NICKEL-BASE PRECIPITATION HARDENABLE ALLOYS WITH IMPROVED HYDROGEN EMBRITTLEMENT RESISTANCE

Abstract

Nickel-base precipitation hardenable alloys with enhanced hydrogen embrittlement resistance and desired yield strength have critical ranges of titanium and iron, among other elements. One of the nickel-base precipitation hardenable alloys has a composition, in wt.%, of Cr from about 18.0% to about 23.0%, Fe from about 7.0% to about 12.0%, Mo from about 6.5% to about 9.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.3% to about 1.3%, Al up to about 0.4%, with a balance of Ni and incidental impurities. This alloy has a yield strength (0.2% offset) greater than or equal to 120 ksi (827 MPa), a plastic strain ratio greater than or equal to 0.35, and a plastic strain to failure greater than or equal to 9.0%.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. Pat. Application No. 63/295,324 filed on Dec. 30, 2021. The disclosure of the above application is incorporated herein by reference.

FIELD

The present disclosure relates to nickel-base precipitation hardenable alloys, and particularly to nickel-base precipitation hardenable alloys with improved hydrogen embrittlement resistance.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Nickel-base precipitation hardenable alloys are used for the manufacture of critical down-hole components in oil field equipment. Such alloys are known to be resistant to chloride-ion stress corrosion cracking, sulfide stress corrosion cracking, and galvanically-induced hydrogen stress corrosion cracking. However, ever increasing resistance to hydrogen embrittlement (HE) is desired. Resistance to hydrogen embrittlement may be evaluated by determining a plastic strain ratio and a plastic strain to failure. As used herein, the phrases “plastic strain to failure” and “plastic strain ratio” refer to the plastic strain to failure and plastic strain ratio as established in NACE Standard TM0198. This standard provides a slow strain rate test for evaluation of Ni-based alloys for resistance to hydrogen-induced stress corrosion cracking (SCC) in simulated oil field production environments at elevated temperatures. More specifically, plastic strain to failure is the maximum plastic deformation in the material before the material breaks. A projection of an elastic line through the stress and strain value at failure is used to determine the amount of strain attributed to sample plastic deformation as the total strain at failure minus the equivalent elastic strain at the failure point. The HE plastic strain ratio is the plastic strain to failure determined from a sample tested in acid divided by the plastic strain to failure determined from a sample tested in an inert environment.

The present disclosure addresses the issue of improved HE resistance of nickel-base precipitation hardenable alloys and other issues related to nickel-base precipitation hardenable alloys for use in oil field environments.

SUMMARY

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

In one form of the present disclosure, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 7.0% to about 12.0%, Mo from about 6.5% to about 9.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.3% to about 1.3%, Al up to about 0.4%, and balance Ni and incidental impurities, a yield strength greater than or equal to 120 ksi, a plastic strain ratio greater than 0.35, and a plastic strain to failure greater than or equal to 9.0%. In at least one variation the alloy has a Ti content about 0.8% to about 1.1% and an Fe content between about 9.0% to about 12.0%. For example, in at least one variation the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 10.0% to about 12.0%. In another alternative, the alloy has a Ti content between about 0.4% to about 0.8% and an Fe content between about 10.0% to about 12.0%.

Although the alloy in one form has a desired plastic strain ratio, i.e., greater than or equal to 0.35, and a plastic strain to failure greater than or equal to 9.0%, the alloy also maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). For example, in at least one variation the alloy has an HE plastic strain ratio greater than or equal to 0.35, a plastic strain to failure greater than 9.0% and the yield strength is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa). Also, in some variations the alloy has a plastic strain ratio greater than or equal to 0.40 and a plastic strain to failure greater than or equal to 10.0%. For example, in at least one variation, the plastic strain ratio is greater than or equal to 0.50 and the plastic strain to failure is greater than or equal to 12.0%.

In another form of the present disclosure, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 9.0% to about 16.0%, Mo from about 4.5% to about 7.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.4% to about 1.3%, Al up to about 0.4%, and balance Ni and incidental impurities, a yield strength greater than or equal to 120 ksi, a plastic strain ratio greater than or equal to 0.30, and a plastic strain to failure greater than or equal to 8.5%. In at least one variation the alloy has a Ti content about 0.8% to about 1.1% and an Fe content between about 11.0% to about 16.0%. For example, in at least one variation the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 12.0% to about 16.0%. In another alternative, the alloy has a Ti content between about 0.5% to about 0.8% and an Fe content between about 12.0% to about 16.0%.

Although the alloy in this form has a desired plastic strain ratio, i.e., greater than or equal to 0.30, the alloy still maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). For example, at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5% and the yield strength is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa). Also, in another form, the alloy has a plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In still another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

In yet another form of the present disclosure, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 15.0% to about 21.0%, Mo from about 3.0% to about 4.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.5% to about 1.3%, Al up to about 0.4%, Cu from about 0.5% to about 3.0%, and balance Ni and incidental impurities. This alloy has a yield strength greater than or equal to 140 ksi, a plastic strain ratio greater than or equal to 0.30, and a plastic strain to failure greater than or equal to 8.0%. In at least one variation of this alloy, the Ti content is about 0.8% to about 1.1% and the Fe content is between about 16.0% to about 21.0%. For example, in at least one variation, the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 17.0% to about 20.0%. In another alternative, the alloy has a Ti content between about 0.5% to about 0.8% and an Fe content between about 18.0% to about 21.0%.

Although this alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.5, the alloy still maintains a desired strength, i.e., greater than or equal to 140 ksi (965 MPa). For example, in at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0% and the yield strength is between about 140 ksi (965 MPa) and 170 ksi (1172 MPa). Also, in some variations, this alloy has a plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In yet another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

While not being bound to any particular theory, it is believed that a careful balance of Ti and Fe results in an alloy that provides high strength and is resistant to hydrogen embrittlement.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Referring to Table 1 below, Unified Numbering System (UNS) composition specifications for nine (9) nickel-based (Ni-base) precipitation hardenable alloys are shown.

Element	UNS N07716	UNS N07718	UNS N07725	UNS N09925	UNS N09935	UNS N09945	UNS N09946	UNS N09955	UNS N07022
	wt.%	wt.%	wt.%	wt.%	wt.%	wt.%	wt.%	wt.%	wt.%
Aluminum (Al)	0 - 0.35	0.2 - 0.8	0 - 0.35	0.1 - 0.5	0-0.5	0.01 - 0.7	0.01 - 0.7	0-0.8	0-0.5
Boron (B)	-	0 - 0.006	-	-	-	-	-	-	0-0.01
Carbon (C)	0 - 0.03	0 - 0.08	0 - 0.03	0 - 0.03	0 - 0.03	0.005 -0.04	0.005 -0.03	0 - 0.03	0-0.01
Chromium (Cr)	19 - 22	17 - 21	19 - 22.5	19.5 -23.5	19.5 - 22	19.5 - 23	19.5 -22.5	20 - 24	20 - 21.4
Cobalt (Co)	-	0 - 1	-	-	0-1	-	-	0 - 1	0 - 1
Copper (Cu)	-	0 - 0.3	-	1.5 - 3	1 - 2	1.5 - 3	1.5 - 3		0 - 0.5
Iron (Fe)	Bal.	Bal.	Bal.	22 min.-Bal.	Bal.	Bal.	Bal.	Bal.	0-1.8
Manganese (Mn)	0 - 0.2	0 - 0.35	0 - 0.35	0 - 1	0 - 1	0 - 1	0 - 1	0 - 0.5	0 - 0.5
Molybdenum (Mo)	7 - 9.5	2.8 - 3.3	7 - 9.5	2.5 - 3.5	3 - 5	3 - 4	3 - 4	5.5 - 7	15 - 17.4
Nickel (Ni)	59 - 63	50 - 55	55 - 59	38 - 46	34 - 38	46.5 - 48	50 - 55	55 - 60	Bal.
Niobium (Nb)	2.75 - 4	4.75 - 5.5	2.75 - 4	0 - 0.5	0.2 -1	2.8 - 3.5	3.5 - 4.5	4 - 5.5	0 - 0
Phosphorus (P)	0 - 0.015	0 - 0.015	0 - 0.015	-	0 - 0.03	0 - 0.02	0 - 0.03	0 - 0.02	0 - 0.03
Silicon (Si)	0 - 0.2	0 - 0.35	0 - 0.2	0 - 0.5	0 - 0.05	0 - 0.5	0 - 0.5	0 - 0.5	0 - 0.08
Sulfur (S)	0 - 0.01	0 - 0.015	0 - 0.01	0 - 0.03		0 - 0.01	0 - 0.03	0 - 0.01	0 - 0.02
Titanium (Ti)	1-1.6	0.65 -1.15	1 - 1.7	1.9 - 2.4	1.8 - 2.5	0.5 - 2.5	0.5 - 2.5	0.5 - 1.5	-
Tungsten (W)	-	-	-	-	0 - 1	-	-	-	0-0.8

The alloys shown in Table 1 are known to be used in a variety of industries and applications, some of which include down-hole components in oil field equipment, and for which enhanced HE resistance is desired. Alloys falling within the UNS specifications shown in Table 1 were subjected to HE testing (see Paper No. 13284, CORROSION 2019 Conference Proceedings; incorporated herein by reference). Also, the inventors performed a statistical analysis of the compositions of the alloys in Table 1 and discovered that the HE resistance of these alloys showed a trend of enhanced HE resistance as a function of decreasing Ti content and increasing Fe content. Particularly, the plastic strain ratio for the alloys was discovered to obey the following relationship based on statistical modeling:

$\text{Plastic}\text{strain}\text{ratio}\text{=}\text{0}\text{.3461}\text{+}\text{0}\text{.016572*Fe}\text{-}\text{0}\text{.2022*Ti}$

with a Coefficient of Determination (R²) equal to 0.997 and Fe, Ti in weight percent (wt.%). As noted from relationship (1) above, reducing the Ti content and increasing the Fe content increases the plastic strain ratio and thereby enhances HE resistance.

Referring now to Table 2, four Ni-based alloys with varying amounts of chromium, iron, molybdenum, niobium, titanium and aluminum are shown. Particularly, specific alloys generally falling within the UNS N07716, UNS N07718, UNS N09925, and UNS N09945 composition ranges are shown in Table 2. It should be understood that the compositions of the alloys shown in Table 2 were obtained from Paper No. 4248 in the CORROSION 2014 Conference Proceedings (incorporated herein by reference) and may not include all of the alloying elements in the UNS specifications listed in the table.

Element	Alloy 625 Plus® (N07716) wt.%	Alloy 718 (N07718) wt.%	Alloy 925 (N09925) wt.%	Alloy 945® (N09945) wt.%	Alloy 945X® (N09946) wt.%
Aluminum	0.19	0.52	0.16	0.18	0.2
Carbon	0.01	0.011	0.01	0.01	0.01
Chromium	21.14	18.55	20.82	20.7	20.5
Cobalt	0.04	0.109	0.05	-	-
Copper	0.01	0.11	1.75	1.93	2
Iron	Bal.	18.11	26.99	22.2	Bal.
Manganese	0.04	0.07	0.56	0.1
Molybdenum	8.01	3.01	2.92	3.18	3.3
Nickel	60.75	53.47	44.09	47.05	53.5
Niobium	3.39	4.95	0.4	3.04	4
Phosphorus	0.002	0.008	0.01	0.008	-
Silicon	0.04	0.09	0.13	0.06	-
Sulfur	0.0005	0.0006	0.001	0.001	0.001
Titanium	1.28	0.98	2.11	1.53	1.5

The alloys in Table 2 were subjected to HE testing (see Paper No. 4248, CORROSION 2014 Conference Proceedings). Also, a statistical analysis of the compositions of the alloys in Table 2 and the HE resistance of these alloys similarly showed a trend of enhanced HE resistance as a function of decreased Ti content and increased Fe content. Particularly, the reduction in area ratio for testing in an HE environment to testing in an inert environment was discovered to obey the following relationship based on statistical modeling:

$\text{Reduction}\text{in}\text{area ratio}\text{=}\text{0}\text{.6348}\text{+}\text{0}\text{.01274*Fe}\text{-}\text{0}\text{.1530*Ti}$

with R² equal to 0.779.

Referring now to Table 3, seven (7) Ni-based precipitation hardenable alloys with varying amounts of chromium, iron, molybdenum, niobium, titanium and aluminum are shown. Particularly, specific alloys generally falling within the UNS N07725, UNS N07716, and UNS N07718 composition ranges are shown in Table 3. It should be understood that the compositions and names of the alloys shown in Table 3 were obtained from Paper No. 11114 in the CORROSION 2018 Conference Proceedings (incorporated herein by reference) and may not include all of the alloying elements provided in a corresponding UNS specification.

Element	Alloy 725-1 (N07725) wt.%	Alloy 725-2 (N07725) wt.%	Alloy 725-3 (N07725) wt.%	Alloy 725-4 (N07725) wt.%	Alloy 716-1 (N07716) wt.%	Alloy 718-1 (N07718) wt.%	Alloy 718-2 (N07718) wt.%
Aluminum	0.24	0.23	0.17	0.15	-	0.44	0.44
Carbon	0.01	0.01	0.011	0.008	0.008	0.018	0.019
Chromium	20.86	20.7	21.52	20.82	20.99	18.6	18.6
Iron	7.79	7.1	7.94	9.07	5.87	17.2	17.1
Manganese	0.07	0.07	0.04	0.06	0.02	0.12	0.13
Molybdenum	7.97	7.93	8.07	7.57	8.02	3.03	3.12
Nickel	57.83	58.9	57.6	56.89	60.38	54.4	54.5
Niobium	3.45	3.44	3.42	3.49	3.4	5.12	5.04
Phosphorus	0.003	0.00001	0.004	0.007	0.001	0.008	0.008
Silicon	0.05	0.03	0.04	0.06	0.03	0.13	0.09
Sulfur	Not listed	0.001	0.0006	0.0006	0.0005	0.0002	0.0002
Titanium	1.52	1.54	1.35	1.45	1.28	0.88	0.91

The alloys in Table 3 were subjected to HE testing (see Paper No. 11114, CORROSION 2018 Conference Proceedings). Also, a statistical analysis of the compositions of the alloys in Table 3 and the HE resistance of these alloys similarly showed a trend of enhanced HE resistance as a function of decreasing Ti content. Particularly, the reduction in fracture load for the alloys testing in an HE environment versus testing in an inert environment was discovered to obey the relationship based on statistical modeling:

$\%\text{Reduction}\text{in}\text{Fracture}\text{Load}\text{=}\text{-43}\text{.4}\text{+}\text{52}\text{.24*Ti}$

with R² equal to 0.876 and a higher value (i.e., less negative) of a reduction in fracture load indicating a higher HE resistance. As shown by relationship (3), the contribution of Fe was statistically irrelevant with respect to the % Reduction in Fracture Load for the alloys shown in Table 3.

It should be understood that the results of the analyses show an increase in HE resistance with a decrease in Ti alloy content in Ni-based precipitation hardenable alloys. Accordingly, new Ni-based precipitation hardenable alloys with reduced Ti content and increased Fe and increased HE resistance have been developed according to the teachings herein.

Additional testing was pursued to further develop the influence of Ti, Fe, and yield strength (YS) on the HE resistance of precipitation hardened nickel alloys. Referring now to Table 4 below, the composition of the tested nickel-based (Ni-base) precipitation hardenable alloys are shown. A combination of commercial and laboratory alloys are included.

Heat No.	Melt Route	Fe	Nb	Ti	Al	C	S	B	Ni	Cr	Mo	Co	Mn	Si	Cu	P
A1	Commercial	11.3	3.77	1.14	0.28	0.006	0.0005	0.0018	56.6	19.5	7.1	0.068	0.070	0.039	0.07	0.004
A2	Commercial	11.3	3.79	1.13	0.29	0.006	0.0006	0.0019	56.5	19.6	7.2	0.063	0.070	0.033	0.08	0.002
A3	Commercial	10.2	3.54	1.10	0.32	0.006	0.0004	0.0018	57.7	19.4	7.5	0.050	0.110	0.045	0.05	0.004
A4	Commercial	7.4	3.48	1.54	0.24	0.002	0.0005	0.0016	58.1	20.9	8.1	0.100	0.070	0.040	0.10	0.004
A5	Laboratory	7.4	3.46	1.42	0.22	0.007	0.0017	0.0024	58.7	20.4	8.0	0.004	-	0.021	0.00	0.001
A6	Laboratory	11.3	3.84	1.12	0.26	0.004	0.0019	0.0023	56.5	19.2	7.2	0.004	-	0.025	0.00	0.001
A7	Laboratory	11.2	4.10	0.93	0.44	0.004	0.0003	0.0022	56.0	19.2	7.3	-	-	0.030	0.00	0.001
A8	Laboratory	11.8	4.36	0.42	0.15	0.009	0.0012	0.0023	56.7	19.3	7.3	-	-	0.023	0.00	0.000
A9	Laboratory	11.9	3.48	1.01	0.18	0.012	0.0017	0.0027	54.4	20.9	8.0	0.003	-	0.021	0.00	0.002
A10	Laboratory	7.5	3.47	1.08	0.21	0.005	0.0008	0.0024	56.6	21.0	8.1	0.004	0.005	0.016	0.00	0.002
B1	Laboratory	9.8	4.22	1.07	0.33	0.007	0.0012	0.0037	59.8	18.5	6.1	0.012	-	0.025	0.05	0.002
B2	Laboratory	14.6	4.26	1.03	0.33	0.007	0.0016	0.0031	54.0	18.6	6.2	0.013	-	0.035	0.05	0.003
B3	Laboratory	14.7	4.29	1.03	0.34	0.004	0.0013	0.0030	55.9	18.7	5.0	0.012	-	0.019	0.05	0.002
C1	Laboratory	15.4	4.14	1.29	0.14	0.007	0.0010	0.0030	53.5	20.2	3.2	0.014	-	0.029	1.79	0.003
C2	Laboratory	18.6	4.37	1.13	0.29	0.003	0.0003	0.0029	51.9	19.7	3.4	0.010	-	0.030	0.01	0.003
C3	Laboratory	18.7	4.38	1.13	0.49	0.003	0.0010	0.0030	51.7	19.7	3.2	0.012	-	0.026	0.01	-
C4	Laboratory	17.5	4.44	0.55	0.08	0.009	0.0001	0.0028	52.8	19.8	3.2	0.014	-	0.024	1.65	-
C5	Laboratory	17.2	4.51	0.64	0.34	0.013	0.0010	0.0038	52.6	19.9	3.3	0.007	-	0.022	1.45	0.002
C6	Laboratory	15.3	4.36	0.81	0.14	0.005	0.0010	0.0032	54.6	20.0	3.2	0.012	-	0.030	1.48	0.003
C7	Laboratory	18.3	4.64	0.96	0.12	0.012	0.0010	0.0027	51.3	19.8	3.2	0.011	-	0.022	1.54	0.003
C8	Commercial	14.5	4.03	1.51	0.12	0.007	0.0019	0.0005	53.5	20.8	3.2	0.184	0.070	0.035	1.94	0.012
C9	Commercial	14.5	4.00	1.50	0.12	0.007	0.0000	0.0020	53.5	20.6	3.2	0.403	0.050	0.047	1.91	0.009
C10	Commercial	16.4	4.45	1.04	0.13	0.007	0.0004	0.0006	52.6	20.1	3.2	0.292	0.060	0.041	1.50	0.009
C11	Commercial	14.7	3.93	1.45	0.13	0.006	0.0010	0.0009	53.6	20.7	3.2	0.233	0.050	0.039	1.95	0.008

The laboratory melted alloys in Table 4 were fabricated from 4-inch diameter 50-pound vacuum induction (VIM) melted ingots in the form of 0.625″ diameter hot-rolled rod product. The homogenized and hot-rolled rod samples were annealed at 1900° F. Age-hardening was performed at 1350° F. for 8 hours with a furnace cool at 100° F. per hour to 1150° F. with a hold for 8 hours followed by air cooling. Production melted alloys were fabricated from commercial VIM-melted material. VIM electrodes at 18″ diameter were vacuum arc re-melted (VAR) to 20″ diameter and forged to finished diameter between 5 and 10″ in diameter with a gyro-rotational forging machine (GFM). As shown in Table 5 below, the finished rods were annealed between 1850-1900° F. Age-hardening was performed at between 1300-1365° F. for 5.5-8 hours with furnace cool at 50-100° F. per hour to 1150° F. with hold for 5.5-12 hours followed by air cooling.

Heat No.	Solution Anneal Temp, °F	First Age Temp, °F	First Age Time (hr)	Second Age Temp, °F	Second Age Time (hr)
A1	1900	1350	8	1150	10.1
A2	1900	1350	5.5	1150	7.2
A3	1900	1350	8	1150	9.5
A4	1900	1350	5.5	1150	5.5
A5	1900	1350	8	1150	8
A6	1900	1350	8	1150	8
A7	1900	1350	8	1150	8
A8	1900	1350	8	1150	8
A9	1900	1350	8	1150	8
A10	1900	1350	8	1150	8
B1	1900	1350	8	1150	8
B2	1900	1350	8	1150	8
B3	1900	1350	8	1150	8
C1	1900	1350	8	1150	8
C2	1900	1350	8	1150	8
C3	1900	1350	8	1150	8
C4	1900	1350	8	1150	8
C5	1900	1350	8	1150	8
C6	1900	1350	8	1150	8
C7	1900	1350	8	1150	8
C8	1900	1300	8	1150	11.8
C9	1900	1325	8	1150	8.5
C10	1900	1300	8	1150	8.5
C11	1885	1300	8	1150	8.5

The alloys in Table 5 were subjected to tensile strength and Charpy impact testing. Table 6 below summarizes the test results per heat:

Heat No.	0.2% YS (ksi)	UTS (ksi)	Elong (%)	RA (%)	-75° F. CVN, C-L(Ft-Lb)
A1	139	177	35	53	60
A2	142	180	33	51	46
A3	124	174	37	58	127
A4	128	178	35	43	73
A5	141	187	34	54	54
A6	132	179	37	59	84
A7	133	180	36	55	57
A8	132	174	35	54	57
A9	134	187	33	54	62
A10	126	184	35	52	61
B1	145	-	-	-	54
B2	143	180	25	39	67
B3	146	181	32	54	60
C1	158	185	29	55	53
C2	162	194	28	50	48
C3	150	185	32	50	30
C4	149	181	28	53	48
C5	149	180	29	56	50
C6	154	187	28	49	51
C7	166	193	27	51	55
C8	159	185	24	40	29
C9	147	178	31	55	65
C10	161	186	27	50	56
C11	154	184	27	48	53

The alloys in Table 5 were further subjected to HE resistance testing. The HE resistance of each variant was tested per NACE TM0198 Method C slow strain rate testing procedure. The slow strain rate test incorporates a slow, dynamic strain applied at a constant extension rate. It evaluates resistance to hydrogen induced stress cracking. Table 7 summarizes the HE resistance average test results per heat. (Blank or no values indicate no test was completed for that alloy).

Heat No.	HE 0.2% YS (ksi)	HE UTS (ksi)	Ave. Plastic Strain Ratio	Ave. Plastic Strain
A1	137.3	170.9	0.53	16.0
A2	143	173.8	0.44	13.4
A3	119	169.2	-	21.9
A4	129.4	159.1	0.31	10.4
A5	133	171.7	0.52	15.1
A6	131	166.1	0.57	17.5
A7	129.1	167.5	0.60	19.1
A8	131.7	164.9	0.67	21.4
A9	130.5	157.6	0.66	21.6
A10	127	171	0.66	22.3
B1	148.2	170.7	0.45	13.0
B2	141.4	171.4	0.51	13.4
B3	146.8	169.9	-	14.4
C1	151.7	173	0.61	12.9
C2	148.1	173.8	0.47	12.0
C3	158.5	183.1	0.59	13.0
C4	143.4	175.7	0.80	15.8
C5	146.9	175.2	0.77	18.7
C6	147.9	175.2	0.70	17.2
C7	166.6	184.6	0.55	12.5
C8	153.9	-	-	4.9
C9	146	171.7	0.49	13.0
C10	160.7	177.8	0.44	10.1
C11	149	167.7	0.34	7.5

All samples were examined with light optical microscopy to confirm the microstructure met the requirements defined in API6A CRA Annex A, Reference Microstructures, and were free of significant grain boundary or intragranular precipitation. It has been shown that such microstructures are prone to intergranular fracture under in HE conditions. Such microstructures were excluded from the current study to isolate the influence of Ti and Fe, and yield strength, on HE performance without the additional influence of significant grain boundary precipitation.

Through data analysis including single and multi-variable regression models and cross-validation, it was determined that Ti content, Fe content, and yield strength each have an influence in HE resistance. In particular, over the yield strength range of 120-170 ksi, lower Ti content and higher Fe content correspond with increased HE resistance.

The results from testing were evaluated and used to guide the claim ranges contained herein. Table 8 below shows a summary of composition ranges, plastic strain ratios and yield strengths for the new alloys according to the present disclosure.

Element	A - New Alloy 725 wt.%	B - New Alloy 735 wt.%	C - New Alloy 945X wt.%
Aluminum	0 - 0.4	0-0.4	0-0.4
Chromium	18 - 23	18 - 23	18 - 23
Iron	7 - 12	13 - 17	15 - 21
Molybdenum	6.5 - 9.5	4.5 - 7.5	3 - 4.5
Nickel	bal	bal	bal
Niobium	3.2 - 5.2	3.2 - 5.2	3.2 - 5.2
Titanium	0.3 - 1.3	0.4 - 1.3	0.5 - 1.3
HE Plastic Strain Ratio	≥ 0.35	≥ 0.43	≥ 0.3
HE Plastic Strain (%)	9	8.5	8
YS (0.2% offset, ksi)	120 - 180	120 - 180	120 - 170

In one form of the present disclosure, shown as “A- New Alloy 725” in Table 8, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 7.0% to about 12.0%, Mo from about 6.5% to about 9.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.3% to about 1.3%, Al up to about 0.4%, and balance Ni and incidental impurities and a plastic strain ratio greater than or equal to 0.35 or a plastic strain to failure of greater than or equal to 9.0 percent. In some variations the alloy has a Ti content between about 0.8% to about 1.1%, while in other variations the alloy has a Ti content between about 0.8% to about 1.0%. In at least one variation the alloys has a Ti content about 0.8% to about 1.1% and an Fe content between about 9.0% to about 12.0%. For example, in at least one variation the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 10.0% to about 12.0%. Also, additional alloying elements such as B, C, Co, Mn, P, Si, and S can be present in amounts corresponding to the UNS N07725 specification and/or normal melting practices for making Ni-based precipitation hardenable alloys while remaining within the scope of the present disclosure.

Although the alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.35, the alloy also maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). That is, even with Ti reduced to lower levels within or below the Ti range for UNS N07725, the alloy still has a desired yield strength for down-hole components in oil field production. For example, in at least one variation the alloy has a plastic strain ratio is greater than or equal to 0.35 and the yield strength is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa). In one form, the alloy has a plastic strain ratio is greater than or equal to 0.3 and the yield strength is between about 130 ksi (896 MPa) and 150 ksi (1034 MPa). In another form, the alloy has a plastic strain ratio greater than or equal to 0.35, a plastic strain ratio greater than or equal to 9.0% and the yield strength is between about 140 ksi (965 MPa) and 150 ksi (1034 MPa). Also, in some variations the alloy has a plastic strain ratio greater than or equal to 0.40 and a plastic strain to failure greater than or equal to 10.0%. For example, in at least one variation, the plastic strain ratio is greater than or equal to 0.50 and the plastic strain to failure is greater than or equal to 12.0%.

In another form of the present disclosure, represented by B- New Alloy 735 in Table 8, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 9.0% to about 16.0%, Mo from about 4.5% to about 7.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.4% to about 1.3%, Al up to about 0.4%, and balance Ni and incidental impurities and a plastic strain ratio greater than or equal to 0.3 or a plastic strain to failure of greater than or equal to 8.5 percent. In one form, the alloy has a Ti content between about 0.8% to about 1.1%, while in other variations the alloy has a Ti content between about 0.8% to about 1.0%. In at least one variation the alloy has a Ti content about 0.8% to about 1.1% and an Fe content between about 14.0% to about 17.0%. In still another form, the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 15.0% to about 17.0%. Also, additional alloying elements such as B, C, Co, Mn, P, Si, and S can be present in amounts corresponding to normal melting practices for making Ni-based precipitation hardenable alloys while remaining within the scope of the present disclosure.

Although the alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.30, the alloy still maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). For example, in at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5% and the yield strength is between about 120 ksi (827 Mpa) and 150 ksi (1034 Mpa). In one form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5%, and the yield strength is between about 130 ksi (896 Mpa) and 150ksi (1034 Mpa). In yet another form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5% and the yield strength is between about 140 ksi (965 Mpa) and 150 ksi (1034 Mpa). In another form, the alloy has an HE plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In yet another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

In still another form of the present disclosure corresponding to C-New Alloy 945X in Table 8, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 15.0% to about 21.0%, Mo from about 3.0% to about 4.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.5% to about 1.3%, Al up to about 0.4%, Cu from about 0.5% to about 3.0%, and balance Ni and incidental impurities and a plastic strain ratio greater than or equal to 0.3 or a plastic strain to failure of greater than or equal to 8.0 percent. In one form, the alloy has a Ti content between about 0.8% to about 1.1%, while in another form, the alloy has a Ti content between about 0.8% to about 1.0%. In at least one variation, the alloy has a Ti content about 0.8% to about 1.1% and an Fe content between about 19.0% to about 22.0%. In yet another form, the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 20.0% to about 22.0%. Also, additional alloying elements such as B, C, Co, Mn, P, Si, and S can be present in amounts corresponding to the UNS N09946 specification and/or normal melting practices for making Ni-based precipitation hardenable alloys while remaining within the scope of the present disclosure.

Although the alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.3, the alloy still maintains a desired strength, i.e., greater than or equal to 140 ksi (965 MPa). For example, in at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0% and the yield strength is between about 140 ksi (965 MPa) and 170 ksi (1172 MPa). In one form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0%, and the yield strength is between about 145 ksi and 170 ksi (1172 MPa). In yet another form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0% and the yield strength is between about 150 ksi (1034 MPa) and 170 ksi (1172 MPa). In still another form, the alloy has a plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

It should be understood from the compositions disclosed herein according to the present disclosure, HE resistance measures (i.e. plastic strain to failure or plastic strain ratio) and strengths (i.e., yield strengths) for the new alloys discussed above, a critical range of Ti is desired. That is, a critical range of Ti in the alloys has been discovered such that a desired HE resistance is provided or exceeded, while a desired level of yield strength is provided or exceeded. Particularly, for Ti levels less than the minimum values shown in Table 8 above, the alloys have an undesirable (e.g., low) yield strength and for Ti levels greater than the maximum values shown in Table 8, the alloys have an undesirable (e.g., low) HE resistance. In some variations of the present disclosure, a critical range of Ti and a critical range of Fe are desired. That is, a critical range of Ti and a critical range of Fe in the alloys have been discovered such that a desired HE resistance is provided or exceeded, a desired level of yield strength is provided or exceeded, and alloying elements such as Mo and Cr remain generally in solid solution, i.e., undesirable Mo- and/or Cr-rich precipitates (e.g., sigma phase) are not present in the new alloys. In at least one variation of the present disclosure there is a synergistic effect between Ti and Fe that provides a combination a high HE resistance, desired yield strength and desired microstructure with reduced or no undesirable Moand/or Cr-rich precipitates.

It should also be understood that the compositions of the alloys shown in Table 8 include all incremental values between the minimum alloying element composition and maximum alloying element composition values listed above. That is, a minimum alloying element composition value for any of the alloys shown in Table 8 can range from the minimum value to the maximum value shown in the table. Likewise, the maximum alloying element composition value for any of the alloys shown in Table 8 can range from the maximum value shown to the minimum value shown in the table. For example, the minimum Ti content for the A- New Alloy 725 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or 1.3, and any value between these incremental values, and the maximum Ti content for the A- New Alloy 725 can be 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3, and any value between these incremental values.

Similarly, the yield strength of the alloys shown in Table 8 include all incremental values between the minimum yield strength and maximum yield strength values listed above. That is, a minimum yield strength value for any of the alloys shown in Table 8 can range from the minimum yield strength value to the maximum yield strength value shown in the table. Likewise, the maximum yield strength value for any of the alloys shown in Table 8 can range from the maximum yield strength value shown to the minimum yield strength value shown in the table.

Similarly, the plastic strain ratio of the alloys shown in Table 8 include all incremental values between the minimum plastic strain ratio and maximum plastic strain ratio values listed above. That is, a minimum plastic strain ratio value for any of the alloys shown in Table 8 can range from the minimum plastic strain ratio value to the maximum plastic strain ratio value shown in the table.

Similarly, the HE plastic strain of the alloys shown in Table 8 include all incremental values between the minimum plastic strain to failure and maximum plastic strain to failure values listed above. That is, a minimum plastic strain value for any of the alloys shown in Table 8 can range from the minimum plastic strain value to the maximum plastic strain value shown in the table.

Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or “approximately” in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability.

As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.

Claims

1. A nickel-based precipitation hardenable alloy comprising: wherein the nickel-based precipitation hardenable alloy has:

a composition, in weight percent, comprising: chromium from about 18.0% to about 23.0%; iron from about 7.0% to about 12.0%; molybdenum from about 6.5% to about 9.5%; niobium from about 3.2% to about 5.2%; titanium from about 0.3% to about 1.3%; aluminum up to about 0.4%; and balance nickel and incidental impurities;

a yield strength (0.2% offset) greater than or equal to about 120 ksi (827 MPa);

a plastic strain ratio greater than or equal to 0.35; and

a plastic strain to failure greater than or equal to 9.0%.

2. The nickel-based precipitation hardenable alloy according to claim 1, wherein the titanium is between about 0.8% to about 1.1% and the iron is between about 9.0% to about 12.0%.

3. The nickel-based precipitation hardenable alloy according to claim 1, wherein the titanium is between about 0.8% to about 1.0% and the iron is between about 10.0% to about 12.0%.

4. The nickel-based precipitation hardenable alloy according to claim 1, wherein the titanium is between about 0.4% to about 0.8% and the iron is between about 10.0% to about 12.0%.

5. The nickel-based precipitation hardenable alloy according to claim 1, wherein the yield strength (0.2% offset) is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa).

6. The nickel-based precipitation hardenable alloy according to claim 1, wherein the plastic strain ratio is greater than or equal to 0.40, and the plastic strain to failure is greater than or equal to 10.0%.

7. The nickel-based precipitation hardenable alloy according to claim 1, wherein the plastic strain ratio is greater than or equal to 0.50, and the plastic strain to failure is greater than or equal to 12.0%.

8. A nickel-based precipitation hardenable alloy comprising: wherein the nickel-based precipitation hardenable alloy has:

a composition, in weight percent, comprising: chromium from about 18.0% to about 23.0%; iron from about 9.0% to about 16.0%; molybdenum from about 4.5% to about 7.5%; niobium from about 3.2% to about 5.2%; titanium from about 0.4% to about 1.3%; aluminum up to about 0.4%; and balance nickel and incidental impurities;

a yield strength (0.2% offset) greater than or equal to about 120 ksi (827 MPa);

a plastic strain ratio greater than or equal to 0.30; and

a plastic strain to failure greater than or equal to 8.5%.

9. The nickel-based precipitation hardenable alloy according to claim 8, wherein the titanium is between about 0.8% to about 1.1% and the iron is between about 11.0% to about 16.0%.

10. The nickel-based precipitation hardenable alloy according to claim 8, wherein the titanium is between about 0.8% to about 1.0% and the iron is between about 12.0% to about 16.0%.

11. The nickel-based precipitation hardenable alloy according to claim 8, wherein the titanium is between about 0.5% to about 0.8% and the iron is between about 12.0% to about 16.0%.

12. The nickel-based precipitation hardenable alloy according to claim 8, wherein the yield strength (0.2% offset) is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa).

13. The nickel-based precipitation hardenable alloy according to claim 8, wherein the plastic strain ratio is greater than or equal to 0.35, and the plastic strain to failure is greater than or equal to 9.0%.

14. The nickel-based precipitation hardenable alloy according to claim 8, wherein the plastic strain ratio is greater than or equal to 0.45, and the plastic strain to failure is greater than or equal to 10.0%.

15. A nickel-based precipitation hardenable alloy comprising: wherein the nickel-based precipitation hardenable alloy has:

a composition, in weight percent, comprising: chromium from about 18.0% to about 23.0%; iron from about 15.0% to about 21.0%; molybdenum from about 3.0% to about 4.5%; niobium from about 3.2% to about 5.2%; titanium from about 0.5% to about 1.3%; aluminum up to about 0.4%; copper from about 0.5% to about 3.0%; and balance nickel and incidental impurities;

a yield strength (0.2% offset) greater than or equal to about 140 ksi (965 MPa);

a plastic strain ratio greater than or equal to 0.30; and

a plastic strain to failure greater than or equal to 8.0%.

16. The nickel-based precipitation hardenable alloy according to claim 15, wherein the titanium between about 0.8% to about 1.1% and the iron is between about 16.0% to about 21.0%.

17. The nickel-based precipitation hardenable alloy according to claim 15, wherein the titanium between about 0.8% to about 1.0% and the iron is between about 17.0% to 20.0%.

18. The nickel-based precipitation hardenable alloy according to claim 15, wherein the titanium between about 0.5% to about 0.8% and the iron is between about 18% to about 21.0%.

19. The nickel-based precipitation hardenable alloy according to claim 15, wherein the yield strength (0.2% offset) is between about 140 ksi (965 MPa) and 170 ksi (1172 MPa).

20. The nickel-based precipitation hardenable alloy according to claim 15, wherein the plastic strain ratio is greater than or equal to 0.35, and the plastic strain to failure is greater than or equal to 9.0%.

21. The nickel-based precipitation hardenable alloy according to claim 15, wherein the plastic strain ratio is greater than or equal to 0.45, and the plastic strain to failure is greater than or equal to 10.0%.