Superaustenitic Material

Abstract

A superaustenitic material is provided for use in chemical plant construction, maritime conditions, oilfield or gas field technology. The material resists corrosion, in particular corrosion in mediums with high chloride concentrations or in sulfuric acid conditions.

Claims

1. A superaustenitic material comprising an alloy with the following alloy elements in % by weight: TABLE-US-00005 Elements Carbon (C) 0.01-0.50 Silicon (Si) <0.5 Manganese (Mn) 0.1-5.0 Phosphorus (P)  <0.05 Sulfur (S)  <0.005 Chromium (Cr) 23.0-33.0 Molybdenum (Mo) 2.0-5.0 Nickel (Ni) 10.0-20.0 Vanadium (V) <0.5 Tungsten (W) <0.5 Copper (Cu) 0.50-5.0  Cobalt (Co) <5.0 Titanium (Ti) <0.1 Aluminum (Al) <0.2 Niobium (Nb) <0.1 Boron (B)  <0.01 Nitrogen (N) 0.40-0.90 balance Iron (Fe) and inevitable impurities.

2. The superaustenitic material according to claim 1, wherein the alloy comprises the following elements in % by weight: TABLE-US-00006 Elements Carbon (C) 0.01-0.30 Silicon (Si) <0.5 Manganese (Mn) 0.5-4.0 Phosphorus (P)  <0.05 Sulfur (S)  <0.005 Chromium (Cr) 24.0-30.0 Molybdenum (Mo) 3.0-5.0 Nickel (Ni) 14.0-19.0 Vanadium (V) <0.3 Tungsten (W) <0.1 Copper (Cu) 0.75-3.5  Cobalt (Co) <0.5 Titanium (Ti)  <0.05 Aluminum (Al) <0.1 Niobium (Nb)  <0.025 Boron (B)  <0.005 Nitrogen (N) 0.40-0.70 balance Iron (Fe) and inevitable impurities.

3. The superaustenitic material according to claim 1, wherein the alloy comprises the following elements in % by weight: TABLE-US-00007 Elements Carbon (C) 0.01-0.10 Silicon (Si) <0.5 Manganese (Mn) 1.0-4.0 Phosphorus (P)  <0.05 Sulfur (S)  <0.005 Chromium (Cr) 26.0-29.0 Molybdenum (Mo) 3.5-4.5 Nickel (Ni) 15.0-18.0 Vanadium (V) below detection level Tungsten (W) below detection level Copper (Cu) 1.0-2.0 Cobalt (Co) below detection level Titanium (Ti) below detection level Aluminum (Al) <0.1 Niobium (Nb) below detection level Boron (B)  <0.005 Nitrogen (N) 0.45-0.60 balance Iron (Fe) and inevitable impurities.

4. The superaustenitic material according to claim 1, wherein the material is produced by a method comprising secondary metallurgical processing of the molten metal, casting into blocks, hot forming, optional cold forming, and optional further mechanical processing.

5. The superaustenitic material according to claim 1, wherein the material has a yield strength R.sub.p0.2 in excess of 500 MPA.

6. The superaustenitic material according to claim 1, wherein the material has a notched bar impact work at room temperature in the longitudinal direction A.sub.v in excess of 300 J.

7. The superaustenitic material according to claim 1, wherein after the cold deformation, the material is fully austenitic.

8. The superaustenitic material according to claim 1, wherein the manganese is present at about 0.5% to about 4.0% by weight of the alloy.

9. The superaustenitic material according to claim 1, wherein the chromium is present at about 24% to about 29.8% by weight of the alloy.

10. The superaustenitic material according to claim 1, wherein the molybdenum is present at about 2.5% to about 4.5% by weight of the alloy.

11. The superaustenitic material according to claim 1, wherein the nickel is present at about 12% to about 18% by weight of the alloy.

12. The superaustenitic material according to claim 1, wherein the nitrogen is present at about 0.50% to about 0.85% by weight of the alloy.

13. The superaustenitic material according to claim 1, wherein the cobalt is present at less than about 1% by weight of the alloy.

14. The superaustenitic material according to claim 1, wherein the copper is present at about 1% to about 4% by weight of the alloy.

15. The superaustenitic material according to claim 1, wherein the tungsten is present at less than 0.3% by weight of the alloy.

16. A method for producing a superaustenitic material, comprising the steps of: providing an alloy comprising the following elements in % by weight: TABLE-US-00008 Elements Carbon (C) 0.01-0.50 Silicon (Si) <0.5 Manganese (Mn) 0.1-5.0 Phosphorus (P)  <0.05 Sulfur (S)  <0.005 Chromium (Cr) 23.0-33.0 Molybdenum (Mo) 2.0-5.0 Nickel (Ni) 10.0-20.0 Vanadium (V) <0.5 Tungsten (W) <0.5 Copper (Cu) 0.50-5.0  Cobalt (Co) <5.0 Titanium (Ti) <0.1 Aluminum (Al) <0.2 Niobium (Nb) <0.1 Boron (B)  <0.01 Nitrogen (N) 0.40-0.90 balance Iron (Fe) and inevitable impurities; melting the alloy; subjecting the alloy to secondary metallurgical processing; casting the alloy into blocks and permitting the blocks to solidify; immediately after solidifying the blocks, heating and hot forming the blocks; and optionally cold forming and mechanically processing the blocks.

17. The method for producing a superaustenitic material according to claim 16, wherein the alloy comprises the following elements in % by weight: TABLE-US-00009 Elements Carbon (C) 0.01-0.30 Silicon (Si) <0.5 Manganese (Mn) 0.5-4.0 Phosphorus (P)  <0.05 Sulfur (S)  <0.005 Chromium (Cr) 24.0-30.0 Molybdenum (Mo) 3.0-5.0 Nickel (Ni) 14.0-19.0 Vanadium (V) <0.3 Tungsten (W) <0.1 Copper (Cu) 0.75-3.5  Cobalt (Co) <0.5 Titanium (Ti)  <0.05 Aluminum (Al) <0.1 Niobium (Nb)  <0.025 Boron (B)  <0.005 Nitrogen (N) 0.40-0.70 balance Iron (Fe) and inevitable impurities.

18. The method for producing a superaustenitic material according to claim 16, wherein the alloy comprises the following elements in % by weight: TABLE-US-00010 Elements Carbon (C) 0.01-0.10 Silicon (Si) <0.5 Manganese (Mn) 1.0-4.0 Phosphorus (P)  <0.05 Sulfur (S)  <0.005 Chromium (Cr) 26.0-29.0 Molybdenum (Mo) 3.5-4.5 Nickel (Ni) 15.0-18.0 Vanadium (V) below detection level Tungsten (W) below detection level Copper (Cu) 1.0-2.0 Cobalt (Co) below detection level Titanium (Ti) below detection level Aluminum (Al) <0.1 Niobium (Nb) below detection level Boron (B)  <0.005 Nitrogen (N) 0.45-0.60 balance Iron (Fe) and inevitable impurities.

19. The method for producing a superaustenitic material according to claim 16, wherein the hot forming comprises a plurality of sub-steps.

20. The method for producing a superaustenitic material according to claim 19, further comprising the steps of: re-heating the block between the sub-steps and after the last sub-step, and optionally solution annealing after the last sub-step.

21. The method for producing a superaustenitic material according to claim 20, wherein after the last sub-step and the optional solution annealing, sufficient cold forming is performed to achieve a tensile strength Rm>1000 MPa.

22. A use of a superaustenitic material according to claim 1 for systems and system components that are exposed to a sulfuric acid corrosion.

23. A use of a superaustenitic material formed according to the method of claim 16 for systems and system components that are exposed to a sulfuric acid corrosion.

24. A superaustenitic material comprising an alloy with the following alloy elements in % by weight: TABLE-US-00011 Elements Carbon (C) 0.01-0.50 Manganese (Mn) 0.1-5.0 Silicon (Si), Vanadium (V) and Tungsten (W) in a combined amount of zero to 1.5 Chromium (Cr) 23.0-33.0 Molybdenum (Mo) 2.0-5.0 Nickel (Ni) 10.0-20.0 Copper (Cu) 0.50-5.0  Cobalt (Co) <5.0 Titanium (Ti), Aluminum (Al), Niobium (Nb), Boron (B), Phosphorous (P) and Sulfur (S) in a combined amount of zero to <0.4 Nitrogen (N) 0.40-0.90 balance Iron (Fe) and inevitable impurities.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0039] The invention will be explained by way of example based on the drawing and in the Tables below. In the drawing:

[0040] FIG. 1: shows a very schematic depiction of the production route and its alternatives.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Table 1 shows the alloy components and percentage ranges for the alloy of the invention.

TABLE-US-00002 TABLE 1 Alloy Components, % by weight Alloying Composition More element range Preferred preferred Carbon (C) 0.01-0.50 0.01-0.30 0.01-0.10 Silicon (Si) <0.5 <0.5 <0.5 Manganese (Mn) 0.1-5.0 0.5-4.0 1.0-4.0 Phosphorus (P)  <0.05  <0.05  <0.05 Sulfur (S)  <0.005  <0.005  <0.005 Iron (Fe) residual residual residual Chromium (Cr) 23.0-33.0 24.0-30.0 26.0-29.0 Molybdenum (Mo) 2.0-5.0 3.0-5.0 3.5-4.5 Nickel (Ni) 10.0-20.0 14.0-19.0 15.0-18.0 Vanadium (V) <0.5 <0.3 below detection level Tungsten (W) <0.5 <0.1 below detection level Copper (Cu) 0.5-5.0 0.75-3.5  1.0-2.0 Cobalt (Co) <5.0 <0.5 below detection level Titanium (Ti) <0.1  <0.05 below detection level Aluminum (Al) <0.2 <0.1 <0.1 Niobium (Nb) <0.1  <0.025 below detection level Boron (B)  <0.01  <0.005  <0.005 Nitrogen (N) 0.40-0.90 0.40-0.70 0.45-0.60

[0042] Table 2 is a table with three different alloys within the concept according to the invention and the resulting actual values of the nitrogen content compared to the theoretical nitrogen solubility of such alloys according to the prevailing school of thought.

TABLE-US-00003 TABLE 2 Examples of the Invention Chemical composition (percentage by weight)/residual Fe Pressure Example C 1.00 Mn Cr Mo Ni V W* Cu Co* Ti* Al* Nb* N [MPa] A 0.01 1.00 5.0 23.01 3.1 15.98 0.05 0 0.15 0 0 0 0 0.51 1.00 B 0.01 1.00 5.0 27 3.1 14 0.05 0 0.10 0 0 0 0 0.7 1.00 C 0.01 0.4 5.0 24 3.1 14 0.05 0 0.10 0 0 0 0 0.55 1.00 N solubility [% N]* Medovar at temperature: Stein Satir Kowanda 1550° C. 1525° C. 1500° C. 1450° C. A 0.36 030 0.34 0.34 0.35 0.36 0.39 B 0.61 0.41 0.65 0.47 0.49 0.51 0.56 C 0.44 0.34 0.45 0.38 0.40 0.41 0.45 *Values are below detectable level **Calculated values for N according to different methods (Source: on Restricting Aspects in the Production of Nonmagnetic Cr—Mn—N—Alloyed Steels, Saller, 2005)

[0043] Table 3 shows the mechanical properties (strengths) of the Examples in Table 2 before a possible strain hardening.

TABLE-US-00004 TABLE 3 Mechanical Properties Examples according Strength [MPa] to the invention R.sub.m R.sub.p0.2 A 905 505 B 960 560 C 915 515

[0044] The components are melted under atmospheric conditions and then undergo secondary metallurgical processing. Then, blocks are cast, which are hot forged immediately afterward. In the context of the invention, “immediately afterward” means that no additional remelting process such as electroslag remelting (ESR) or pressure electroslag remelting (PESR) is carried out.

[0045] According to the invention, it is advantageous if the following relation applies:

MARC.sub.opt: 40<% Cr+3.3×% Mo+20×% C+20×% N−0.5×% Mn

[0046] The MARC formula is optimized to such an effect that it has been discovered that the otherwise usual removal of nickel does not apply to the system according to the invention and the limit of 40 is required.

[0047] Then cold forming steps are carried out as needed in which a strain hardening takes place, followed by the mechanical processing, which in particular can be a turning, milling, or grinding.

[0048] FIG. 1 shows examples of the possible processing routes for the production of the alloy composition according to the invention. One possible route will be described below by way of example. In the vacuum induction melting unit (VID), molten metal simultaneously undergoes melting and secondary metallurgical processing. Then the molten metal is poured into ingot molds and in them, solidifies into blocks. These are then hot formed in multiple steps. For example, they are pre-forged in the rotary forging machine and are brought into their final dimensions in the multiline rolling mill or are rolled into sheet form in two-high rolling stands. Depending on the requirements, a heat treatment step can also be performed.

[0049] In order to further increase the strength, a cold forming step can also be performed.

[0050] A superaustenitic material according to the invention can be produced not only by means of the production routes described (and in particular shown in FIG. 1), the advantageous properties of the alloy according to the invention can also be achieved by means of a production route using powder metallurgy.

[0051] Table 2 (above) shows three different variants within the alloy compositions according to the invention, with the respectively measured nitrogen values, which have been produced with the method according to the invention in connection with the alloys according to the invention. These very high nitrogen concentrations contrast with the nitrogen solubility indicated in the subsequent columns according to Stein, Satir, Kowandar, and Medovar from “On restricting aspects in the production of non-magnetic Cr—Mn—N-alloy steels, SaIler, 2005.” In Medovar, different temperatures are indicated. It is clear, however, that the high nitrogen values far exceed the theoretically expected values.

[0052] This is even more astonishing since with the alloy according to the invention, a route was taken that does not in fact justify the expectation of a high nitrogen solubility, particularly because the manganese content, which has a very positive influence on the nitrogen solubility, is sharply reduced compared to known corresponding alloys.

[0053] The invention therefore has the advantage that an austenitic, high-strength material with an increased corrosion resistance and low nickel content is produced, which simultaneously exhibits high strength and paramagnetic behavior. Even after the cold forming, a fully austenitic structure is present so that it has been possible to successfully combine the positive properties of an inexpensive CrMnN steel with the outstanding corrosion-related properties of a CrNiMo steel.

[0054] One special feature of the invention is that because of the high nitrogen content, the strain hardening rate is higher than in other superaustenites in order to thus be able to achieve tensile strengths (R.sub.m) of 2000 MPa. It is thus possible as a last production step to achieve a high strain hardening by means of cold rolling or other cold forming processes with high deformation rates.

[0055] Typical application fields of the materials according to the invention are shipbuilding and chemical plant construction or the combination of the two, in this case particularly in flue-gas desulfurization systems of seagoing vessels, but also in all other areas in which sulfuric acid corrosion is particularly expected.

[0056] Especially in applications in which very high strengths are required, the strength can be increased even more by means of cold deformation, as described above.