EP2511394A1 - Cast iron with niobium and component - Google Patents

Abstract

An iron-based alloy comprises (in weight%) silicon (2-4.5, preferably 2.3-3.9), carbon (2.9-4, preferably 3.2-3.7), niobium (0.05-0.7, preferably 0.05-0.6), molybdenum (0.3-1.5, preferably 0.4-1), cobalt (0.1-2, preferably 0.1-1), manganese (0.3 or less, preferably 0.15-0.3), nickel (0.5 or less, preferably 0.3), magnesium (0.07 or less, preferably 0.03), phosphorus (0.05 or less, preferably 0.02-0.035), sulfur (0.012 or less, preferably 0.005), chromium (0.1 or less, preferably 0.05), antimony (0.004 or less, preferably 0.003), and remainder of iron.

Description

The invention relates to a cast iron with niobium according to claim 1 and a component according to claim 19.

The known and used cast iron alloys (so-called GJS alloys: nodular cast iron) mainly use silicon and molybdenum to increase creep resistance, scale resistance and LCF behavior. However, these elements lead to a significant drop in toughness over time.

Molybdenum also shows a very high tendency to increase.

It is therefore an object of the invention to provide an alloy and a component which overcome the above-mentioned disadvantages and have better mechanical strength over the period of use.

The object is achieved by an alloy according to claim 1 and a component according to claim 19.

In the dependent claims further advantageous measures are listed, which are arbitrarily linked with each other in an advantageous manner.

The invention is that cobalt and / or niobium can partially replace molybdenum. Thus, the application limits, which have the previous GJS alloy can be overcome.

The iron-based alloy according to the invention has high elongations for the range of application in the temperature range of 450 ° C - 550 ° C and has the following composition (in wt .-%): Silicon (Si) 2.0% - 4.5%, especially 2.3% - 3.9% Carbon (C) 2.9% - 4.0%, in particular 3.2% - 3.7%, Niobium (Nb) 0.05% -0.7%, in particular 0.05% -0.6%, very particular 0.1% to 0.7%, Molybdenum (Mo) 0.3% - 1.5%, in particular 0.4% - 1.0% very particular 0.5% optional Cobalt (Co) 0.1% - 2.0%, in particular 0.1% - 1.0%, Manganese (Mn) ≦ 0.3%, in particular 0.15-0.30%, Nickel (Ni) ≤ 0.5%, in particular ≤ 0.3%, Magnesium (Mg) ≤ 0.07%, in particular at least 0.03%, very particular 0.03% - 0.06% Phosphorus (P) ≤ 0.05%, in particular 0.02% - 0.035%, Sulfur (S) ≤ 0.012%, in particular ≤ 0.005%, especially between 0.003% and 0.012%, Chrome (Cr) ≤ 0.1%, in particular ≤ 0.05%, Antimony (Sb) ≤ 0.004%, in particular ≤ 0.003%, Iron (Fe), especially residual iron.

Advantageously, the proportion of silicon, cobalt, niobium and molybdenum is ≦ 7.5% by weight, in particular ≦ 6.5% by weight.

Even small amounts of cobalt and / or niobium and molybdenum improve the mechanical properties.

Niobium improves creep strength with consistently high LCF strength and good toughness.

Niobium causes a higher heat resistance due to the precipitation of finely distributed Nb carbides, whereby the application limits are shifted to high temperatures.

Cobalt causes a solid solution which positively influences the properties of the alloy at high temperatures and low stresses.

By alloying molybdenum (preferably 0.4% - 1.0%), the hot strength (Rp0,2 and Rm in the elevated temperature range) and the creep strength are positively influenced.

Preferably, the proportion of cobalt in the alloy is between 0.5 wt% to 1.5 wt%.
Advantageous mechanical values are achieved for the alloy in each case if the cobalt content is from 0.1% by weight to 1.0% by weight of cobalt.

By magnesium, the spherical formation of the graphite is obtained and magnesium is preferably present at least 0.03 wt .-%, a maximum of 0.07 wt .-%.
Depending on the application, preference is given to chromium (Cr) having at least 0.01% by weight but not more than 0.05% by weight, which increases the oxidation resistance.
The alloy can have further elements.

Optionally, in the alloy low minimum admixtures of Phosphorus (P) 0.05% by weight Sulfur (S) 0.001% by weight Magnesium (Mg) 0.01% by weight Antimony (Sb) Cerium (Ce) present, which have a positive influence on the castability and / or the formation of nodular graphite, but also should not be too high, otherwise outweigh the negative influences.

Furthermore, preferably no chromium (Cr) is present in the alloy.

Embodiments of the invention will be explained in more detail with reference to the following figures.

• Figur 1 eine Dampfturbine,
• Figur 2 eine Gasturbine.

Show it:

• FIG. 1 a steam turbine,
• FIG. 2 a gas turbine.

The component with the alloy shows an optimal ferritic microstructure with nodular graphite.

The table shows exemplary alloys of the invention having improved mechanical properties. C Si Not a word Co Nb mg Mn P S sb 1 3.2 3.5 0.5 0 0.5 0.04 0.2 0.03 0.005 0.0009 2 3.3 3.6 0.5 0 0.1 0.05 0.2 0.03 0.005 0.0003 3 3.7 2.7 1.0 0.9 0.4 0.05 0.2 0.03 0.005 0.0004 4 3.5 2.4 1.0 0 0.5 0.06 0.3 0.03 0,004 0.0002 5 2.3 3.9 0.5 0 0.4 0.03 0.3 0.03 0,007 0.0030 6 3.3 3.4 0.5 1.0 0.5 0.04 0.2 0.02 0.005 0.0030 7 3.3 3.4 0.5 0.5 0.5 0.04 0.2 0.02 0.005 0.0039 8th 3.0 3.3 0.4 0 0.2 0.05 0.2 0.03 0,004 0.0014

Preferably, the alloy contains no vanadium (V) and / or titanium (Ti) and / or tantalum (Ta) and / or copper (Cu).

The ratio of C and Si should give a near-eutectic composition, that is, correspond to a carbon equivalent CE between 4.1% and 4.4% $$\left(\mathrm{CE}=\mathrm{weight}\mathrm{,}-\%\mathrm{C}+\frac{\mathit{weight}\%\mathit{Si}+\mathit{weight}\%P}{3}\right)\mathrm{,}$$

In FIG. 1 a steam turbine 300, 303 is shown with a turbine shaft 309 extending along a rotation axis 306.

The steam turbine has a high-pressure turbine section 300 and a medium-pressure turbine section 303, each having an inner housing 312 and an outer housing 315 enclosing this. The high-pressure turbine part 300 is designed, for example, in Topfbauart. The medium-pressure turbine part 303 is designed, for example, double-flow. It is also possible for the medium-pressure turbine section 303 to be single-flow.

Along the axis of rotation 306, a bearing 318 is arranged between the high-pressure turbine section 300 and the medium-pressure turbine section 303, the turbine shaft 309 having a bearing region 321 in the bearing 318. The turbine shaft 309 is supported on another bearing 324 adjacent to the high pressure turbine sub 300. In the area of this bearing 324, the high-pressure turbine section 300 has a shaft seal 345. The turbine shaft 309 is sealed from the outer housing 315 of the medium-pressure turbine section 303 by two further shaft seals 345. Between a high-pressure steam inflow region 348 and a steam outlet region 351, the turbine shaft 309 in the high-pressure turbine section 300 has the high-pressure impeller blade 357. This high-pressure bladed runner 357, together with the associated blades, not shown, represents a first blading area 360.

The medium-pressure turbine part 303 has a central steam inflow region 333. Associated with the steam inflow region 333, the turbine shaft 309 has a radially symmetrical shaft shield 363, a cover plate, on the one hand for dividing the steam flow into the two flows of the medium-pressure turbine section 303 and for preventing direct contact of the hot steam with the turbine shaft 309. The turbine shaft 309 has in the medium-pressure turbine section 303 a second blading area 366 with the medium-pressure blades 354 on. The hot steam flowing through the second blading area 366 flows out of the medium-pressure turbine section 303 from a discharge connection 369 to a downstream low-pressure turbine, not shown.

The turbine shaft 309 is composed for example of two partial turbine shafts 309a and 309b, which are fixedly connected to one another in the region of the bearing 318. Each turbine shaft 309a, 309b has a cooling line 372 formed as a central bore 372a along the axis of rotation 306. The cooling line 372 is connected to the steam outlet region 351 via an inflow line 375 having a radial bore 375a. In the medium-pressure turbine part 303, the coolant line 372 is connected to a cavity not shown below the shaft shield. The feed lines 375 are configured as a radial bore 375a, allowing "cold" steam from the high pressure turbine section 300 to flow into the central bore 372a. Via the discharge line 372, which is also designed in particular as a radially directed bore 375a, the vapor passes through the storage area 321 into the medium-pressure turbine section 303 and there to the mantle surface 330 of the turbine shaft 309 in the steam inflow area 333. The steam flowing through the cooling line has a significantly lower temperature as the reheated steam flowing into the Dampfeinströmbereich 333, so that an effective cooling of the first blade rows 342 of the medium-pressure turbine section 303 and the mantle surface 330 is ensured in the region of these blade rows 342.

The FIG. 2 shows by way of example a gas turbine 100 in a longitudinal partial section.
The gas turbine 100 has inside a rotatably mounted about a rotation axis 102 rotor 103 with a shaft 101, which is also referred to as a turbine runner.

Along the rotor 103 follow one another an intake housing 104, a compressor 105, for example, a toroidal combustion chamber 110, in particular annular combustion chamber, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust housing 109th

The annular combustion chamber 110 communicates with an annular annular hot gas channel 111, for example. There, for example, four turbine stages 112 connected in series form the turbine 108.

Each turbine stage 112 is formed, for example, from two blade rings. As seen in the direction of flow of a working medium 113, in the hot gas channel 111 of a row of guide vanes 115, a series 125 formed of rotor blades 120 follows.

The guide vanes 130 are fastened to an inner housing 138 of a stator 143, whereas the moving blades 120 of a row 125 are attached to the rotor 103 by means of a turbine disk 133, for example.
Coupled to the rotor 103 is a generator or work machine (not shown).

During operation of the gas turbine 100, air 105 is sucked in and compressed by the compressor 105 through the intake housing 104. The compressed air provided at the turbine-side end of the compressor 105 is supplied to the burners 107 where it is mixed with a fuel. The mixture is then burned to form the working fluid 113 in the combustion chamber 110. From there, the working medium 113 flows along the hot gas channel 111 past the guide vanes 130 and the rotor blades 120. On the rotor blades 120, the working medium 113 expands in a pulse-transmitting manner so that the rotor blades 120 drive the rotor 103 and drive the machine coupled to it.

The components exposed to the hot working medium 113 are subject to thermal during operation of the gas turbine 100 Charges. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, viewed in the flow direction of the working medium 113, are subjected to the greatest thermal stress in addition to the heat shield elements lining the annular combustion chamber 110.
To withstand the prevailing temperatures, they can be cooled by means of a coolant.

Likewise, substrates of the components can have a directional structure, ie they are monocrystalline (SX structure) or have only longitudinal grains (DS structure).
As the material for the components, in particular for the turbine blade 120, 130 and components of the combustion chamber 110, for example, iron-, nickel- or cobalt-based superalloys are used.
Such superalloys are for example from EP 1 204 776 B1 . EP 1 306 454 . EP 1 319 729 A1 . WO 99/67435 or WO 00/44949 known.

Also, the blades 120, 130 may be anti-corrosion coatings (MCrAlX; M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and is yttrium (Y) and / or silicon , Scandium (Sc) and / or at least one element of the rare earth or hafnium). Such alloys are known from the EP 0 486 489 B1 . EP 0 786 017 B1 . EP 0 412 397 B1 or EP 1 306 454 A1 ,

On the MCrAlX may still be present a thermal barrier coating, and consists for example of ZrO ₂ , Y ₂ O ₃ -ZrO ₂ , that is, it is not, partially or completely stabilized by yttria and / or calcium oxide and / or magnesium oxide.
By means of suitable coating processes, such as electron beam evaporation (EB-PVD), stalk-shaped grains are produced in the thermal barrier coating.

The guide vane 130 has a guide vane foot (not shown here) facing the inner housing 138 of the turbine 108 and a vane foot opposite Guide vane head on. The vane head faces the rotor 103 and fixed to a mounting ring 140 of the stator 143.

Claims (19)

Iron-based alloy comprising (in% by weight): Silicon (Si) 2.0% - 4.5%, especially 2.3% - 3.9% Carbon (C) 2.9% - 4.0%, in particular 3.2% - 3.7%, Niobium (Nb) 0.05% -0.7%, in particular 0.05% -0.6%, very particular 0.1% to 0.7%, Molybdenum (Mo) 0.3% - 1.5%, in particular 0.4% - 1.0% very particular 0.5% optional Cobalt (Co) 0.1% - 2.0%, in particular 0.1% - 1.0%, Manganese (Mn) ≦ 0.3%, in particular 0.15-0.30%, Nickel (Ni) ≤ 0.5%, in particular ≤ 0.3%, Magnesium (Mg) ≤ 0.07%, in particular at least 0.03%, very particular 0.03% - 0.06% Phosphorus (P) ≤ 0.05%, in particular 0.02% - 0.035%, Sulfur (S) ≤ 0.012%, in particular ≤ 0.005%, especially between 0.003% and 0.012%, Chrome (Cr) ≤ 0.1%, in particular ≤ 0.05%, Antimony (Sb) ≤ 0.004%, in particular ≤ 0.003%, Iron (Fe), especially residual iron. Alloy according to claim 1,
containing 0.1 wt .-% - 0.2 wt .-% of niobium (Nb), in particular 0.1 wt .-% niobium. Alloy according to claim 1,
containing 0.4 wt .-% - 0.6 wt .-% of niobium (Nb), in particular 0.5 wt .-%. Alloy according to one or more of claims 1, 2 or 3,
that does not contain cobalt (Co). Alloy according to one or more of claims 1, 2 or 3,
containing from 0.4% by weight to 0.6% by weight of cobalt, in particular 0.5% by weight of cobalt. Alloy according to one or more of claims 1, 2 or 3,
containing 0.9% by weight to 1.0% by weight of cobalt, in particular 1.0% by weight of cobalt. Alloy according to one or more of the preceding claims 1, 2 or 3,
containing 1% by weight to 2% by weight of cobalt (Co), in particular 1.5% by weight of (Co),
in particular 2.0% by weight (Co). Alloy according to one or more of the preceding claims 1, 2 or 3,
containing 0.1 wt .-% cobalt. Alloy according to one or more of the preceding claims,
their content of silicon (Si), cobalt (Co), molybdenum (Mo) and niobium (Nb) is less than 6.5% by weight. Alloy according to one or more of the preceding claims,
their content of molybdenum (Mo) and niobium (Nb) does not exceed 1.5% by weight. Alloy according to one or more of the preceding claims,
containing 2.0 wt .-% - 3.0 wt .-% silicon (Si), in particular 2.3 wt .-% - 2.7 wt .-% silicon. Alloy according to one or more of the preceding claims,
containing 3.0 wt .-% - 4.5 wt .-% silicon (Si). in particular 3.3 wt .-% - 3.5 wt .-% silicon. Alloy according to one or more of the preceding claims,
that does not contain nickel (Ni) except as a potential contaminant. Alloy according to one or more of the preceding claims,
containing at least 0.01 wt .-% nickel,
in particular at least 0.05% by weight. Alloy according to one or more of the preceding claims,
containing 2.5 wt .-% to 3.7 wt .-% carbon (C), in particular 2.9 wt .-% - 3.0 wt .-% carbon. Alloy according to one or more of the preceding claims,
that does not contain chromium (Cr) except as a potential contaminant. Alloy according to one or more of the preceding claims 1 to 16,
which has at least 0.01wt% chromium,
in particular at least 0.05 wt%. Alloy according to one or more of the preceding claims 1 to 17,
which has a CE equivalent of 4.1% to 4.4% for carbon (C), silicon (Si) and phosphorous (P), $$\mathrm{where\; CE}=\mathrm{weight}\mathrm{,}-\%\mathrm{C}+\frac{\mathit{weight}\%\mathit{Si}+\mathit{weight}\%P}{3}\mathrm{applies}\mathrm{,}$$

component
in particular consisting of an alloy according to one or more of claims 1 to 18,
in particular a housing part,
in particular a steam turbine (300, 303) or a gas turbine (100).

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