EP4211284A1

EP4211284A1 - Piston for an internal combustion engine, internal combustion engine having a piston, and use of an iron-based alloy

Info

Publication number: EP4211284A1
Application number: EP21773566.1A
Authority: EP
Inventors: Thomas Kirste; Roman Morgenstern; Robert Willard; Martin Popp; Thomas Hutzler; Andreas Hörauf; Philipp Koch
Original assignee: Federal Mogul Nuernberg GmbH
Current assignee: Federal Mogul Nuernberg GmbH
Priority date: 2020-09-08
Filing date: 2021-09-08
Publication date: 2023-07-19
Anticipated expiration: 2041-09-08
Also published as: CN116194608A; WO2022053484A1; DE102020211246A1; US20230383708A1

Abstract

A piston for an internal combustion engine, in particular for a diesel engine, consists of an iron-based alloy comprising the following alloy elements in percent by weight (wt%): carbon (C): 0.07 to 0.24; chromium (Cr): > 7.0 to 12.5; molybdenum (Mo): 0.3 to 1.2; manganese (Mn): 0.3 to 0.9; silicon (Si): < 0.5; copper (Cu): < 0.3; nickel (Ni): < 0.8; vanadium (V): 0.15 to 0.35; sulphur (S): < 0.015; phosphorus (P): < 0.025; niobium (Nb): < 0.1; nitrogen (N): < 0.07; aluminium (Al): < 0.04; tungsten (W): < 2.5 and the remainder being iron (Fe) and unavoidable impurities. The invention also relates to the use of such an iron-based alloy for pistons of an internal combustion engine, in particular of a diesel engine.

Description

Pistons for an internal combustion engine, Internal combustion engine having a piston and using an iron-based alloy

field of invention

The present invention relates to a piston for an internal combustion engine and an internal combustion engine with such a piston and the use of an iron-based piston

Alloy for internal combustion engine pistons.

Prior Art and Background of the Invention

Driven by the economic and ecological demand for consumption and emission-optimized means of transport, a rapid development of ever more powerful and lower-emission internal combustion engines has succeeded in the last 20 years. A decisive key to this continuous progress are engine pistons, which can be used at ever higher combustion temperatures and pressures, but are still light and lightweight. Have the total weight of the piston group (pistons, rings, bolts and, if necessary, connecting rods). This is essentially made possible by the development of more efficient piston materials.

Another very important change is the change from aluminum to steel engine pistons, especially in diesel engine pistons. Despite the higher density and poorer thermal conductivity of the steel material, its advantages such as higher strength and higher maximum operating temperature can be used to advantage. To date, low-alloy and very inexpensive steels of the types 42CrMo4 and 38MnVS 6 have been used for steel pistons. However, their area of application is limited and is already reaching its limits with current developments. Here plays above all the comparatively low resistance to oxidation (oxidation = scaling or high-temperature corrosion) plays a decisive role.

It is known that alloying elements in steel are crucial for the formation of the properties and this is used in the conventional steels mentioned above. The addition of chromium causes an increase in oxidation resistance, an increase in strength, a reduction in thermal conductivity but also an increase in material costs. The addition of molybdenum causes an increase in oxidation resistance, an increase in (hot) strength but also an increase in material costs. The addition of vanadium increases the (hot) strength but also increases the material costs. The addition of niobium causes grain refinement, the formation of carbides and nitrides and a reduction in toughness and in turn an increase in material costs. This is also the case with the addition of tungsten, which also leads to an increase in (hot) strength.

The invention described here is based on the object of providing a piston for an internal combustion engine, which consists of an iron-based or consists of a steel alloy that ideally combines and transfers the following in a positive way to the piston:

■ higher oxidation resistance compared to the steel materials previously used;

■ A strength sufficient for the intended use at high temperatures under TMF stress (“Thermo Mechanical Fatigue” = “TMF”) d. H . adequate thermomechanical fatigue strength;

■ an isothermal fatigue strength sufficient for the intended use (“High Cycle Fatigue”=“HCF”); good weldability, especially for induction welding and friction welding, and generally good machinability; a thermal conductivity sufficient for the intended use; and a limited increase in material and machining costs.

Presentation of the invention

The present invention is defined by the appended independent and dependent claims. The dependent claims define optional features and special embodiments.

The above object is achieved in particular by the piston according to claim 1. The piston according to claim 1 is a piston for an internal combustion engine, preferably a diesel engine, which has an iron-based alloy or consists of this as the piston material, which has the following alloying elements in percent by weight (% by weight or "% by weight"):

Carbon (C): 0.07 to 0.24 inclusive;

Chromium (Cr) :

> 7.0 up to and including 12.5;

Molybdenum (Mo): 0.3 to 1.2 inclusive;

Manganese (Mn): 0.3 to 0.9 inclusive;

Silicon (Si) :

<0.5; Copper (Cu) :

<0.3;

Nickel (Ni ) :

< 0.8;

Vanadium (V): 0.15 to 0.35 inclusive;

Sulfur (S) :

<0.015;

Phosphorus (P) :

<0.025;

Niobium (Nb) :

<0.1;

Nitrogen (N) :

<0.07;

Aluminum (Al) :

<0.04;

Tungsten (W) :

<2.5 and the remainder iron (Fe) and unavoidable impurities, where optionally all other elements present are <0.01% by weight each.

The iron-based alloy according to the invention can preferably be characterized or referred to as high-alloy steel and more preferably as heat-treatable steel. In order to increase and improve the high-temperature properties, the contents of relevant alloying elements have been further increased. The iron-based alloy of the piston is characterized in particular by the alloying elements chromium, molybdenum, tungsten, niobium and vanadium, which are used in greatly increased amounts compared to the previous series alloys 42CrMo4 and 38MnVS6 to achieve improved oxidation resistance and sufficient high-temperature (alternating) strength. In particular, the chromium content is advantageously selected to be comparatively high. Although significantly higher proportions of these elements would be possible in steel, these were deliberately restricted in order to optimize weldability, machinability, costs and thermal conductivity for production and application. The piston material according to the invention therefore represents an iron-based alloy or. a steel that has increased oxidation resistance and sufficient strength at high temperatures and under TMF stress. The piston material is nevertheless still easy to weld (e.g. by inductive welding, friction welding and/or laser welding) and can be machined. In addition, the thermal conductivity is not too low and within a usable range. However, the material costs are still within an acceptable range. The piston according to the invention represents an optimal compromise between material properties and material costs, in particular when it comes to optimized oxidation resistance at high temperatures.

Advantageously, the iron-based alloy of the piston can also in percent by weight (% by weight):

Chromium ( Gr ) : 9 , 0 up to and including 12 , 0 and/or

Molybdenum (Mo): 0.8 to 1.1 inclusive.

These ranges are to be understood as preferred sub-ranges of the broader content ranges defined above, in which the technical effects and advantages of the present invention are particularly evident. Within the scope of the present invention, the preferred sub-ranges can be combined as desired with the broader content ranges and with one another and from the upper content limits and Salary limits and any new salary ranges can be created.

It is particularly preferred that the iron-based alloy is a steel of the type X10CrMoVNb9-l or X22CrMoV12-l, i. H . consists of these . These steels are readily available and can be used directly to produce the piston according to the invention with its positive properties.

The iron-based alloy of the piston according to the invention is advantageously a heat-treated alloy that has or consists of at least one tempered structure, preferably tempered martensite and/or an intermediate structure, preferably bainite, and optionally has a ferrite content of <10% in the structure. It is preferred that the alloy has or has one or more of the above types of structure. consists of . Furthermore, the alloy according to the invention is preferably a tempering steel which is tempered by tempering d. H . a combination of hardening and subsequent tempering or optional bainitizing is produced. The existing carbide formers Gr, Mo and V decisively change the formation mechanism of carbides formed during tempering. At tempering temperatures of up to around 400 °C, FeaC precipitations are also predominantly formed in alloyed heat-treatable steels. Above 400 to 450 °C the ability of the carbide formers to diffuse becomes so great that thermodynamically much more stable alloyed carbides (special carbides) can form. Existing FesC is dissolved in favor of the more stable special carbides. Processes of special carbide formation during tempering of alloyed steels are often also referred to as 4 . referred to as an initiation stage. The advantages of temper-resistant, alloyed heat-treatable steels are therefore the significantly lower diffusibility of the carbide formers, which prevent special carbide formation, i. H . shifts the drop in strength to higher temperatures and longer times. In addition, the special carbides separated out are considerably finer than those Iron carbides, resulting in an additional increase in strength. The heat treatment (quenching and tempering) according to the invention achieves a particularly important combination of properties, namely a yield point that is still adequate, combined with a high level of ductility, which is important for safety against brittle fracture, e.g. B. the notched impact strength . Therefore tempering of the tempering structure is carried out at at least 400°C.

A further aspect of the present invention is an internal combustion engine, in particular a diesel engine, with a piston according to the configurations described so far. The piston according to the invention transfers all of its technical advantages to the internal combustion engine, which contains the piston as a component.

Furthermore, the present invention includes the use of the previously defined iron-based alloy in all its configurations, preferably in the form of the above steels of the type X10CrMoVNb9-l or X22CrMoV12-l, for pistons of an internal combustion engine, in particular a diesel engine.

Claims

8 patent claims

1. Pistons for an internal combustion engine, in particular a diesel engine, which consists of an iron-based alloy which contains the following alloying elements in percent by weight

(wt.%) :

carbon (C): 0.07 to 0.24; Chromium (Cr): >7.0 to 12.5; molybdenum (Mo): 0.3 to 1.2; manganese (Mn): 0.3 to 0.9; Silicon (Si): <0.5;

Copper (Cu): <0.3; Nickel (Ni): <0.8;

vanadium (V): 0.15 to 0.35; Sulfur (S): <0.015;

Phosphorus (P): <0.025; niobium (Nb): <0.1; Nitrogen (N): <0.07; Aluminum (Al): <0.04; Tungsten (W): < 2.5 and balance iron (Fe) and unavoidable

has impurities.

2. The piston of claim 1, wherein the iron-based alloy in percent by weight (wt%):

Chromium (Cr): 9.0 to 12.0 and/or

Molybdenum (Mo): 0.8 to 1.1.

3. Piston according to any one of the preceding claims, wherein the iron-based alloy is a steel of the type

XI is 0CrMoVNb9-1 or X22CrMoV12-1. 9

4. Piston according to one of the preceding claims, wherein the iron-based alloy is a heat-treated alloy which has at least one tempering structure and/or an intermediate structure and optionally has a ferrite content of <10% in the structure.

5. Internal combustion engine, especially diesel engine, with a

Piston according to any one of the preceding claims.

6. Use of an iron-based alloy containing the following alloying elements in percent by weight (wt%):

Copper (Cu): <0.3; Nickel (Ni): <0.8;

vanadium (V): 0.15 to 0.35; Sulfur (S): <0.015;

has impurities.

7. Use according to claim 9, wherein the iron-based alloy in percent by weight (wt%):

Chromium (Gr): 9.0 to 12.0 and/or

Molybdenum (Mo): 0.8 to 1.1. 10

8. Use according to claim 6 or 7, wherein the iron-based alloy is a steel of the type XI 0CrMoVNb9-1 or X22CrMoV12-1.