US2153978A - Cupro-nickel alloys - Google Patents

Description

Patented Apr. 11, 1939" UNITED STATES OUPRO-NICKEL ALLOYS Richard A. Wilkins, Rome, N. Y., assignor to Revere Copper and Brass Incorporated, Rome,

N. Y.,acorporation of Maryland No Drawing. Application July 13, 1938; Serial No. 218,947

4 Claims.

This application is a continuation-in-part of applicant's co-pending application Serial Number 117,562, filed December 24, 1936.

The invention relates to alloys for use in situa- 5 tions where resistance to the action of industrial corrosive media is of primary importance, the invention having among its principal objects to increase the chemical corrosion resistance of commercial cupro-nickels.

It will be understood that cupro-nickels are employed in the arts primarily because of their relatively high resistance to chemical corrosion, although they are expensive because of their high nickel content. Applicants invention seeks primarily to increase this corrosion resistance by the addition of relatively small amounts of other metals, thus increasing the value of cupro-nickels in respect to this property which primarily makes them useful, or, because with these additions the amount of nickel may be decreased for a given corrosion resistance, making it possible to' produce at less cost a cupro-nickel of given corrosion resistance.

According to the present invention applicant secin'es these results by adding both chromium and vanadium to cupro-nickels within the ranges of chromium, vanadium and nickel hereinafter specified.

It has been found that, aside from the vanadium and chromium additions rendering the resulting alloy per se non-resistant to corrosion, the vanadium, when, in sufllcient amount-in proportion to the amount of nickel, causes the formation of an invisible protecting film on the cupronickel surface, the film being rapidly self healing when mechanically ruptured, the chromium, 'when suflicient vanadium and nickel are present, causing the film to be tenacious so as to resist rupture. It has been found that the more difficult 40 it is mechanically to rupture such film, andthe more rapidly it heals when ruptured, the more the film protects the underlying metal from. the action of, corrosive media. Thus by the present in- I 55 marked'increase in the tensile strength and hardness of the fully annealed cupro-nickel and tensile strength of the cold worked cupro-nickel with little or no effect on the hardness or ductility of the cold worked cupro-nickel, the chromium, within the ranges thereof and of vanadium and 5 nickel hereinafter specified, causing no important change in the physical properties of the cupronickels as compared to those to which only vanadium has been added. At the same time the cupro-nickels with these additions may be read- 10 ily drawn, rolled and extruded both hot and cold to form sheets, tubes, rods and other shapes, the facility with which thealloy may be welded and reduced by hot drawing, rolling and working, and with which sound castings may be produced, 15 being much increased by the addition of vanadium. Thus the addition of both vanadium and chromium'to a cupro-nickel having an amount of nickel within the range hereinafter specified not only increases the chemical corrosion resist- 20 ance of the cupro-nickel and improves its physical properties but results, when shapes are fabricated from the alloy, in lessened working costs which more than offset the cost of the addition of vanadium to the cupro-nickel. 25'

Applicant has found that for the resistance of the cupro-nickel to chemical corrosion to be increased the amounts of vanadium 'and chromium and of any further metal or metals added to the cupro-nickel must be such as to produce 'substan- 30 tially a single solid metal solution. The existence of a mixture of two or more solid solutions will result in a decrease in the corrosion resistance of the mixture as compared to the cupro-nickel, and the same will be true if the additional metals 35 cause the presence of metallic segregates. If two solid solutions are present a galvanic battery effect will be produced at the surface of the metal when exposed to an acid or oxidizing substance, resulting in chemical corrosion, and a similar 40 effect ,will take place if metallic segregates are present.

Ithas been found that the nickel causes the vanadium to be dissolved in the cupro-nickel, and that the action-of the vanadium in conjunction with the chromium causes the above mentioned efiects in respect to increasing the resistance of the metal to corrosion. Apparently, if lessthan about 20% nickel is present in the cupro-nickel, it is so diluted by the relatively largev amount (80% or more) of copper present that no eflect on the corrosion resistan-e will be observed in respect to either the corrosion resistance of the metal per se or that-which. results from protecting it by reason of the formation thereon of the above described film, and further this amount of nickel and its extreme dilution are such that no more than about 0.1% vanadium can be dissolved in such cupro-nickels, the attempt to add more than 0.1% vanadium resulting in the presence of segregates which actually cause a decrease in the corrosion resistance of the cupro-nickel. If the vanadium is increased about 50% over this amount to 0.15% it will be all dissolved in cupronickels having 20 to just under 26% nickel without any noticeable effect on the corrosion resistance of the cupro-nickel per se, although where the metal surface is subjected to marked impingement in connection with exposure to the corrosive media, such as might occur in a fluid conducting pipe, the metal will to some extent, if 0.15% or more of vanadium is present, tend to be protected by the above mentioned fllm against the action of that media, which film will tend to form with that amount of vanadium if 20% or more of nickel is present. An increase in the corrosion resistance of the alloy per se, however, is noticed if the vanadium is not less than 0.15% and is used in conjunction with small amounts of chromium when the amount of nickel is 26% and more. Applicants improved alloys therefore contain at least 26% nickel and 0.15%

, vanadium to secure the improved results mentioned herein, the general formula of the alloy being, approximately, nickel 26 to 40%, vanadium 0.15 to 1%, chromium 0.05 to 2%, copper balance. Amounts of vanadium and chromium in excess of these will cause segregates of these metals or alloys or compounds thereof, which will form foci I for pitting when the alloy is subjected to corrosion. A less amount of nickel with these amounts of vanadium will cause segregates of vanadium or alloys or compounds thereof with like deleterious results.

In addition the alloys, while essentially com-' ganese which, although imparting no direct beneflcial effect, insures against the deleterious effect on the nickel of any sulphur that may be present. Manganese has a greater afiinity for sulphur than has nickel, and will flux off the sulphur into the slag. The amount of manganese added to the melt should not exceed such amount as will leave approximately more than 1% thereof in the alloy, and preferably not more than 0.5%, so as to avoid the presence in the alloy of deleterious segregates of manganese or alloys or compounds thereof.

The presence of aluminum in amounts in excess of about 0.2% should be avoided, as in excess of this amount it tends to make it diflicult to secure sound castings in producing the billets from which the alloys are worked, and if present in any appreciable amount commonly necessitates the use of expensive and special casting methods it the alloy is to be worked. Further, in excess of 0.2% it imparts brittleness to the alloys, making them cold short and therefore unsuitable for commercial fabrication into shapes. Further, amounts of aluminum in excess of 0.5% will cause the formation of segregates of aluminum or alloys or compounds thereof which will cause fool for pitting when subjected to a corrosive medium.

Iron when present even in small amounts im parts a displeasing yellow color to the cupronickel and thus tends to oifset the effect of the chromium in respect to the latter acting to whiten the alloy. Additions of iron in excess of about 0.3% will reduce the resistance of the cupronickel to corrosion in spite of the addition of chromium and vanadium, and acts to make the alloy refractory and difllcult to work particular] when cold.

Zinc as usual tends to reduce the corrosion resistance of the alloy and its resistance to atmos pheric tarnish, and further acts to decrease the tensile strength, ductility and toughness of the alloy. Further, the annealing temperature of cupro-nickel is such that at that temperature the zinc. will volatilize out and, as a result, introduce expensive cleansing operations between the passes in mill processes of reducing the alloy. The amount of zinc present should not exceed 1% lest it offset the increase in corrosion resistance imparted by the vanadium and chromium, and in fact when present in excess of that amount it ordinarily will actually reduce the corrosion resistance 01' the cupro-nickel in spite of the presence of vanadium and chromium.

The effect of the addition of vanadium and chromium within the ranges thereof above specified to cupro-nickels containing the amounts of nickel above specified is well illustrated by the effect of 0.5% each of vanadium and chromium added to 70:30 cupro-nickel. These amounts of vanadium and chromium increase about 40% the resistance of the cupro-nickel to the corrosive attack of a mixture of 10% sulphuric and hydrochloric acids when alternately dipped in the mixture and exposed to the air. Approximately the same increase also is noted when the improved metal is similarly subjected to the action of a sodium hyposulphate solution, 3% sodium chloride solution, 10% acetic acid solution, and other industrial corrosive reagents. At the same time the addition increases the tensile strength of the fully annealed cupro-nickel from about 47,000 to 66,000 pounds per square inch, and the tensile strength of the fully annealed alloy reduced 80% by cold rolling without subsequent annealing from about 84,000 to 105,000 pounds per square inch with no noticeable eifect on the ductility of that cold rolledalloy. At the same time the hardness of the fully annealed cupro-nickel is markedly increased from about 65 to 88 Rockwell (F hardness-B scale, ball, 60 kg. load), while the hardness of the cold rolled alloy is increased from about 107 to 114 Rockwell.

I claim:

1. Hot and cold workable alloys in substantially the form of a single solid solution substantially free from segregates consisting essentially of copper, nickel, chromium and vanadium in the following proportions: nickel 26 to 40%, chromium 0.05 to 2%, vanadium 0.15 to 1%, copper balance.

2. The alloys according to claim 1 containing, approximately, 0.5% each of chromium and vanadium.

3. The alloys according to claim 1 containing, approximately, 30% nickel.

4. The alloys according to claim 1 containing, approximately, 30% nickel and 0.5% each of chromium and vanadium.

RICHARD A. WILKINS.