CrMoV steel casting alloys and processes for their production and use in turbines

Abstract

Cast alloy comprising, by weight, 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, balance iron and usual impurities.

Description

AREA OF INVENTION

[0001] The invention relates generally to the field of steel alloy castings and related processes and articles. In one embodiment, a CrMoV steel casting alloy for high temperature and high strength is generally disclosed together with a process for manufacturing an article therefrom. BACKGROUND OF THE INVENTION

[0002] Components of steam turbines, gas turbines, gas turbine engines, and jet engines are subject to a range of operating conditions along their axial lengths. These varying operating conditions not only complicate the selection of a suitable casting material and manufacturing process, but also influence the material and manufacturing of stationary components within such turbines. For example, a material optimized for one operating condition may not be optimal for another. The inlet and outlet regions of a steam turbine casting, for instance, have different material property requirements compared to those of a gas turbine. Steam turbine castings are generally pressurized chambers at high temperatures, and consequently, creep resistance is a limiting factor.On the other hand, gas turbine castings are typically subjected to frequent thermal cycles, so fatigue can be a limiting factor. These sometimes conflicting properties are managed with a suitable mix of heat treatment cycles to achieve an optimal balance of strength, toughness, creep resistance, and fatigue properties, depending on the application.

[0003] For casting bodies and other cast components, the steam turbine industry currently favors low-alloy CrMoV steels for temperatures below 1050°F. If higher inlet temperatures, e.g., up to 1060°F (approximately 575°C), are desired to increase steam turbine efficiency, chromium steel alloys with approximately 9–14 wt% chromium and varying amounts of molybdenum, vanadium, tungsten, niobium, and boron are typically used to meet the higher temperature requirements in the high-pressure (HP) stage of the steam turbine. While capable of operating at temperatures above 565°C within the HP stage of a steam turbine, cast components made from these alloys involve higher costs, and additional measures are often required to manage thermal expansion mismatches with alloys used in colder-stage cast components.

[0004] Such high-alloy chromium steel alloys are not only expensive to produce, but they are also not particularly well-suited for the casting processes used to form the various stationary components of such turbines (e.g., casing, valve, diaphragm, sealing head, or sealing ring). Currently, various stationary components of such turbines are typically manufactured from CrMoV steel alloys (for components exposed to temperatures up to 1050°F) and steel alloys with 9–12% chromium (for applications requiring either higher temperature or higher stress). In high-temperature applications, the cost of steel alloys with 9–12% chromium—primarily due to the relatively high chromium content—can significantly impact the turbine design, component selection, and final cost.

[0005] BE 700 498 A discloses a turbine with a component cast from a cast alloy having the following composition by weight: 0.05% to 0.4% carbon, 0.25% to 1.0% manganese, 0.1% to 1.0% silicon, 0.25% to 1.00% nickel, 1.5% to 5.0% chromium, 0.5% to 1.5% molybdenum, 0.1% to 1.00% vanadium, 0.01% to 0.1% titanium, 0.001% to 0.01% boron, balance iron and usual impurities. BRIEF DESCRIPTION OF THE INVENTION

[0006] Aspects and advantages of the invention are set out in the following description or will become apparent from the description or implementation of the invention.

[0007] Generally, a casting alloy is provided together with components constructed from the casting alloy (e.g., stationary components of a turbine). In one embodiment, the cast alloy includes, by weight, 0.12% to 0.20% carbon (e.g., 0.14% to 0.17% carbon), 0.50% to 0.90% manganese, 0.25% to 0.60% silicon (e.g., 0.25% to 0.35% silicon), 0.10% to 0.50% nickel (e.g., 0.20% to 0.35% nickel), 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium (e.g., 0.74% to 0.77% vanadium), and 0.0075% to 0.060% titanium (e.g., 0.010% to 0.035% titanium). 0.008% to 0.012% boron (e.g. 0.009% to 0.010% boron), the remainder iron and common impurities, such as, but not limited to, up to 0.012 wt% phosphorus, up to 0.012 wt% sulfur, up to 0.010 wt% tin, up to 0.015 wt% arsenic, up to 0.015 wt% aluminum, up to 0.0035 wt% antimony and up to 0.15 wt% copper.

[0008] The usual impurities of any of the above-mentioned cast alloys may, by weight, include up to 0.012% phosphorus, up to 0.002% sulfur, up to 0.010% tin, up to 0.015% arsenic, up to 0.015% aluminum, up to 0.0035% antimony and up to 0.15% copper.

[0009] The usual impurities of any of the above-mentioned cast alloys may include, by weight, 0.001% to 0.005% phosphorus, 0.0005% to 0.002% sulfur, 0.001% to 0.004% tin, 0.001% to 0.004% arsenic, 0.001% to 0.005% aluminum, 0.001% to 0.0025% antimony, and 0.005% to 0.015% copper.

[0010] The casting alloy of any of the above-mentioned types may consist of carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, boron, iron, up to 0.012 wt% phosphorus, up to 0.012 wt% sulfur, up to 0.010 wt% tin, up to 0.015 wt% arsenic, up to 0.015 wt% aluminum, up to 0.0035 wt% antimony and up to 0.15 wt% copper.

[0011] The casting alloy of any of the above-mentioned types may consist, by weight, of carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, boron, iron, 0.001% to 0.005% phosphorus, 0.0005% to 0.002% sulfur, 0.001% to 0.004% tin, 0.001% to 0.004% arsenic, 0.001% to 0.005% aluminum, 0.001% to 0.0025% antimony and 0.005% to 0.015% copper.

[0012] The casting alloy of any of the above-mentioned types may contain 0.25% to 0.35% silicon by weight.

[0013] The casting alloy of any of the above-mentioned types may contain, by weight, 0.14% to 0.17% carbon.

[0014] The casting alloy of any of the above-mentioned types may contain, by weight, 0.010% to 0.035% titanium.

[0015] The casting alloy of any of the above-mentioned types may contain 0.20% to 0.35% nickel by weight.

[0016] The casting alloy of any of the above-mentioned types may contain, by weight, 0.009% to 0.010% boron.

[0017] The casting alloy of any of the above-mentioned types may contain 0.74% to 0.77% vanadium by weight.

[0018] A turbine can be provided which has at least one stationary component cast from the casting alloy of any type mentioned above.

[0019] Thus, the casting alloy, for example, in a particular embodiment, can consist of, based on weight, 0.12% to 0.20% carbon (e.g., 0.14% to 0.17% carbon), 0.50% to 0.90% manganese, 0.25% to 0.60% silicon (e.g., 0.25% to 0.35% silicon), 0.10% to 0.50% nickel (e.g., 0.20% to 0.35% nickel), 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium (e.g., 0.74% to 0.77% vanadium), 0.0075% to 0.060% titanium (e.g., 0.010% to 0.035%). titanium), 0.008% to 0.012% boron (e.g. 0.009% to 0.010% boron), iron, up to 0.012 wt% phosphorus, up to 0.012 wt% sulfur, up to 0.010 wt% tin, up to 0.015 wt% arsenic, up to 0.015 wt% aluminum, up to 0.0035 wt% antimony and up to 0.15 wt% copper.

[0020] The stationary component of the turbine can be a jacket, a sealing head, or a sealing ring.

[0021] Generally, methods are also provided for forming a casting alloy. In one embodiment, the method includes forming an alloy precursor, melting the alloy precursor to form a molten alloy composition, arranging the molten alloy composition in a mold, and cooling the molten alloy composition within the mold to form the casting alloy. The alloy precursor may contain, by weight, 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, the remainder iron, and common impurities such as, but not limited to, up to 0.012 wt% phosphorus, up to 0.012 wt% sulfur, up to 0.010 wt% tin, up to 0.015 wt% arsenic, up to 0.015 wt% aluminum, up to 0.0035 wt.-% antimony and up to 0.15 wt% copper.

[0022] In a particular embodiment, the method further includes heat-treating the cast alloy at a treatment temperature of about 1700°F to about 1975°F for about 4 hours to about 48 hours and tempering the cast alloy by heating it to a tempering temperature of about 1200°F to about 1300°F for about 4 hours to about 48 hours.

[0023] A process for forming a casting alloy may include: forming an alloy precursor comprising, by weight, 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, the remainder being iron and common impurities; melting the alloy precursor to form a molten alloy composition; arranging the molten alloy composition in a mold; and cooling the molten alloy composition within the mold to form the Cast alloy.

[0024] Any of the above-mentioned processes may include the usual impurities, by weight, up to 0.012% phosphorus, up to 0.012% silicon, up to 0.010% tin, up to 0.015% arsenic, up to 0.015% aluminium, up to 0.0035% antimony and up to 0.15% copper.

[0025] Any of the above-mentioned processes may include an alloy precursor consisting of carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, boron, iron, up to 0.012 wt% phosphorus, up to 0.012 wt% silicon, up to 0.010 wt% tin, up to 0.015 wt% arsenic, up to 0.015 wt% aluminium, up to 0.0035 wt% antimony and up to 0.15 wt% copper.

[0026] Any of the above-mentioned processes may further include: heat-treating the cast alloy at a treatment temperature of about 1700°F to about 1975°F for about 4 hours to about 48 hours, and tempering the cast alloy by heating it to a tempering temperature of about 1200°F to about 1300°F for about 4 hours to about 48 hours.

[0027] Any of the above-mentioned procedures may involve a treatment temperature of approximately 1900°F to approximately 1950°F.

[0028] Any of the above-mentioned procedures may involve a treatment temperature of approximately 1750°F to approximately 1800°F.

[0029] These and other features, aspects, and advantages of the present invention will be better understood with reference to the following description and the attached claims. The accompanying drawing, which is included and forms part of this application, illustrates embodiments of the invention and, together with the description, serves to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWING

[0030] A complete and enabling disclosure of the present invention, including the best form thereof, to a person skilled in the art, is set out in the description which refers to the accompanying figures in which: Fig. 1 a schematic side view of an exemplary steam turbine according to an embodiment of this invention; Fig. 2 an enlarged sectional view of a sealing head for the in Fig. The steam turbine shown is; Fig. 3 a section of a sealing assembly for the in Fig. 1 steam turbine shown according to an embodiment of this invention is and Fig. Figure 4 shows a flow diagram of an exemplary process suitable for forming a casting alloy according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] Detailed reference will now be made to embodiments of the invention, one or more examples of which are illustrated in the drawing. Each example is given to explain the invention, not to limit it. It will be clear to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope or spirit of the invention. For example, features shown or described as part of one embodiment can be used together with another embodiment to give yet another embodiment. It is therefore intended that the present invention covers such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0032] It should be clear that the areas and boundaries mentioned herein include all areas (i.e., sub-areas) located within the prescribed limits. For example, an area from approximately 100 to approximately 200 also includes areas from 110 to 150, 170 to 190, 153 to 162, and 145.3 to 149.6. Furthermore, a limit of up to approximately 7 also includes limits up to approximately 5, up to 3, and up to approximately 4.5, as well as areas within the limit, such as from approximately 1 to approximately 5 and from approximately 3.2 to approximately 6.5.

[0033] In the present disclosure, chemical elements are discussed using their usual chemical abbreviations, as they are commonly found in the periodic table of elements. Thus, for example, hydrogen is represented by its usual chemical abbreviation H; helium is represented by its usual chemical abbreviation He, and so on.

[0034] A low-alloy CrMoV steel casting alloy is generally supplied with processes for casting objects from it. In one embodiment, the low-alloy CrMoV steel casting alloy bridges the performance gap between 9-12% Cr CrMoV steels and traditional CrMoV steels, and it has the potential to reduce costs (as a replacement for 9-12% Cr steels in an application up to 1080°F). Additionally, the low-alloy CrMoV steel casting alloy has improved properties over currently available CrMoV steels, including better creep characteristics compared to materials currently in use. The wall thickness of certain stationary components in a turbine (e.g., a casing) can be reduced without compromising reliability.The low-alloy CrMoV steel casting alloy can, in a particular embodiment, be used as a replacement for steel castings containing 9-12% Cr in applications at 1050°F to 1080°F. To avoid the use of steel castings with 9-12% Cr and other alloys with coefficients of thermal expansion that differ from conventional CrMoV steel alloys, castings made from the alloy provided here can be used in the service market as part of a modification package to improve the performance of existing turbine units, as well as in new turbine designs.

[0035] The low-alloy CrMoV steel casting alloy is particularly suitable for use in the formation of stationary turbine components (e.g., steam turbines, gas turbines, gas turbine engines, and jet engines). To achieve the mechanical properties necessary for use as a stationary turbine component, the alloy is configured for use at operating temperatures of 1050°F to 1080°F.

[0036] In one embodiment, the cast alloy includes, by weight, 0.12% to 0.20% carbon (e.g., 0.14% to 0.17% carbon), 0.50% to 0.90% manganese, 0.25% to 0.60% silicon (e.g., 0.25% to 0.35% silicon), 0.10% to 0.50% nickel (e.g., 0.20% to 0.35% nickel), 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium (e.g., 0.74% to 0.77% vanadium), and 0.0075% to 0.060% titanium (e.g., 0.010% to 0.035% titanium). The alloy contains 0.008% to 0.012% boron (e.g., 0.009% to 0.010% boron), the remainder iron, optionally small amounts of other alloying elements, and common impurities. In a particular embodiment, the cast alloy consists, for example, by weight, of 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, the remainder iron, and common impurities.

[0037] Due to the casting processes used to form the low-alloy CrMoV steel casting alloy, silicon was incorporated while the relative amount of carbon present was reduced, compared to the low-alloy CrMoV steel described in US Publication No. 2011 / 0070088, which is directed toward a low-alloy CrMoV alloy steel adapted for forging into rotating turbine components. Without being bound to any specific theory, it is assumed that the relatively large amount of silicon and the relatively small amount of carbon in the casting alloy (especially compared to the low-alloy CrMoV steel described in US Publication No. 2011 / 0070088) allow sufficient fluidity during melting to permit the molten alloy composition to flow into the mold.

[0038] As explained, common impurities may be present in the casting alloy. In certain embodiments, the usual impurities that may be present in the casting alloy, based on weight, may be up to 0.012% phosphorus (e.g., 0.001% to 0.005% phosphorus), up to 0.002% sulfur (e.g., 0.0005% to 0.002% sulfur), up to 0.010% tin (e.g., 0.001% to 0.004% tin), up to 0.015% arsenic (e.g., 0.001% to 0.004% arsenic), up to 0.015% aluminum (e.g., 0.001% to 0.005% aluminum), up to 0.0035% antimony (e.g., 0.001% to 0.0025% antimony), and / or up to 0.15% copper (e.g., 0.005% to 0.015% copper). In a particular embodiment, the casting alloy consists of carbon (e.g., 0.12% to 0.20% carbon), manganese (e.g., 0.50% to 0.90% manganese), silicon (e.g., 0.25% to 0.60% silicon), nickel (e.g., 0.10% to 0.50% nickel), chromium (e.g., 1.15% to less than 1.50% chromium), molybdenum (e.g., 0.90% to 1.50% molybdenum), vanadium (e.g.,0.70% to 0.80% vanadium), titanium (e.g., 0.0075% to 0.060% titanium), boron (e.g., 0.008% to 0.012% boron), iron, up to 0.012% phosphorus (e.g., 0.001% to 0.005% phosphorus), up to 0.002% sulfur (e.g., 0.0005% to 0.002% sulfur), up to 0.010% tin (e.g., 0.001% to 0.004% tin), up to 0.015% arsenic (e.g., 0.001% to 0.004% arsenic), up to 0.015% aluminum (e.g., 0.001% to 0.005% aluminum), up to 0.0035% antimony (e.g., 0.001% to 0.0025% antimony) up to 0.15% copper (e.g. 0.005% to 0.015% copper) and other common impurities (if present).

[0039] As explained, the low-alloy CrMoV steel casting alloy is particularly suitable for use in forming stationary turbine components. Referring, for example, to Fig. Figure 1 shows a general schematic representation of an exemplary steam turbine 10. The steam turbine 10 has a first or generator end section 12 and an opposing second or turbine end section 14. The steam turbine 10 closes a (in Fig. 1 (not shown) rotor shaft, which extends along at least a portion of an axial centerline 16 of the steam turbine 10. During operation of the steam turbine 10, high-pressure steam from a steam source, such as a (not shown) power boiler, enters the steam turbine 10 at the steam inlet 19 and exits at the turbine end section 14, as shown in Fig. 1 shown, off.

[0040] A stationary inner shell 20 is arranged around the rotor shaft and extends along the axial centerline 16. The inner shell 20 encloses a generator end surface 21 and an opposing turbine end surface 22. The inner shell forms a chamber 23 within which the rotor shaft is arranged. As shown in Fig. As shown in Figure 1, a sealing head 24 is connected to the inner shell 20 and arranged within the chamber 23. The sealing head 24 is arranged circumferentially around the rotor shaft and the axial centerline 16. Referring to Fig. 2. The sealing head 24 includes a plurality of channels 26. In one embodiment, the sealing head 24 includes eight channels 26 formed along an axial length of the sealing head 24. Further referring to Fig. 2 Each channel 26 extends circumferentially around the axial centerline 16 and is dimensioned to receive a sealing ring 28. As in Fig. As shown in Figure 3, each sealing ring 28 is held in a corresponding channel 26 defined in the sealing head 24. In alternative embodiments, the sealing head 24 includes any suitable number of channels 26.

[0041] In one embodiment, steam turbine 10 includes a sealing assembly 30, as shown in Fig. 3 shown. In Fig. Figure 3 illustrates only a portion of a rotor shaft 32 and a portion of the sealing head 24. A radial clearance 33 is defined between the rotor shaft 32 and the sealing head 24 and / or sealing rings 28. Each sealing ring 28 includes an inner ring section 34 with teeth 36 extending from a radially inner surface 37 of the inner ring section 34 and a radially outer surface 38, facilitating control of the radial clearance or gap 33 by contacting a radial surface 41 of the sealing head 24. Each sealing ring 28 also includes an outer ring section 42 located within the channel 26.

[0042] Sealing ring 28 encloses a plurality of teeth 36 arranged opposite a plurality of rotor shaft circumferential projections 48 extending outward from the rotor shaft 32. A positive force can force a fluid flow through the many restrictions formed within the radial distance 33, which is defined at least partially between the teeth 36 and the rotor shaft 32. More specifically, the radial distance 33, the number and relative sharpness of the teeth 36, the number of rotor shaft circumferential projections 48, and / or the operating conditions, including pressure and density, are factors that determine the extent of leakage flow. Alternatively, other geometric arrangements can be used to provide multiple or single leakage restraints.

[0043] As in Fig. As shown in Figure 1, the steam turbine 10 encloses an outer shell 60 arranged around the inner shell 20. The outer shell 60 includes a first or generator end surface 61 and an opposing second or turbine end surface 62, which generally correspond to the generator end surface 21 and the turbine end surface 22 of the inner shell 20. In one embodiment, the inner shell 20 is aligned with the outer shell 60 along a transverse centerline of the steam turbine 10. Although the turbine casing has been shown with an inner shell 20 and an outer shell 60, in an alternative embodiment it may also have a single-shell configuration.

[0044] As explained, stationary components of the turbine 10 (e.g., inner casing 20, outer casing 60, sealing head 24, sealing rings 28, etc.) can be constructed from the low-alloy CrMoV steel casting alloy described above. Although explained with reference to the steam turbine 10, it should be clear that the low-alloy CrMoV steel casting alloy can be used in stationary components of other types of turbines, including, but not limited to, gas turbines, gas turbine engines, and jet engines.

[0045] Any suitable casting process can be used to form the stationary components from the low-alloy CrMoV steel, including, but not limited to, sand casting, centrifugal casting, etc. For example, Fig.4 An exemplary process 100 for forming a casting alloy. Process 100 includes the formation of an alloy precursor at 102, the melting of the alloy precursor to form a molten alloy composition at 104, the arrangement of the molten alloy composition in a mold at 106, and finally the cooling of the molten alloy composition within the mold to form the casting alloy at 108.

[0046] Generally, the alloy precursor, which is formed in 102 and melted in 104, is formed from the components of the final casting alloy in the desired weight percent. For example, in one embodiment, the alloy precursor comprises, by weight, 0.12% to 0.20% carbon (e.g., 0.14% to 0.17% carbon), 0.50% to 0.90% manganese, 0.25% to 0.60% silicon (e.g., 0.25% to 0.35% silicon), 0.10% to 0.50% nickel (e.g., 0.20% to 0.35% nickel), 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium (e.g., 0.74% to 0.77% vanadium), and 0.0075% to 0.060% titanium (e.g., 0.010% to 0.035% titanium). 0.008% to 0.012% boron (e.g., 0.009% to 0.010% boron), the remainder iron, optionally small amounts of other alloying elements and common impurities. For example, it consists of..., in a particular embodiment, the alloy precursor, based on weight, consists of 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, the remainder being iron and usual impurities, such as up to 0.012% phosphorus (e.g., 0.001% to 0.005% phosphorus), up to 0.002% sulfur (e.g., 0.0005% to 0.002% sulfur), up to 0.010% tin (e.g., 0.001% to 0.004% tin), up to 0.015% arsenic (e.g., 0.001% to 0.004% arsenic), up to 0.015% aluminum (e.g., 0.001% to 0.005% aluminum), up to 0.0035% antimony (e.g., 0.001% to 0.0025% antimony), and / or up to 0.15% copper (e.g., 0.005% to 0.015% copper). In a particular embodiment, the alloying precursor consists, for example, of carbon (e.g., 0.12% to 0.20% carbon), manganese (e.g., 0.50% to 0.90% manganese), silicon (e.g., 0.25% to 0.60% silicon), nickel (e.g.,0.10% to 0.50% nickel), chromium (e.g., 1.15% to less than 1.50% chromium), molybdenum (e.g., 0.90% to 1.50% molybdenum), vanadium (e.g., 0.70% to 0.80% vanadium), titanium (e.g., 0.0075% to 0.060% titanium), boron (e.g., 0.008% to 0.012% boron), iron, up to 0.012% phosphorus (e.g., 0.001% to 0.005% phosphorus), up to 0.002% sulfur (e.g., 0.0005% to 0.002% sulfur), up to 0.010% tin (e.g., 0.001% to 0.004% tin), up to 0.015% arsenic (e.g., 0.001% to 0.004% arsenic), up to 0.015% aluminum (e.g. 0.001% to 0.005% aluminum), up to 0.0035% antimony (e.g. 0.001% to 0.0025% antimony), up to 0.15% copper (e.g. 0.005% to 0.015% copper) and other common impurities (if present).

[0047] After forming, the casting alloy can be heat-treated within the mold at a treatment temperature of approximately 1700°F to 1975°F for approximately 4 to 48 hours (e.g., approximately 4 to 24 hours). This heat treatment influences the microstructure of the resulting casting alloy, which in turn affects certain properties of the alloy (e.g., creep and fatigue properties). In one embodiment, the temperature and duration of the heat treatment can be adjusted to control certain properties of the resulting treated casting alloy. For example, the heat treatment temperature can be set from approximately 1900°F to approximately 1950°F to improve the creep properties of the resulting treated casting alloy, which may be particularly desirable in cast alloy components of a steam turbine.Alternatively, the heat treatment temperature can be approximately 1750°F to approximately 1800°F to improve the fatigue properties of the resulting treated cast alloy, which may be particularly desirable in cast alloy components of a gas turbine.

[0048] After heat treatment, the cast alloy can then be tempered by heating it to a temperature of approximately 1200°F to approximately 1300°F for approximately 4 hours to approximately 48 hours (e.g., approximately 8 hours to approximately 24 hours). In one embodiment, the temperature and duration of the tempering treatment can be adjusted to control certain properties of the resulting treated cast alloy (e.g., its strength).

[0049] This description uses examples to disclose the invention, including the best possible way, and also to enable a person skilled in the art to carry out the invention, including manufacturing and using any devices or systems and carrying out any methods included. The patentable scope of the invention is defined by the claims and may include other examples that would be apparent to a person skilled in the art. Such other examples shall fall within the scope of the claims if they include structural elements that do not differ from the wording of the claims or if they include equivalent structural elements with insignificant differences from the wording of the claims.

[0050] A casting alloy is generally provided, along with methods for forming the casting alloy and components constructed from the casting alloy (e.g., stationary turbine components). The casting alloy may contain, by weight, 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, the balance being iron, optionally small amounts of other alloying elements, and common impurities. REFERENCE MARK LIST 10 steam turbine 12 Generator end section 14 Turbine end section 16 axial midline 19 Steam inlet 20 inner coat 21 Generator end surface 22 Turbine end surface 23rd Chamber 24 Sealing head 26 channels 28 sealing rings 30 sealing assembly 32 Rotor shaft 33 gap 34 inner ring section 36 teeth 37 radial inner surface 38 radial outer surface 41 radial surface 42 outer ring section 48 rotor shaft circumference projections 60 outer coat 61 Generator end surface 62 Turbine end surface 100 procedures

Claims

[1] Cast alloy comprising, by weight, 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, balance iron and usual impurities. [2] Cast alloy according to claim 1, wherein the usual impurities, based on weight, comprise up to 0.012% phosphorus, up to 0.002% sulfur, up to 0.010% tin, up to 0.015% arsenic, up to 0.015% aluminium, up to 0.0035% antimony and up to 0.15% copper. [3] Cast alloy according to claim 1, wherein the usual impurities, based on weight, comprise 0.001% to 0.005% phosphorus, 0.0005% to 0.002% sulfur, 0.001% to 0.004% tin, 0.001% to 0.004% arsenic, 0.001% to 0.005% aluminium, 0.001% to 0.0025% antimony and 0.005% to 0.015% copper. [4] Cast alloy according to claim 1, wherein the cast alloy consists of carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, boron, iron, up to 0.012 wt.% phosphorus, up to 0.012 wt.% sulfur, up to 0.010 wt.% tin, up to 0.015 wt.% arsenic, up to 0.015 wt.% aluminium, up to 0.0035 wt.% antimony and up to 0.15 wt.% copper. [5] Cast alloy according to claim 4, wherein the cast alloy, based on weight, consists of carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, boron, iron, 0.001% to 0.005% phosphorus, 0.0005% to 0.002% sulfur, 0.001% to 0.004% tin, 0.001% to 0.004% arsenic, 0.001% to 0.005% aluminium, 0.001% to 0.0025% antimony and 0.005% to 0.015% copper. [6] Cast alloy according to claim 1, wherein the cast alloy comprises 0.25% to 0.35% silicon by weight and / or wherein the cast alloy comprises 0.14% to 0.17% carbon by weight and / or wherein the cast alloy comprises 0.010% to 0.035% titanium by weight and / or wherein the cast alloy comprises 0.20% to 0.35% nickel by weight and / or wherein the cast alloy comprises 0.009% to 0.010% boron by weight and / or wherein the cast alloy comprises 0.74% to 0.77% vanadium by weight. [7] Turbine with at least one stationary component cast from the casting alloy according to claim 1. [8] Turbine according to claim 7, wherein the stationary component is a jacket, a sealing head or a sealing ring. [9] Method for forming a casting alloy, comprising: Forming an alloying precursor, comprising, by weight, 0.12% to 0.20% carbon, 0.50% to 0.90% manganese, 0.25% to 0.60% silicon, 0.10% to 0.50% nickel, 1.15% to less than 1.50% chromium, 0.90% to 1.50% molybdenum, 0.70% to 0.80% vanadium, 0.0075% to 0.060% titanium, 0.008% to 0.012% boron, balance iron and usual impurities; Melting the alloy precursor to form a molten alloy composition; Arranging the molten alloy composition in a mold and Cooling of the molten alloy composition within the mold to form the casting alloy.

Images