DE102020132910A1 - Hardenable nickel alloy - Google Patents

Abstract

Hardenable nickel alloy with (in % by weight):

Description

The invention relates to a hardenable nickel alloy.

Alloy Nicrofer 4320 Ti (Alloy 925) is a precipitation hardenable material. In the offshore industry, Alloy 925 is used for components and parts such as completion tools, packers, hangers, valves and flanges where high strength, yield strength and hardening of the materials are required for design reasons and to save weight. Alloy 925 alloy combines high strength with the required resistance in "sour gas" media to chloride induced stress corrosion cracking and sulfide induced stress corrosion cracking induced by hydrogen sulfide or polythionic acids. The high nickel content of approx. 43% in Alloy 925 is largely responsible for the resistance to sulfide-induced forms of corrosion.

925 Alloy is used when component strength requirements are slightly less stringent than Alloy 718 alloy. Minimum yield strength requirements for Alloy 925 are 110 ksi (758 MPa) compared to 120 ksi in typical customer specifications (827 MPa) for Alloy 718. On the other hand, Alloy 925 offers slightly better resistance to pitting corrosion and stress corrosion cracking in acid gas media than Alloy 718. Alloy 925 also contains the elements molybdenum, copper, titanium and aluminum in its nickel-chromium-iron matrix . The chemical composition of this alloy is a modification of Alloy 825 - Nicrofer 4221 with the addition of titanium.

In the case of thick-walled pipes, large forged parts, flanges and rods made from nickel-based alloys, the desired strengths with the necessary homogeneous distribution over the cross-section of such components can no longer be achieved by strain hardening. Alloy 925 hardens through the addition of aluminium, titanium and/or niobium as alloying elements and suitable heat treatment. The increase in strength is achieved through the formation of intermetallic phases in the austenitic structure.

Nicrofer 4320 Ti/ Alloy 925 obtains its strength primarily from the precipitation of the γ'-phase Ni ₃ (Ti/Al). The relationship between the yield point and the titanium content is for Alloy 925 in 1 shown.

In 2 Titanium levels outside of the usual oil and gas specifications for Alloy 925 material are reported and relate to this application. In the case of thin-walled components, it is also possible to achieve a further increase in strength through previous strain hardening and additional hardening.

This is for example in the EP 52941 A1 set forth.

A tube for acid oil wells is described, made from an alloy consisting of 38 to 46% nickel, 19.5 to 23.5% chromium, up to 1.5% aluminum, 0.9 to 3% titanium, 2.5 to 3.5% molybdenum, 1.5 to 3% copper, up to 3.5% niobium, the aluminum plus titanium content being at least 1% but not more than 3.25% when niobium is in amounts of 1.5 % or more, and is at least 1.3% but not more than 3.25% when niobium is absent or in amounts less than 1.5%, not more than 0.15% carbon, up to 0.005% boron, up to 1% manganese, up to 0.5% silicon and up to 2% cobalt, the remainder being iron, apart from impurities, and the alloy is in the age hardened state.

Also described is a method of tempering such an alloy, wherein the alloy is hardened by heating in the temperature range of 621 to 732°C for a period of up to 24 hours, with additional subsequent heating at a lower temperature, if desired.

The size and distribution of the precipitated γ'-phase for hardening of the material depends on the heat treatment conditions. The precipitated γ'-phase is metastable and changes to the stable η-phase (Ni ₃ Ti/Al) if the heat treatment is not carried out correctly. Due to its brittle behavior, this is harmful, for example, to the mechanical properties of the material. this is in 5 shown (metallographic images with eta phase). There is also the possibility of the formation of a brittle, iron-rich sigma phase.

The object of the invention is to optimize the Alloy 925 alloy, which is known per se, so that it is also suitable for other types of applications.

This problem is solved by a nickel alloy with (in % by weight): no 41.0-44% Cr 19.5-22.0% Cu > 1.5 - < 2.0% Mon > 2.5 - < 3.5% Ti >2.0 - <3.5% Al < 0.4% Nb >0.05 - <0.4% C <0.01% Mn <0.7% si > 0 - 0.2% N 0.01% or less S 0.01% or less co 0.5% or less ta max 0.012% Nb + Ta max 0.4% feet remainder and process-related impurities.

Advantageous developments of the subject of the invention can be found in the associated dependent claims.

The alloy can optionally contain the following elements: B 0.001 - 0.006% mg 0.001 - 0.03% Approx 0.001 - 0.03%.

Furthermore, a nickel alloy is proposed which is subjected to at least one heat treatment, the material being subjected to solution annealing temperatures between 1,000 and 1,060°C.

In addition, the alloy according to the invention can be subjected to at least one heat treatment, with the material being hardened at temperatures between 720 and 740° C. in a first step and temperatures between 610 and 650° C. in a further step with a total annealing time of at least 1 hour and a maximum of 20 hours h is suspended.

Another way to harden the material is to work harden it and then heat treat it in the temperature range between 720 and 740°C, with the material being annealed in a further step at temperatures between 610 and 650°C, with a total annealing time of min 1 hour and a maximum of 20 hours.

Alternatively, there is the option of hardening the material directly without solution annealing in the temperature range between 720 and 740°C and then annealing it in a temperature range between 610 and 650°C in a further step, with a total annealing time of at least one hour and a maximum of 20 hours.

The subject matter of the invention can preferably be used as a material for components in the petrochemical and oil and gas industries and in corrosive environments containing halides, in particular seawater.

Compared to the alloys used in the oil and gas sector with niobium contents in the percentage range of 0.5% to about 5%, the proposed alloy also has advantages with a nickel content of 43% by weight and the limitation of the niobium content to less than 0.4% by weight recognized by the absence of a Laves phase in the solidification. This undesired segregation phase is characterized by high element contents of niobium and molybdenum. This eliminates the need for extensive homogenization anneals of the proposed new alloy, which are typical, for example, of Alloy 718 with its high niobium content.

In laboratory tests (see Table 1) it could be shown by laboratory melting that the desired increased yield strengths can be achieved by increasing the titanium content, which is essential for the gammaprime precipitation, and adapted heat treatments to avoid the undesired eta phase. Table 1 alloying elements target alloy [wt%] LB2226 LB2227 LB2228 C 0.002 0.002 0.004 S 0.0023 0.0023 0.0022 Cr 20.21 20:13 20:16 NO 42.95 43:12 42.86 Mn 0.51 0.5 0.47 si 0.03 0.03 0.01 Mon 2.83 2.83 2.82 Ti 2.47 3.01 3.58 Nb 0.25 0.25 0.24 Cu 1.68 1.64 1.68 co 0.01 0.01 0.01 Al 0.28 0.28 0.28 W 0.03 0.03 0.01 B 0.002 0.002 0.002 mg 0.0062 0.0052 0.005 feet 28.70R 28.12R 27.82R

It is therefore essential to eliminate these undesirable brittle phases, such as eta and sigma phases, by using suitable solution annealing temperatures and times (see Table 2).

Table 2 shows the heat treatment parameters of the alloy according to the invention on the one hand and of the prior art described at the outset on the other hand.

As-cast heat treatments

homogenization annealing VDM INCO EP19266 Remark: Temperatures always with tolerances +- 15° C homogenization annealing 1180°C / 24h / air storage 1149°C 12-16h / shelf: not specified

Heat treatments on the formed material

Solution annealing and hardening

Table 2 Example heat treatments VDM INCO EP19266 Note: Temperatures always have tolerances of +- 15° C solution annealing 1060°C / 1 hour / water cooling q 941 °C / 1 hour / air cooling age hardening annealing 740°C / hold 8h/ furnace cooling to 620°C / hold 8h/ air cooling total annealing time up to 16-20hh 732°C / hold 8h/ furnace cooling to 621°C / hold 8h / air cooling Total annealing time up to 24h

The yield strengths are for titanium grades above the limits defined for the original A925 for the range between 2.5 and 3.5% titanium between 115 and 130ksi. (792MPa and 896MPa).

The Rockwell C hardnesses were measured between 38 and 40 HRC (s. 3 ).

4 shows the eta phase solvus temperature of Alloy 925 var.

6 shows compared to 5 using the LB2228 alloy shown in Table 1, shows the solution heat treated condition of a forged and hot worked alloy with a significantly lower eta phase.

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 52941 A1 [0007]

Claims (7)

Hardenable nickel alloy with (in % by weight): no 41.0-44% Cr 19.5-22.0% Cu > 1.5 - < 2.0% Mon > 2.5 - < 3.5% Ti >2.0 - <3.5% Al < 0.4% Nb >0.05 - <0.4% C <0.01% Mn <0.7% si > 0 - 0.2% N 0.01% or less S 0.01% or less co 0.5% or less ta max 0.012% Nb + Ta max 0.4% feet remainder and process-related impurities. according to nickel alloy claim 1 , wherein the alloy optionally further contains: B 0.001 - 0.006% mg 0.001 - 0.03% Approx 0.001 - 0.03%. according to nickel alloy claim 1 or 2 with a yield strength Rp _0.2 > 115 ksi (792 MPa), especially > 120 ksi (823 MPa). Nickel alloy according to one of Claims 1 until 3 , which is subjected to at least one heat treatment, whereby solution annealing temperatures between 1,000 and 1,060°C are reached. Nickel alloy according to one of Claims 1 until 4 which is subjected to at least one heat treatment, with hardening temperatures between 720 and 750°C being achieved in a first step and temperatures between 610 and 650°C being achieved in a further step with a total annealing time of at least 1 hour and at most 20 hours. Nickel alloy according to one of Claims 1 until 5 , which has a Rockwell C hardness > 30 HRC and < 41 HRC. Use of the hardenable nickel alloy according to one of Claims 1 until 6 as a material for components in the petrochemical and oil and gas industries and in corrosive environments containing halides, particularly seawater.

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