US3246980A

US3246980A - Corrosion-resistant alloys

Info

Publication number: US3246980A
Application number: US354113A
Authority: US
Inventors: Stern Milton
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1964-03-23
Filing date: 1964-03-23
Publication date: 1966-04-19
Anticipated expiration: 1983-04-19

Description

United States Patent Ofiice 3,246,980 CORROSION-RESISTANT ALLOYS Milton Stern, Indianapolis, Ind., assignor to Union Carbide Corporation, a corporation of N ew York No Drawing. Filed Mar. 23, 1964, Ser. No. 354,113 9 Claims. (Cl. 75-134) This is a continuation-in-pa-rt of application S..N. 225,-

851, filed September 24, 1962, and now abandoned, said application S.N. 225,851, being a continuation-in-part of application S.N. 821,134, filed June 18, 1959, now US. Patent No. 3,063,835, granted November 13,1962, said application S.N. 821,134 being a continuation-in-part of application S.N. 732,793, filed May 5, 1958 and now abandoned.

This invention relates to corrosion-resistant alloys and particularly, to corrosion resistant alloys in which chromium is the predominant metal.

Chromium and many of its alloys, as Well as titanium and many of its alloys, are noted for excellent resistance to oxidizing corrosive media. In non-oxidizing corrosive media, such as hydrochloric and sulfuric acid solutions, these metals and alloys exhibit little or no resistance. It would be most desirable to have available alloys capabie of withstanding corrosive environments ranging from strongly oxidizing to Weakly oxidizing or nonoxidizing. An alloy of this type would have the widest utility. For example, such an alloy would be invaluable in chemical plant equipment.

Hydrochloric and sulfuric acids are prime examples of non-oxidizing corrosive media. These acids enter into many important commercial processes. They require storing and handling equipment which combine the desirable properties cited above. If a chromium alloy, for example, were to possess resistance tov non-oxidizing acid solutions, in addition to its natural endowments of lightness, strength, and resistance to oxidizing acid solutions, it would be extremely useful in such applications.

One widely used method for preventing corrosion is to add passivating inhibitors to the environment which, it is believed, operate by producing local action current to anodically polarize a metal into the passive potential region. It is not always desirable, however, to alter the composition of a solution to prevent corrosion of the equipment in which it is contained, particularly when the composition of the solution is critical or specific to some process. Such a means of preventing corrosion is limited to the particular case where the composition of the contained solution is not critical.

According to scientific theory, corrosion resistance can be achieved in non-oxidizing environments by artificially anodically polarizing the base metal by applying an external current (which might be termed anodic protection as opposed to cathodic protection). This method, for obvious reasons, would be extremely difficult to accomplish in chemical plant equipment.

It is, therefore, the primary object of this invention to provide alloys of chromium which are resistant to the attack of oxidizing and non-oxidizing corrosive media.

It is also an object of this invention to provide a method for increasing the resistance to non-oxidizing corrosive media of the metal chromium, and its alloys.

Other aims and advantages of this invention will be apparent from the following description and the appended claims.

In accordance with these objects a corrosion resistant alloy is provided consisting essentially of from 0.005 to 5 percent by Weight in the aggregate of at least one metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, rhenium, up to 10 percent molybdenum, up to 40 percent iron, up to 2 percent copper, and the balance chromium.

A preferred embodiment of the present invention is an alloy consisting essentially of 0.05 to 0.5 percent by weight in the aggregate of at least one metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, rhenium, up to 10 percent molybdenum, up to 40 percent iron, up to 2 percent copper, and the balance chromium.

This alloy is characterized by excellent resistance to strong acid solutions and comparatively lower cost.

It is believed that the important factor in obtaining the desired improvement, and the principle upon which the invention operates, lies in the production of sufficient local action current to anodically polarize the alloy into the passive region. High local action currents are created by high potential diiferences between the elecrodes of the galvanic couple and by shallow polarization curve slopes. The current required to change the potential of either cathode or anode a given amount by polarization is proportional to the cathode and anode areas which, in turn, are determined by the noble metal content of the alloy.

Table I indicates the results of noble metal additions to substantially pure chromium. Table II provides the same informtaion as to noble metal additional to binary and tertiary chromium-base alloys. The percentages given in each case are percentages by weight of the total alloy.

TABLE I Eflect of noble metal additions on corrosion rate of chromium Corrosion Rate (Mils/Year) Nominal Composition Percent Noble Metal Boiling H SO Boiling H01 Cr 1 1 Cr plus 0.1 Pt- 1. 8 1.0 7 E37 Cr plus 0.5 Pt. 0 5 2. 7 9 0. 42 Cr plus 1.0 PL 8 0. 46 Cr plus 2.0 Pt. 10 0. 42 Cr plus 5.0 Pt. 1. 0.41 Cr plus 0.5 Rh a 2. 0.68 Cr plus 0.5 Os 4 16.0 Cr plus 0.5 Pd 0.79 Cr plus 0.5 Ru 0.84 Or plus 0.5 It 0. 46

1 Dissolved.

Patented Apr. 19, 1966 aaaaoeo TABLE 11 chromium-base alloys Corrosion Rate (Mils/Year) Nominal Composition Percent Noble Metal Boiling H1804 Boiling H01 Cr plus 2 Cu 2060 Or plus 2 Cu plus 0.5 Pt.. 30 84 988 Cr plus 10 Mo -e Cr plus 10 Mo plus 0.5 Pt... 8 18 125 0. 7 40 Or plus 40 Fe plus 10 Mo 40 Or plus 40 Fe plus 10 Mo plus 0.5 Pt 2 29 130 1 Dissolved.

In Table I, the corrosion resistance of chromium Withterms of its specific embodiments. Modifications and out any addition is given first to serve as a comparison. 20 equivalents will be apparent to those skilled in the art Pure chromium, it will be noted, dissolves in both boiling and this disclosure is intended to be illustrative of, but sulfuric acid and boiling hydrochloric acid in the connot necessarily to constitute a limitation upon, the scope centrations indicated. It will be observed that all the of the invention. noble metals tested were extremely effective in reducing What is claimed is: the corrosion rate of chromium. The degree of effec- 1. A corrosion-resistant alloy consisting essentially of tiveness varies with the quantity of noble metal added as from about 0.05 to 0.5 percent by weight in the agshown in the tables. It will be observed that as little as gregate of at least one metal selected from the group con- 0.l% by weight platinum renders chromium practically sisting of ruthenium, rhodium, palladium, osmium, insoluble in 20% boiling sulfuric acid. As shown in iridium, platinum, rhenium, up to 10 percent molybde- Table I, the 0.5 osmium addition, while it decreases 3O num, up to percent iron, up to 2 percent copper, balthe rate drastically, is not as effective as an equal amount ance chromium. of platinum. It will further be observed that, in gen- 2. A corrosion-resistant alloy consisting essentially of eral, additions of noble metal reduce the rate of corabout 0.1 percent by weight platinum, and the balance rosion of chromium in boiling non-oxidizing acids of conchromium and incidental impurities. centrations as high as 60%. The proportion of noble 3. A corrosion-resistant alloy consisting essentially of metal addition may be varied according to the anticiabout 0.5 percent by weight platinum, and the balance pated use. Where contact with a more rigorous environchromium and incidental impurities. ment is anticipated, such as strong concentrations of acid, 4. A corrosion-resistant alloy consisting essentially of more noble metal is required. For best results in conabout 0.5 percent by weight palladium, and the balance ditions where exposure to strong solutions is encountered, 40 chromium and incidental impurities. the additive is used in amounts of between 0.05 and 5. A corrosion-resistant alloy consisting essentially of 0.5%. With amounts below 0.05% noble metal addition, about 10 percent by Weight molybdenum about 0.50 perthe desired improvement in corrosion resistance may not cent by weight platinum, and the balance chromium and be sutlicient to meet the particular needs. As little as incidental impurities.

0.005% of noble metal addition may sufiice for low con- 6. A corrosion-resistant alloy consisting essentially of centration of acid, however. With amounts substanabout 40 percent by weight iron, about 10 percent by tially in excess of about 5%, no marked degree of imweight molybdenum, about 0.5 percent by weight platiprovement results while the cost of the alloy increases num, and the balance chromium and incidental impuriconsiderably. The noble metals. may be present either ties.

singly or in combination with each other. so '7. A corrosion-resistant alloy consisting essentially of In Table II, the corrosion rate of several chromiumabout 2 ercent by weight copper, about 0.50 percent by base alloys, together With the fate of the Same alloy With weight platinum, balance chromium and incidental imthe platinum addition is given for comparison. It will mbe seen that base aUOYS 9 13 modgrate t 8. A corrosion-resistant alloy consisting essentially of strong concentration of lil'lfil" sulfuric or hydrochlor1c about 0.1 to about 05 percent by Weight platinum up acid. However, with the addltron of as little as 0.5% to 10 s a A percent by wei ht molybdenum, up to 40 percent platinum to the base alloy, a very marked decrease In the b W i ht b l" h a d 1 rate of corrosion results. The effectiveness of the noble e g Iron a C mmmn an mcl enta Imp metal addition, as before, depends on the strength of the L163 g corrosive madium and on the amount of noble metal 9. A corros1on-res1stant alloy consistlng essentially Or added Moreover some alloys are more effectively about 0.1 to about 0.5 percent by weight platinum, about .tected by the same amount of noble metal addition than by Weight molybdenum about 40 Percent by others. An 0.5% addition of platinum, for instance, While Y balance chmmium and incidental p it decreases the rate of corrosion of a chromium-base alloy containing 2 percent Cu in 40 percent boiling sulfuric References Cited by the Examine! acid, is not as effective as with a chromium-base alloy con- UNITED STATES PATENTS taining 10 percent molybdenum, or an alloy consisting 1,167,827 1/1916 Kaissr 75 176 of 40 percent iron, 10 percent molybdenum and the 3 008 854 11/1961 G rant 75l76 balance chromium Additions of noble metals may also 3 063 835 11/1962 Stem be made to chromium electrodeposit. 3131059 4/1964 Kaarlel'a 176 The alloys of the present invention may be prepared according to current metallurgical practice, although the FOREIGN PATENTS invention is not limitedby the method f preparation. 1 12 7/1914 Great Britain The ingredients may be in any commercially pure form.

The description of the invention above has been in 75 (Other references on following page) 3,246,980 5 6 References Cited by the Applicant Hansen: Constitution of Binary Alloys, McGraw-Hill UNITED STATES PATENTS BOOK CO., 1H0, New YOIk, 1959, pages 550, 555.

Pietrokowsky et 211., Journal of Metals, v01. 8, August 2,247,755 7/1941 Hensel at 1956, pages 93o 935. Published by the A.I.M.E., New 2,659,669 11/1953 Muller. 5 York NY 2,780,545 2/1957 Blank e161.

OTHER REFERENCES BENJAMIN HENKIN, Primary Examiner.

ASM Metals Handbook, 1949 edition, page 22. Pub- WINSTON A, DOUGLAS, Examiner. lished by the ASM, Cleveland, Ohio.

Claims

1. A CORROSION-RESISTANT ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 0.05 TO 0.5 PRECENT BY WEIGHT IN THE AGGREGATE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF RUTHENIUM, RHODIUM, PALLADIUM, OSMIUM, IRIDIUM, PLATINUM, RHENIUM, UP TO 10 PERCENT MOLYBDENUM, UP TO 40 PERCENT IRON, UP TO 2 PERCENT COPPER, BALANCE CHROMIUM.