DE10320397B4 - Cast iron alloy for cylinder crankcase - Google Patents

Abstract

Cast iron alloy for lamella gray cast iron for the production of cylinder crankcases with nitrogen and a Titanium, niobium and / or tantalum and with a microincluded structure Niobium and / or tantalum carbides, in which the titanium content is above the trace level by adding niobium and / or tantalum, in each case or in total 0.01, in particular 0.3 to 5 wt .-% is at least partially replaced.

Description

The The present invention relates to a cast iron alloy for production of cylinder crankcases according to the preamble of claim 1 or 5 and corresponding Engine blocks.

Engine blocks or cylinder crankcases are made according to the prior art to a large extent of cast iron materials. So it is for example from the DE 197 80 253 C2 known to produce engine piston rings made of lamellar gray cast iron. Since particular demands are placed on the cylinder regions of reciprocating engines, in particular with regard to the tribological properties of the cylinder surface, it is known to provide hard, cube-shaped titanium carbide, titanium nitride and titanium carbonitride inclusions in cast iron materials, particularly in highly loaded diesel engines, by the coefficient of friction and cylinder wear reduce. Furthermore, the titanium carbide, titanium nitride and titanium carbonitride inclusions form micro oil pockets when they break out of the cylinder surface, in which lubricating oil can be absorbed. This also contributes to the reduction of wear but also of oil consumption. These micro-oil pockets, for example, are also produced during processing of the cylinder surface by hoisting through microbursts, which are also caused by cubic micro inclusions.

Of the required for this Titanium content of 0.03 to 0.06% is usually in part the base melt with 0.01 to 0.02% in equilibrium with the silicon content 1.8 to 2.3% as trace element before; the rest is by adding of suitable titanium carriers alloyed.

Also the nitrogen is present in the base melt as a trace element, mostly at levels of 60 to 90 ppm. The final content must be carried out with suitable nitrogen carriers be brought to such a value, sufficient education TiN, TiC / N and iron nitride.

at the present used cast iron materials, in which titanium carbide, titanium nitride and Titanium carbonitride inclusions are provided, but is disadvantageous that by the chemical Reaction of titanium with nitrogen to form titanium nitride and titanium Titanium carbonitride inclusions Cast iron nitrogen is extracted. This, however, affects with titanium held by over 0.03 wt .-% very negative on the strength of the cast iron materials because of the withdrawal of the nitrogen dissolved in the structure and the prevention The strength of the formation of iron nitrides at the grain boundaries can be reduced. The prior art is attempted counteract this by adding strength-enhancing alloying elements, such as chrome zulegiert. However, this increases the risk of voids formation and leads to a poorer workability of the cast iron material.

Finally, from the DE 196 29 970 C1 Cast iron alloys are known for engine piston rings, which are distinguished by a pearlitic basic structure with spherical or vermicular graphite precipitates in order to achieve high strength values. For further perlitization, titanium, niobium and tantalum, among others, may be added up to 4.0% by weight.

It is therefore an object of the present invention, a cast iron material for the Manufacture of cylinder crankcases or corresponding engine blocks, which in a simple way the properties strength, wear resistance and combine good machinability.

These Task is solved by a cast iron alloy having the features of claim 1 respectively of claim 5 Advantageous embodiments are the subject of dependent Claims.

The invention is based on the recognition that the disadvantages of the titanium content in cast iron alloys with respect to the reduction in strength due to the formation of titanium nitrides can be counteracted by using niobium and tantalum as alloying additives instead of the titanium, the tribological properties of the cast iron alloy, in particular in the cylinder region can be maintained in the known alloys by the hard, cube-shaped titanium carbide, titanium nitride and titanium carbonitride inclusions can be maintained. This is due to the properties of niobium and tantalum, which have a lower affinity for nitrogen and a higher affinity for carbon and sulfur and form cubic micro inclusions with these elements. Due to these properties, less nitrogen is removed by niobium and / or tantalum to form titanium nitrides or niobium or tantalum nitrides, which is important for the strength properties of the cast iron alloy. At the same time, however, niobium and / or tantalum form hard inclusions due to the higher affinity for carbon and sulfur, for example salt-like carbides, for example in angular, in particular in cubic form, which play the role of titanium carbide, titanium nitride and titanium carbonitride inclusions for the can take tribological properties. In addition, niobium and tantalum, which are added as micro-alloying components in proportions of 0.01 to 5 wt .-%, preferably 0.3 to 0.9%, or preferably with values of at most 5 wt .-%, one such Density, which avoids a floating out of the melt. In addition, niobium and tantalum have a low tendency to slagging the cast iron melts, so that this too favors the processability of the alloy with a higher accuracy.

The niobium and tantalum components, which normally have a higher melting point than the cast iron alloy, can be introduced into the melt in a known manner via carrier alloys, for example, ferroniobium, ferrotantal or ferroniobtantalene, such as, for example, US Pat DE 19 728 771 C2 described.

Even though already achieves the advantages of the present invention, if titanium is only partially replaced by niobium and / or tantalum, it is preferred that the titanium content is ≤ 0.02 % By weight, ie titanium essentially via the trace element content completely to replace.

Around to achieve sufficient strength of the cast iron alloy it is preferable that the nitrogen content is in a range of 0.01 to choose 0.025 wt .-%. With this nitrogen content can the desired Strength values in particularly favorable Be achieved manner.

A preferred hypoeutectic cast iron alloy according to the invention has the following composition in% by weight:
Carbon 2 to 4%, especially 2.5 to 3.4%, preferably 2.8 to 3.3%
Silicon 0.5 to 3%, in particular 1.7 to 2.6%, preferably 1.8 to 2.3%
Niobium 0.3 to 5%, in particular 0.5 to 5.0%, preferably 0.3 to 1.0%
Tantalum 0.3 to 5%, in particular 0.5 to 5.0%, preferably 0.3 to 1.0%
Titanium 0.01 to 0.02% (track level)
Chrome 0.15 to 0.35%
Sulfur 0.10 to 0.17%
Remaining iron, iron companion, trace elements and unavoidable impurities.

To In another aspect of the present invention, the above described cast iron alloys for the production of cylinder crankcases for reciprocating engines, especially for Used diesel engines. By training the hard, preferably angular, in particular cubic inclusions of niobium and / or tantalum carbides When machining the cylinder surface, it comes close to the existing graphite fins to small outbreaks the hard particles, so that micro oil pockets form. This reduces the oil consumption and improves wear resistance. Furthermore become low due to the hard particles in the cylinder surface Friction coefficients and thus also increased wear resistance guaranteed.

Example for you production of cylinder crankcases from the alloy according to the invention:

Such Parts are according to the prior art in sand casting with Resin bonded cores and outer molds made of synthetic resin or Bentonite-bound sand produced. These molding materials and the Sand thickness set the solidification and Abkühlverhältnisse and thus essential the microstructure education firmly. The mechanical properties are also affected by these conditions characterized. For cylinder crankcase with a gross weight of 35 to 250 kg and wall thicknesses of 7 up to 15 mm in the cylinder tube area in the cast state are with the alloy according to the invention while preserving the tribological advantages and good machinability Tensile strengths of 260 to 320 MPa achieved.

Claims (5)

Cast iron alloy for lamella gray cast iron for manufacturing of cylinder crankcases with nitrogen and a titanium, niobium and / or tantalum component and having a structure with micro inclusions of niobium and / or tantalum carbides, at the titanium portion over the trace content by adding niobium and / or tantalum with each or in total 0.01, in particular 0.3 to 5 wt .-% at least partially is replaced. Cast iron alloy according to claim 1, characterized that the titanium content ≤ 0.02 wt .-% is. Cast iron alloy according to claim 1 or 2, characterized characterized in that the nitrogen content is 0.01 to 0.025% by weight is. Cast iron alloy according to one of the preceding Claims, characterized in that the niobium and tantalum portion together maximum 5 wt .-% is. Cast iron alloy for lamellar gray cast iron for producing cylinder crankcases, characterized by the following composition in% by weight: carbon 2 to 4%, in particular 2.5 to 3.4%, preferably 2.8 to 3.3% silicon 0.5 to 3 %, in particular 1.7 to 2.6%, preferably 1.8 to 2.3% niobium 0.3 to 5%, in particular 0.5 to 5.0%, preferably 0.3 to 1.0% tantalum 0 , 3 to 5%, especially 0.5 to 5.0%, preferably 0.3 to 1.0% titanium 0.01 to 0.02% (trace level) Chromium 0.15 to 0.35% sulfur 0.10 to 0.17% balance Iron, iron, trace elements and unavoidable impurities.