US2184305A - Corrosion-resistant chromium-manganese-iron alloys - Google Patents

Description

Patented Dec. 26, 1939 UNITED STATES CORRO SION-RESISTAN T CHROMIUM-MAN- GANESE-IRON ALLOYS Alfred Kropf, Wetzlar, Lahn, Germany No Drawing. Application October 1,1936, Se-

rial No. 103,527. In Germany April 8, 1935 1 Claim.

The present invention relates to ferrous-chromium-manganese alloys which approach German silver in appearance and properties and may be used as a substitute therefor.

Manganese has heretofore been suggested as a substitute for the nickel of chromium-nickel steels for increasing the corrosion resistance of such steels. In these known alloys, however, the chromium content exceeds the manganese content. These alloys as a result, unlike silver and German silver, possess a high ultimate strength and little ability to be stamped. Besides they do not have a silvery sheen and this fact alone absolutely precludes their use as substitutes for silver and German silver. Finally they are difficult to plate with silver and, when plated, do not take a plating that is durable. They cannot, therefore, hope to compete with silver or German silver in those fields in which these metals find such extensive use.

An object of this invention is to produce an alloy of manganese and chromium which has an appearance like that of silver and which can be used as a substitute for silver and German silver.

An additional object is to produce a'corrosion resistant manganese-chromium alloy that can be readily worked and shaped mechanically either in the warm or cold condition.

I have now discovered that alloys similar in practically every respect to German silver can be obtained by including in an iron-chromium-copper alloy a quantity of manganese in excess of the chromium content, while maintaining the chromium content below 25%. Generally speaking, the chromium content will range from 3 to 25% and the manganese content from 'I to 50%. The copper content is usually relatively low, at no time exceeding 10%. As a matter of fact, the presence of copper is not absolutely essential. However, copper has a favorable influence on the corrosion resistance and extensibility of the alloys and, therefore, the presence of small amounts of copper is recommended. Further copper has the ability of imparting a warm color tone verging on yellow to the alloys. Where such an appearance is desirable, copper should be present in amounts of up to about 5%, the quantity of manganese at the same time not exceeding about 35%. It may be said as a general rule with regard to copper that the quantity thereof should increase as the quantity of manganese increases and the quantity of chromium decreases. Carbon should be omitted as far as possible. In amounts up to about 0.4%, however, the carbon has little effect except to increasethe ultimate strength to a slight extent.

For the purpose of imparting a high standard of resistance to the alloys, especially against attack by certain organic acids, such as lactic, the addition of small amounts of nickel and cobalt has been found satisfactory. These metals efiect the result desired when present in quantities ranging from about 0.5 to about 5%. recommend the addition of aluminum in a quantity of from about 0.2 to about 5% since this metal furnishes the alloys with an increased resistance at high temperatures as well as resistance to hot furnace gases. The mechanical properties of the alloys as regards workability and formability and resistance to abrasion are also improved by the presence of nickel, cobalt and aluminum.

The balance of the alloy is iron, the iron of course containing the small amounts of the usual impurities. Consequently, wherever occurring in the specification and claim, the term iron" is to be so construed.

My invention is further illustrated in the following examples to which, however, the invention is not restricted:

It has been previously stated that'my alloy has mechanical properties closely approaching those of German silver. This fact is clearly developed in the following table which compares certain mechanical properties of the alloy of Example 2 with a German silver containing 16.9% of nickel, 69.75% of copper, the balance being zinc:

Yield Ultimate Elongapoint strength tiou Kg. per Kg. per meter per meter per sq. meter sq. meter Percent German silver 30. 2 47. 0 30, 0 Alloy of Example 2 30. 0 58.0 25, 0

It is clear from this comparison that my alloys are similar to German silver as to yield point, excel German silver as to ultimate strength and are capable of only a slightly lower elongation.

My alloy alsopossesses many other valuable characteristics which make it admirably suitable for use as a substitute for German silver. Thus it is cheaper than German silver. It is capable of being mechanically worked and shaped in either hot Similarly I- or cold condition and in addition may be worked with chipping tools. Because 01 its low yield point at a moderate ultimate strength, it possesses an especially high flowability and hence'may be readily stamped to produce the finest of engravings. It has an appearance very closely resembling silver and like silver is capable ottaking a high glossy polish. It is corrosion-resistant and unlike the corrosion-resisting steels 'at present suggested as substitutes for German silver can be galvanically coated to produce durable platings of any desired thickness. In short, my alloys possess all the properties necessary to recommend it as a substitute for German silver. Thus, my alloy may be used for the manufacture of utensils and the like which up to now have been manufactured from silver or German silver. In

addition it may be used to replace silveror German silver in the formation of armatures,

Percent Manganese 7 -50 Chromium 6 -25 Copper 0.5-10 Carbon Up to 0.4 Iron Balance the manganese content being in excess of the chromium content.

ALFRED KROPF.