US2108047A - Nontarnish alloy - Google Patents

Description

Patented .Feb.1 5, 1 938 UNITED, STATES PATENT OFFICE NONTARNISH ALLOY No Drawing. Original application December 24,

1934, Serial No. 759,053.

Divided and this al plication April 20, 1937, Serial No. 137,912

14 Claims.

I 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, zinc and iron, 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.

The individual elements of thealloy may vary over a limited and prescribed range in percentage but the amounts of nickel, chromium, and iron must be carefully controlled and proportioned and the copper, manganese and zinc contentscarefully proportioned and balanced against the nickel, chromium and iron contents, with carbon and other impurities kept below predetermined values.

In order to produce the alloy of our invention which offers substantially complete resistance to tarnish and corrosion by household reagents,

foodstuffs, 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, we have found a higher percentage of chromium than that which corresponds to the .125 atomic fraction (about 11 per cent by weight) to be of great value, as for example up to 20%. In alloys for use in applications not involving acid corro-.

sion, smaller proportions of chromium in solid solution may be employed, as for example as low as four or five per cent.

The nickel content serves to bring, the other constituents of the alloy into uniform solid solution and preferably suflicient 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 offset by increase in melting point, greater cost, darker color, etc. Accordingly, the nickel content is kept as low as is permissible, though it may vary from forty to seventy per cent by weight.

' By incorporating manganese and zinc not only may the proportion of copper 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 125 to 170 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, a 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 and zinc tend to reduce the possible rolling reductions between annealings, this effect is quite small up to proportions of 10% and our alloy with a component of as much as 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 -55% by weight of nickel, either around 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 may be incorporated.

The copper element, like manganese and zinc, aids in obtaining a low melting point and other desired characteristics of the alloy, such for ex ample 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 ofcopperalso aids in the 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%), 5% to 20% for alloys of the higher chromium range, and in alloys of the lower chromium range copper may be alloyed up to a limit of about by weight.

Our alloy is essentially non-ferrous, but we have found it an advantage to include in the alloy a small percentage of iron, since it increases the solubility of chromium for a given nickel content and promotes a more homogeneo s structure, or to put it differently it reduces the necessary quantity of nickel by an amount greater than the iron content. Further, it is beneficial in that the copper content is reduced to a point where the corrosive resistant properties of the alloy are not lowered by the copper. It also renders possible a substantial reduction in cost of producing the alloy, since ferrochrome is much cheaper than chromium metal and also is more easy to introduce into the melt because of its lower melting point. In this respect ferrochrome has a distinct advantage over pure chrome in that it minimizes evaporation losses during .melting, especialiythat of zinc. The cost. may also be reduced by substituting ferromanganese for manganese metal. The iron content of the melt, however, is

best limited to that which results from psing ferro alloys as the original source of chromium or manganese, because the further addition of iron causes reduction in amount of those elements (copper, zinc and manganese) which assure the desired low annealing andmelting points and otherwise contribute to the advantages above described. The iron content should not exceed ten per cent by weight and preferably should be sublower. We have obtained particularly good results with iron content of from 2% to 6% in alloys of chromium content of approximately 12%, nickel 50% to with the remainder copper, manganese and zinc, but in certain instances the iron content may be as great as 60% per and the nickel contents, and this applies to 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 dimculty 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, evenin 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 35% nickel, .12 per cent at 50% nickel, .15 per cent at 60% nickel, or .20 per cent at nickel.

The following are examples of embodiments of our invention, showing their approximate analyses, freezing points and workability. The degree of workability is the approximate reduction in cold rolling which the particular alloy withstands without cracking.

Cnsmcsr. snsmrsrs Group! Ni 01' Cu Mn Zn Fe Si 0 l 2 00.5 11.1 1.2 2.0 4.0 4.8 .14 10 2450r 02 00.5 14.2 5.0 0.2 8.0 1.1 .10 13 2215 1 53 11110 53.2 15.5 13.0 5.3 5.0 1.0 .32 01 2150 1 00 11110 50.3150 8.8 4.2 4.0 1.0 .24 05 2400r 11 55.2 10011.2 5.0 4.5 1.2 .10 04 2315 1 01 51010.0 0.5 4.5 1.0 1.8 .11 00 2425r 11 50.0 20.5 8.7 3.0 1.0 0.0 .33 01 240000 35 Group II 51.010.018.4 0.1 0.1 1.0 .25 .00 2225F 50 111111 520100150 0.0 0.3 5.0 .24 .00 2275F 01 51.0 11.0 17.3 5.5 9.0 5.5 .15 .054 2275F 60p1us 111.011.1115 5.5 0.1 5.0 .15 .014 2215 1" 60plus 52.0 11.1100 0.5 0.3 2.1 .30 .053 2215 1 00 11110 51.1123 14.0 5.5 0.0 0.2 .30 .040 2215 2 50.4 13.2 5.0 11.5 11.0 0.0 .10 .14 2150r 55 11110 512141155 0.3 0.0 1.0 .22 .005 2250 0 50 11110 GroupIII l. approximate ircezingtempemturo 2. orksbllity-Percent reduction between snnealings.

per cent, nickel 40 to 70 per cent, manganese 2 to 18 per cent, zinc from 2 to 14 per cent, iron 1 to 10 per cent and the balance copper in excess of 5 per cent with the carbon content limited as described above.

Group I of the examples includes alloys whose condition of complete immunity to tarnish or corrosion by mayonnaise and vinegar or any other ordinary household agent is obtained by any annealing treatment of commercial duration. These alloys may also be used in the cast condition, after any commercial furnace annealin; treatment or after soldering, etc., with substantially complete immunity to tarnish or corrosion. The, only exception to this applies to severely stressed or cold-worked alloys of' this class and also to prolonged heating at temperatures somewhat below 1600 F.

Group II includes alloys which by means of pletely 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 at tack that does take place is much slower and not as severe as would take place on any relatively inexpensive alloys now known to the artwhich 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 ear or hydrogen sulphide.

In the practical production of the alloy it is impossible to avoid traces of one or more other elements being present aslmpurities 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. a

Small additions of magnesium to the alloy are harmless, and preferably 0.1 per cent oi magnesium as a copper alloy is added to the melt just before pouring to remove oxygen and other harmful cases. 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 or a. copper alloy containing 20% magnesium to every 100 pounds of total melt one or two minutes before casting.

Any suitable. method may be utilized for bringing the constituents of the alloy of our invention into a melt or 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 iree oi carbon. lit is very lmportaut that the metal come only in contact with non-carbonaceous materials during the melting period.

Chromium may m added in the to of low melting point addition alloys such can 50-50 chrome-nickel alloy, or a so-s'r-cs chi-m: w nickel-copper alloy, but low carbon ierrochrome may be added directly to the melt without formation of a lower melting alloy previously. The

method of adding the various ingredients to the I melt or our invention may be varied in any way provided the ingot analyses produced be within the limits described above.

After the ingot casting is obtained it may be converted into strip, sheet, or any type of hollowware, flatware, hardware or ornamental articles in essentially a similar manner to that now used by the art, vlz.: hot working, cold working and annealing. Cold 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 sufiiciently 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 chromlum and nickel ranges are to be used. For any material Whichls to be soldered, brazed or welded into finished articles an alloy of our invention containing more than 54% nickel and 171% chromium by weight should be used.

An alloy within the Group I of our invention is suitable, as indicated, for use in the cast con dition for tarnish and corrosion resistance, and, since mecharrlcalworkability is not a factor here, we'may add about 1% 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 wherethe material can beannealed at a high temperatiue just before or after final fabricating processes either of the embodiments Groups I or H can be used. For example, for manufacture into spoons, fork-s, knives, and other tableware an alloy of our invention containing more than lt% nickel, more than 11% chromium and no greater than 30% copper is preferable. The dual annealing treatment before or after fabrication into final form should consist of heathm the alloy to a temperature between about 1900" and 2100 F. and cooling rapidly.

For manufacture of hardware and other artielse 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 ill preierred.

We claim:

l. an alloy containing nickel, ohroml copper, manganese and iron in the approximate proportions of i to 20% chromium, 36 to 70% nickel, 2 to l8% manganese,- 1.5 to 18% zinc, l to 10% iron 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-tarnish characteristics and consisting of 10 to 20% chromium, 45 to 70% nickel, l to ll0% iron, 2 to 10% manganesefi to 14% 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, nickel, 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%, iron 1 to 10% but not in excess oil of the chromium content, and the balance copper in excess of 5% and not greater than 30%, with traces of other elements including a small trace oi 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 nickel 36 to 60%, manganese 2 to 18%, zinc 2 to 12%, iron 1 to 10% but not in excess of 60% oi' the chromium content, 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. An alloy of the character set forth in claim 1 wherein the iron content is from 40 to 60%.

of the chromium content.

6. A cold workable, low melting point alloy having non-tarnish characteristics consisting of 54 to 70% nickel, 11 to 20% chromium, 5.8 to

carbon with the carbon not in excess of 0.12.

8. 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, 1 to 10% of iron, but not in excess of six-tenths the chromium content, and the remainder manganese 2 to 18% and zinc 1.5 to 18% with the sum of the manganese and zinc contents between 6 to 20% and traces of,

other elements including carbon with the carbon not in excess of 0.2%.

9. 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, to 70% nickel, 6 to 20% manganese and zinc, with the manganese 2 to 18% and the zinc 1.5 to 18%, and 1 to 10% iron, but not in excess of six-tenths the chromium content, with the remainder cop-' per in excess of 5% and traces of other elements including carbon with the carbon not in excess of 0.2%.

10. An alloy of the character set forth in claim 3 wherein the chromium content is from 10 to 16% by weight, the nickel content is from to 70%, and the iron content is from oneeighth to six-tenths the chromium content.

11. An alloy containing nickel, chromium, copper, manganese, zinc and iron in the approximate proportions of 53.2 nickel, 15.5 chromium, 13.0 copper, 5.3 manganese, 5.6 zinc, and 7.0 iron, with traces of other elements including carbon with the carbon not in excess of .07.

12. An alloy containing nickel, chromium, copper, manganese, zinc and iron in-the approximate proportions 01' 50.2 nickel, 7.4 chromium, 19.2 copper, 6.3 manganese, 12.4 zinc, and 4.3 iron, with traces of other elements including carbon with the carbon not in excess of .04.

13. An alloy consisting of nickel, chromium,

copper, manganese, zinc and iron in the relative proportions of 40 to 70% nickel, 4 to 20% chromium, 6 to 10% manganese, 4 to 10% zinc, and 1 to 10% iron but not exceeding 60% of the chromium content, with the balance copper in excess of 5%, with traces bf other elements including carbon with the carbon not in excess of 0.20%.

14. An alloy consisting of nickel, chromium, copper, manganese, zinc and iron in the relative proportions of to nickel, around 11% chromium, 6 to 10% manganese, 4 to 10% zinc, and 1 to 10% iron but not exceeding of the chromium content, with the balance copper in excess of 5%, with tracesiof other elements including carbon with the carbon not in excess of BIRGER EGEBERG.' ROY W. i'I'INDULA.