US3578440A

US3578440A - Nickel-copper alloy

Info

Publication number: US3578440A
Application number: US715898A
Authority: US
Inventors: Herbert L Eiselstein; Carl B Haeberle
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1968-03-25
Filing date: 1968-03-25
Publication date: 1971-05-11
Anticipated expiration: 1988-05-11
Also published as: GB1225721A; FR2004669A1; DE1914632A1; BE730405A; SE342473B

Abstract

AN AGE HARDENABLE NICKEL-COPPER ALLOY HAVING MARKEDLY IMPROVED WELDABILITY AND MACHINABILITY WHICH ALLOY CONTAINS NOT MORE THAN ABOUT 0.1% CARBON, NOT MORE THAN ABOUT 0.5% TITANIUM, ABOUT 2.5% TO ABOUT 3.5% ALUMINUM, ABOUT 63% TO ABOUT 70% NICKEL AND THE BALANCE, EXCEPT FOR INCIDENTAL ELEMENTS AND IMPURITIES, ESSENTIALLY COPPER.

Description

United States Patent O 3,578,440 NICKEL-COPPER ALLOY Herbert L. Eiselstein and flat! B. Haeberle, Huntington,

W. Va., assignors to The International Nickel Company, Inc., New York, NY.

Filed Mar. 25, 1968, Ser. No. 715,898 Int. Cl. C22c 19/00 US. Cl. 75-170 Claims ABSTRACT OF THE DISCLOSURE Age hardenable nickel-copper alloys have been known for many years and one such alloy, which nominally contains about 0.15% carbon, about 0.25% to about 1% titanium, about 2% to about 4% aluminum, about 63% to about 70% nickel and the balance, except for incidental elements and impurities, essentially copper, has had a long history of successful industrial use. The alloy is strongly age hardenable by a heat treatment in the neighborhood of 1100 F. It is strong, tough and ductible, is characterized by retention of strength and ductility to very low temperatures and has excellent corrosion resistance in a wide variety of environments. Despite the commercial success which the alloy has enjoyed, machinability of the alloy has always been limited and a high rate of tool wear has been encountered in machining the alloy. Furthermore, diificulties have been encountered in welding the alloy, particularly in respect to repair welding in the field with the result that the alloy is not welded in commercial terms. In addition, the heat treatment which has been applied to the alloy has traditionally been a very long heat treatment involving a furnace time on the order of 28 hours or even more in order to develop high age hardened properties therein.

The machining problem, in particular, has been a vexing problem in connection with the alloy and, despite many efforts, no commercially feasible improvement in machinability has been discovered. For example, one expedient which has been found actually to improve machinability of the alloy to a marked extent has been an anneal at a high temperature, e.g., 2100 F. or higher. However, it was found that heat treatment at a high enough temperature to provide an improvement in machinability of the alloy resulted in production of extremely large grains, a condition which could not be tolerated in commercial practice.

It is an object of the invention to provide an age hardenable nickel-copper alloy having improved machinability and weldability as compared to alloys of the prior art.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawing in which is depicted a plot of cutting speed against tool life as established in machinability testing applied to the alloy of the invention.

Broadly stated, the present invention comprises an age hardenable nickel-copper alloy containing not more than 0.10% carbon, e.g., about 0.03% to about 0.10% carbon, not more than 0.5% titanium, e.g., about 0.1% or about 0.2% to about 0.5% titanium, about 2.5 to about 3.5% aluminum, about 63% to about 70% nickel and the balice ance, with the exception of incidental elements and impurities, being essentially copper. A preferred alloy in accord ance with the invention nominally contains about 0.07% carbon, about 0.3% titanium, about 3% aluminum, about 63% to about 70% nickel and the balance essentially copper.

In providing the alloy in accordance with the invention, the carbon content is controlled within the range of about 0.03% to about 0.10%, and the titanium content is controlled so as not to exceed 0.5 to confer weldability and machinability to the alloy while at the same time enabling the production of high strength therein upon aging. The aluminum is maintained in the range of about 2.5 to about 3.5% to permit production of high properties upon aging the alloy. The alloy may contain small amounts of incidental elements which do not materially affect the basic and novel characteristics of the alloy including up to about 2% iron, up to about 1.5% manganese, and up to about 0.5 silicon. In common with other nickel-base alloys, sulfur is an undesirable impurity and should not exceed 0.010% while phosphorus should not exceed about 0.02%. In the interests of preserving weldability, machinability and hot malleability in the alloy, the boron content should not exceed 0.01%.

The alloy is age hardened by heating to a temperature in the range of about 1100 F. to about 1225" F. and then slowly cooling, e.g., at a rate of 25 F. per hour or less, the alloy to a temperature of about 900 F. Alternatively, the alloy can be held successively at temperatures of about 1150 F., 1050 F. and 950 F. for periods of up to about 8 hours at each temperature and with furnace cooling between each step. The alloy displays a maximum rate of hardening at about 1150 F. A preferred particularly satisfactory heat treatment comprises a heating at about 1150 F. for about 2 to about 8 hours, e.g., 2 hours, furnace cooling to 1050 F., holding for about 2 to about 6 hours, e. g., 4 hours, furnace cooling to 950 F., holding for about 2 to about 6 hours, e.g., 4 hours, and then cooling. It is thus possible to age the alloy by means of a time cycle only a little over 10 hours in length. Longer aging cycles improve the mechanical properties only slightly, and it was surprising to find that the short cycle heat treatment was so effective in aging the alloy. Hot finished and aged, e.g., hot rolled and aged or forged and aged products will provide a yield strength (0.2% offset) of at least 80,000 pounds per square inch (p.s.i.), a tensile strength of at least 130,000 psi. and an elongation of at least 20% measured over a gage length four times the specimen diameter. Higher strengths are obtained in cold finished, aged material made from the alloy. In order to develop maximum mechanical properties, the alloy is solution treated or annealed at temperatures in the range of about 1350 F. to about 1400 for times on the order of about /z hour, al though shorter annealing times, even as short as five minutes can be employed in the case of cold worked materials, e.g., rod, wire, strip, sheet, tubing, etc., with the higher annealing temperatures. The low solution or annealing temperature is a further important advantage of the alloy in that oxidation, distortion, grain growth and thermal shock effects are reduced or eliminated as compared to the case wherein higher annealing temperatures are used. Higher annealing temperatures and shorter times, e.g., about 1600 F. for one minute, can. be employed in special situations to anneal out all prior work hardening and to provide material for deep drawing, spinning, flow turning, etc., operations which are usually performed upon thin strip or sheet material. It is not necessary to employ a solution treatment prior to aging; instead, worked material can be directly aged, usually with advantage in terms of higher mechanical properties in the aged material.

It is found that the alloy is immune to strainage cracking after welding and, in addition, that the machinability of the alloy in all conditions of working and heat treatment is excellent. The material produces a long, stringy chip in machining and surface finish of machined pieces is excellent. Horsepower requirements for cutting the alloy are about the same as those for the known free machining stainless steel AISI Type 303 (Se), i.e., about 0.7 to about 0.8 horsepower per cubic inch of metal removed per minute. In general, best machinability is manifested when the alloy is machined in the annealed condition. This factor promotes the desired practice in conjunction with age hardenable alloys of machining the alloy almost to finish size before hardening followed by finished machining after hardening.

It is difficult to correlate machineability of an alloy with alloy composition. However, intensive investigation of the machining problem has resulted in development of a standardized testing technique utilizing an instrumented lathe and a single point tool of standardized design. A series of test runs is made with a standardized depth of cut and a standard feed rate per revolution in cutting a round piece of the test alloy. The cutting speed (measured in surface feet per minute) is varied for each In order to give those skilled in the art a better appreciation of the advantages of the invention, the following example is given:

A commercial scale electric arc furnace air melt was produced and cast into inch x 2.0 inch x 90 inch ingots. The alloy contained 65.37% nickel, 3% aluminum, 0.07% carbon, 0.84% iron, 0.54 manganese, 0.11% silicon, 0.30% titanium, 0.009% sulfur and the balance copper. One ingot was hot rolled to a 4-inch diameter round without difliculty. A portion of the material was cold drawn to 3 /8 inch diameter rod while another portion was forged into a 2-inch square and a further portion was further worked into the form of 4- inch diameter cold drawn rod. The resulting: material was subjected toroom temperature tensile testing in various conditions, including as-rolled, as-drawn, annealed and aged conditions with the results set forth in the following Table II in which the term annealed indicates a heat treatment at 1400 F. for /2 hour and the term aged indicates a heat treatment comprising heating at 1150 F. for 2 hours, furnace cooling to 1050" F. and hold for 4 hours (2 hours where symbol (A) appears), furnace cooling to 950 F. and hold for 4 hours followed by air cooling to room temperature.

TABLE II Y.S. (0.2% T.S., E1., R.A., Hard- Diameter size, inches Condition ollset), p.s.i. p.s.i. percent percent ness in area.

run and the tool life in minutes to develop a 0.015 inch wearland on the tool point in the case of carbide tools and a 0.050 inch wearland on the tool point in the case of high speed steel tools was measured on each run. The resulting data are plotted to develop curves such as those illustrated in the drawing. Good machinability is indicated by the plotted data when the resulting lines are straight and follow a uniform path. Erratic tendencies revealed by the plotted data and lack of straightness in the lines is in indication of poor machinability. High ordinate values for the plotted data constitute a further indication of good machinability. In order to reduce variables, most of the testing was done using carbide tools. Sufficient testing was done with high speed steel tools to indicate similar trends to the results obtained using carbide tools. The results can be compared by a machinability index based on 30-minute tool life (V in accordance with the relation:

condition tested (V X 100 standard condition (V Using the hot rolled, annealed (1400 F. /2 hour) condition as standard, the comparisons are shown in the following Table I:

Machinability index Fatigue testing on annealed and aged material from the 2-inch square forging as determined by the rotating bend fatigue test demonstrated a life at 10 cycles of 46,200 p.s.i. reversed stress and a life at 10 cycles of 43,500 p.s.i. reversed stress.

Material from the heat in various conditions was subjected to a machining test using single point carbide tools with the results illustrated in the drawing. The tool material employed was a tungsten-titanium carbide material with a cobalt binder. The tool was cut with a back rake angle of 0, a side rake angle of 5, an end clearance angle of 5, a side clearance angle of 5, an end cutting edge angle of 15, a side cutting edge angle of 15 and a nose radius of inch. The cutting site was flooded with a commercial coolant. A feed rate of 0.00825 inch per revolution with a depth of cut of 0.050 inch was employed in the test. A tool life end point was taken as 0.015 inch flank wear. Excellent surface finish was observed in the testing. As illustrated in the drawing, the machinability data was plotted in uniform straight lines and no tendency toward erratic behavior was observed. In addition, the ordinate values (cutting speed velocity) are very high, further indicating excellent machinability. The mill condition, e.g., hot rolled and annealed, in which the alloy was subjected to the machinability test is indicated on the tool life lines in the drawmg.

Weldability of the material was demonstrated by means of restrained butt welds made on l-inch thick forged flats in the age hardened condition resulting from an anneal at 1400 F. for /2 hour, air cooled and aged at 1150 F. for 2 hours, furnace cooled to 1050" F., hold 4 hours, furnace cooled to 950 F., hold for 4 hours and air cool. The aged flats were butted together with a V- groove therebetween and welded to a 4-inch thick steel strongback. The V-groove was then completely filled with a standard nickel-copper covered Welding electrode. The entire assembly was then given a further aging treatment as described hereinbefore. The welded nickel-copper alloy assembly was then cut from the strongback and the weld was sliced for examination. No strainage or underbed cracking was observed and side bend tests in which Aa-inch thick transverse slices cut through the weld were bent about a 1 /2 inch diameter pin indicated there were no fissures or voids in the weld area. The tensile properties of the aged weld material were determined by means of transverse tensile tests produced from tensile specimens, including the weld, together with all weld metal tests. The results are set forth in the following Table III:

TABLE III Y.S. (0.2% T.S., EL, Location of Test oflset), p.s.i. p.s.i. percent fracture Transverse 95,500 138, 500 22. Parent metal.

D0 93, 500 137, 500 22. 0 DO. Longitudinal all 112, 000 150, 000 7. 0 Weld.

weld metal.

Do 109, 500 148, 000 17. 0 Do.

very low level of machinability. Thus, the machinability level with carbide tools was lower than that of high speed steel tools. Again, a heat of 0.15% carbon, 0.54% titanium, with essentially no other change in composition from the alloy described in the example, indicated very poor to no machinability. Thus, the tool life line had a reverse curve at a very low machinability level indicating a highly undesirable condition as shown by Curve A in the drawing for cold drawn, as-drawn material made of the alloy. Curve B in the drawing is the tool life line for cold drawn, aged material made of this alloy outside of the invention.

The alloy provided in accordance with the invention is characterized by high strength, toughness and ductility over a wide range of temperatures and is useful over the temperature range from minus 423 F. to about 800 F. The alloy may be fabricated into such articles as pump shafts and impellers, propellor shafts, oil well drill c01- lars and instruments, doctor blades and scrapers, valve trim, springs, etc. The alloy is readily produced in any of the common mill forms, including rod, bar, sheet, strip, tubing, extruded shapes, forgings, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An age hardenable alloy having improved machinability and weldability in wrought form consisting essentially of about 63% to about nickel, about 2.5% to about 3.5% aluminum, about 0.07% carbon, about 0.3% titanium, not more than about 2% iron, not more than about 1.5% manganese, not more than about 0.5% silicon, not more than about 0.010% sulfur and the balance essentially copper.

2. In the production of wrought age hardenable nickelcopper alloys containing aluminum and titanium as age hardening ingredients, the improvement in compositional control therefor to provide enhanced machinability and freedom from weld cracking while retaining high strength in the aged condition which comprises controlling the carbon content in the range of about 0.07% the titanium content in the range of about 0.3% the aluminum content in the range of about 2.5% to about 3.5%, the nickel content in the range of about 63% to about 70% and with the balance essentially copper.

3. The process for age hardening an alloy consisting essentially of about 63% to about 7 0% nickel, about 2.5 to about 3.5% aluminum, about 0.03% to about 0.10% carbon, about 0.1% to about 0.5% titanium, and the balance essentially copper which comprises heating the alloy at a temperature of about 1150 F. for about 2 to about 8 hours, furnace cooling to about 1050 F., holding at about 1050 F. for about 2 to about 6 hours, furnace cooling to about 950 F., and holding at about 950 F. for about 2 to about 6 hours.

4. The process according to claim 3 wherein the alloy is annealed, prior to aging, at a temperature not exceeding about 1400 F.

5. The process according to claim 3 wherein the alloy is held at about 1150 F. for about 2 hours, at about 1050 F. for about 2 to about 4 hours, and at about 950 F. for about 4 hours.

References Cited UNITED STATES PATENTS 3/1939 Bieber -170 3/1941 Bieber et al. 75-170 US. Cl. X.R. l4812.7, 162