AU621565B2 - Air meltable castable corrosion-resistant (ni+cr+mo+co+fe) base alloy - Google Patents

Description

i f 4 A.

AUSIRIA (51)

PATENT

(43) Ai-A-24236/88 ft PCT WORLD INTELLECTUAL PROPERTY ORGANIZATION International Bureau INTERNATIONAL APPLICA LIS ED F9D P F TENT COOPERATION TREATY (PCT) (51) Inernational Patent Classification (11) International Publication Number: WO 89/ 01985 C22C 19/03, 19/05 Al (43) International Publication Date: 9 March 1989 (09.03.89) (21) International Application Number: PCT/US88/02977 (22) International Filing Date: (31) Priority Application Number: (32) Priority Date: (33) Priority Country: 26 August 1988 (26.08.88) 090,657 28 August 1987 (28.08.87)

US

Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (European patent), DK, FI, FR (European patent), GB (European patent), IT (European patent), JP, LK, LU (European patent), NL (European patent), SE (European patent).

Published With international search report.

Before the expiration of the time limit for amending the claims and to be republished in the event of the receipt of amendments.

A.O.J.P. 1 MAY 1989 (71) Applicant: CHAS. S. LEWIS CO., INC. [US/US]; 8625 Grant Road, St. Louis, MI 63123 (US).

(72) Inventors: JOHNSON, Thomas, Edward N6018 Farmington Road, Helenvil!e, WI 53137 (US).

McBROOM, John, Kellett, Jr. W315 N7315 Highway 83, Hartland, WI 53029 (US).

(74) Agent: RENNER, Edward, Cohn, Powell Hind, 7700 Clayton Road, Ste. 103, St. Louis, MO 63117

(US).

AUSTRAUAN

3 1 MAR 1989 PATENT OFFICE (54) Title: AIR MELTABLE CASTABLE CORROSION RESISTANT ALLOY (57) Abstract A highly corrosion resistant, durable, strong, hardenable and relatively ivexpennive nickel based alloy containing chromium and a high iron content has improved castability and weldability, The alloy contains approximately the quantities indicated: nickel 33 to 53 (to balance to 100 percent), chromium 20 to 25 percent, molybdenum 6 to 9 percent, cobalt 4 to 8 percent, iron 15 to 20 percent, manganese 2 to 4 percent, cooper less than about 0.15 percent, carbon up to 0.2 percent and silicon 0.3 to 1.0 percent. The alloy is air meltable and produces a highly fluid castable melt. All percentages are by weight.

WO 89/01985 PCT/US88/02977 -1- Air Meltable Castable Corrosion Resistant Alloy Technical Field Equipment used in highly corrosive environments typically is constructed of metal alloys such as stainless steel or other high alloys. These alloys are necessary to withstand the extremely corrosive effects of environments in which the equipment encounters chemicals such as concentrated sulfuric acid or concentrated phosphoric acid. A particularly difficult environment is encountered in making phosphate fertilizer. In the digestion of phosphate rock with hot, concentrated sulfuric acid, equipment must resist the environment at temperatures up to about 100 C. The impure phosphoric acid which is produced can be extremely corrosive and contains some residual sulfuric acid.

The corrosive effect is often increased by other impurities in the phosphoric acid, particularly by halogen ions such as chloride and fluoride, which are normally present in the phosphate rock feedstock used in the process. An extremely corrosive environment is encountered in the concentration of the crude phosphoric acid.

Background Art Typically, the art has used high alloys, such as Hasteloy C276, for the extremely corrosive environments. The high alloys require expensive qvL14 special processing, such as vacuum or elec t roslag 2 processing. High alloys requiring such low carbon and silicon residuals must be melted using specialized melting techniques and are generally available only in wrought formn. They cannot be produced by casting in commercial foundries using air melting techniques.

The very low carbon and silicon contents which are specified for the commercial high alloys are produced by these expensive melting techniques. It is known that a relatively high silicon content promotes fluidity of the molten metal and renders the melt castable. At the extremel, low silicon content specified for the high alloys, the molten metal lacks fluidity and cannot be cast by conventional sand, investment or centrifugal foundry methods.

Disclosure of Invention Applicants have produced a new alloy which has particular corrosion resistance in the environment encountered in producing phosphate fertilizer. In addition to superior corrosion resistance, the new alloy is relatively inexpensive and is highly castable to form complex parts and shapes. The alloy may be prepared by conventional and inexpensive air melt techniques, which is a particular advantage. According to the present invention there is provided an air meltable, castable, nickel base alloy having high corrosion resistance to severe phosphoric acid environments, the alloy containing to 25% chromium, 6 to 9% molybdenum, 4 to 8% cobalt, to 20% iron, 2 to 4% manganese, 0.5 to 1.0% silicon, up to 0.15% copper, up to 0.2% carbon, up to 0.2% nitrogen, and the balance nickel, the alloy melt being highly fluid and castable, the alloy having a high resistance to concentrated phosphoric acid environments and the like.

Applicants' alloy is an air melted, substantially 1

I

i WO 89/01985 PCT/US88/02977 -3copper free, nickel base corrosion resistant alloy.

Applicant has discovered, contrary to conventional wisdom, that an essentially copper free alloy exhibits corrosion resistance equal to and in most instances significantly better than similar alloys containing copper, particularly in the severe environment encountered in the concentration of phosphoric acid for fertilizers. This is particula.

true where quantities of halogen ions, as chloride and fluoride, are present.

A licants have discovered that their particular substantially copper free alloys are significantly superior to commercial alloys normally used in this service, such as Hasteloy C276. Applicants' alloys have the significant advantage that they may be formed by standard air smelting techniques and do not required the special techniques required by conventional high alloys used in this service.

It is generally known that copper content in corrosion resistant alloys, such as the austentic stainless steel s and certain other high nickel alloys, enhances the corrosion resistance of these alloys in environments where the alloys are exposed to acids of sullfur and phosphorus. Typical corrosion resistant .alloys make use of a significant copper content to achieve better corrosion resistance. It is known that if the copper content is too high, it cpn cause a condition known as hot shortness in the alloys which makes them difficult to cast or hot work. Copper also may reduce thet' weldability of these alloys, but conventionally, significant copper content is desirable- Applicant's have found, however, that they can WO 89/01985 PCT/US88/02977 -4product a highly corrosion resistant alloy which is essentially copper free. In doing so, applicants also have produced an alloy which is weldable, which can result in high process yields and in a reduction of scrap and waste metal. These factors all contribute to a much lower pr6duct cost in applicants' alloy.

Phosphate rock deposits at various locations in the world vary greatly in chemical composition. The most severe corrosion environments are typically encountered in processing deposits of phosphate rock which contain a high content of halogens, such as chloride or fluoride. It is an object of applicants' invention to produce a material of construction suitable for use in processing such phosphate rock which presents severely corrosive environment.

It is also an object of applicants' invention to produce a corrosion resistant which is low in copper and which has an enchanced corrosion resistance.

It is a further object of applicants' invention to produce a highly corrosion resistant alloy which contains silicon in sufficient quantity to render the alloy castable by conventional methods.

It is an object of applicants' invention to produce a highly corrosion resistant alloy which contains silicon.

It is an object of applicants' invention to produce a corrosion resistant alloy that is essentially copper free.

It is an object of applicants' invention to produce a corrosion resistant alloy which has high strength and hardness properties.

5 Applicants' substantially copper free alloy may be made in two forms, depending upon the level of carbon in each form. The ultra low carbon alloys of applicants' invention have a carbon content of less than 0.08% and have an austenitic solid solution structure when soluticn treated. The low carbon alloys, with a carbon content of between 0.10 and 0.20%, exhibit a precipitation of a Chinese script configuraxion. It will be understood that, as used herein, the terms "low carbon" and "ultra low carbon" are meant to describe alloys having the above carbon c ntents. The precipitates have been identified as heavy ,tal carbides. The micro hardness test, converted to Rockwell C scale, shows a matrix hardness in the low carbon alloy matrix of about 26.7 and about 52.3 hardness in the catbide. The low carbon alloys do not have the exceptionally high corrosion resistance exhibited by the ultra low carbon alloy. However, the fee': low carbon alloys have a structure which may be highly useful in corrosive services whe.re physical abrasion, erosion or galling is encountered.

The invention may be further understood by reference to the following Best Mode for Carry .ng out the Invention.

so a Best Mode for Carrving Out the Invention .5 The alloys of the invention are nickel base alloys with high iron and moderate to high chromium content.

sets **so The alloys contain between 33 to 53 percent nickel, preferably about 42 percent (to balance to 100 percent), to 25 percent ,hromium, 6 to 9 percent molybdenum, 4 to 8 percent cobalt, 15 to 20 percent iron, 2 uo 4 percent manganese and 0.5 to 1.0 percent silicon. The alloy is substantially copper free, having less than 0.15 percent copper and preferably having zubstantially less than 0.15%., The alloy may contain up to 0,2 percent Carbon, up /iL 4 to 0.08% carbon and having an austenitic composition or d C~ -OFI 6 containing 0.10 and 0.20 percent carbon and having an extremely hard Chinese script precipitated structure in an austenitic matrix. The alloy may also contain minor amounts of tramp or extraneous elements, as is typical in alloy composition, for example, sulfur and phosphorous.

It is preferred that these elements be kept to as low a level as conveniently possible. Preferably sulfur is maintained below 0.025 percent by weight and phosphorous below 0.025 percent by weight. Nitrogen, up to 0.20% by weight, may be used as an alloy ingredient to promote formation of an austenitic structure and to increase strength.

Nickel is present in the alloy as the base metal and at a relatively high percent. Nickel adds greatly to the .4o corrosion resistance of the alloy. The chromium level s at a moderate/high level of between 20 and 25 percent by weight. It is preferred that the chromium present be added, within these limits, at a high level to add S. corrosion resistance and strength to the alloy. The addition of cobalt and manganese to the alloy also adds additional strength and contributes the corrosion resistance.

Applicants have found that the elimination of copper from the alloy, to the greatest extent

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I __1 c V WO 89/01985 PCT/US88/02977 -7possible, greatly improves the castability of the alloy and unexpectedly provides an alloy having as high or higher corrosion resistance than conventional alloys containing copper. In addition, the weldability of the alloy is greatly improved by the omission of copper from the alloy. It is preferred that the copper content be kept as low as possible and preferably substantially below 0.15 percent by weight.

The silicon content in this alloy should be as low as possible to provide increased corrosion resistance in the severe halogen containing phosphoric acid environments. However, reducing silicon in alloys is known to reduce the fluidity of the melt and inhibit the castability of the alloys, particular using conventional air melt, gravity casting techniques. Applicants have found- however, that they can reduce the silicon content substantially below 1.0 percent by weight, in this alloy, and still provide an alloy which is highly fluid in the molten state. Applicants' alloys produce superior cast articles, even when casting complex shapes. In addition, applicants have found that, at this low silicon content, the corrosion resistance of their alloy against halide contianing phosphoric acid is greatly improved. Preferably the silicon content is between 0.5 and 1.0 percent by weight.

It is desirable that, within the limits set, iron also be included at as high a level as conveniently possible. Having a high iron content reduces the cost of the alloy, since iron is a much less expensive constituent then nickel, chromium and the WO 89/01985 PCT/US88/0297 7 -8other high alloy metals. Moreover, having the high iron content permits the inclusion of alloy constituents in their alloyed form with iron, rather than requiring the use of pure alloying metals.

This reduces the cost of preparation of the alloy.

Moreover, applicants have found that within the limits of their alloy, the presence of iron does not detract from the overall corrosion resistance, weidibility, and castability of their alloy product. While applicants' alloy is descrhed as a castable alloy, it will be understood that .t may be readily machined by conventional processes, such as turning, milling or drilling, as riequired to produce a finished product.

Applicants' alloy may take two finished forms.

In the first form, applicants' alloy has a carbon composition of up to 0.08 percent, preferably between abe 0.02-0.08%. this form, designated the ultra low carbon form, exhibits an austenitic structure and has very high corrosion resistance in the target environment, particularly where the environment contains halide ion, such as chloride and fluoride. The second type of applicants' alloy is designated the low carbon form. This form typically has the carbon content between t& 0.1 and 0.2 percent by weight. The low carbon form has a two phase structure having an austenitic matrix containing Chinese script carbon precipitates. The precipitates have exceptional hardness. While the low carbon alloys do not have the very high corrosion resistance in the target environment exhibited by the ultra low carbon alloys, they may 4 0LIA' be used for service exhibiting corrosion, abrasion, -9erosion and galling. The low carbon alloys can find exceptional utility in an environment having both high corrosion and abrasive factors, such as pumping of slurries of acidified phosphate rock, as might be encountered in phosphoric acid production.

The preferred composition of applicants, ultra low carbon alloy is nickel about 41.7%, chromium about 22.5%, molybdenum about cobalt iron about 16%, manganese carbon up to about 0.08%, silicon I 0.6-0.75% and copper below about 0.15%.

IThe following tables show examples of alloys made j within the concepts of the invention compared with I conventional alloys. LEWMET (Registered Trade Mark) is a comaercial version of alloys disclosed in US Patent No 3,738,296. All of the examples, as summarized in Tables I through IV, are alloys made by conventional air Seg melt techniques with the exception of the commercial alloys Hasteloy C276 and Carpenter (Registered Trade S Mark) 20Cb3. Hasteloy C276 is an example of a super low carbon and silicon wrought alloy requiring a specialized melting process. Carpenter 20Cb3 is a commercial wrought material. Also compared in the Tables are two versions of conventional type 316 stainless steel (CF8M and CFBMX). Table I shows a comparison of the compositions of these alloys. The experimental material shown in the 90 tables was made in a conventional electric furnace by melting the ingredients together in the proper proportions, deoxidizing and casting test bars using conventional gravity casting techniques. The cast bars were heat treated and subjected to the tests shown in Tables I through IV. A solution heat treatment, such as V *0 X E4TM- WO 89/01985 WO 8901985PCT/11S88/02977 solution heat treating in excess of 20000 (105? 0 C) and water quench, is satisfactory.

Element Carbon C-h r omium Nickel (bWy difference) Molybdenum silicon Manganese Copper Iron Cobalt Nitrogen sulfur Phosphor us TABLE I A 3ummary Experimental Heats Analysis WeightPercent J526 0.02 22 .62 4 5 6 7 .75 0.58 2.41 o .08 16.62 6 .34 010 .012 Ultra Low Carbon Heats N318 N340. N853 0.04 22.74 43.45 8. .25 0.59 2 .42 0.11 16.55 5.83 0 .06 .012 .013 0.05 24.69 43.12 6.31 0.93 1. 93 0108 18.81 3.98 0.07 .008.

.024 0.02 22.40 43 .69 8.05 0.67 2.85 0.10 16.17 5.95 0.08 .012 .012 Element Low Carbon Heat.s P3483 N339 N1148 Carbon Chromiium Nickel (by difference) Molybdenum Silicon manganese Copper Iron cobalt Nitrogen Sulfur Phosphoru~s 0.*02 22.*45 43.56 8.78 0.88 2.86 0.06 15.*25 5.92 0.22 .009 .005 6.10 20.02 43.06 9.06 0.75 3.12 0.09 15 ,67 8.06 0.05 .007 .017 0.18 20.15 42.43 8.69 0.*52 3.75 0.09 15.98 8.20 .006 .006

-C

ii WO 89/01985 PCT/US88/02977 -11- TABLE I B Analysis of Other Alloy r .d Weight Percent Element Hastelloy C276 Alloy 20Cb3 CF8M Carbon .002 0.03 0.06 Chromium 15.63 19.31 18.72 Nickel 54.28 33.09 9.26 Molybdenum 15.47 2.18 2.29 Silicon .002 0.40 1.57 Manganese 0.42 0.25 0.70 Copper 0.10 3.23 0.55 Iron 5.91 Bal Bal Cobalt 2.13 Tungsten 3.53 Sulfur .002 .001 NA Vanadium 0.13 Aluminum 0.23 Cb Ta 0.66 Phosphorus .006 .023 NA Element CF8MX LEWMET (J525) Carbon 0.02 0.03 Chromium 17.39 22.45 Nickel 11.94 41.76* Molybdenum 1.96 7.36 Silicon 0.50 0.81 Manganese 1.30 2.63 Copper 0.33 2.93 Iron Bal 17.67 Cobalt 6.14 tungsten 0.43 Sulfur .012 .007 Vanadium Aluminum Cb Ta Phosphorus ,030 .010 By Analysis S'G 89/01,985 PCT/US88/02977 -12- Table II summarizes the comparison of corrosion testing of these alloys in the environment noted in Table II. the alloys were prepared as conventional test blanks and subjected to a series of corrosion tests. A series was tested in phosphoric acid at 0 C. The test were run for 96 hours. Where noted, the test samples were subjected to temperatures of 115 C for twelve hours. This extremely severe test occurred as a result of the malfunction of the test equipment. The composition of phosphoric acid was adjusted to have the chloride ion content as noted. The phosphoric acid was a crude phosphoric acid typical of acids used in producing phosphate fertilizer using Florida phosphate rock. Two standard grades, 32% and 54% P 2 0 5 were tested. A third grade tested, 42% P 2 0 5 was manufactured by a different commercial process also using Florida rock. These acids contained approximately 2.2 per. ,'nt fluoride ion, in the 54 percent P20 2 acid, and 1.25 percent fluoride ion the 32 percent

P

2 0 5 M hese acid compositions are typical of those which would be encountered in severe phosphoric acid environments with high halide ion content.

As can be seen from Table II, applicants' new ultra low carbon alloys in particular tested as being superior to conventional wrought and cast materials. The resistance of applicants' new alloys to 32% P205 solutions containing halide ion tested as being highly superior to the best conve'-ional material tested, LEWMET 25. The 32% P205 solutions are typical of environments encountered in phosphoric acid concentration.

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WO 89/01985 WO 8901985PCT/US88/02977 -13- TABLE II A, Static Corrosion Laboratory Tests in H3P04 Rates mils per year (0.001 inch per year) S (Test run for 96 hours in non-aerated aci3., at 90 0 C, except where noted) Utlra Low Carbon Acid Environment J526 N318 N340 N853 32% P 2 0 5 0.5 1.0 0.4 0.6 32% P 2 0 500 ppm Cl- 1.3 0.7 0.7 i.0 32% P205 1000 ppm Cl- 0.9 0,9 0.7 0.7 32% P 2 0 5000 ppm Cl- 0.8 0.6 0.7 1.3 32% P 2 0 10,000 ppm Cl- 1.0 1.1 5.5 1.1 P205 15,000 ppm Cl- 0.7 0.6 54% P205 1.2. 1,5 0.9 1.4 54% P205 500 ppm Cl- 2.7 '1.9 1.5 1.7 54% P205 1000 ppm Cl- 1.7 1.5 1.3 54% P 2 5000 ppm Cl- 3.6* 3.8* 4.2* 2.9* 42% P 2 0 20,000 ppm Cl- 42% P 2 0 30,000 ppm Cl- 1.1 Temperature to 115 degrees C for 12 hours P CT/U 588/02977 WO 89/01985 -14- Low Carbon N3 30 Acid Environment P34 83 1.4 N1148 9.7 32% P 2 0-5 32% P 2 0 500 ppm Cl- 32% P 2 0 5 1000 ppm Cl- 0.7 1.0 1.0 6.3 12.6 8.2 52.7 32% P 2 0 5000 ppm, Cl- 18.4 32% P 2 10,000 ppm Cl- 32% P 2 0 15,000 ppm, Cl- 54% P,2Oq 54% P 2 500 ppm Cl- 54% P205 1000 ppm. Cl- 1.9 13 1.9 4.1* 2.9 3.7 2.4 4.2* 11 ,3* 154.0 54% P 2 0 5 5000 PPM Cl- 42% P205 z0"000 ppm Cl- 42% P205 30,000 PPM Cl- 27.3 Temperature to .115 degrees C for 12 hours PCT/US88/02977 WO 89/01983P TABLS II B Static Corrosion Labora.tory Tests in H3P04 Rates mil~s per year (0.001 inch per year) (Test run for 96 hours in non-aerated acid at 90 0 C, except where noted) Acid Environment C-276 CF8MX CF8M 20Cb3 L ewme t (J52,5) 32% P205 7.8 32% P 2 0 500 ppm Cl- 32% P 2 0 1000 ppm Cl- 32% P 2 0 5000 ppm C>- 32% P205 LO.,000 ppm Cl- 32% P205 15,000 ppm Cl- 4.6 10.0 4.2 19.7 5.1 534 3.3 1.3 3.9 2.8 6.9 4.2 25,2 459 0.4 1.4 1.6 1.1 8.7 1.5 54% P205 54% P205 500 ppm Cl- 7.9 7.1 4.1 5.6 53.63 1.6 103 54% P205 1000 ppm Cl- 54% P205 5000 ppm Cl- 42% P 2 20,000 ppm Cl- 4Z% P,)0 30,900 ppm Cl- 2.0 2.8 6.8 5.0 148 94 1.8 2.4 3.6 1.1 1. 1 WO 89/01985 PCT/US88/0297 7 -16- In Table III a number of applicants' alloys were subjected to comparative tests in aerated 98 percent sulfuric acid. 'he tests were conducted at 1000C, 1100C and 120 C. As can be seen, the alloy exhibits a high degree of corrosion resistance in concentrated sulfuric acid, particularly at temperatures of 100 C and below, as would normally be encountered in handling sulfuric acid in a phosphoric acid plant.

4 WO 89/01985 PCT/US88/02977 -17- TABLE III Average corrosion rates Ultra Low C Low Cu experimental heats in 98% Sulfuric acid Rate s inches per year Heat No.

1000OC Tests i py 110 0

C

Tests i P-y J526 N318 N3 40 3 P3 483 010 .021 .017 .010 022 .014* .041 .019 0141 048 015 .030* 1200C Tests Heat No.

J526 N 318 N340 N8 53 P3 483 i py 044 .060 .043 .029 .051

C-

.045* Weighted Average Raters WO 89/01985 PCT/US88/02977 -18- Table IV shows the hardness and strength data for applicants' alloys. It can be seen that applicants' alloys have a high degree of mechanical strength and hardness, which makes them particularly suited for structural and mechanical components in contact with corrosive environments.

TABLE IV A Mechanical Test Data (solution heat treated at 2150 0 F 2235 0 F for one hour per inch of metal section and water quenched) Yield Tensile Elong.

HEAT NO. -psi -psi J526 37,090 69,670 56.0 N318 42,190 83,370 61.5 N340 45,290 90,600 6'4.0 P3483 49,320 92,100 66.5 N853 40,760 80,020 59.5 P339 45,360 77,940 21.0 N1148 48,180 75,140 11.0

R.A.

HEAT NO. Brinell Type J526 58.4 163 Cast N318 60.8 170 Cast N340 59.5 166 Cast P3483 66.8 207 Cast N853 56.4 153 Cast P339 22.5 197 Cast N1148 10.4 207 Cast WO 89/01985 PCT/US88/02977 -19- TABLE IV B Mechanical Properites of Other Alloys Tested Yield Tensile Elong.

Alloy -p2si psi HasteJlloy (TM) C276 Carpenter (TM) 20Cb3 CF 8MX CF8M* Lewinet 25 (TM) 53,000 58,000 30,800 42,000 37,850 113, 000 98,500 65,700 80,000 71,430 38 50 415 50.0 63.5 Alloy Hastelloy (TM) C276 Carpenter (TM) 20Cb3 CF8MX CF8M* R .A.

Brinell Type 67 67

NA

62.9 170 197 137 170 163 Wrought Wrought Cast Cast Cast Lewinet 25 (TM) Typical Value C 3-311I 20 i s 1 i l *i j f 0* S S S. S S S .5

I

9.

A leg of standard cast keel bar as described in ASTM Standard A370 was sectioned from a bar cast from experimental heat No N318. A section was removed from the cut surface of the bar and weld filler metal applied.

The bar was then solution heat treated and submitted to an independen'- commercial laboratory for evaluation. No fracture was observed in bending the bar 180 degrees on 1 1/2 inch radius. This test indicated excellent weldability.

Evaluation of the castability of the experimental alloys was made by making experimental castings of the general type used in this service. These included pump propellers and pump casings. The molten metal exhibited adequate fluidity filling all voids in the molds. No hot shortness or cracking was evident even when castings were water quenched from high temperature in the heat treating process.

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Claims (9)

1. An air meltable, castable, nickel base alloy having high corrosion resistance to severe phosphoric acid environments, the alloy containing 20 to 25% chromium, 6 to 9% molybdenum, 4 to 8% cobalt, 15 to 20% iron, 2 to 4% manganese, 0.5 to 1.0% silicon, up to 0.15% copper, up to 0.2% carbon, up to 0.2% nitrogen, and the balance nickel, the alloy melt being highly fluid and castable, the alloy having a high resistance to concentrated phosphoric acid environments and the like.

2. The alloy of cla,'a 1 containing 22.5% chromium, 8% molybdenum, 6 to 8% cobalt, 16% iron, 2.5 to 3% I manganese, 0.6 to 0.75% silicon, up to 0.15% copper, up i to 0.8% carbon, and the balance nickel.

3. The alloy of claim 1 or claim 2, wherein the alloy v contains up to 0.08 percent by weight carbon.

4. The alloy of any one of the preceding claims, wherein the alloy has an austenitic matrix.

The alloy of any one of the preceding claims, wherein the alloy is highly corrosion resistant in phosphoric acid environments containing halogen ions.

6. The alloy of claim 1, wherein the alloy contains between 0.1 to 0.2% carbon.

7. The alloy of claim 6, wherein the alloy has an austenitic base matrix containing a hard carbide precipitate phase. S/ w

8. The alloy of claim 7, wherein the precipitate phase Shas a Chinese script configuration. t II I 22

9. A method of producing a castable alloy having high corrosion resistance to severe phosphoric acid environments defined in any one of the preceding claims comprising, air melting a nickel base containing a high iron content and moderate to high chromium content, adding an amount of silicon effective to produce a highly fluid castable melt, and maintaining the copper content at less than 0.15% by weight, casting the alloy to form structural elements and heat treating the formed structural elements. The method of claim 9 wherein the structural elements are solution heat treated. DATED THIS 14TH DAY OF JANUARY 1992 CHAS S. LEWIS CO, INC By its Patent Attorneys t GRIFFITH HACK CO. jj Fellows Insti.tute of Patent h Attorneys of Australia lils I~ 0 ""i INTERNATIONAL SEARCH REPORT International Application No, PCT /US 88 /02977 L. CLASSIFICATION OF SUBJECT MATTER (if several classification symbols apply, indicate all) According to International Patent Classification (tt'C) or to. both National Classification anl IPC JpC4 C22C 19/03; C22C 19/05 U.S. CL. 420/4'7:41,42,444,454,585; 148/410 If. FIELDS SEARCHED, Minimum Documentation Searched Classification Syatem ClassifIcation Symbols U.S. CL. 420/441, 442, 444; 454, 585 148/410 i0ocurnentation Searched other than Minimum Doqumeration to i,~e Extent that such Documents aro Included In the Fleldi -Searcheda 111, DOCUMENTS CONSIDERED TO BE RELEVANT 9 Category Citation of Document, il with Indication, where appropriate, o1 the re'evant passages i2 Relevant to Claim No. 13 X US, A, 4,155,751 (HERCI-ENROEDER) 1-5, 11 and 22 MAY 1979 (Note colum~ns 3 and 4, 13 to 18 lines 10 to 22 for alloy examples) X US, A, 3,817,747 (Schultz et al) 1-5, 13, and 18 JUNE 1984 (Note columns 5 and 6, 13 to 18 Table I for alloy examples) special Categories of O.ted documentat 10 later document published alter the international Miing date document defloiig the general stale of the art which Is not or priority dale and not in conflict with the application but consdaro tobe o paticuar elevncecited to understand the principle or theory underlying the conidarlerdome but parularhe oracerhnentoa invention fi'ealieg docuen buIule"n ratrteInentoa document ot particular relevancet the claimed invention filin datecannot be cortaidered novel or cannot be considered to 110 document which may throw doubts on priority clalm~s) or Involve an Inventive step which Is cited to establish the publication date o1 another Y dou ntopaiclreeacothcamdIvnio cita~onor oherspeial easn ls spcifed)cannot be considered to Involve en inventive step when the 110, document referring to an oral disclosure, use, exhibition or document is Combined with one ,or more other such docui, other means Merits, such Combination being obvious to a person skilled O" document published prior to the International Oilng date but in the art, lter than the priority dale Claimed di'cumunt member of the same patent family IV, CERTIFICATION Date oft the Actual Completion of the International Search Date o1 Mailing of this Iternational Search t',port, 23 NOVEMBER 1988 0 6JAN 1989 International Searching Authority Slgnature of Authqrlgod OffIcet ISA/US DEBORAH YEE P orniPOTttSMalO(seond000 (POV.1.87)