NICKEL BASE CASTING ALLOY, CASTING, AND METHOD FOR MANUFACTURING AN IMPELLER OF A ROTARY MACHINE

Abstract

A nickel base casting alloy includes a composition, by weight percent: 19.0-22.5 chromium, 7.0-9.5 molybdenum, 2.75-4.0 niobium, 1.0-1.7 titanium, 0.35-1.0 manganese, 0.2-1.0 silicon, 0 - 0.03 carbon, 0-0.015 phosphorus, 0-0.01 sulfur, 0-0.35 aluminum, 0-13.25 iron, the balance being nickel and incidental impurities.

Claims

1. A nickel base casting alloy consisting of: a composition, by weight percent: 19.0-22.5 chromium, 7.0-9.5 molybdenum, 2.75 4.0 niobium, 1.0-1.7 titanium, 0.35-1.0 manganese, 0.2-1.0 silicon, 0-0.03 carbon, 0-0.015 phosphorus, 0-0.01 sulfur, 0-0.35 aluminum, 0-13.25 iron, the balance being nickel and incidental impurities.

2. The alloy in accordance with claim 1, wherein the composition includes 57-61 weight percent nickel.

3. The alloy in accordance with claim 1, wherein the composition includes at least 0.25 weight percent silicon.

4. The alloy in accordance with claim 1, wherein the composition includes at least 0.40 weight percent manganese.

5. The alloy in accordance with claim 1, wherein the composition includes at least 0.25 weight percent silicon and at least 0.40 weight percent manganese.

6. The alloy in accordance with claim 1, wherein the composition includes at most 10 weight percent iron.

7. The alloy in accordance with claim 1, wherein the composition includes 4-6 weight percent iron.

8. The alloy in accordance with claim 1, wherein the composition includes a 0.2% proof stress of at least 750 MPa, at 20 Celsius.

9. A casting cast from an alloy according to claim 1.

10. The casting in accordance with claim 9, wherein the casting is an impeller of a rotary machine.

11. A method for manufacturing an impeller of a rotary machine, the method comprising: providing a melt of the alloy in accordance with claim 1, introducing the melt into a mold for producing a casting, removing the casting from the mold after solidification of the melt, and finishing the casting to produce the impeller.

12. The method in accordance with claim 11, wherein the solidified casting is densified by applying an isostatic pressure of at least 10 MPa.

13. The method in accordance with claim 12, wherein the casting is densified by hot isostatic pressing at a temperature of at least 700 C.

14. An impeller of a rotary machine manufactured with a method according to claim 11.

15. The alloy in accordance with claim 1, wherein the composition includes at least 0.50 weight percent silicon.

16. The alloy in accordance with claim 1, wherein the composition includes at least 0.60 weight percent manganese.

17. The alloy in accordance with claim 1, wherein the composition includes at most 8 weight percent iron.

18. The alloy in accordance with claim 1, wherein the composition includes a 0.2% proof stress of at least 850 MPa, at 20 Celsius.

19. The impeller of a rotary machine in accordance with claim 14, wherein the rotary machine is a pump.

Description

EXAMPLE

[0047] C: 0.01%; Mn: 0.8%; P: 0.008%; S: 0.005%; Si: 0.7%; Cr: 21%; Mo: 8.5%; Nb: 3.3%; Ti: 1.3%; Al: 0.2%; Fe: 5.2%; Ni: balance. This results in a Ni content of approximately 59 weight percent. The PREN of this specific example is approximately 49.1.

[0048] The nickel base casting alloy according to the invention is particularly suited for the casting or the investment casting of impellers of a rotary machine, for example pump impellers.

[0049] According to an embodiment of the method for manufacturing an impeller, a melt is provided for the casting process, the melt having the nominal composition of a nickel base casting alloy according to the invention. E.g. the melt has the composition as given in the Example above. The melt may be produced in any known manner. For example, a feedstock is prepared from different components that might be powders, or grains, or pellets or other pieces of material, or combinations thereof. Each component may contain one or more of the elements used for the alloy. For example, ferroalloys may be used for preparing the feedstock. The feedstock is proportioned to attain the nominal composition of the alloy to be produced.

[0050] The feedstock is molten and stirred to produce a homogeneous melt. The melt is poured in a casting mold which is designed for creating the desired shape of the impeller. Of course, the mold may comprise a plurality of compartments each of which is designed for forming an impeller such that a plurality of impellers may be produced in a single casting step. After the melt has solidified the casting or the castings is/are removed from the mold.

[0051] Preferably the casting(s) is/are subjected to a densification or consolidation process after being removed from the mold. The densification for reducing the porosity of the casting(s) or for reducing internal and undesired cavities in the structure of the casting(s) is preferably performed by applying an isostatic pressure of at least 10 MPa to the casting(s). Most preferred the densification is performed at an elevated temperature of at least 700 C., preferably of at least 750 C. The densification may be achieved by hot isostatic pressing (HIP) of the casting(s). The HIP process for densifying castings as such is known in the art and therefore not explained in more detail. Typically, in such a HIP process an isostatic pressure in the range of 10 to 200 MPa is applied.

[0052] After the densification the impeller may be finished by machining, grinding polishing or other known finishing methods.