US20150292066A1

US20150292066A1 - Metallic material

Info

Publication number: US20150292066A1
Application number: US14/647,375
Authority: US
Inventors: Matthias Kuntz; Friedrich Muehleder; Stefan Marsoner; Reinhold Ebner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-11-27
Filing date: 2013-11-25
Publication date: 2015-10-15
Also published as: WO2014082945A1; EP2925899B1; DE102012221607A1; EP2925899A1; EP2925899B8

Abstract

A metallic material includes at least iron, carbon, chromium, molybdenum and vanadium, which metallic material has a bainitic basic structure and carbidic phases. The carbidic phases are at least partially formed by molybdenum carbide, vanadium carbide and/or chromium carbide. The carbidic phases at least partially have a diameter no greater than 200 nm.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a metallic material. Furthermore, the present invention relates to a method for manufacturing a metallic material, and to the use of a metallic material for the production of a component part in an internal combustion engine.
2. Description of the Related Art
Metallic materials are used in a multitude of applications. For instance, metallic materials are known as components of an internal combustion engine. An essential limitation in the possible utilization of high-strength materials such as metallic materials, for example, is the result of their mechanical properties and also their processing capability. The cyclical load capability and economical processing capability, such as the plasticity, machinability or weldability may be of particular importance.
For instance, in this regard it is known to obtain a cyclical load capability through special hardening of a material, such as steel, in particular, by way of a heat treatment. However, such hardening methods known from the related art often leave room for improvement, especially with regard to the specific manufacturing process of the individual material, such as steel, in particular.

BRIEF SUMMARY OF THE INVENTION

The subject matter of the present invention is a metallic material which contains at least iron, carbon, chromium, molybdenum and vanadium, the material having a bainitic basic structure; carbidic phases, which are at least partially formed by molybdenum, vanadium and/or chromium present the form of carbide, are provided in addition, the carbidic phases at least partially having a diameter ranging from less than to equal to 200 nm.

DETAILED DESCRIPTION OF THE INVENTION

The present invention thus relates to a metallic material having a plurality of metals, which, for instance, may at least partially be present as an alloy or as pure metals. The main component of the metallic material in particular may include iron (Fe), and carbon (C) may be provided in addition. For example, the carbon content may be present in a range from more than or equal to 0.01 wt. % to less than or equal to 2.06 wt. %, so that the metallic material could be a steel material, in particular.
In addition to iron and carbon, such a metallic material furthermore includes at least chromium (Cr), molybdenum (Mo) and vanadium (V). The aforementioned metals may be present in the form of an alloy, for instance, at least partially as pure metals, or also at least partially as carbide, as will be explained in the following text. In addition, the material may include further components, such as may be required for a suitable manufacturing process or for a particular application field. To be mentioned as further components are elements that are common in the production of steel, such as sulfur and phosphorus.
Moreover, such a metallic material has a bainitic basic structure. A bainitic basic structure may be a structure which can include ferritic phases and cementite phases (Fe₃C), in particular. A bainitic structure specifically may include ferrite crystals oversaturated in carbon, which are present as cubic body-centered crystal lattice. In other words, a bainitic structure can be recognized by a ferritic mixed crystal oversaturated with regard to carbon, possibly including further elements such as especially chromium, molybdenum and vanadium, in combination with iron-rich metal carbides such as cementite, for example, a non-limiting typical iron content of the metallic components of the carbides being in a range from greater than or equal to 50 atom-%. As a rule, the combination of the mixed crystal and the carbides may exist side-by-side, but this may often be quite difficult to discern.
Moreover, carbidic phases may be present or specified in the afore-described material. These carbidic phases may at least partially be formed by molybdenum, vanadium and/or chromium present as carbide. Each aforementioned metal may be present as carbide, or single metals or a suitable mixture of said metals may be present as carbides. It is obvious to one skilled in the art that the aforementioned metals need not be present entirely as carbides, but may additionally also be included in the material in non-carbidic form.
The carbidic phases are at least partially present at a diameter that lies in a range from less than or equal to 200 nm, in particular in a range from less than or equal to 100 nm. Molybdenum and/or vanadium in particular are present as carbides in this order of magnitude. These carbides, in particular, may be responsible for an increase in hardness, as will be discussed in detail in the following text. Further carbides that have a larger diameter, such as carbide of iron and/or chromium, for instance, may be present in addition.
The aforementioned material thus is a carbide-hardened steel, in particular. In an especially advantageous manner said steel allows an increase in the cyclical load capability, such as in particular an improved vibration resistance and greater ductility, while at the same time showing little dimensional change in the heat treatment.
The described carbide-hardened steel specifically makes it possible to combine processing in the soft state with an increase in the cyclical load capability. The carbide hardening offers the possibility of an increase in strength with low dimensional change of the steel structure by way of precipitation or heat treatment at moderate temperatures. During the production of the material according to the present invention, it is possible by adjusting a soft bainitic base structure, for instance having a hardness in a range of less than 37 HRC (Rockwell hardness); The Rockwell hardness of a material results from the penetration depth of a test body in response to the application of a certain preforce and test force and may be ascertained according to DIN EN ISO 6508-1), for example, via following carbide precipitation and high strength increases of up to 10 HRC or even higher may be realizable.
The afore-described material thus makes it possible to keep the costs down during possibly required subsequent reworking in the hard state. Reworking in a hard state in particular may be dispensed with completely in the production of an afore-described material, which makes it possible to shorten the value chain for an adjustment of the desired component property. This makes for an especially uncomplicated and cost-effective production method. It is furthermore possible to adapt the material to an especially broad application field.
Said material is particularly cost-effective in its manufacture and may also satisfy future requirements; the ability of tailoring it to the specific usage specifications may exist in addition.
The afore-described metallic material or the afore-described carbide-hardened steel allows an especially advantageous application under particularly harsh conditions, such as high temperatures, oxidative atmospheres and high pressures, for instance. One advantageous use may be seen in internal combustion engines. The afore-described material in particular may be used in injection systems, e.g., of a diesel engine. Specific examples of application include the development of nozzles or injectors, pressure reservoirs or high-pressure pumps in injection systems, because said material can be used without any problems even under the conditions that arise in such applications, such as high injection pressures of 3000 bar, for example, while offering cost-effective manufacturability.
In addition to the afore-described advantages with regard to the mechanical stability or the cyclical load capability, the material or its structure retains sufficient ductility even after hardening, so that further strength-increasing technologies may be employed, such as autofrettage.
In summary, the afore-described material allows the production of components that can tolerate high mechanical and/or cyclical loading, an adjustment of heretofore unavailable characteristics combinations in steels, and an especially simple and cost-effective production method in addition.
Within the framework of one development, the material may furthermore include at least one additional component from the group made up of silicon and manganese. Providing at least one of these further components makes it possible to improve the characteristics of the material even further, especially with regard to mechanical resistance or the cyclical load capability. By providing manganese, for instance, it is possible to improve the hardenability, tensile strength and weldability and, in general, the processing capability, which may offer considerable advantages, depending on the individual application case or the manufacture, in particular. For example, cooling that occurs during the production can be improved because of a larger cooling window. Silicon, for instance, may be used, especially in the production of the material, in order to improve the processing capability and also as deoxidizer in order to thereby protect the material from negative influences. Another advantage derived from providing silicon can be seen in the ability to increase the tensile strength, the elastic limit and the oxidation resistance of the material. In general, silicon is furthermore able to increase the strength. In addition, silicon as mixed crystal hardener can improve the mechanical properties even further.
Within the framework of a further development, the material may include:

- carbon at a level of greater than or equal to 0.25 wt. % to smaller than or equal to 0.4 wt. %;
- chromium at a level of greater than or equal to 0.3 wt. % to smaller than or equal to 0.6 wt. %;
- molybdenum at a level of greater than or equal to 1.5 wt. % to smaller than or equal to 3.2 wt. %;
- vanadium at a level of greater than or equal to 0.2 wt. % to smaller than or equal to 0.6 wt. %;
- silicon at a level of greater than or equal to 0 wt. % to smaller than or equal to 0.35 wt. %;
- manganese at a level of greater than or equal to 0 wt. % to smaller than or equal to 0.35 wt. %,
  said components jointly being present at a level of less than 100 wt. %, and the further components being distributed among iron and possibly additional components such as known from the steel manufacture, for instance phosphorus or nitrogen.

Surprisingly, it was discovered that in this development in particular the outstanding properties of the afore-described material, such as especially the mechanical stability and cyclical load capability may be particularly pronounced. Said level limits in particular describe an integral composition, i.e., the presence of the individual quantities of the corresponding atoms of the substances in any chemical compound. Chromium, for instance, may therefore be present as an alloy component, i.e., in non-carbidic form, or also at least partially in the form of a carbide. Additional components not specifically mentioned may be contained in said material in addition, for instance in order to optimize the production method or to allow an adaptation to special application fields.
In one specific embodiment, it may be preferred that the material includes the following components:

- carbon at a level of 0.35 wt. %;
- chromium at a level of 0.5 wt. %;
- molybdenum at a level of 3.0 wt. %;
- vanadium at a level of 0.45 wt. %-;
- silicon at a level of 0.3 wt. %; and
- manganese at a level of 0.3 wt. %,
  said components jointly being present at a level of less than 100 wt. %, and the further components being distributed among iron and possibly additional components known from the steel manufacture, for instance phosphorus or nitrogen.

The afore-described integral composition of the material is ascertainable by a spark spectrum analysis, in particular. In a manner known per se, a spark spectrum analysis is a method in which the individual atoms, especially the metal atoms, are excited and the correspondingly emitted spectrum lines are analyzed, the quantity being ascertainable based on the intensity, or the type of atoms being ascertainable based on the wavelength.
Within the framework of another development, the material may have a hardness of more than or equal to 45 HRC. In this development, in particular, the material has a hardness that could not be achieved according to the related art or only by considerably more involved manufacturing steps than required for the described material. Moreover, the material having a hardness of this magnitude in particular has very high mechanical stability or cyclical load capability, so that an especially broad application field is possible. HRC specifically may describe the hardness according to Rockwell. The Rockwell hardness of a material results from the penetration depth of a test body in response to the application of a certain pre-force or test force and can be ascertained according to DIN EN ISO 6508-1, for example.
With regard to additional technical features and advantages of the material according to the present invention, explicit reference is made here to the explanations in connection with the method of the present invention, the use according to the present invention, and the injection component according to the present invention.
The subject matter of the present invention is furthermore a method for manufacturing a metallic material developed as described above, having the method steps:

- a) Providing a metallic composition which includes at least the components iron, carbon, chromium, molybdenum, vanadium, and possibly silicon and possibly manganese;
- b) Treating the metallic composition at a temperature that is higher than or equal to the austenitizing temperature;
- c) Cooling the metallic composition at a predefined cooling rate;
- d) Treating the product obtained under method step c) at a temperature ranging from greater than or equal to 400° C.; and
- e) Cooling the product obtained under method step d).

The afore-described method in particular is based on the adjustment of a bainitic basic structure with subsequent carbide precipitation during a two-step temperature treatment or precipitation at moderate temperatures with subsequent cooling.
In a first method step a), a metallic composition such as an alloy composition is provided for this purpose, which includes at least the following components: iron, carbon, chromium, molybdenum and vanadium, and possibly silicon and manganese.
This may essentially be realizable by a method known from the production of steel. In particular, the electric steel method known per se may be used, in which the individual components of a suitable composition are melted in an electric arc furnace, in particular.
The aforementioned components may be present in the metallic composition in particular at the levels described below:

- carbon at a level of greater than or equal to 0.25 wt. % to smaller than or equal to 0.4 wt. %;
- chromium at a level of greater than or equal to 0.3 wt. % to smaller than or equal to 0.6 wt. %;
- molybdenum at a level of greater than or equal to 1.5 wt. % to smaller than or equal to 3.2 wt. %;
- vanadium at a level of greater than or equal to 0.2 wt. % to smaller than or equal to 0.6 wt. %;
- silicon at a level of greater than or equal to 0 wt. % to smaller than or equal to 0.35 wt. %; and
- manganese at a level of greater than or equal to 0 wt. % to smaller than or equal to 0.35 wt. %,
  said components jointly being present at a level of less than 100 wt. %, the further components being distributed among iron and possibly additional components known from the steel manufacture, for instance phosphorus or nitrogen.

The afore-described metallic composition thus is a steel, in particular. It furthermore has the potential for carbide precipitation through the elements of carbon in combination with chromium, molybdenum and vanadium.
To develop the material, a treatment of the metallic composition at a higher temperature takes place in a further method step b). The metallic composition may be heated, in particular to or above its austenitizing temperature or austenite forming temperature. Heating to a temperature in a range that is greater than or equal to 950° C. up to a temperate in a range of smaller than or equal to 1100° C. takes place for the present metallic composition. This temperature may be retained for a predefined period of time, such as typically 15 to 120 minutes. During method step b) an austenite formation of the metallic composition thus occurs.
In a further method step c), cooling of the metallic composition at a predefined cooling rate takes place as well. The predefined cooling rate, for example, may be selected as a function of the specifically selected metallic composition or its percentage composition. As a matter of principle, cooling rates that lie in a range from more than or equal to 0.2K/s to less than or equal to 3K/s may be suitable for the described metallic composition. The formation of a bainitic basic structure takes place in this method step c). A steel which already has a hardness ranging from 32 to 40 HRC, such as 35 HRC, for example, may be obtained in the process.
In a further method step, another heat treatment of the obtained product takes place at a temperature in a range that is greater than or equal to 400° C., especially at a temperature in a range that is greater than or equal to 450° C. to smaller than or equal to 600° C., for instance for a range of more than one hour, e.g., for two hours. Because of the further heat treatment, the formation of the corresponding metal carbides, in particular of carbidic phases or nano-scale carbide precipitations in a range from less than or equal to 200 nm, in particular in a range from 100 nm, takes place, in particular by the provision of carbon and furthermore, chromium, molybdenum and vanadium. This further increases the hardness by a range of approximately 10 HRC, so that a material is achievable that has a hardness of 45 HRC or even higher.
Subsequently, further cooling of the finished material takes place according to method step e).
By slight modifications in the choice of the chemical composition of the metallic composition and, in particular, the parameters of the heat treatments or the parameters of the treatment at an increased temperature as well as the cooling, the basic hardness of the bainitic structure and the increase in hardness or strength is able to be adapted to the desired application field in the afore-described method.
For example, the material or its structure retains sufficient ductility even after hardening, so that further technologies that increase the strength, such as autofrettage, may be employed.
With regard to additional technical features and advantages of the method according to the present invention, explicit reference is made here to the explanations in connection with the material of the present invention, the use according to the present invention, and the injection component according to the present invention.
Additional subject matters of the present invention are a use of a material developed as described above or a method developed as described above for the production of a component for an internal combustion engine, in particular for the production of an injection component.
Because of the outstanding characteristics of the afore-described material as far as mechanical stability as well as the cyclical load capability are concerned, said material is suitable in particular for producing a component of this type which is operated under harsh conditions. Specifically, the aforementioned material or the aforementioned method are suitable for enabling the production of a component for an internal combustion engine. Within the meaning of the present invention, an internal combustion engine in particular denotes a heat engine which converts the chemical energy of a fuel into mechanical energy by way of a combustion process. Examples of internal combustion engines in particular are a combustion engine such as a diesel engine or an Otto engine. To be mentioned as specific application fields are injection components, such as nozzles or injectors, high-pressure pumps or pressure reservoirs, especially for a diesel engine.
With regard to additional technical features and advantages of the use according to the present invention, explicit reference is made here to the explanations in connection with the material of the present invention, and the injection component according to the present invention.
Furthermore, an injection component for an internal combustion engine which includes a material developed as described before is a subject matter of the present invention. The subject matter of the present invention in particular is an injection component, such as a nozzle or an injector, a high-pressure pump or a pressure reservoir, which are at least partially, e.g., completely, made from the afore-described material. The concept of an injection component within the sense of the present invention in particular denotes a pressure-conducting or pressure-loaded component of an injection system, especially for a diesel engine. Because of the outstanding characteristics of the afore-described material as far as the mechanical stability as well as cyclical load capability are concerned, said material is suitable in particular for producing an injection component, especially for a diesel engine.
With regard to additional technical features and advantages of the injection component according to the present invention, explicit reference is made here to the explanations in connection with the material of the present invention, the method of the present invention, and the use according to the present invention.

Claims

1-11. (canceled)

12. A metallic material, comprising:

iron, carbon, chromium, molybdenum and vanadium;

wherein the metallic material has a bainitic basic structure, and wherein the metallic material has carbidic phases which are at least partially formed by at least one of molybdenum carbide, vanadium carbide, and chromium carbide, and wherein the carbidic phases at least partially have a diameter no greater than 200 nm.

13. The material as recited in claim 12, further comprising:

at least one of silicon and manganese.

14. The material as recited in claim 13, wherein:

carbon is provided in the range of 0.25 wt. % to 0.4 wt. %;

chromium is provided in the range of 0.3 wt. % to 0.6 wt. %;

molybdenum is provided in the range of 1.5 wt. % to 3.2 wt. %;

vanadium is provided in the range of 0.2 wt. % to 0.6 wt. %;

silicon is provided in the range of 0 wt. % to 0.35 wt. %; and

manganese is provided in the range of 0 wt. % to 0.35 wt. %.

15. The material as recited in claim 14, wherein:

carbon is provided at a level of 0.35 wt. %;

chromium is provided at a level of 0.5 wt. %;

molybdenum is provided at a level of 3.0 wt. %;

vanadium is provided at a level of 0.45 wt. %;

silicon is provided at a level of 0.3 wt. %; and

manganese is provided at a level of 0.3 wt. %.

16. The material as recited in claim 15, wherein the material has a hardness of no less than 42 HRC.

17. A method for producing a metallic material, comprising:

a) providing a metallic composition which includes at least iron, carbon, chromium, molybdenum, and vanadium;

b) treating the metallic composition at a temperature no less than an austenitizing temperature;

c) cooling the metallic composition at a predefined cooling rate;

d) treating the resulting product obtained from the cooling step c), at a temperature no less than 400° C.; and

e) cooling the resulting product obtained from the method step d) to form the metallic material, wherein the metallic material has a bainitic basic structure, and wherein the metallic material has carbidic phases which are at least partially formed by at least one of molybdenum carbide, vanadium carbide, and chromium carbide, and wherein the carbidic phases at least partially have a diameter no greater than 200 nm.

18. The method as recited in claim 17, wherein the method step b) is performed in a temperature range of 950° C. to 1100° C.

19. The method as recited in claim 18, wherein the method step d) is carried out in a temperature range of 450° C. to 600° C.

20. The method as recited in claim 19, wherein a cooling rate used in method step c) is in the range of 0.2K/s to 3K/s.

21. The material as recited in claim 12, wherein the material is part of an injection component of an internal combustion engine.