US2108051A

US2108051A - Nontarnish alloy

Info

Publication number: US2108051A
Application number: US759053A
Authority: US
Inventors: Egeberg Birger; Roy W Tindula
Original assignee: International Silver Co
Current assignee: International Silver Co
Priority date: 1934-12-24
Filing date: 1934-12-24
Publication date: 1938-02-15
Anticipated expiration: 1955-02-15

Description

Feb. l5, 1938. B. EGEBERG r-:r AL

NONTARN ISH ALLOY Filed Dec. 24, 1934 BY Egger E gebezr` @MA/@w71 M nu ATTORNEYS Patented Feb. v15, 1938 PATENT 'OFFICE NoN'rA-Rmsn ALLoY Birger Egeberg and Roy W. Tindula, Meriden,

Conn., asslgnors to International Silver Company, Mei-iden,` Conn., a corporation of New Jersey Application December 24, 1934, serial ro. 759,053

11 claims. (ci. 'z5-171) This invention relates to alloys.

Ihe 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 producedn 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. At the same time the alloy has superior resistance to many strong mineral acids, such as sulphuric and nitric. f

Many so-called non-tarnish and non-corrosive 'alloys have been proposed and used in the arts.

Certain of these alloys are only mildly resistant `to tarnish and when exposed to humid or sulf phur-bearing atmospheres acquire a visible colored oxide or sulphide coating. 'They also becomecorroded orA tarnished in contact with various salt, acid, or alkaline materials present in foodstuffs. It is the common practice to apply, 'as by electrodeposition, a surface deposit of a metal, such as chromium or silver that has greater tarnish or corrosion resistance. Such commercial metals and alloys as copper, zinc, nickel,

brasses, bronzes, capro-nickel, nickel silver, and

l low alloy steels come within this class.

'I'he commercial stainless alloys now known to the art consist largely of chromium added to either iron or nickel. For example, we have high and low carbon steels with chromium, or chromium and nickel alloyed in various amounts. It

is well known to the'present art thata fairly definite minimum amount of chromium is'necessary`to confer rustless and stainless'properties to iron and the nal heat treatment is also of great importance. Substantial additions of chromium have also been found to endow nickel.with

objectionable in that they are difficult to cold work into shapes. l

The alloy of our inventionnot only possesses -thedesired resistance to tarnishan'dborrosion to all ordinary materials found in vfoodstuifs,`

such as sulphur-compounds, salt solutions, and weak organic acids and therefore does not require any superimposed non-tarnish coating, mbut also possesses a comparatively low melting point and does not harden up as rapidly under coldforming processes as the stainless ferrous materials now in use. It differs from nickel-chromium alloys in having a much lower melting point and having a much lower cost per pound of melt, and is characterized' generally by its favorable chemical resistance, desirable physical properties, ease of polishing to a high luster, ease of treatment, ease of production and low cost. It also compares favorably to other stainless alloys in resistance to strong mineral acids.

Our alloy in its prefer-red form embodies chromium, nickel, copper, and manganese or zinc or both, with or without iron in relatively small proportions, all in substantially complete solicl solution, and in proportions, coupled with special heat treatment in some instances, to endowthe same with Vthe non-tarnish and non-corrosion characteristics, the low melting and annealing points and the easy cold working and other physical characteristics indicated above. While the proportion of each principal individual constituent of the alloy may vary within a limited and prescribed range, we have found that by properly balancing the chromium and nickel against thecopper, manganese and zinc contents,` an improved alloy of the exact characteristics desired may be attained.

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 particularalloy withstands Without cracking.

.CHEMICAL ANALYSIS f Group I lus high temperature nal annealing treatmentv (generally from 1900 F. up followed by rapid Group!! Ni C1' Cn Mn Zn Fe Si C 1 2 50.3 12.9 25.1 1.2 9.6 0.6 .18 .07 2300F 34 51.6 10.9184 8.7 9.1 1.0 .25 .06 2225F 50plus 52.9 10.9150 6.6 9.8 5.0 .24 .06 2275F 67 51.0 11.0 17.3 5.5 9.6 5.5 .15 .054 2275F 601111111 51.0 11.1 17.5 5.5 9.1 5.6 .15 .1174 2275F 60111116 52.0 11.1 19.0 6.5 8.3 2.7 .30 .053 2275F 60111118 51.1 12.3 14.9 5.5 9.6 6.2 .36 .040 2275*1` 52 50.4 13.2 5.8 17.5 11.9 0.9 .19 .14 2150F 51.111118 51.2 14.1 15.5 8.3 9.6 1.0 .22 .065 2250F 50plus 53.5 12.1 14.4 121 0.0 6.6 .22 .06 2300F 50111119 GroupIII 43.4 10.2 20.0 8.3 11.6 6.1 .14 .09 2200F 42 42.2 12.1 14.4 18.5 10.8 1.7 J. 19 12 2100F 35 41.5 13.5 20.0 7.911.11 5.2 .15 .09 2200F 31 48.0 10.1 20.0 7.6 6.6 6.6 .96 .06 2275r 55 47.2113 21.7 5.8 6.7 6.3 .83 .06 230oF 55` 46.0-13.117.3 7711.0 4.5 .17 .11 2200F 54- 50.0 9.8 18.5 9.2 11.7 0.3 .41 .14 220011` 55 51.6 11.9 13.2 16.0 0.0 1.5 .2 ..16 2250F. 33 36.0 5.5 54.6 0.2 2.0 0.2 0.10 0.04 '2300F. 60111118 42.5 4.8 42.7 k8.8 0.0 0.5 0.03 0.032 2250F. 60111118 Y41.0 5.0 42.5 0.4 10.8 0.2 0.1 0.020 `2275" F. 6051118 30.9 5.9 38.2 0.1 18.4 0.4 0.1 0.015 2200F. 60111115 48.6 7.2 33.1 0.1104 0.5 0.11 2300 F. 60111118 54.3 9.9 18.4 0.3 16.6 0.6 0.11 0.023 2300F 6051115 37.2 5.2 36.5 9.2 11.1 0.6 0.12 0.056 2150r 60p111s 43.1 7.0 28.8 8.8 11.7 0.4 0.10 2175F 60p111s 39.2 6.6 26.2 8.9 18.5 0.4 0.11 21008` 60111118 48.5 8.7 13.2 9.3 19.7 0.4 0.12 0.029 2150F 60111115 54.589 15.8 8.6 11.4 0.6 0.13 0.061 2250F 60111118 50.0 4.7 20.6 8.9 13.4 2.1 0.25 0.04 2200F 60p111s 50.2 7.4 19.2 6.3 12.4 4.3 0.27 0.04 2250F 60p111s l. Approximate Feezing temperature.

2. Workability-percent reduction between annealings.

Group I' 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 annealing 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 includesalloys which-by means of 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 class are 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 vimproved 1n this respect by heat treatment. similar to the heat treatment for Group II. However, any such attack that does take 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 orfhydrogen sulphide.

We have found that by carefully controlling the amounts of nickel, chromium, carbon, and iron and by properly balancing the copper, manganese, and zinc contents against the nickel and and when properly selecting the heat treatment temperature offers a complete or superior resistance to atmospheric tarnish and to all household tarnish and corrosive conditions. The individual elements may vary over a considerable range in percentage provided the proper balancing and relative proportioning of the elements exist. f

Chromium can be dissolved up to about 46 per cent. by weight (or about 49 atomic per cent.) in solid nickel and binary alloys of these two elements possess excellent non-tarnish and mechanical properties. Chromium dissolves to a very minor extent in solid copper and binary alloys of these two elements as a result are inferior in these qualities.

In order to produce the alloy of our invention included in Groups I and II, having the essential non-tarnish properties necessary to resist household reagents, foodstuffs, weak organic acids, and corrosive vapors, 'wend it necessary that about one atom (or over) of every eight atoms 1n the alloy be of chromium (that isfat least approximately 11% by weight of chromium) and furthermore -that the other elements be so proportioned that the annealing treatment given will bring this amount of chromium into solid solution.

In order to produce an alloy having the essential non-tarnish properties involved in resistance to household reagents, foodstus, weak organic acids, and corrosive vapors such as given by Groups I and II, it is necessary, first, that the relationship of the heat treatment temperature given the alloy and the amounts of the various metals permit the solubility of 0.125 atomic fraction (or more) of chromium (about 11% by weight); and second, that the amount of chromium found to be present in the alloy (by chemical analysis) must be equal to about 11% by weight. The carbon must also be carefully controlled.

In the practical embodiment of our invention, for complete non-tarnish properties to household reagents (Groups I and II) we may then choose alloy compositions which contain about .125 atomic fraction (about 11 per cent. by weight) or over of chromium, 45 to '70 per cent. by weight of nickel, with the remainder composed of copper with one or more of the elements manganese, iron, or zinc. The charged materials may be placed in any suitable furnace, melted, and cast into any suitable formswith precautions to be listed below preventing contact with carbonaceous materials br. gases. The cast ingots `may be reduced in thickness by any suitable .cold working and annealing cycle, or by hot working, with the final heat treatment being carried out at a high enough'temperature and long enough time to bring the requisite .12,5 atomic fraction of chromium into solid solution (about 11% by weight) `It is required to cool s'uliiciently rapid from this annealing temperature to retain the chromium in solution because slower cooling rates may render the alloy vsubject to intergranular corrosive attack in strong acids when these are used to 'remove the surface scale. The cooled alloy may then beformed. in the coldl (or at teme.

peratures relatively low) to the shape and size desired .and used in this form. Other operations may be carried out on the alloys provided Ythe solubility of the .125 atomic fraction. of chromium is not interfered with.

In the embodiment of Group III of our invention we do not 4have the complete tarnish prothe mildest of atmospheric conditions and this will require at least thirty-five per cent. by weight l of nickel.

In order to obtain both the non-tarnish properties desired and the low frictional wear re'- sistance for easy polishing properties, the carbon content should be limited to a predetermined maximum amount. In order to obtain both the non-tarnish properties and low` frictional wear resistance for easy polishing properties, the carbon content must be limited to notgreater than: .05 per cent at 35% nickel, .12 per cent at 50% nickel, .15 per cent at 60% nickel, .20 per cent at 70% nickel.

The copper element, like manganese and zinc., aids in obtaining a low meltlngpoint and other desired characteristics of the alloy, such for example as its cold working properties, and we have found that by alloying manganese or zinc or both with copper and for alloys of Groups I and II limiting the copper to not more than about 30%, With the corresponding proportions of nickel and chromium 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 in the alloying of the zinc with the other elements. It cannot be entirely displaced by manganese and zinc and generally should not be less than of the composition by weight and preferably is substantially larger (around 15%) for alloys of Groups I and II. In the alloys of Group'III more copper may be alloyed up' to a limit of about 55% by Weight.

By incorporating manganese or zinc or both not only may the proportion ofcopper 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 v50 F. for each 10% of copper alloyed with it, of zinc and manganese will lower the melting point by approximately 125 to 170 F.

ing furnace scale is more soluble in strong acids, y

and appreciably better resistance for a given chromium and nickel content to tarnish and corrosion in sulphur bearing compounds, salts. or Weak acids.

The presence of manganese or zinc or both in these alloys causes them to harden slightly greater during cold working and, therefore, such alloys cannot be given quiteas great a reduction between -annealings This effect, however, yis

quite small up to additions f about 10% zinc or manganese and while greater proportions ofthese elements result in adecrease of the permissible rolling reduction between hannealings, an alloyposs'essing 15 to 20% of zinc or manganese separately or not over 30% together still possesses a limited degree of cold working ability.` For best results we prefer to use with an alloy containing about 11% chromium and 50-55% by weight of nickel either around 6% manganesel and 8% zinc, or about 9% manganeseand 4% zinc. For the lower chromium alloys of Group` III we prefer to use around 10% each of zinc and manganese.

Chromium alloyed with the other elements and brought into solid solution by proper heat treatment and balancing of the composition is relied upon for endowing immunity to tarnish and corrosion by sulphur' compounds, industrial or saline atmospheres, weak organic acids, salts, and foodstuffs in general, and around 11 or 12% by weight (or .125 atomic fraction) of chromium in our alloy is necessary for completely reliable non-tarnish properties, although a smaller amount can b e used for special purposes not involving acid corrosion as in Group III. For re-i sistance to nitric ,acid we have found a' higher percentage of chromium than what corresponds to the .125 atomic fraction (about 11% by weight) to be of great value.

The nickel .serves to bring'the other constit uents of the alloy into uniform solid solution and preferably suflicient nickel must be incorporated for'this purpose- It also substantially, along with chromium, affects the degree of resistance to various tarnishing and corroding media by affecting the solubility of chromium atA varioustemperatures. While, however, the increase in nickel content carries greater assurance of complete resistance to all household tarnish materials, as well as .improved workability and somewhat increased luster in the polished state, these advantagesA are somewhat odset by increase in melting point; greater cost, darker color, etc. and accordingly weA keep the nickel content as low as is permissible.

While carbon cannot be entirely eliminated it must be kept below the upper limits above described 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 impairsl ance of the alloy and isconsequently detrimental from the standpoint of ease-of `polishing and the amount of labor involved.

Our alloy is essentiallynon-ferrous, although iron is necessarily present to a small degree, `due to the presence of at least small traces of iron in the materials used in theformation o-fl the alloy. Moreover, we have found it an advantage to include in the alloy a small percentage of iron since it tends to'increase the solubility of chromium for a given nickel content and promotes a more homogeneous structure. 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. 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 using 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 and melting points and otherwise contribute to the advantages above described. The iron content should not exceed 10% by weight and preferably should be substantially lower, as indicated in the embodiments described above. 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 60%, with the remainder copper or copper with manganese or zinc, or both. For the lower chromium contents of alloys in Group III the iron contents are correspondingly lower.

As indicated above with respect to iron, any practical embodiment of the alloy of our invention may embody one or more other elements such as silicon, carbon, cobalt, tin, aluminum, etc., present as impurities in the essential .elements making up the charge or extracted from the furnace lining or slag.y

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.

' Any suitable method mayL be utilized for bringing the constituents of the alloy of our invention into a 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 nearlyV 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 33-37-25 chromiumnickel-copper alloy, but low carbon ferrochrome may be added directly to the melt without formation of a lower melting alloy previously. 'Ihe method of adding the various ingredients to the melt of our invention may be varied in any way l 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 holllo are, flatware, hardware or ornamental articl in essentially a similar manner to -that now use by the art, viz: 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 suiliciently soft for 'further working by annealing between 1600 and 2000 F.

Certain ofA the subject matter contained in this application is set forth and-claimed in divisional applications Serial Nos. 137,912, 137,913, 137,914, and 137,915, led April 20, 1937.

We claim:

1. 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 ofk six tenths the chromium content, and the remainder of manganese between 6 and 20% and traces of other elements including a small trace of carbon.

2. An alloy containing nickel, chromium, cop'- per, manganese and iron, in the approximate proportions of 53.5 nickel, 12.1 chromium, 12.1 manganese, 6.6 iron, with traces of other elements including carbon with the carbon not in excess of 0.13, and the balance copper.

3. An alloy containing nickel, chromium, copper, manganese and iron in the approximate proportions of 4 to 20% chromium, 36 to 70% nickel, 2 to 18% manganese, l to 10% iron and the balance copper, not less than 5%, with traces of other elements including a small trace of carbon.

4. A cold workable, low melting point alloy having non-tarnish characteristics, and consisting of 10 to 20 per cent chromium, 45 to 70 per cent nickel, 1 to 10 per cent iron, 2 to 20 per cent manganese and the balance copper in excess of five per cent, with traces of other elements including carbon with the carbon not in excess of 0.2 per cent.

5. A cold workable, low melting point alloy having non-tarnish characteristics consisting of chromium, nickel, copper, iron and manganese, wherein the chromium content is 10 to 20 per cent, nickel 45 to '70 per cent, `manganese 2 to 12 per cent, iron 1 to 10 per cent, but not in excess of 60 per cent of the chromium content, and the balance copper in excess of 5 per cent and not greater than 30 per cent, with traces of other elements including a small trace of carbon.

6. A cold workable, low melting point alloy having non-tarnish characteristics consisting of chromium, nickel, copper, iron and manganese, wherein the chromium content isI 4 to 10 per cent, nickel 36'to 60 per cent, manganese 2 to 18 per cent, iron 1 to 6 per cent, but not in excess of 60 per cent of the chromium content, and the' elements including carbon with the carbon not in excess of 0.2 per cent,

7. An alloy of the character set forth in claim 3 wherein the ironcontent is from 40 to 60 per cent of the chromium content and the manganese content is from 6 to 15 per cent.

8. A cold workable alloy having non-tarnish characteristics, consisting of nickel, chromium, copper, manganese and iron in the approximate proportions of 50 to 55% nickel, 11% chromium, 6 to 14% manganese, 1 to 10% iron and the balance copper in excess of 5% with traces of other elements including'carbon, with the, carbon not in excess of 0.2%.

9. A cold workable, low melting point alloy consisting of nickel, chromium, copper, manganese and iron in the approximate proportions of 50.2 nickel, '7.4 chromium, 19.2 copper, 18.5

manganese, 4.3 iron, with traces of other ele ments including carbon, with the carbon content less than 0.2.

10. A cold workable alloy having non-tarnish characteristics consisting of nickel, chromium, copper, manganese and iron in the approximate proportions of 59.3 nickel, 15.6 chromium, 8.8 copper, 9.0 manganese, 7.0 iron and traces of other elements including carbon, with the carbon content not in excess of 0.2.

11. An alloy of the character set forth in I BmGER EGEBERG. ROY W. TINDULA.