US3547625A - Steel containing chromium molybdenum and nickel - Google Patents

Description

Dec. 15, 1970 STEEL CONTAINING CHRQMIUM MQLYBDENUM AND N'IdKEL C. G. BIEBER ETAL Filed 3111 27, 1967 1 6 F 1 l I Y K A/ B 6 0 EL Q W04 YBDE/VU/V z INVENTORS.

3,547,625 STEEL CONTAINING CHROMIUM MOLYBDENUM AND NICKEL Clarence George Bieber, Sutfern, N.Y., and Roger Allen Covert, Middletown, N.J., assiguors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware Continuation-impart of application Ser. No. 574,995, Aug. 25, 1966. This application July 27, 1967, Ser. No. 656,542

Int. Cl. C22c 39/20 US. Cl. 75--128 11 Claims ABSTRACT OF THE DISCLOSURE Iron-base alloys containing, among other constituents, interrelated amounts of nickel, molybdenum, and chromium offer a relatively high degree of resistance to various forms of corrosion in either or both the annealed and cold worked conditions. Alloys are also hot and cold workable and exhibit high tensile strength.

This is a continuation-in-part of application Ser. No. 574,995 filed Aug. 25, 1966.

The present invention relates to corrosion resistant alloys, particularly to iron-nickel alloys of novel composition and which are of comparatively low cost, both hot and cold workable, and which manifest enhanced resistance to corrosion, including crevice, pitting, intergranular and stress corrosion cracking, especially in chlorid media, notably marine environments such as sea water.

As is generally well known, there has been a substantial increase over the years in the tonnage of metals and alloys used in resisting the corrosive effects of chlorides, including salt solutions, strongly oxidizing chloride solutions and marine environments. Commercial interest has been particularly expanding in respect of marine applications and this has been undoubtedly spurred by recent activities in oifshore drilling, desalinization, undersea mining, etc. However, unless improved and more corrosion resistant materials are developed, the heavy toll in metal damage inflicted by corrosion will continue to increase. It is perhaps interesting to reflect that a recent report indicates the overall loss exacted by corrosion is currently on the order of about five billion dollars annually. Such an economic burden self-explains the necessity of at least curtailing this trend.

A number of metals and alloys are currently being used or have been proposed for marine application, including the austenitic stainless steels, carbon and alloy steels, copper and copper alloys including various brasses, nickel alloys, titanium and alloys thereof, etc. However, depending upon intended purpose, such materials suffer from one or more drawbacks. The austenitic stainless steels, e.g., AISI, 304, 310, 316, are readily workable and of reasonably low cost but do not exhibit superior resistance to crevice corrosion. This applies to an even greater extent concerning the carbon and low alloy steels. Copper alloys manifest a propensity to pit when immersed in sta nant sea water or when the rate of flow is less than about five feet per second (also true of austenitic stainless steels). This is not an unusual occurrence since it is known that as sea water velocity increases, fouling and pitting diminish in respect of many (although not all) materials. Certain nickel-base alloys have been used rather extensively. One of the most popular of such alloys contains about 17% chromium, 16% molybdenum and 4% tungsten but is costly and, at best, diificultly workable and usually requires several intermediate annealing treatments during the working cycle, a factor contributing to increased cost. Titanium and titanium alloys suffer from United States Patent m Patented Dec. 15, 1970 the shortcoming of being of comparatively high cost and catastrophic corrosion has been experienced with certain titanium alloys.

The general problem is somewhat complicated by the fact that while certain applications require alloys which must resist chloride attack in the annealed condition, for other applications, e.g., marine cable (rope), it is more important that alloys manifest both high strength and exceptional resistance to chloride corrodents in the cold rolled condition. The ultimate, of course, would be to have available low cost alloys highly satisfactory in either condition, thus obviating concern as to which condition an alloy behaves more favorably. Each of these objectives is accomplished in accordance with the instance invention which is addressed to the specific problem of providing low cost, hot and cold workable alloys which exhibit markedly improved resistance to crevice, pitting, intergranular and stress corrosion cracking in oxidizing chloride media, marine environments, etc.

It has now been discovered that the objectives abovediscussed can be readily achieved with certain alloys containing special and correlated amounts of iron, nickel, chromium, molybdenum, and controlled amounts of aluminum, titanium, calcium, carbon, silicon, manganese, etc.

It is an object of the invention to provide improved iron-nickel-chromium-molybdenum alloys of novel composition.

Another object of the invention is to provide novel iron-nickel-chromium-molybdenum alloys of enhanced resistance to corrosive media, particularly chloride environments such as marine atmospheres, sea water, salt solutions, strongly oxidizing chloride solutions, etc.

It is a further object of the invention to provide new low cost, hot and cold workable corrosion resistant alloys.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which there is depicted a chart in respect of nickel and molybdenum contents pertaining to alloys within the invention as herein more fully described.

Generally speaking and in accordance with the present invention, alloys contemplated herein contain (in percent by weight) about 20% to 40% nickel, about 6% to 12% molybdenum, about 14% to 21% chromium, the chromium content being at least about 18% and advantageously at least 18.5% when the molybdenum content is not greater than about 6.5% or 7% and not exceeding 20% and preferably not exceeding 19% when the molybdenum content is from 10% to 12%, up to 0.2% carbon, up to 0.5% silicon, up to 1% but beneficially not more than 0.5% manganese, the sum of the silicon plus manganese not exceeding about 1.25%, up to 0.7% titanium, up to 0.7% aluminum, up to about 0.15% calcium, up to 12% cobalt, and the balance essentially iron, the iron constituting at least 30% of the alloys. In consistently achieving good hot workability characteristics, the alloys advantageously contain titanium or aluminum (most beneficially both) in amounts of from 0.05% to 0.6% each, e.g., 0.15% to 0.5%. Further, it is most preferred and desirable that the alloys contain calcium, e.g., 0.001% or 0.01% to 0.15% calcium, in consistently achieving highly satisfactory results. The theory which might explain the role of calcium is not completely understood, but apart from other possible benefits, it has been found that calcium markedly influences and enhances resistance to crevice corrosion in both the annealed and cold worked conditions, particularly the latter and particularly with regard to alloys containing not more than about 8% molybdenum, e.g., 7.5% molybdenum, or lower. Calcium must be present when the molybdenum content of the alloys is not greater than about 7.5% or 8%; otherwise, crevice corrosion resistance is adversely affected even inthe annealed condition.

Other constituents which can be present in the alloys include the following: up to 2%, e.g., up to 0.5% or 1%, columbium, up to 1% vanadium, up to 1% copper, up to 1% tungsten and up to 2% tantalum. However, elements such as phosphorus, sulfur, oxygen, nitrogen, and the like should be kept at low levels consistent with good commercial practice. Sulfur is deemed particularly detrimental and particular care should be exercised in this regard. It is thought that one of the attributes of calcium is that it counteracts the deleterious effects of sulfur. Nitrogen should be maintained below about 0.03%, preferably below about 0.01%.

In carrying the invention into practice, the alloys should contain at least 20% nickel. With nickel levels lower by an appreciable extent, corrosion resistance in marine and other environments is not only unsatisfactory but there is the added danger of forming delta ferrite. If present in an excessive although relatively low amount, delta ferrite promotes or potently contributes to embrittlement problems whereby workability is, at best, impaired. In this connection and in accordance with the invention, the alloys should be substantially austenitic (single phase) and devoid of detrimental delta ferrite and/or other deleterious phases such as sigma.

Further, consistently highly satisfactory results do not always obtain even with nickel contents of, say, about 20% to 23%. For example, when the content of molybdenum in the alloys is above about 9.5%, e.g., and up to 12%, it has been found that unless the nickel content exceeds about 23%, both hot and cold workability are rendered more difficult such that intermediate annealing may be required and this increases cost. Moreover, at a nickel level of less than about 23%, resistance to crevice corrosion, especially in respect of alloys in the cold rolled condition, is inferior when both the molybdenum and chromium are at the low end of their respective ranges. When the nickel content is as low as and the molybdenum content is from 6% to about 6.5%, the alloys should contain about 18% or more of chromium, e.g., 18.5%, as indicated above herein. Generally speaking, at a molybdenum level above about 6.5% to about 7.5%, a chromium content of about 17% and upwards should be used with nickel contents as low as 20%. At about 7.5% to 8% molybdenum, about 15.5% or 16% chromium and above can be used with such low (as well as higher) nickel contents. It is beneficial, however, for an optimum combination of resistance to crevice corrosion coupled with good workability, that the alloys contain at least 23% and more advantageously at least 24% or nickel.

In respect of the higher end of the nickel range, to wit, to nickel, a particularly noteworthy feature of the invention stems from the fact that not only is resistance to crevice and pitting corrosion and the like markedly good in chloride media but resistance to stress corrosion cracking is excellent. As will be illustrated herein, this obtains not only in marine environments, sea water, but most significantly when the alloys are exposed to the extreme aggressive attack so characteristic of boiling magnesium chloride. Alloys resistant to stress corrosion cracking should contain, in addition to 35 to 40% nickel, above about 9%, e.g., 9.5%, and up to 12% molybdenum and about 14% to not more than about 19% chromium, the balance of the composition being in accordance with that given before herein. Up to 10% cobalt can be used to replace an equivalent amount of nickel. Where outstanding resistance to crevice and pitting corrosion coupled with resistance to stress corrosion cracking is required, it is beneficial that the alloys contain, in addition to a nickel plus cobalt content of about 35% to 40%, about 10% to 12% molybdenum and about 14% or 15% to 18% chromium.

Low molybdenum contents result in inferior resistance to crevice corrosion. For example, molybdenum contents of 4% are markedly poor. Too, as will be shown herein, an amount of molybdenum of, say, 6% is quite unacceptable should the chromium content be on the low side, e.g., 14% to 17%. It is most advantageous that at least 8% molybdenum be present in the allows and even then satisfactory results will not consistently obtain unless the molybdenum, nickel, and also the chromium contents are correlated. In this regard, it is not a question of using high nickel contents to attain a desired degree of resistance. Increasing the amount of nickel beyond about 27% or 28% has been found to result in lower crevice corrosion resistance at molybdenum levels of about 7%. But by using 8% or more of molybdenum particularly with chromium contents of at least 17%, highly satisfactory results can be obtained at higher nickel levels. The correlation between nickel and molybdenum is represented by the accompanying drawing. It should be pointed out that with respect to the area, ABCLA, an area encompassing a fair number of alloys at nickel percentages above 28% but amounts of molybdenum of less than 8%, the chromium content for such compositions should be about 18% or more.

In addition and subject to the foregoing, where resistance to stress corrosion cracking in potently aggressive agents such as boiling magnesium chloride is not necessary, and thus a nickel minimum of 35% is not required, highly satisfactory results are attained when the molybdenum and nickel contents are interrelated to represent a point within the area ABCDEFA of the accompanying drawing, the chromium content of the alloys advantageously being from 14% or 15% to 20%, e.g. 17% to 20%. Alloys containing from about 15% to 20% chromium and having molybdenum and nickel contents representing a point falling within the area BGHJKB, and particularly within the area GHJKG, are deemed especially attractive commercially since they would be the most economical, are readily amenable to both hot and cold working, and provide good resistance to crevice corrosion in both the hot and cold worked conditions.

In addition to what has been said before herein in respect of chromium and while it contributes to resisting corrosive attack, excessive amounts thereof can lead to poor results, particularly by promoting a multiple phase structure. This, in turn, would bring about adverse consequences. A chromium content of, say, 22%, part from being unnecessary, is particularly undesirable to molybdenum levels of 9% and above. Accordingly, when the molybdenum content is from about 9.5% or 10% to 12%, the chromium content, as indicated before herein, should not exceed 20% and advantageously does not exceed about 19%.

Careful control must be exercised with regard to silicon and manganese. Silicon in appreciable quantities, e.g., 1% or 2%, is notably undesirable by reason of the fact that it impairs hot workability and weldability. Manganese in comparatively high amounts, e.g., 1.5% to 2%, also significantly impairs corrosion resistance. As indicated above herein, it is preferred that the total silicon plus manganese content not exceed 1.25%. Advantageously, the silicon content should not exceed 0.25% and the total silicon plus manganese should not exceed about 0.75%.

Although the amount of carbon in the alloys can be as high as 0.2%, carbon somewhat in excess of 0.1%, e.g., 0.15%, results in diminishing crevice corrosion resistance in otherwise outstanding alloys. In achieving both good crevice corrosion resistance and resistance to intergranular corrosion, it is advantageous that the carbon content not exceed about 0.05%, e.g., 0.03%, or less. However, in this regard, columbium when present, will combine with the carbon such that carbon contents up to 0.1% are satisfactory. Columbium also obviates the necessity of solution treating weldments.

Particularly satisfactory hot workability characteristics are conferred by titanium and/ or aluminum. Contributing to the desideratum of low cost is the fact that air melting techniques can be employed. Thus recourse to more expensive processing is unnecessary. Titanium is also useful to stabilize nitrides, thereby preventing the occurrence of porosity in ingots. Accordingly, it is preferred that at r least one, beneficially both, of these constituents be present in amounts of at least 0.05%, advantageously at least 0.1% or'0.25%, and up to 0.5%. Appreciable amounts of these elements, however, e.g., 1.5% or 2%, are quite undesirable since the net etfect would be to subvert workability characteristics without benefit corrosionwise.

As indicated herein, air melting practice can be readily employed in preparation of the alloys, although vacuum techniques can also be used. It might be mentioned, as will be appreciated by those skilled in the art, recovery of titanium and/or aluminum and/or calcium is usually not 100%. Where it is desired that the alloys contain about 0.15% of titanium or aluminum, about 0.25% of each should be added to the melt. Calcium, which can be incorporated in the form of a calcium-silicon addition,

tested in the cold rolled and also in the annealed condition. Cold rolled specimens having a surface area of about square centimeters were immersed for about 72 hours in the 10% ferric chloride solution, rubber bands being wrapped thereabout to intentionally create crevices. This test is deemed equivalent to an extreme long-time exposure in sea water and is described by M. A. Streicher in Journal of the Electrochemical Society, vol. 103, pages 375390, No. 7, July 1956. Other cold rolled specimens of the same alloys (same area) were annealed at about 2150 F. to 2200 F. for about one-half hour and tested in the annealed condition and in the same manner as the cold rolled specimens. Nominal compositions and data are given in Table I for both the cold rolled and the annealed specimens. In addition to the percentages of the various constituents set forth in Table I, about 0.03% carbon (except Alloy 21), 0.1% silicon, 0.15 manganese, and about 0.06% calcium (as calcium-silicon) were added to the melts. Both titanium and aluminum were used in preparing the alloys, about 0.25% of each being added.

TABLE I Weight loss in milligrams Cold rolled Ni, G M0, Other, Fe, Cold and percent percent percent percent percent rolled annealed should be added in an amount of about two to three times that desired in the final alloys. Ingots can be hot Worked from about 2200 F. to 2300 F. down to about 1800 F. to 1600 F. Suitable annealing temperatures include about 2000 F. to 2300 F., e.g., 2200" F. A final annealing temperature of about 2200" F. has been found satisfactory. In producing strip and the like, the alloys can be hot rolled, annealed, pickled and cold rolled. Intermediate annealing between cold rolling stages can be carried out over the temperature range of 2000 F. to 2200" F. It is rather ironic to note that it has been found difficult to pickle the alloys due to the exceptional corrosion resistance thereof.

In order to give those skilled in the art a better appreciation of the invention, the following illustrative description and data are given:

A substantial number of alloys (Alloys 1 through 25, Table I) within the invention were prepared using air melting techniques. Ingots were soaked at about 2300 F. and thereafter hot rolled to billets, the hot working temperature range being on the order of 1600 F. to 2300 F.

The hot rolled alloys were annealed at about 2150" F. to 2200 F. for about one-half hour and were cold rolled to strip about inch thick (the hot rolled thickness was approximately inch). Corrosion tests were conducted using an aggresive corrodent commonly used for test purposes, to wit, a 10% ferric chloride solution. In this regard, two different tests were conducted. Specimens were In respect of the data in Table I, it is clear that Alloys 1 through 20 exhibited highly satisfactory resistance to crevice corrosion. No pitting was observed. Regarding All0y 21, this alloy nominally contained 0.15% carbon, the composition otherwise being the same as for Alloys 2 and 3. While Alloy 21 is acceptable for castings and for applications concerning alloys in the annealed condition, it will be noted that the high carbon content resulted, comparatively speaking, in quite a loss in crevice corrosion. As indicated above herein, it is much more desirable to maintain the carbon content at a level not above 0.1% and advantageously less than 0.05% or 0.03%. (It should be mentioned that alloys to be acceptable in the 10% ferric chloride test described herein should not manifest a loss greater than about 15 milligrams and advantageously not greater than about 10 milligrams, the optimum being a maximum loss of about 5 milligrams.)

Some dilficulty was experienced in hot working Alloys 22 through 25, particularly Alloys 22 and 24 (which alloys contained only 20% nickel), although crevice corrosion resistance was good. Edge cracking was noted primarily in respect of Alloys 22 and 24 and with such low nickel contents, in combination with the molybdenum content of 10%, intermediate annealing would be necessary. However, as referred to herein and as illustrated by Alloys 7 and 13, nickel contents above 23%, to wit, 25%, resulted in good hot working characteristics.

Both cold rolled and annealed specimens of Alloys 3,

10, 11, 16 and 17 were exposed to sea water at ambient temperature (How of 2 feet per second) at the renowned testing station at Harbor Island, N.C. Specimens to determine both crevice corrosion and stress corrosion cracking (U-bends) behavior were employed. Alloy 3 was exposed for a period of about 450 days, each of the others being exposed for about 300 days (exposure continues in all cases), examinations being made periodically. Each of the specimens was free of any evidence of stress corrosion cracking. A very slight and inconsequential amount of crevice corrosion was Observed in connection with the cold rolled specimen of Alloy 3 after 90 days, but this proved to be very incipient and did not progress further. It is more than likely that machining prior to exposure was not perfect. In summary, the specimens behaved remarkably well.

U-bend specimens of Alloys 2, 3, 10, ll, 12 and 16 were also exposed to boiling 42% magnesium chloride (154 C.) to determine stress corrosion cracking tendencies under the extremely severe conditions imposed by this test (a test commonly used to determine stress corrosion cracking behavior of the austenitic stainless steels).

ance essentially iron, when drawn to wire (94% reduction) had a tensile strength of about 264,000 p.s.i. together with good bend and kink ductility. It is considered that tensile strengths on the order of up to 300,000 p.s.i. are obtainable. Such strength levels would render alloys contemplated herein particularly suitable for marine cable applications, although there are cable applications in which strength levels of about 265,000 p.s.i. are quite satisfactory.

In addition to the foregoing, a number of alloys both within (numerals) and outside (letters) the invention were prepared and tested in the same manner, except as otherwise noted, as the alloys of Table I. The compositions are given in Table II together with the test results obtained. Included are alloys conforming to various prior art compositions and stainless steels AISI 310 and 316 which were produced commercially. It should be emphasized that neither calcium nor titanium or aluminum was added to Alloys EE, FF, HH through PP, 27, 28 and 29. Unless otherwise indicated, the alloys did not contain more than about 0.03% carbon, 0.1% silicon, and 0.15% manganese.

TABLE II Ni, Cr, M0, Other, Fe, Cold Anpereent percent percent, percent percent rolled nealed 4 Balance...

Nil

*Not Determined. Chemical analysis. Norm-Specimens of Alloys 30 through 39 were cold worked to inch thick.

Alloys 2, 10, 11 and 12 were exposed in the annealed condition, Alloy 3 in the cold rolled condition and Alloy 16 in both conditions. Alloys 2, 3, and (each of which contained less than 35% of nickel plus cobalt) failed in 16, 8 and 12 days, respectively. No cracking was observed in days for the other specimens. As indicated herein, for optimum resistance to stress corrosion cracking in chloride media at least about nickel plus cobalt should be present in the alloys.

As an additional feature of the invention, alloys contemplated herein exhibit high tensile strengths, e.g., about 250,000 p.s.i. and above when cold drawn to wire. An alloy nominally containing 25% nickel, 20% chromium and 8% molybdenum, and less than 0.04% carbon, bal- Alloys AA through DD illustrate the inferior results characteristic of alloys with low amounts of molybdenum (4%) and regardless of increase in the nickel content. Alloys EE and FF are representative of prior art alloys, free of calcium and also titanium and aluminum. Again, crevice corrosion resistance was outstandingly poor. Alloy GG also manifested poor corrosion resistance even though it contained calcium, titanium and aluminum. However, an alloy within the invention and of the same nominal composition (Alloy 26) but with 20% chromium reflected satisfactory corrosion behavior. As indicated before herein, when the molybdenum content is less than about 6.5% the chromium content should be at least about 18%. Alloys GG and 26 illustrate this aspect. Alloy HH Was characterized by such poor hot workability that corrosion tests in the cold rolled and annealed conditions were not made. It will be noted the alloy contained high silicon 1.1%) and titanium (2%) contents as well as a high amount of silicon plus manganese (1.8%). In most marked contrast thereto are Alloys 15 and 9, alloys within the invention.

As indicated above herein, neither calcium nor titanium or aluminum was added to the melts of Alloys HH through PP and 27, 28 and 29. In this regard, JJ through MM, 27, 28 and 29 (also Alloy 5) are of particular interest. As will be observed, Alloys J], K and LL each exhibited poor corrosion resistance whether in the cold rolled or annealed condition. Alloys 27, 28 and 29, however, were satisfactory in the annealed condition and are thus within the invention for that reason. It is, of course, interesting to compare Alloy 5 (which contained calcium and also titanium and aluminum) with Alloys 27, 28 and 29. It is thought the difference in results is strikingly remarkable.

Alloys 30 through 39, 3 and QQ illustrate in a general manner alloy behavior as the nickel content is increased over the lower end of the molybdenum range. Note that Alloy 32 is an extremely marginal composition at best and only then in the annealed condition. With 18% chromium, an otherwise similar alloy (Alloy 31) exhibited considerably better corrosion resistance whereas, increasing the nickel content to 30% as in Alloy QQ resulted in inferior resistance particularly in the cold rolled condition. As indicated before herein, improper correlation of the nickel and molybdenum contents can lead to poor results. Alloys 3, 35 and 34 afford an interesting comparison with Alloy 39 concerning the effect of increasing the chromium content (16.6% to 21%) as the percentage of nickel increased (25% to 34%). The standard stainless steels AISI 310 and 316 as well as prior art Alloys NN and PP behaved poorly in test.

Alloys contemplated within the invention are generally useful for vessels, boat hulls, and structures and components therefor employed in (or in the vicinity of) marine environments, including sea water and sea atmospheres. More specifically, the alloys are useful for pumps and parts therefor (including vanes and impellers), propellers, pipes, valves, fasteners, tubing in general including heat exchanger tubing and tube sheet, water boxes, seawater evaporators, including plate, shafting, marine hardware, e.g., chocks, cleats, pulleys, wrought fittings, trim and fasteners, buoys, floating platforms, oil well equipment, etc. Chemical plant equipment for handling of oxidizing acids and salts thereof, containers and pressure vessels for the storage or transportation of various corrosive chemicals are illustrative of other uses for the alloys. Also, the alloys can be used in conventional mill forms including sheet, strip, bar, rod, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Under certain circumstances it may be permissible to use magnesium together with or in place of calcium but it is much preferred to use the latter. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An iron-nickel-moly-bdenum-chromium alloy characterized by enhanced resistance to various corrosive chloride environments, said alloy consisting essentially of about 20% to 40% nickel, about 6% to 12% molybdenum, the nickel and molybdenum being correlated to represent a point falling within the area LFEDCL of the accompanying drawing, about 14% to 21% chromium, the chromium being (a) at least about 18% when the molybdenum content is not greater than about 6.5% and (b) not greater than 20% when the molybdenum content is from about to 12%, up to 0.05 carbon,

up to 0.15% calcium with the proviso that at least 0.001% of calcium is present when the molybdenum content is not greater than about 7.5%, at least one metal selected from the group consisting of titanium in an amount up to about 0.7% and aluminum in an amount up to about 0.7%, up to about 12% cobalt, up to 0.5% silicon, up to 1% manganese, the sum of any silicon and manganese not exceeding 1.25%, up to 1% columbium, up to 1% vanadium, up to 1% copper, up to 1% tungsten, up to 2% tantalum and the balance essentially iron.

2. An alloy as set forth in claim 1 containing at least 23% nickel and in which columbium, if present, does not exceed about 0.5%.

3. An alloy as set forth in claim 1 and containing about 0.001% to 0.15% calcium and from 6.5% to 8% molybdenum.

4. An iron-nickel-molybdenum-chromium alloy characterized by enhanced resistance to various corrosive chloride environments, said alloy consisting essentially of about 20% to 40% nickel, about 6% to 12% molydenum, the nickel and molybdenum being correlated to represent a point falling within the area ABCDEFA of the accompanying drawing, about 14% to 21% chromium, the chromium being (a) at least about 18% when the molybdenum content is not greater than about 6.5 and (b) not greater than 20% when the molybdenum content is from about 10% to 12%, up to 0.05% carbon, up to 0.15 calcium with the proviso that at least 0.001% of calcium is present when the molybdenum content is not greater than about 7.5%, at least one metal selected from the group consisting of titanium in an amount up to about 0.7% and aluminum in an amount up to about 0.7%, up to about 12% cobalt, up to 0.5% silicon, up to 1% manganese, the sum of any silicon and manganese not exceeding 1.25%, up to 1% columbium, up to 1% vanadium, up to 1% copper, up to 1% tungsten, up to 2% tantalum and the balance essentially iron.

5. An alloy as set forth in claim 4 wherein calcium is present in an amount of at least 0.001%.

6. An alloy as set forth in claim 4 and containing at least one metal from the group consisting of titanium and aluminum in an amount of 0.05 to 0.6% of each.

7. An alloy as set forth in claim 4 in which silicon does not exceed 0.25% and manganese does not exceed 0.5

8. An iron-nickel-molybdenum-chromium alloy consisting essentially of from 23% to 30% nickel, from about 8% to about 10% molybdenum, the nickel and molybdenum being correlated to represent a point within the area BGHJKB of the accompanying drawing, about 15% to about 20% chromium, up to 0.05% carbon, up to 0.15% calcium, at least one metal selected from the group consisting of titanium in an amount up to 0.7% and aluminum in an amount up to 0.7%, up to 12% cobalt, up to 0.5 silicon, up to 1% manganese, the sum of the silicon plus manganese not exceeding 1.25%, up to 2% of columbium, up to 1% of vanadium, up to 1% copper, up to 1% tungsten, up to 2% tantalum and the balance essentially iron.

9. An alloy as set forth in claim 8 in which calcium is present in an amount of at least 0.01%.

10. An alloy as set forth in claim 8 in which silicon does not exceed about 0.25% and manganese does not exceed about 0.5

11. An iron-nickel-molybdenum-chromium alloy which manifests excellent resistance to stress corrosion cracking and crevice corrosion in chloride media, said alloy consisting essentially of about 25% to 40% nickel, about 9.5% to 12% molybdenum, about 14% to 19% chromium, up to 0.05% carbon, up to 0.15 calcium, at least one metal selected from the group consisting of titanium in an amount up to 0.7% and aluminum in an amount up to 0.7%, up to 0.5% silicon, up to 1% manganese, the sum of the silicon plus manganese being not greater than about 1.25%, up to 12% cobalt, the sum of the cobalt 1 1 plus nickel being at least about 35%, up to 2% columbium, up to 1% vanadium, up to 1% copper, up to 1% tungsten, up to 2% tantalum and the balance essentially iron.

References Cited UNITED STATES PATENTS Bieber 75171C Gibson 75-128.9

Bieber 75171H Franklin 75171A Abkowitz 75171H Heydt 75128.9

HYLAND BIZOT, Primary Examiner

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