, such a heat treatment process, combined with subsequent curing after additive manufacturing, can provide significant advantages over the prior art solutions in conjunction with the use of a case hardening steel.

For a heat treatment of the molded component by a low-pressure carburizing with subsequent hardening can allow an effective increase in hardness by a carbon enrichment, wherein the enrichment can be carried out in particular in a peripheral zone on the outer surface of the component. For example, a particularly effective increase in hardness can be made possible with a good hardening depth, for example at a depth of at least 1 mm from the surface. Up to a depth of 0.75 mm, a particularly high hardness can be achieved.

Basically, by the method described above components of high edge hardness, such as a Rockwell hardness of up to more than 58 HRC after EN ISO 6508-1 and moreover with a high core hardness of, for example, a Rockwell hardness of at least 40 HRC EN ISO 6508-1 also be produced in components with large cross sections.

This enables the production of components which have a particularly high mechanical stability, high hot hardness and wear resistance of the edge zone.

The method described above allows a process that is essentially free of postforming after curing, such as removing roughness or shape changes, such as smoothing, grinding, milling, etc., because of the method described above, and in particular by using a low-pressure carburizing and subsequent curing in a vacuum, the component can be present after curing in a particularly high dimensional accuracy and exact shape and size, so that post-treatment steps are not necessary. In other words, the shape and size of the additive-fabricated component is not changed by the low-pressure carburizing so that a post-treatment for restoring the manufactured shape and / or size is necessary. In particular, this can be a significant advantage over the solutions of the prior art are made possible, in which after curing often aftertreatment was mandatory.

Because with an enrichment of the edge zone with carbon by low pressure carburizing, there is no influence, such as roughening or edge oxidation of the surface or grain boundary attack and the dimensional stability of the components produced is also not or at least only to a tolerable extent.

Therefore, the above-described method surprisingly enables the disadvantages of the prior art to be overcome, at least in part, by a combination of processing a case hardening steel with an additive manufacturing process and heat treatment by low pressure carburizing with subsequent hardening, in particular vacuum hardening.

With respect to the heat treatment, it may be advantageous that the low-pressure carburizing process takes place at a temperature in a range of greater than or equal to 850 ° C to less than or equal to 1000 ° C, such as in an acetylene atmosphere as a carbonaceous atmosphere. The carbon-containing atmosphere can be present in a pressure of, for example, 2 to 25 millibars. The low-pressure carburizing can take place for an exemplary period of time of ≥ 10 h to ≦ 50 h.

With regard to the subsequent curing, a further heating, optionally for a number of case-hardened steels, then takes place at a temperature of ≥ 800 ° C. to ≦ 1150 ° C., with further heating for the preferred steel M50NiL, for example to a temperature of ≥ 1050 ° C. to ≤ 1150 ° C, may be advantageous. Subsequently, a curing process is carried out under reduced pressure, such as in a vacuum, followed by gas quenching, preferably with nitrogen or helium, at high pressure, such as up to about 15 bar. In detail, the carbon-enriched and heated component, in particular under reduced pressure in a vacuum, can be heated to the above-described temperature and then the pressure can be increased to an overpressure of, for example, ≥ 5 to ≦ 15 bar. In this case, protective gas, such as nitrogen or helium, can be used. Thus, curing preferably takes place under reduced pressure with subsequent high pressure gas quenching.

The Niederdruckaufkohlung together with the hardening can be carried out in an oven as a continuous operation with changing the temperature and the pressure with the respective gas.

It has surprisingly been found that low-pressure carburization with subsequent hardening, in particular using the aforementioned parameters, permits sufficient hardening of the case-hardening steel, in particular steel M50NiL steel, without necessitating a considerable modification of the geometry or the surface properties, in particular to be reworked.

As indicated above, it may be particularly preferred that the case steel comprises a M50NiL steel. For example, the case steel may consist of a M50NiL steel. In particular, such steels have preferred mechanical properties and may be suitable for many applications. Moreover, in particular, the processing of this steel by conventional component manufacturing processes can be problematic, so that in particular the specific combination of M50NiL case hardening steel with an additive manufacturing process and low pressure carburizing and curing can be advantageous.

Further, since the steel M50NiL is an air-hardening steel, especially in this embodiment, it becomes possible to cure even large cross-sections. Furthermore, dimensional and dimensional changes in the heat treatment, in particular in vacuum curing, especially in this embodiment extremely low, so that can be largely dispensed formerneuernde or shape-recovering post-treatment steps after curing.

• – Kohlenstoff (C) in einem Gehalt von ≥ 0,11 Gew.-% bis ≤ 0,15 Gew.-%;
• – Chrom (Cr) in einem Gehalt von ≥ 4,0 Gew.-% bis ≤ 4,25 Gew.-%;
• – Molybdän (Mo) in einem Gehalt von ≥ 4,0 Gew.-% bis ≤ 4,5 Gew.-%;
• – Vanadium (V) in einem Gehalt von ≥ 1,1 Gew.-% bis ≤ 1,3 Gew.-%;
• – Nickel (Ni) in einem Gehalt von ≥ 3,2 Gew.-% bis ≤ 3,6 Gew.-%;
• – Mangan (Mn) in einem Gehalt von ≥ 0,15 Gew.-% bis ≤ 0,35 Gew.-%;
• – Silizium (Si) in einem Gehalt von ≥ 0,1 Gew.-% bis ≤ 0,25 Gew.-%, und
• – Eisen,

wobei sich die vorgenannten Bestandeile auf einen Gehalt von ≤ 100 Gew.-% addieren, wobei ein gegebenenfalls vorliegender Rest durch Verunreinigungen oder weitere Legierungsbestandteile gebildet sein kann.A steel M50NiL may in particular be understood as meaning a case hardening steel which has the following alloy constituents:

• - Carbon (C) in a content of ≥ 0.11 wt .-% to ≤ 0.15 wt .-%;
• - Chromium (Cr) in a content of ≥ 4.0 wt .-% to ≤ 4.25 wt .-%;
• - Molybdenum (Mo) in a content of ≥ 4.0 wt .-% to ≤ 4.5 wt .-%;
• - Vanadium (V) in a content of ≥ 1.1 wt .-% to ≤ 1.3 wt .-%;
• - Nickel (Ni) in a content of ≥ 3.2 wt .-% to ≤ 3.6 wt .-%;
• - Manganese (Mn) in a content of ≥ 0.15 wt .-% to ≤ 0.35 wt .-%;
• - Silicon (Si) in a content of ≥ 0.1 wt .-% to ≤ 0.25 wt .-%, and
• - iron,

wherein the aforementioned constituents add up to a content of ≤ 100 wt .-%, wherein an optionally present residue may be formed by impurities or other alloying constituents.

• – Kohlenstoff (C) in einem Gehalt von 0,13 Gew.-%;
• – Chrom (Cr) in einem Gehalt von 4,2 Gew.-%;
• – Molybdän (Mo) in einem Gehalt von 4,25 Gew.-%;
• – Vanadium (V) in einem Gehalt von 1,20 Gew.-%;
• – Nickel (Ni) in einem Gehalt von 3,40 Gew.-%;
• – Mangan (Mn) in einem Gehalt von 0,25 Gew.-%;
• – Silizium (Si) in einem Gehalt von 0,2 Gew.-%, und
• – Eisen,

wobei sich die vorgenannten Bestandeile auf einen Gehalt von ≤ 100 Gew.-% addieren, wobei ein gegebenenfalls vorliegender Rest durch Verunreinigungen oder weitere Legierungsbestandteile gebildet sein kann.For example, a steel M50NiL may be one such case steel having the following alloying ingredients:

• - Carbon (C) in a content of 0.13 wt .-%;
• Chromium (Cr) in a content of 4.2% by weight;
• Molybdenum (Mo) in a content of 4.25% by weight;
• - Vanadium (V) in a content of 1.20 wt .-%;
• Nickel (Ni) at a level of 3.40% by weight;
• Manganese (Mn) at a level of 0.25% by weight;
• - Silicon (Si) in a content of 0.2 wt .-%, and
• - iron,

wherein the aforementioned constituents add up to a content of ≤ 100 wt .-%, wherein an optionally present residue may be formed by impurities or other alloying constituents.

It may be advantageous that after process step c) the further process step takes place: d) nitriding of the hardened component. In this embodiment, the hardness and mechanical stability of the component can be further improved, which can further increase the scope of application.

Nitriding can be understood in a manner known per se as treating the molded and cured component with nitrogen under suitable pressure for a suitable period of time and at elevated temperature.

For example, the component can be plasma-nitrided with a gas mixture comprising nitrogen and hydrogen. Suitable process parameters include, for example, a temperature range of ≥ 450 ° C to ≤ 600 ° C and / or process times of ≥ 20h to ≤ 100h. Also, gas nitriding with a mixture of ammonia and optional proportions of hydrogen or nitrogen at similar temperatures and process times is possible.

Furthermore, it may be advantageous that the further process step takes place before process step c) or before process step d): d) hot isostatic pressing of the molded component.

This can be particularly advantageous for materials which have been processed by an additive process or for components which are produced by an additive manufacturing process. In particular, in this case, the components often still have a low residual porosity, which can be at least significantly reduced by such a pressing operation, which can improve the stability or strength.

By such a pressing process by means of hot isostatic pressing components can also be produced with a particularly fine and homogeneous grain size or structure and almost no porosity. This configuration may therefore also be of advantage, since a high grain size is usually not critical in roll over stress with a pronounced triaxial stress state, but a comparatively coarse grain results in a significant reduction in the strength of resistance given a predominant bending stress with a uniaxial stress state with maximum on the surface can. Such stresses can occur, for example, in applications in high performance transmissions with integrated bearing and gear functions.

For example, in the conventional use of M50NiL case hardening steel, this has a relatively high grain size as a crude product, for example in a range of 3 to less than 5 according to the Standard ASTM E 112 , Although the grain size could be somewhat reduced by forging processes, during carburization and hardening, however, a grain growth takes place again, so that the grain size of the cured components can again be in the predetermined range. A grain refinement by normalizing is not or only partially possible, in particular for the case hardening steel M50NiL due to the alloy.

By processing a powder, in particular of the steel M50NiL by an additive manufacturing process, the grain size can be significantly reduced. Because of the powder produced as a crude product may be a finer grain. This makes it possible that components made of a case-hardened steel, in particular from the case-hardening steel M50NiL, have a finer grain compared to the solutions of the prior art. For example, such a small grain size in the finished component of greater than or equal to 5 according to the Standard ASTM E 112 , approximately in a range of 5 to 7 according to the Standard ASTM E 112 be achieved.

Thus, it may be preferred that a component is produced having a grain size of greater than or equal to 5 ASTM E 112 , in particular in a range of greater than or equal to 5 to less than or equal to 7 according to ASTM E 112 ,

Thus, in particular in this embodiment, improved fatigue strength under bending stresses due to a reduced grain size, in particular for components made of the M50NiL case hardening steel, can be made possible.

In the context of the present invention, a hot isostatic pressing may in particular be understood as a simultaneous pressing and heating. For example, the component can be compressed at temperatures of up to 1200 ° C and pressures of for example 100MPa to 200MPa under inert gas.

With regard to the component to be produced, it may be advantageous that a component is formed as a component, which is selected from a bearing component, a transmission component, a spring component and a tool. In particular, the aforementioned components are often subjected to high mechanical stresses and often have complex shapes, so that in particular the aforementioned components have advantages when they are configured by the method described above from a case-hardening steel.

Exemplary specific components include, for example, rolling bearing and transmission components in aircraft engines, because components for highly stressed rolling bearings in aircraft engines are currently often made of the heat-resistant steel case M50NiL. This material achieved after appropriate heat treatment a very high rollover resistance at the same time high toughness in the core and allows the production of bearing rings with integrated additional functions, such as Spring elements. Furthermore, by way of example, a variety of heavy-duty tools can be mentioned.

In summary, the method described above creates an additive manufacturing process for raw material from case-hardened steels or for processing alloyed case-hardening steels, especially the martensitic hardenable high-performance case hardening steel M50NiL, for example by means of 3D printing, with the formation of components preferably of complicated geometry. The method comprises a heat treatment, for example, carried out immediately after the molding by low-pressure carburizing and curing and optionally previous hot isostatic pressing. Subsequently, for example, nitriding can take place. If necessary, it can be followed by a reworking of mating surfaces in the heat-treated state, which can also be dispensed with in the method described above.

Furthermore, the component can be started.

The components thus produced have a high surface hardness, such as a Rockwell hardness of 58 HRC or more. In this case, the above-described method makes it possible that, even in the prior art, steels that are not or only with difficulty can be processed by additive manufacturing processes and hardened substantially without post-processing. In particular, a processing of martensitic hardening steels according to the current state of the art is very problematic and thermosetting tool steels are currently not processed by 3D printing process reliable. These problems of the prior art can be avoided according to the invention.

With regard to further technical features and advantages of the method described above, reference is made to the description of the component, the figures and the description of the figures.

The subject matter of the present invention is further a component made of a case hardening steel, in particular made of a M50NiL steel, characterized in that the component is produced by an additive manufacturing method and has a grain size of 5 or finer according to ASTM E 112 in particular in a range of 5 to 7 according to ASTM E 112 , A component, in particular of a M50NiL steel, with such a fine grain was often not produced in the prior art, but can be produced in particular by an additive manufacturing process, in particular a combination with a low pressure carburizing and subsequent curing can be beneficial.

Such a component can have a particularly good stability and strength.

With regard to further technical features and advantages of the above-described component, reference is made to the description of the method, the figures and the description of the figures.

In the following, a particularly preferred embodiment of the invention will be explained with reference to the accompanying drawings, wherein it is explicitly pointed out that the object according to the invention is not limited to the exemplary embodiment described. It shows:

1 a schematic view of a hardness profile from the surface into the interior of the component, wherein the component is produced by a method according to the invention.

• a) Bereitstellen eines Pulvers aus einem metallischen Werkstoff; und
• b) Formen eines Bauteils mittels eines additiven Fertigungsverfahrens aus dem bereitgestellten Pulver; wobei

der metallische Werkstoff einen Einsatzstahl umfasst, und wobei
das Verfahren den weiteren Verfahrensschritt aufweist:

• c) Durchführen eines Niederdruckaufkohlens mit anschließendem Härten des geformten Bauteils.

In the 1 is a diagram showing a hardness profile of the surface of a component, which is produced by a method, comprising the method steps:

• a) providing a powder of a metallic material; and
• b) forming a component by means of an additive manufacturing process from the powder provided; in which

the metallic material comprises a case hardening steel, and wherein
the method comprises the further method step:

• c) carrying out a low-pressure carburizing with subsequent hardening of the molded component.

1 shows a diagram in which on the X-axis the distance from the surface of the component in [mm] and on the Y-axis the Vickers hardness is given in [HV 1]. It can be seen that the component has a large case depth and a significant drop in hardness occurs only at about 0.75 mm. The measured hardness values of approx. 750 HV 1 after EN ISO 6507-1: 2005 on the surface of the component are sufficient for a variety of applications for highly stressed components. The component is made from a M50NiL steel, low-pressure carburized and hardened and is available in particular as fine-needle martensite.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014214957 A1 [0003]

Cited non-patent literature

• DIN EN 10084 [0009]
• EN ISO 6508-1 [0019]
• EN ISO 6508-1 [0019]
• Standard ASTM E 112 [0038]
• Standard ASTM E 112 [0039]
• Standard ASTM E 112 [0039]
• ASTM E 112 [0040]
• ASTM E 112 [0040]
• ASTM E 112 [0049]
• ASTM E 112 [0049]
• EN ISO 6507-1: 2005 [0055]

Claims (10)

A method of processing a case hardening steel to form a component, comprising the steps of: a) providing a powder of a metallic material; and b) forming a component from the powder provided by an additive manufacturing process; characterized in that the metallic material comprises a case hardening steel and that the method comprises the further step of: c) carrying out a low pressure carburizing with subsequent hardening of the shaped component. A method according to claim 1, characterized in that a low-pressure carburizing takes place at a temperature in a range of greater than or equal to 850 ° C to less than or equal to 1000 ° C. A method according to claim 1 or 2, characterized in that the curing takes place under reduced pressure with subsequent high-pressure gas quenching. Method according to one of claims 1 to 3, characterized in that the insert steel comprises a M50NiL steel. A method according to claim 4, characterized in that the metal material comprises the following alloy components: - carbon (C) in a content of ≥ 0.11 wt .-% to ≤ 0.15 wt .-%; - Chromium (Cr) in a content of ≥ 4.0 wt .-% to ≤ 4.25 wt .-%; - Molybdenum (Mo) in a content of ≥ 4.0 wt .-% to ≤ 4.5 wt .-%; - Vanadium (V) in a content of ≥ 1.1 wt .-% to ≤ 1.3 wt .-%; - Nickel (Ni) in a content of ≥ 3.2 wt .-% to ≤ 3.6 wt .-%; - Manganese (Mn) in a content of ≥ 0.15 wt .-% to ≤ 0.35 wt .-%; - Silicon (Si) in a content of ≥ 0.1 wt .-% to ≤ 0.25 wt .-%, and - iron, wherein the aforementioned constituents add up to a content of ≤ 100 wt .-%. Method according to one of claims 1 to 5, characterized in that after step c) of the further process step is carried out: d) nitriding the cured component. Method according to one of claims 1 to 6, characterized in that before process step c) or before process step d) the further process step takes place: d) hot isostatic pressing of the molded component. Method according to one of claims 1 to 7, characterized in that as a component such is formed, which is selected from a bearing component, a transmission component, a spring member and a tool. Method according to one of claims 1 to 8, characterized in that a component is produced with a grain size of 5 or finer, in particular in a range of 5 to 7 according to ASTM E 112th A component made from a case hardening steel, in particular from a M50NiL steel, characterized in that the component is produced by an additive manufacturing process and has a grain size of 5 or finer according to ASTM E 112, in particular in a range of 5 to 7 according to ASTM E 112.

Images