US2108049A - Nontarnish alloys - Google Patents

Description

Patented Feb. 15, 1938 I 2,108,049 PATENT OFFICE.

NONTARNISH ALLOYS Birgel' Egeberg, Merlden, Conn, and Boy W. Tlndnla, Bufialo, N. Y., assignors to International Silver Company, Meriden, Conn.,-a corporation of New Jersey Original application December 24', 1934, Serial No. 759,053.

No Drawing.

Divided and this applicatlon April 20, 1937, Serial No. 137,914

12 Claims.

This invention relates to alloys and this application is a' division of application Serial No. 759,053 filed December 24, 1934.

The object of the invention generally is a tarnish and corrosion resistant alloy which may be readily cold worked, may be melted and cast more easily than prior non-tarnish and. non-corrosive alloys, and may be economically produced, and particularly an alloy adapted for use in the manufacture of tableware and various kinds of hardware where a complete or substantially complete resistance to weak organic acids, salt solutions,

and organic sulphur compounds is necessary, or

where superior resistance to many strong mineral acids, such as sulphuric and nitric, is desired.

A further object of the invention is an alloy which, being resistant to tarnish and corrosion by all ordinary materials found in foodstuffs, such as sulphur compounds, salt solutions, and weak organic acids, requires no superimposed nontarnish coating for use in the manufacture of tableware, and which is characterized generally by its favorable chemical .resistance, desirable physical properties, ease of cold working, ease of polishing to a high luster, ease of treatment, low melting point, ease of production, and low cost.

To these ends we have produced an alloy embodying chromium, nickel, copper, manganese, and zinc all in substantially complete solid solution, and in proportions, coupled with special heat treatment when desired, to endow the same with the desired characteristics above indicated.

foodstufis, weak organic acids, sulphur compounds, saline or industrial atmospheres, and corrosive vapors, we find it necessary that about one atom (or over) of every eight atoms in the alloy be of chromium (that is at least approximately 11 per cent by weight of chromium in solid solution), and, furthermore, that the other elements be so proportioned that the annealing treatment given will bring this amount of chromium into solid solution. For resistance to the more corrosive materials such as nitric acid wehave found a higher percentage of chromium than that which corresponds to. the .125 atomic fraction (about 11% by weight) to be of great value, as for example up to 20%. In alloys for use in applications not involvingacid corrosion,

smaller proportions of chromium in solid solution gnay be employed, as for example as low as 4 or The nickel content serves to bring the other constituents of the alloy into uniform solid solu-- tion and preferablysumcient nickel must be incorporated for this purpose. It also substantially, along with chromium, favorably affects the degree of resistance to various tarnishing and corroding media by affecting the solubility of chromium at various temperatures, and tends to improve the workability and give somewhat increased luster in the polished state, but these advantages are somewhat ofiset bylncrease in melting point, greater cost, darker color,etc. Accordingly, the nickel content is kept as low as is permissible, though it may vary from 40 to 70% by weight.

By incorporating manganese and zinc not only may the proportions of copper and nickel be thereby reduced, but the alloy becomes endowed with certain of the special properties and characteristics above described. For example, while the melting point of pure nickel may be progressively lowered about 50 .F. for each 10% of copper alloyed with it, 10% of zinc and manganese will lower the melting point by approximately to F. respectively. Thus with a given chromium and nickel content the substitution of 10% manganese and zinc (for example 5% each) in place of 10% of copper produces an alloy with a melting point 100? F. lower. This greatly facilitates melting and makes it possible to obtain a much more fluid melt and better ingots. The substitution of 5 to 10% manganese and zinc also results in an alloy with greater softness on annealing the cold worked alloy, 8. better surface on alloys which have been annealed and pickled, greater ease of pickling because annealing furnace scale. is more soluble in strong acids, and appreciably better resistance for a given chromium and-nickel content to-tarnish and corrosion in sulphur bearing compounds, salts or weak acids.

While large proportions of manganese andzinc 'tend to reduce the possible rolling reductions between annealings, this effect is quite small up to proportions of 10% and ouralloy with a 'component of as much as 30% manganese and zinc still possesses a limited degree of cold workability. For best results we. prefer'to use with an alloy containing about 11% chromium and 50-55% by weight of nickel, eitheraround 6% manganese and 8% zinc, or about 9% manganese and 4% zinc. For the alloys of the lower chromium range we prefer to use around 10% each of zinc and manganese. In certain cases larger proportions of these elements mayibe incorporated'.

- The copper element, like manganese and zinc,

aids in obtaining a low melting point and other desired characteristics of the alloy, such for example as its cold working properties, and we have found that by alloying manganese and zinc with copper (and the other elements) and for alloys of the higher chromium range limiting the copper to less than about 30%, with the corresponding proportions of nickel, chromium and iron above described, superior or complete resistance of the alloy to tarnish and corrosion by sulphur compounds and organic acids is secured. The presence of copper also aids inthe alloying of the zinc with the other elements. The copper content should not be less than 5% of the composition by weight and preferably is substantially larger (around 15%), 5K, to 20% for alloys of below because it may remove a considerable amount of chromium from effective service in preventing tarnish, thus making a greater chromium content necessary than if it were not present. It tends to form a hard and insoluble constituent within the alloy that greatly impairs malleability and ductibility which can only be partly counteracted by higher nickel contents, and these insoluble particles add greatly to the diiliculty in polishing and if more than the below amounts of carbon are present it is detrimental to the luster of the polished alloy. Maintaining the carbon content as low as possible is of utmost importance in developing the desired properties; also because the carbon content, even in proportions less than the below mentioned amounts, increases the frictional wear resistance of the alloy and is consequently detrimental from the standpoint of ease of polishing and the amount of labor involved. We have found that the carbon content should not exceed .05 per cent at nickel, .12 per cent at 50% nickel, .15 per cent at 60% nickel, or .20 per cent at 70% nickel.

The following are examples of embodiments'of our invention:

Grumman ANALYSIS Group I N1 Fe 81 GHEMIOAKL ANALYSIS, Group II cow OIOO

Cannon. ANALYSIS Group III 35 .3 38 OIGII "H O CONN PPFFPPP paw-moo:

1. A proximate freezing temperature. I I 2. orkability-per cent reduction between annealing's.

These examples of the alloy show a range in proportions of chromium from around 4 to 17%,

nickel 36 to 70%, manganese 2 to 18%, zinc from 2 to 19%, and the balance copper in excess of 5% with the carbon content limited as described above.

Group 11 includes alloys which by means of high temperature final annealing treatment v(generally from 1900" F. up followed by rapid cooling) can be rendered completely immune to tarnish or corrosion by mayonnaise and vinegar. After final annealings carried out at lower temperatures, alloys in this classare very slightly attacked by these materials. For complete resistance to milder conditions as atmospheric tarnish, corrosion by salt-spray, or tarnish by egg or hydrogen sulphide, this high annealing temperature will not be necessary.

Group III includes alloys which are not completely immune to attack by mayonnaise and vinegar but may be somewhat improved in this respect by heat treatment similar to the heat treatment for Group II. However, any such attack that doestake place is much slower and not as severe as would take place on any relatively inexpensive alloys now known to the art which do not contain chromium; At the same time, these alloys in Group III are substantially immune to atmospheric tarnish. corrosion by salt spray, or tarnish by egg or hydrogen sulphide.

In the practical production of the alloy it is impossible to avoid-traces of one or more other elements being present as impurities in the essential elements making up the charge or extracted from the furnace lining or slag, such for example as traces of silicon, carbon, cobalt, tin, aluminum, etc., but it is understood that such impurities as described above with respect to carbon are reduced to the lowest practicable value.

Small additions of magnesium to the alloy are harmless, and preferably 0.1% of magnesium as a copper alloy is added to the melt just before pouring to remove oxygen and other harmful gases. For example, in order to produce a sound ingot free of excessive blowholes, it is desirable to add to the melt a small amount of magnesium, aluminum, calcium, barium, lithium, or other strongly reactive metal or alloy. The preferred practice is to add about one-half pound of a copper alloy containing 20% magnesium to every 100 pounds of total melt one or two minutes before casting.

ing the constituents of the alloy of our invention intoa melt of the desired proportions and the following is merely suggestive of one procedure. It is desirable to use a furnace or crucible lined with a material free or nearly free of carbon. It is very important that the metal come only in contact with non-carbonaceous materials during the melting period.

Chromium may be added in the form of low melting point addition alloys such as a 50-50 chrome-nickel alloy, or a 38-37-25 chromiumnickel-copper alloy. The method of adding the various ingredients to the melt of our invention, maybe varied in anyway provided the ingot analyses produced be within the limits described above.

- used by the art, viz: hot working, cold working and annealing. rolling and annealing schedules will vary considerably for the various alloys, but in general-it can be stated that most of the alloys embodied in our invention will withstand at least 50% reduction in thickness by cold rolling between successive annealings, and can be made sufficiently soft for further working by annealing between 1600 and 2000 F.

We have thus set forth the relative proportions of our alloy and have given certain limited ranges in proportions together with certain specific examples and it is understood that the proportions may be varied within the limited range described depending on the particular use to which the alloy is to be put. Where an alloy of maximum workability, luster, and complete tarnish and corrosion resistance is desired, the higher chromium and nickel ranges are to be used. For any material which is to be soldered, brazed or welded into finished articles, an alloy of our invention containing more than 54% nickel and 11% chromium by weight should be used.

An alloy within the Group I of our invention is suitable, as indicated, for use in the cast condition for tarnish and corrosion resistance, and, since mechanical workability is not a factor here, we may add about 1% of silicon to the alloy for improved sharpness in casting.

For manufacture of cutlery articles and other materials which require complete or essentially complete non-corrosive and non-tarnish properties, and where the material can be annealed at a high temperature just before or after final fabricating processes either of the embodiments Groups I or II can be used. For example, for manufacture into spoons, forks, knives, and other tableware an alloy of our invention containing more than 48% nickel, more than 11% chromium and no greater than 30% copper is preferable. The final annealing treatment before or after fabrication into final form should consist of heating the alloyto a temperature between about 1900 and 2100" F. and cooling rapidly.

For-manufacture of hardware and other articles where extreme corrosion resistance is not as important as strength, lower cost, and ease of manufacture, any of the alloys within the limits of our invention set forth previously may be used,-

with the low chromium alloys of Group III preferred.

We claim:

1. An alloy containing nickel, chromium, copper, manganese and iron in the approximate proportions of 4 to 20% chromium, 36 to nickel, 2 to 18% manganese, 2 to 18% zinc, and the balance copper, not less than 5%, with traces of other elements including a small trace of carbon.

2. A cold workable, low melting point alloy having non-tarnishcharacteristics and consisting of 10 to 20% chromium, 45 to 70% nickel, 2 to 18% manganese, 2 to 18% zinc and the balance copper, in excess of 5%, with traces of other elements including a small trace of carbon.

3. A cold workable, low melting point alloy having non-tarnish characteristics, consisting of chromium,.nlckel, copper, iron and manganese and zinc, wherein the chromium content is 10 to 20%, nickel 45 to 70%, manganese 2 to 18%,

zinc 2 to 12% and the balance copper in excess of 5% and not greater than 30%, with traces of other elements including a small trace of carbon.

4. A cold workable, low melting point alloy having non-tarnish characteristics, consisting of nickel, chromium, copper, iron, manganese and zinc, wherein the chromium content is 4 to 10%, nickel 36 to 60%, manganese 2 to 18%, zinc 2 to 12%, and the balance copper in excess of 13% and not greater than 55%, with traces of other elements including carbon with the carbon not in excess of 0.2%.

5. A cold workable, low melting point alloy having non-tarnish characteristics consisting of 54 to 70% nickel, 11 to 20% chromium, 5.8 to 25% copper, 2 to 10% manganese, 1.5 to 10% zinc, with traces of other elements including carbon with the carbon not in excess of 0.2%.

6. An alloy containing nickel, chromium, copper, manganese and zinc in the approximate proportions of 37.2% nickel, 5.2% chromium, 36.5% copper, 9.2% manganese and 11.1% zinc, with traces of other elements including carbon with the carbon not in excess of 0.20%.

7. A cold workable, low melting point alloy having non-tarnish characteristics and capable of being endowed with increased corrosion resistance by heat treatment at temperatures between 1900 F. and the melting point consisting of 11 to 15% chromium, 48 to 54% nickel, 5.8 to 30%copper, and the remainder manganese 2 to 18% and zinc 2 to 18% and with the sum of manganese and zinc contents between 6 and 20% and traces of other elements including carbon with the carbon not in excess of 0.2%.

8. A cold workable, non-tarnish, low melting point alloy which consists of chromium, nickel, copper, iron and manganese and zinc in the proportions of 4 to 20% chromium, 35 to 70% nickel, 6 to 20% manganese and zinc with the manganese 2 to 18% and the zinc 2 to 18%, with the remainder copper in excess of 5% and traces of other elements including carbon with the carbon not in excess of 0.2%.

9. An alloy of the character set forth in claim 3 wherein the chromium content is from 10 to 16% by weight, and the nickel content is from 45 to 70%.

10. An alloy consisting of nickel, chromium, copper, manganese and zinc in the approximate proportions of 50.3% nickel, 12.9% chromium, 25.1% copper, 1.2% manganese, 9.6% zinc with traces of other elements including carbon but with the carbon content less than 0.2%.

11. An alloy consisting of nickel, chromium, copper, manganese and zinc in the proportions of .11 to 15% chromium, 50 to 55% nickel, 6 to 10% of 4 to 10% chromium, 35 to 60% nickel, 8 to 1 12% manganese, 8 to 12% zinc and the balance copper in excess of 5%, with traces of other elements including carbon with the carbon not exceeding 0.2%;

' BIRGER EGEBERG. ROY W. TINDU'LA.