Ni-BASE WEAR AND CORROSION RESISTANT ALLOY

Abstract

Nickel base alloys for use in applications for highly corrosive and abrasive environments. The alloys contain a large volume fraction of metallic carbide particles that provide wear and abrasion resistance. The alloys are produced by induction melting and gas atomization to form alloy powder particles. The particles are consolidated by hot isostatic pressing to form a solid article.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) shows the etched microstructure (magnification of 200×) of an alloy of the invention and specifically alloy WR-11;

FIG. 1( b) shows the etched microstructure (magnification of 1000×) of an alloy of the invention and specifically alloy WR-11;

FIG. 2( a) shows the etched microstructure (magnification of 200×) of an alloy of the invention and specifically alloy WR-9;

FIG. 2( b) shows the etched microstructure (magnification of 500×) of an alloy of the invention and specifically alloy WR-9;

FIG. 3( a) shows the SEM microstructure (magnification of 100×) of an alloy of the invention and specifically alloy WR-12;

FIG. 3( b) shows the backscattered electron SEM image of the microstructure (magnification of 1000×) of an alloy of invention and specifically alloy WR-13.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Chemistry

TABLE 1
WEAR CORROSION RESISTANT Ni-BASED ALLOYS OF INVENTION
Alloy ID	Bar ID	Ni	Cr	V	Mo	Co	Ti	Al	Zr	Si	Mn	C
WR-9	01-184	bal.	21.73	13.83	11.07	7.31	4.97	1.88	0.75	0.06		4.49
WR-10	02-173	bal.	20.19	19.38	9.40	6.89	4.42	2.06	1.35	0.12		5.25
WR-11	02-259	bal.	18.15	10.20	8.75	10.10	3.04	1.46	—	—		2.00
WR-12	02-260	bal.	18.18	11.93	8.74	10.00	2.98	1.54	—	—		2.45
WR-13	02-261	bal.	16.77	15.15	8.64	9.23	3.04	1.55	—	—		3.00
WR-14	02-262	bal.	22.06	15.82	12.03	7.91	3.49	1.68	—	—		3.74
WR-15	04-033	bal.	19.87	12.09	11.93	10.95	3.39	1.45	0.12	0.06		2.38
WR-16	04-034	bal.	19.96	12.70	11.91	9.88	3.85	1.36	0.01	0.008		2.75
Reference Alloys of Prior Art
440C	bal.Fe	17.50	—	0.50	—	—	—	—	0.30	0.50	1.00
CPM ® S90V	bal.Fe	14.00	9.00	1.00	—	—	—	—	0.40	0.50	2.30
Alloy 625	bal.	22	4.0 Nb	9	3.0 Fe	0.2	0.2	—	0.3	0.15	0.05

Experimental Alloys

TABLE 2
WEAR AND CORROSION RESISTANCE OF ALLOYS
OF THE INVENTION AND REFERENCE ALLOYS
				Pitting Pot. vs.	Corrosion
				SCE	Rate
		Hardness	WR	5% NaCl	5% HF
Alloy ID	Bar ID	[HRC]	[mg]	Epit, [mV]	[mm/yr]
Alloys of the Invention
WR-9	01-184	61.4	109		0.41
WR-10	02-173	63.4	71
WR-11	02-259	50.1	424
WR-12	02-260	51.7	240
WR-13	02-261	52.9	155	503	0.7
WR-14	02-262	62.7	60	357	0.34
WR-15	04-033	55.2	301		0.4
WR-16	04-034	55.0	284	389	0.43
Reference Alloys
440C	57.0	646	−220
CPM ® S90V	59.0	84	5	27
Alloy 625	34	3275	—	0.07

The compositions of the experimental alloys were defined by carefully balancing the amount of alloying content and carbon. The alloys were design to provide a sufficient amount of carbon to form primary carbides. The compositions of the experimental alloys are listed in Table I. All alloys were melted in an electric induction furnace and gas atomized to produce a prealloyed powder. The produced powder was collected, screened to −16 mesh fraction, loaded into cylindrical containers and consolidated using hot isostatic pressing (HIP). All alloys were successfully consolidated into solid bars from which sample coupons were sectioned for corrosion and wear resistance testing. Corrosion and wear testing were performed on alloys of the invention in the as-HIP condition. One of the advantages of the alloys of the invention is that they can be used in the as-HIP condition and do not require heat treatment. This may shorten and simplify the entire manufacturing process. Several alloys were tested as reference alloys for comparative purposes. These include two martensitic wear and corrosion resistant tool steels, conventional 440C and powder metallurgy CPM S90V. These alloys were selected for comparison because they are typical tool materials often used in applications for which the alloys of the invention are intended to be used. Additionally, a nickel based superalloy, Alloy 625, was included for comparative testing because it is used sometimes in applications involving a HF environment. However, its performance is often unsatisfactory because it lacks adequate wear resistance.

The alloys of the invention combine the performance characteristics of iron based tool steels and nickel based superalloys, i.e., the alloys of the invention have a wear resistance similar to martensitic wear resistant tool steels and maintain corrosion resistance similar to that of nickel based alloys.

Corrosion resistance: Potentiodynamic tests were used to evaluate the corrosion resistance of several alloys of the invention and the reference alloys for comparison. The pitting resistance of the alloys was measured in a 5% NaCl solution. The tests were conducted according to ASTM G5. The pitting resistance of the alloys is defined by the pitting potential (E_pit) obtained from a potentiodynamic curve. The more positive the pitting potential, the more resistant the alloy is to pitting. The alloys of the invention were tested in the as-HIP condition, the reference alloys were tested in a typical heat treat condition commonly used for typical applications. The test results of the corrosion tests are given in Table II.

The pitting potentials for the iron based alloys, 440C and CPM S90V, were −220 mV and 5 mV, respectively. The pitting potentials for several of the alloys of the invention, i.e., WR-13, WR-14 and WR-16, were 503 mV, 357 mV and 389 mV, respectively, which indicates much better resistance to pitting of the alloys of the invention than the wear/corrosion resistant tool steels.

The second corrosion test was conducted in 5% hydrofluoric acid (HF). The tests were conducted according to ASTM G59. The corrosion rates, Table II, were calculated from the data collected during the test according to ASTM F102. In this test, the lower the corrosion rate, the more resistant the alloy is to general corrosion. Alloy 625 and CPM S90V were tested for reference. The best corrosion resistance in the HF solution was measured for Alloy 625; its corrosion rate was 0.07 mm/yr. The corrosion rate in the HF solution of the alloys of the invention was 0.34-0.7 mm/yr. This corrosion rate is somewhat higher than the corrosion rate of the Ni-based superalloy but it is much lower than the corrosion rate of CPM S90V, which was measured to be 27 mm/yr. CPM S90V is considered as one of the best commercially available wear/corrosion resistant martensitic tool steels.

Wear Test: Wear resistance was tested using a dry sand rubber wheel abrasive test which is often used to test materials for applications such as plastic injection molding, plastic extrusion or food processing. Testing was performed according to ASTM Standard G65, Dry Sand Rubber Wheel Abrasive Test. Again, the alloys of the invention were tested in the as-HIP condition, and the reference alloys were heat treated to their typical application hardness. The test results are given in Table II. The abrasion weight loss in the ASTM G65 test for CPM S90V tool steel was 84 mg and for 440C tool steel was 646 mg. The abrasion weight loss for the alloys of the invention varied from 60 mg to 424 mg, depending on the alloy composition and the volume fraction of carbides. The alloys with the larger amount of carbon and carbide forming elements (alloys WR-9, WR-10, WR-14) had a lower weight loss and were comparable to the weight loss of CPM S90V. The alloys of the invention containing lower amounts of carbon and carbide forming elements had a weight loss somewhat higher, from 155 mg to 424 mg, but still lower than another wear/corrosion resistant tool steel 440C, for which the abrasion weight loss was 646 mg. The weight loss for superalloy Alloy 625 was 3275 mg, at least an order of magnitude larger than those for the alloys of the invention.

Microstructure: The microstructure of alloys of the invention was examined with optical and scanning electron microscopes (SEM). Metallographic specimens for optical microscope examination were polished and etched with Beraha's etchant. Examples of the optical microstructure are shown in FIG. 1 and FIG. 2. The microstructure consists of alloy carbide particles uniformly distributed in the Ni-based matrix. The volume fraction of primary carbide particles depends on the carbon content and the amount of carbide forming elements, and in the compositions with the largest amount of carbon and carbide formers the volume fraction of carbides can be up to 55%. SEM examination of the microstructure was performed on metallographic specimens in the as-polished condition. An example of an SEM microstructure is shown in FIG. 3. EDS analysis of the carbide particles revealed the presence of three types of carbides:

titanium-vanadium-molybdenum-chromium rich;

vanadium-molybdenum-titanium-chromium rich, and;

chromium-molybdenum-vanadium rich.

The elements are listed in order of decreasing content within a given type of carbide.

Manufacturing Experience: The alloys of the invention, WR-13 and WR-16, were used to produce twin HIP/Clad barrels for plastic injection molding machines. Both alloys were successfully applied to the inside diameter (ID) of the barrel openings by hot isostatic pressing, which resulted in full consolidation of the powder and good metallurgical bonding of the HIP/Clad layer to the barrel substrate. Both barrels were successfully finished machined to original specifications and were submitted to a customer for field trials.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1. A nickel based wear and corrosion resistant alloy consisting essentially of, in weight percent: carbon—1%-6%; chromium—14%-25%; vanadium—8%-22%; molybdenum—6%-15%; cobalt—5%-14%; titanium—1%-7%; aluminum—1%-4%; zirconium—up to 2%; silicon—up to 1%; and balance essentially nickel and incidental impurities.

2. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—2%-5.5%; chromium—16%-22.5%; vanadium—10%-20%; molybdenum—8%-13%; cobalt—6%-12%; titanium—2.5%-5%; aluminum—1%-2.5%; zirconium—up to 1.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

3. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—4%-5%; chromium—20%-23%; vanadium—12%-15%; molybdenum—10%-12.5%; cobalt—6.5%-8.0%; titanium—4%-6%; aluminum—1.5%-2.5%; zirconium—up to 1.2%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

4. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—5%-6%; chromium—19%-21%; vanadium—18%-20%; molybdenum—8.5%-10.5%; cobalt—6%-8%; titanium—4%-5%; aluminum—1.5%-2.5%; zirconium—up to 2%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

5. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—1.5%-2.5%; chromium—17%-19%; vanadium—9.5%-12%; molybdenum—8%-10%; cobalt—9%-11%; titanium—2.5%-4%; aluminum—1%-2%; zirconium—up to 0.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

6. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—2%-3%; chromium—17%-19%; vanadium—11%-13%; molybdenum—8%-10%; cobalt—9%-11%; titanium—2.5%-4%; aluminum—1%-2%; zirconium—up to 0.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

7. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent; carbon—2.5%-3.5%; chromium—15.5%-18%; vanadium—14%-16%%; molybdenum—8%-10%; cobalt—8%-10%; titanium—2.5%-4%; aluminum—1%-2%; zirconium—up to 0.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

8. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—3.25%-4.25%; chromium—21%-23%; vanadium—14%-16%; molybdenum—11%-13%; cobalt—7%-9%; titanium—3%-4%; aluminum—1%-2%; zirconium—up to 0.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

9. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—2%-3%; chromium—19%-21%; vanadium—11%-13%; molybdenum—11%-12%; cobalt—10%-12%; titanium—2.5%-4%; aluminum—1%-2%; zirconium—up to 0.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

10. A nickel based wear and corrosion resistant alloy consisting essentially of in weight percent: carbon—2.25%-3.25%; chromium—19%-21%; vanadium—12%-14%; molybdenum—11%-13%; cobalt—9%-11%; titanium—3%-4.5%; aluminum—1%-2%; zirconium—up to 0.5%; silicon—up to 0.5%; and balance essentially nickel and incidental impurities.

11. The nickel based wear and corrosion resistant alloys of claims 1-10 produced by gas atomization of the prealloyed melt and containing 10-55% of primary alloy carbides.