US2744822A - Copper base alloys - Google Patents

Description

United States Patent COPPER BASE ALLOYS James L. Briggs, In, Rome, N. Y., and Cyril H. Harmon, Pittsfield, Mass., assignors of one-half to Revere Copper and Brass Incorporated, Rome, N. Y., a corporation of Maryland, and one-half to General Electric Company, Schenectady, N. Y., a corporation of New York No Drawing. Application July 9, 1951, Serial No. 235,898

6 Claims. (Cl. 75-159) Our invention relates to copper base alloys of the copper-nickel-silicon type.

The invention has among its objects the provision of an alloy of the above mentioned type characterized by a high resistance to rupture when subjected to so-called stress-corrosion, that is to say, a combination of high tensile or torque loading and electrochemical corrosion induced by more or less prolonged exposure to a corrosive medium, as hereinafter more fully explained. This and other objects of the invention, however, will be best understood from the following description, while the scope of the invention will be more particularly pointed out in the appended claims.

Applicants have found that the copper-nickel-silicon type of alloy is highly desirable for many industrial applications, but that alloys of that type which have heretofore been proposed are unsatisfactory in respect to resisting cracking and other forms of rupture when subjected to stress-corrosion, even when otherwise strong and resistant to chemical corrosion. It is believed that this susceptibility to stress-corrosion cracking or other failure of the alloys of this type heretofore proposed results because, within the structure of the alloy, more or less continuous zones exist that are anodic to contiguous portions of the alloy. Consequently, when the alloy is subjected to the action of a corrosive medium, fissures are initiated at the surface of the metal as the result of electrochemical action between the anodic and cathodic areas of the structure, and, if high tensile stresses resulting from tensile or torque loading of the article made of thealloy are present at that surface, these small fissures increase the magnitude of local stresses at the fissures and that increases the depths of the fissures. This increase in the depths of the fissures exposes new metal at the bottoms of the fissures, which new metal is consumed by electrolytic corrosion with consequent further increase in the magnitude of the stresses at the fissures, and as the action proceeds the material ultimately fails. In general the present invention consists in eliminating this susceptibility of the copper-nickel-silicon type alloy to stress-corrosion by in substance adding to the alloy a critical amount of iron within narrow ranges of nickel and silicon, it being believed that the resulting lack of susceptibility of the improved alloy to failure when subjected to stress-corrosion is caused by the resulting absence in the alloy of the above mentioned contiguous zones of different electrochemical potential which when present and exposed to a corrosive medium set up galvanic cells causing the electrolytic or electrochemical solution of the anodic areas.

Applicants have found that the desired properties of the alloy are secured when it contains, approximately, 3.5 to nickel, 0.7 to 2% silicon, 0.3 to 1% iron, with the balance essentially all copper. Such alloys may be employed to form satisfactory articles by casting, and when an amount of silicon not exceeding 1% is present in conjunction with an amount of iron not exceeding 0.5% may be satisfactorily hot forged, hot or cold rolled and drawn, and hot extruded to form various shapes. Furr' Ice thermore these improved alloys are very resistant to nonelectrolytic chemical corrosion and season cracking, and have the valuable property of being age hardenable by suitable heat treatment. The tensile and yield strengths of the improved alloys are markedly high. Cast alloys with as high as 80,000 pounds per square inch tensile strength and 65,000 pounds per square inch yield strength are readily secured. By Working the alloys, or by working and subsequently age hardening them, the tensile and yield strengths may be much increased above these values.

The above properties make the improved alloy very attractive for use in electric cable pressure terminals, fixtures for electric power transmission lines, turnbuckle and other eye-bolts, and other articles which in use are subjected to high loads and the prolonged electrochemical corrosive effect of industrial atmospheres.

The cast alloy has its optimum properties in all the respects above mentioned, and particularly in respect to satisfactory machinability, high tensile and yield strengths, and lack of susceptibility to stress-corrosion, when it contains, approximately, '4% nickel, 1% silicon, and 0.4% iron, while the worked alloy has its optimum properties in these respects, and in respect to the facility with which it may be worked without failure while it is being worked, when it contains, approximately, 4.3% nickel, 1% silicon, and 0.5% iron.

Cast and worked alloys, of numerous compositions within the ranges. of constituents above specified for the improved alloys, have been tested by immersing screwthreaded inch diameter machined round studs or rods, having 16 United States standard screw-threads per inch in an A. S. T. M. standard mercurous nitrate water solution of 10% concentration for 15 minutes at room temperature while subjecting them to various torque loads. All the studs or rods so tested, including those made of the alloys as cast and machined without work hardening or age hardening them, withstood torque loads of the satisfactorily high value, considering the small diameter of the rods, of 20 foot pounds without rupture or cracking, while all the rods made of the worked and age hardened alloys withstood a very much higher torque load without rupture or cracking, in the instance of rods of the above mentioned. optimum composition for the worked alloy a torque load of about 47 foot pounds. It will be understood in these connections that mercurous nitrate was selected as the corrosive medium in these tests because of its property of vigorously attacking copper base alloys of high stressed copper content. In a few minutes such medium will produce the corrosive effect that it would take the ordinary industrial atmosphere years to produce. Also it will be understood that screw-threaded rods of small diameter were selected, and those rods subjected to torque loading in making the tests, because the notch effect of the screw-threads on rods of small diameter and the twisting effect on such rods produced by such loading present the optimum conditions for failure by stress-corrosion when the rods are subjected to the action of a corrosive medium.

Apparently in order for the improved alloy to have its desired properties it must contain a minimum amount of nickel silicide. It has been found that if less than 3.5% nickel is present in the alloy, and the silicon is within the range thereof specified, sufiicient nickel silicide will not be formed and the alloy will lack its desired properties, particularly that of effectively resisting stresscorrosion, even if there is chemically uncombined nickel and silicon in the alloy. Within the specified ranges of 3.5 to 5% nickel and 0.7 to 2% silicon sufficient nickel silicide apparently will be formed, and the addition of about 0.3 to 1% iron will give the alloy its property of highly resisting stress-corrosion. On the other hand, if the amount of nickel exceeds about 5% the alloy cannot be given the property of resisting stress-corrosion by adding more iron because in such case iron segregates will be present which will make the alloy subject to chemical and electrochemical corrosion. diflicult to machine, and impossible to Work satisfactorily without cracking while being worked. With less than about 0.3% iron within the ranges of 3.5 to nickel and 0.7 to 2% silicon the alloy, besides having a very poor resistance to stress-corrosion, will have an unsatisfactory low yield point, neither of which defects can be corrected by increasing the amount of silicon to above 2%. Furthermore, with the improved alloys which are to be worked if the silicon exceeds about 1%, or if the iron exceeds about 0.5%, the alloys, as hereinbefore stated, cannot be satisfactorily worked without cracking while being worked.

It has been found that the casting properties of the improved alloys may be improved by deoxidizing the melt with manganese or phosphorus, but that the residual amount of manganese remaining in the alloy cannot exceed about 0.5% without rendering the cast alloy unsatisfactorily susceptible to stress-corrosion. Furthermore, it has been found that a residual amount of manganese in the alloy is undesirable if the alloy is to be worked, as even a very low residual amount of managnese tends to cause the alloy to crack while being worked. Hence, if the melt is to be deoxidized and the resulting alloy worked, phosphorus is preferably substituted for manganese as a deoxidizer, the alloy still having satisfactory properties when it contains a small residual amount of phosphorus.

Additions of aluminum to the improved alloys are undesirable as they make the alloys difiicult to machine, while amounts of aluminum in excess of about 0.2% cause the alloys to be subject to season cracking, particularly the worked alloys.

The presence of even very small amounts of lead or zinc in the improved alloys should be avoided as they both tend to an unsatisfactory extent markedly to reduce the resistance of the alloys to stress-corrosion.

It will therefore be understood that in respect to the nickel, silicon and iron in the improved alloy the balance of the alloy, except for possible impurities not materially impairing its above specified properties, is substantially all copper, any residual manganese remaining in the manganese deoxidized alloy and any aluminum in the alloy up to the amounts of manganese and aluminum above specified being considered as impurities.

We claim:

1. An alloy composed of, approximately, 3.5 to 5% Cir nickel, 0.7 to 2% silicon, 0.3 to 1% iron, the balance essentially all copper, characterized by a high yield strength, and by a high resistance to failure when subjected to stress corrosion as evidenced by inch diameter round rods of cast alloy having 16 United States standard screw-threads per inch withstanding without failure a torque load of at least 20 foot pounds while immersed for 15 minutes in a 10% water solution of mercurous nitrate at room temperature.

2. Manganese deoxidized alloys according to claim 1 in which the residual amount of manganese contained therein does not exceed approximately 0.5%.

3. Wrought alloys according to claim 1 in which the silicon does not exceed approximately 1% and the iron does not exceed approximately 0.5

4. An alloy composed of, approximately, 4% nickel, 1% silicon, 0.4% iron, balance essentially all copper, characterized by a high yield strength, and by a high resistance to failure when subjected to stress corrosion as evidenced by inch diameter round rods of cast alloy having 16 United States standard screwthreads per inch withstanding without failure a torque load of at least 20 foot pounds while immersed for 15 minutes in a 10% water solution of mercurous nitrate at room temperature.

5. A manganese deoxidized alloy according to claim 4 in which the residual amount of manganese contained therein does not exceed approximately 0.5%.

6. A wrought alloy composed of, approximately, 4.3% nickel, 1% silicon, 0.5% iron, balance essentially all copper, characterized by a high yield strength, and by a high resistance to failure when subjected to stress corrosion as evidenced by inch diameter round rods of cast alloy having 16 United States standard screw-threads per inch withstanding without failure a torque load of at least 20 foot pounds while immersed for 15 minutes in a 10% water solution of mercurous nitrate at room temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,658,186 Corson Feb. 7, 1828 2,031,315 Jennison Feb. 18, 1936 2,185,956 Strang et a1. Jan. 2, 1940 OTHER REFERENCES Copper-The Metals, Its Alloys and Compounds; A. Butts; Reinhold Pub. Co., 1954, pages 396-397 relied on.

Claims (1)

1. AN ALLOY COMPOSED OF, APPROXIMATELY, 3.5 TO 5% NICKEL, 0.7 TO 2% SILICON, 0.3 TO 1% IRON, THE BALANCE ESSENTIALLY ALL COPPER, CHARACTERIZED BY A HIGH YIELD STRENGTH, AND BY A HIGH RESISTANCE TO FAILURE THEN SUBJECTED TO STRESS CORROSION AS EVIDENCE BY 3/8 INCH DIAMETER ROUND RODS OF CAST ALLOY HAVING 16 UNITED STATES STANDARD SCREW-THREADS PER INCH WITHSTANDING WITHOUT FAILURE A TORQUE LOAD OF AT LEAST 20 FOOT POUNDS WHILE IMMERSED FOR 15 MINUTES IN A 10% WATER SOLUTION OF MERCUROUS NITRATE AT ROOM TEMPERATURE.