EP2052094B1 - Steel material having a high silicon content for producing piston rings and cylinder sleeves - Google Patents

Description

The present invention relates to a silicon-alloyed cast steel material which is particularly suitable for piston rings and cylinder liners. Furthermore, the invention relates to piston rings and cylinder liners, which comprise such a steel material as the base body. The invention further relates to a method for producing a silicon-alloyed cast steel material.

Piston rings seal the gap between the piston head and the cylinder wall with respect to the combustion chamber. In the up and down movement of the piston piston ring slides on the one hand with its outer peripheral surface in constant resilient engagement against the cylinder wall, on the other hand slides the piston ring, due to the tilting movements of the piston, oscillating in its Kolbenringnut, with its edges alternately at the top or bottom Abut groove flank of the piston ring groove. In each case sliding against each other occurs depending on the material, a more or less severe wear, which can lead to so-called scuffing, scoring and finally to a destruction of the engine in a dry run. In order to improve the sliding and wear behavior of piston rings against the cylinder wall, they were provided on the peripheral surface with coatings of different materials.

For the production of highly stressed parts of internal combustion engines, such as piston rings, usually cast iron materials or cast iron alloys are used. Piston rings, in particular compression rings, are subject to increasing loads in highly stressed engines, including compression peak pressure, combustion temperature, EGR, lubricating film reduction, which significantly affect their performance characteristics, such as wear, fire resistance, microwelding and corrosion resistance. For example, the DE 3717297 a cast-iron piston ring as the only material with cast iron whitened in its outer peripheral surface only in a region caused by the cast iron material being exposed to a high energy density radiation and having a thermally charged intermediate region formed between the cast iron base metal and the white solidified region. In the EP 0 821 073 discloses a cast iron alloy with pearlitic basic structure and spherical or vermicular graphite precipitates, which is particularly suitable for use in piston rings due to the resistant even at high temperatures strength values. JP 60-155645 concerns a forged steel for disc brakes among others with the proportions C: 0.1-0.6%, Si: 0.8-5% and Ni: 0.2-5%, the high braking effect with simultaneous resistance to wear and heat to reach.

However, the cast iron materials according to the prior art have a high risk of breakage, so that there is often ring breakage when using existing materials. Increased mechanical-dynamic loads lead to shorter lifetimes of piston rings or cylinder liners. Likewise, it comes to heavy wear and corrosion on the tread and flank.

Higher ignition pressures, reduced emissions and direct injected Krattstoff mean increasing loads on piston rings. The result is damage and plating of piston material, especially on the lower piston ring flank.

Due to the higher mechanical and dynamic loads of piston rings, more and more engine manufacturers are demanding piston rings made of high-quality steel (tempered and high-alloyed, such as material 1.4112). Ferrous materials containing less than 2.08% by weight of carbon are referred to as steel. If the carbon content is higher, this is called cast iron. Steel material has better strength and toughness properties compared to cast iron, since there is no disturbance due to free graphite in the basic structure.

Mostly high-chromium-martensitic steels are used for the production of steel piston rings. However, the use of these steels has the disadvantage that the manufacturing costs are significantly higher compared to cast iron components. As the steel as Wire (analytically defined material) is purchased relatively inexpensively from external suppliers, a small added value is achieved.

Steel piston rings are made of profile wire. The supplied profile wire is wound around, cut open and pulled over a "non-circular" mandrel. On this mandrel receives the piston ring by an annealing process its desired non-circular shape, whereby the required tangential forces are set. Another disadvantage of the production of piston rings made of steel is that from a certain diameter, the ring production (winding) made of steel wire is no longer possible. In contrast, cast iron piston rings are already cast out of round so that they have an ideal shape right from the start.

Other disadvantages of this manufacturing process of steel piston rings are the dependence on the supplier (since there are only a few suppliers) and the inflexibility regarding material changes and chemical composition.

Cast iron has a much lower melting temperature than steel. The difference can be up to 350 ° C, depending on the chemical composition. Cast iron is therefore easier to melt and cast, since a lower melting temperature means a lower casting temperature and thus a smaller shrinkage due to shrinkage, whereby the cast material has fewer voids or hot and cold cracks. A lower casting temperature also leads to a lower load on the molding material (erosion, gas porosity, sand inclusions) and the furnace and lower melt costs.

• Mechanische Eigenschaften wie E-modul, Biegefestigkeit
• Wiederstandsfähigkeit gegenüber Brüchen
• Gestaltfestigkeit
• Flankenverschleiß
• Laufflächenverschleiß

It is therefore an object of the present invention to provide a steel material which, by production by gravity casting, exceeds the properties of tempered ductile iron in at least one of the following points:

• Mechanical properties such as modulus of elasticity, flexural strength
• Resistance to fractures
• Gestaltfestigkeit
• flank wear
• Treadwear

Furthermore, the steel material should be inexpensive to produce using the techniques that are also used for the production of cast iron.

According to the invention the object is achieved by a cast iron material according to claim 1, a piston ring according to claim 2, a cylinder liner according to claim 4 and a method according to claim 6. In the subclaims advantageous embodiments of the invention are included.

The melting temperature of the iron material depends not only on its carbon content, but also on the "degree of saturation". The simplified formula applies: $${\mathrm{S}}_{\mathrm{c}}=\mathrm{C}/\left(\mathrm{4}.\mathrm{26}-\mathrm{1}/\mathrm{3}\left(\mathrm{Si}+\mathrm{P}\right)\right)\mathrm{,}$$

The closer the saturation level is to 1, the lower the melting temperature. For cast iron, a saturation level of 1.0 is usually desired, wherein the cast iron has a melting temperature of 1150 ° C. The degree of saturation of steel is about 0.18, depending on the chemical composition. Eutectic steel has a melting temperature of 1500 ° C.

The saturation level can be significantly influenced by the Si and / or P content. For example, a 3% by weight higher content of silicon will be similar to a 1% higher C content. It is thus possible to produce a steel material with a C content of 1% by weight and 9.78% by weight of silicon, which has the same melting temperature as cast iron with a degree of saturation of 1.0 (C: 3.26% by weight). -%, Si: 3.0 wt .-%).

By drastically increasing the Si content, the degree of saturation of the steel material is increased and the melting temperature is lowered to the level of cast iron. Thus, it is possible to produce steel by means of the technique which is also used for the production of cast iron, for example GOE 44.

Higher amounts of silicon negatively affect the hardenability of the material as the austenite transition temperature "Ac3" is increased. Against this negative "silicon effect" According to the invention, nickel is added which, as an austenite former, widens the gamma region and shifts the Ac3 downwards, thereby enabling hardening of the high-silicon-containing steel.

A steel material according to the invention is characterized by the following composition in% by weight: C: 0.5 to 1.2 Mo: 0.1 to 0.5 Nb: 0 to 0.005 Si: 3.0 to 10.0 Mn: 0.1 to 0.5 Ti: 0 to 0.01 Ni: 2.0 to 3.5 Al: 0 to 0.01 V: 0 to 0.05 P: 0 to 0.02 Co: 0 to 0.02 Sn: 0 to 0.05 S: 0 to 0.035 Cu: 0 to 0.05 Mg: 0 to 0.01 Cr: 0 to 3.0 Remainder: Fe and production-related impurities,
wherein the steel material does not contain tungsten.

The Stahlwerkstotf may further contain at least one element which is selected from the group consisting of tantalum, boron, tellurium or bismuth or combinations thereof, in particular in an amount of up to 0.1 wt .-%.

Furthermore, the steel material may contain at least one additive selected from the group consisting of aluminum, zirconium, antimony, calcium, strontium, lanthanum. Cerium, rare earth metals or combinations thereof, preferably in an amount of up to 1 wt .-%. Rare earth metals, as well as NiMg, NiSiMg, FeMg or FeSiMg, are used as nucleants and / or for deoxidation. Particularly preferred is the addition of FeSiMg. Rare earth metals also include mixtures of lanthanides with oxides of other metals. These elements and additives may be impurities due to production or added to the melt during the process for producing the steel material according to the invention.

The ingredients are included such that the sum of all said or not explicitly mentioned starting materials, ingredients, ingredients, elements, additives in each case give 100 wt .-%. The proportion of starting materials. Ingredients, ingredients, elements and additives may be adjusted by various methods known to those skilled in the art. The chemical composition is adjusted in particular depending on the workpiece to be produced.

The steel material according to the present invention is particularly suitable for the production of piston rings and / or cylinder liners. Prefabricated piston rings and cylinder liners are coated on the flank and / or treads.

The steel material according to the invention reduces the tendency of the workpieces produced therefrom to change their shape under high heat and thus ensures a permanently high performance and, moreover, reduces the oil consumption. Due to its outstanding properties, the steel material according to the invention is therefore particularly suitable for the production of piston rings in the automotive and LB range, or for valve seat rings and Guides. In addition, drive liners (LWDs), pads for disc brake pads (Black Plates) as well as rings for cooling units, pump nozzles, as well as cylinder liners (liners) and protective bushings or parts for the chemical industry can be manufactured.

The steel material according to the invention furthermore has the advantage that the production of, for example, steel piston rings and cylinder liners with the machines and technologies necessary for the production of cast iron workpieces is made possible. In addition, the manufacturing costs correspond to those of cast iron piston rings or cylinder liners, which offers the manufacturer a cost advantage and a better added value. Likewise, material parameters can be set freely by the supplier.

According to the invention, a process is also provided for producing a steel material in which a melt preferably has the abovementioned chemical compositions.

During the melting process in an oven, preferably a cupola, the chemical composition of the melt is adjusted as needed by adding alloys. The tapping temperature of the melt is between 1480 and 1640 ° C. The properties of the melt can be controlled before casting or during casting by inoculation of the melt. Preferably, 650 g FeSiMg and / or 130 g Al and / or 650 g FeSiZr per 130 kg melt are used as nucleating agent.

Subsequently, a blank is produced with solidification of the melt. The blank can be cast with methods known in the art, such as centrifugal casting, continuous casting, stamp pressing, croning or green sand molding as a single or multiple blank, then heat treated and further processed into a piston ring or cylinder liner. The person skilled in the art will select the appropriate method due to the purpose of the blank and its general knowledge.

Preferably, a heat treatment includes austenitizing the steel material at 900 to 1000 ° C for one hour, quenching the steel material in oil or other suitable quench medium, and tempering the steel material at 420 to 470 ° C for one hour.

The following example illustrates the invention without limiting it.

Example (according to the invention)

Using the method according to the invention, a material is produced which has the following composition (% by weight): C: 1.05 Mo: 0.487 Nb: 0.0027 Si: 5.91 Mn: .464 Ti: 0.0074 Ni: 2.94 Al: 0.0082 V: 0.0148 P: 0.0171 Co: 0.0141 Sn: 0.0082 S: 0.0285 Cu: 0.0433 W: 0 Cr: 0.0331 Remainder: Fe and manufacturing impurities.

The tapping temperature is 1560 ° C. The casting temperature is 1448 ° C. The melt is seeded with 650 g FeSiMg per 130 kg melt. Table 1 shows the mechanical properties of the blank according to the invention in the tempered state.

In the figures shows

• Fig. 1 an enlarged section (100: 1) of a material produced by the method according to the invention;
• Fig. 2 an enlarged section (500: 1) of the material Fig. 1 ;
• Fig. 3 an enlarged section (1000: 1) of the material Fig. 1 ,

Table 1 Mechanical properties in the tempered state (according to DIN EN 10083-1, 10/96) Diameter [mm] <16 > 16-40 > 40 - 100 > 100 - 160 > 160 - 250 Thickness [mm] <8 8 <t <20 20 <t <60 60 <t <100 100 <t <160 Yield strength Re [N / mm ² ] minute 900 minute 750 minute 650 minute 550 minute 500 Tensile strength Rm [N / mm ² ] 1100-1400 1000-1300 900 - 1200 900 - 1100 750 - 950 Elongation at break A [%] minute 9 minute 10 minute 11 minute 12 minute 13 Fracture Z [%] minute 40 minute 45 minute 50 minute 50 minute 55 Impact test ISO-V [J] minute 30 minute 35 minute 35 minute 35 minute 35

Claims (7)

1. Highly siliciferous steel material, more preferably for piston rings and cylinder liners, characterized by the following composition in % by weight: C: 0.5 to 1.2 Mo: 0.1 to 0.5 Ti: 0 to 0.01 Si: 3.0 to 10.0 Mn: 0.1 to 0.5 V: 0 to 0.05 Ni: 2.0 to 3.5 Al: 0 to 0.01 Sn: 0 to 0.05 P: 0 to 0.02 Co: 0 to 0.02 Mg: 0 to 0.01 S: 0 to 0.035 Cu: 0 to 0.05 Cr: 0 to 3.0 Nb: 0 to 0.005 Remainder: Fe and contaminations due to the manufacture, wherein the steel material does not contain any tungsten.
2. The piston ring which as main casting comprises a steel material according to Claim 1.
3. The piston ring according to Claim 2, characterized in that it furthermore is coated on the flank and/or running surfaces.
4. A cylinder liner which as main casting comprises a steel material according to Claim 1.
5. The cylinder liner according to Claim 4, characterized in that it furthermore is coated on the running surfaces.
6. A method for the manufacture of a steel material according to Claim 1, comprising the following steps:

   a. producing a melt,

   b. casting in a prefabricated mould

   c. heat treatment of the blank.
7. The method according to Claim 6, wherein the heat treatment comprises the following steps:

   c1. austenitisation of the steel material at 900 to 1000°C for one hour,

   c2. quenching of the steel material in a suitable quenching medium, for example in oil,

   c3. annealing of the steel material at 420 to 470°C for one hour.

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