US2938786A - Nickel base alloys containing boron and silicon - Google Patents

Description

May 31, 1960 T. E. .JOHNSON NICKEL BASE ALLOYS CONTAINING BORON AND SILICON Filed July 29, 1959 0 0 x Imi( e 0^ o M N X, m a Hwa/3322 M .Z 0. 0 0 0. 1X, fw O- f m Z 4. 7 2 6 ,X w. /\\U dfi/@e5 vl A444444 5999999 0 0 wwmwmmwmwwmw.

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United States Patent "O NICKEL BASE ALLOYS CONTAINING BORON AND SILICON Thomas E. Johnson, Milwaukee, Wis., assignor to Stainless Foundry & Engineering, Inc., Milwaukee, Wis., a corporation of Wisconsin Filed July 29, 1959, Ser. No. 830,277

Claims. (Cl. 75-171) This invention relates to nickel base alloys containing boron and silicon which are readily machinable and characterized by high corrosion resistance and hardness. More particularly, the invention relates to improved alloys cornposed primarily of nickel, but including a substantial amount of chromium and smaller amounts of other elements including specific amounts of boron and silicon which are in such relative amount as to impart high corrosion resistance and hardness tothe alloys.

The chemical processing industry, in handling chemicals and solutions of corrosive materials, such as acids, alkalis, and the like, is beset `by many requirements. Not only is it desirable that equipment and parts in contact with the corrosive environments be of a material possessing a high resistance to corrosion, but other desirable properties should be provided by this corrosion-resistant material. Such properties as strength, hardness, machinability, and abrasion resistance are highly desirable. Equipment and parts, such as pumps, impellers, shafts, valves, pipes, bearings, pipe fittings, vessels, tanks, and the like in this industry frequently have been made from nickel base alloys.

An alloy presently used in the chemical process industry is a nickel base alloy of the type described in U.S. Patent 1,115,239 to Paar, issued October 27, 1914. This alloy has found wide use because of an economical basemetal composition coupled with resistance to corrosion, density, strength when subjected to high pressure, and machinability. As initially developed, this alloy was of a composition substantially as follows: chromium l5 to 2l percent, molybdenum 5 to 8 percent, copper 5 to 11 percent, iron up to 0.1 percent, carbon up to 0.1 percent, and the balance nickel (55 to 65 percent) except for a small amount of residual elements and concomitant impurities (Le. manganese, silicon, phosphorus, sulfur, eter) usually present in nickel alloys. Since this development, this alloy composition has been modified, andprior to the present invention the recent composition has been substantially as follows: chromium .2l to 23 percent, molybdenum 5 to 8 percent, copper 4 to 7 percent, iron up to 8 percent, manganese 1.0 to 1.5 percent, carbon 0.18 to 0.22 percent, silicon 0.50 to 0.85 percent, and the balance nickel (52 to 62 percent) except for an extremely small amount of residual elements and impurities generally present in nickel alloys.

Silicon, usually present in the foregoing known nickelbase alloys, was present only as an incidental concomitant element in the amount of a fraction of one percent. Boron, if used in the foregoing known alloys, was used in extremely small amounts for purposes of a ilux or degasifier with little or no boron content remaining in the finished alloy upon analysis thereof.

All compositions given above andinthefolloWing-description and claims are on a Weight basis.

Patented May 31, '1960 While the foregoing prior art nickel-base alloys are of great utility, there have been limitations and drawbacks of the same, which have handicapped their usefulness in industry. Equipment made of these alloys under some conditions abrades and wears rapidly, with frequent replacement being necessary. For example, cutter blades in the rayon processing industry wear dull and lose their sharp edges rapidly, and bearings operated in some acidic media tend to abrade, gall, and wear rapidly. This wearing and galling of items, such as bearings, blades, shafts, impellers, valves, and the like, proceeds at elevated temperatures in intermediate and highly concentrated reducing-acid environments, generally at rates in excess of normai expectations from erosion by the corrosive environment and from abrasion of moving, contacting metal surfaces. Frequent replacements of such items have resulted in excessive costs.

It is an object of this invention to provide nickel base alloys in which silicon and boron are used in related amounts to obtain selected increased hardness without excessive brittleness along with good corrosion resistance in both oxidizing and reducing media.

Another object of this invention is to provide nickel base alloys with silicon and boron therein in selected and related amounts so that the alloys have good corrosion resistance comparable to that of prior art alloys but possess other desirable properties, such as selectively increased hardness and superior resistance to abrasion, as compared to such prior art alloys.

A further object of this invention is to provide new nickel base alloys containing selected amounts of silicon and boron, which amounts complement each other to provide a corrosion resistance substantially superior to prior art nickel alloys and which amounts supplement each other to provide harder, more durable, and, therefore, more useful alloys that are superior to prior art nickel base alloys.

Still another object of this invention is to provide nickel base alloys containing silicon and boron in such related amounts that although the alloys have high hardness, they have low brittleness with resulting good machinability so that desired surfaces may be machined thereon without chipping and such surfaces Will be retained in corrosive environments for longerr periods than with prior art nickel base alloys.

A further object of this invention is to provide nickel base alloys containing silicon and boron in such selected amounts that the alloys will have good mechanical strength, will not only be readily machinable as indicated above Ibut will also have enhanced weldability.

A further object of this invention is to provide a series of nickel base alloys containing silicon and boron in such relatedamounts that the resultant hardness of any alloy within such series may be predetermined, and thus a wide range of alloysrof varied hardness, all possessing good corrosion resistance in both oxidizing and reducing media can be made, consequently increasing the utility of the alloys Vfor varied industrial applications.

Various other objects will be readily apparent from the following description and claims.

The accompanying drawing is a graph relating corrosion resistance and hardness properties of alloys covered by this invention.

Generally, silicon, when included in nickel base alloys and a 'high 'corrosion resistance to acid. Silicon, when 3. Y added in "such substantialamounts, resulted in nickel alloys that, while of increased hardness, also were extremely brittle, dicult to machine, and capable of little or no hot or cold working. Boron, when included in nickel alloys in amounts larger than ,minute residual amounts, generally tended to increase hardness and to deleteriously affect corrosion resistance. Boron contents of substantial amounts also resulted in extremely brittle alloys susceptible to littleor no machining.

It has been discovered that nickel ,basefY alloys, substantially of the general composition already described, alpon modication by including therein certain amounts 0f boron and silicon, provide new alloys superior to prior :art alloys. 'Inthe alloys of Ythis invention, the boron fand silicon contents complement eachother in that a tdeleterious effect of boron onthe corrosionresistance is toffset by a beneficial effect on the corrosion resistance "rby silicon. The resulting alloys possess a corrosion resist- 'possess other desirable properties and' characteristics such 20 tas mechanical strength, requisite for use in the chemical process industry. In the alloys of this invention, the boron and silicon contents supplementeach other to pro-d Y `vide new alloys having a significantly increased hardness :and durability over known nickel alloys Ywithout an ac- 'companying excessive brittleness. By varying known lamounts of boron and silicon additions, an alloy of predicted hardness may be manufactured. This increased hardness of the alloys without excessive brittleness provides superior abrasion resistance and superior anti- 30 galling properties. Furthermore, Ythese alloys are more Yreadily machinable to receive a sharpened Yedge without chipping and retain this sharpened edge in corrosive environments kfor longer periods than is possible with known nickel alloys. The boron content in these alloys makes a `noticeable contribution to the machinability properties. This overall superiority of the alloys of the invention results in important economies for numerous applicationsl inthe chemical processing industry. f

The alloys of the invention may be prepared by con- 40 ventional melt procedures for nickel alloys with only minor variations in these procedures. Desirably, inpracvtice, the various constituents employed are inV a comnier-` d cially pure state to avoid introduction of unwanted constituents'and to control carefully the final alloy Vcompo- 45 sition. Addition of boron Yand silicon constituents to assure the desired composition are made. Preferably the boron and silicon additions are made, after therjaddition of a scavenger, with the molten composition at or near a desired pouring temperature (usually between 27750 t0 50 2950 F.) and just prior (usually a few minutes) to quickly pouring and casting into a suitable form yor molcl.V The boron and silicon constituents both should be introduced through `any scavenger slag to avoid losses thereof., Pref- Y 2,938,7se Y. Y

"arecapable of being welded,

erably boronis added in the Yform of a compound or master alloy, such as ferroboron, nickelboron, chromeboron, or the like. Also preferably, the silicon is added in the form of siliconmetal, although a silicon master alloy may be used if the desired iinal alloy composition can be realized. Generally, amounts of boron and silicon, slightly in excess of the amounts desired in the iinal alloy, are used tovallow for oxidation losses with the excess amounts being determined by the losses during mixing and the time elapsing before pouring,

The alloys of this invention usually are cast into various shapes which are useful in cast form as impellers, blades, pump casiugs, valves, and the like.` These castings while extremely hard are not excessively brittle. Machining, such as latherturning, drilling, milling and sawing, of the castings is possible. The cast alloys also In accordance with the inventioinrthe composition, by analysis of the improved alloysvis as lfollows: chromium 19 to 26 percent, molybdenumS to 9 percent, copper 4 to 7 percent, iron up to l0 percent, manganese up to l.5 percent, carbon up to 0.3 percent, silicon 1.5 to 7.5 percent, boron 0.025 to 0.55 percent and the balance essentially nickel (46 to 69Vpercent), except for an extremely small amount (less than 0.25 percent) of residual elements and concomitant impuritiesY generally present in prior art nickel alloys. The preferred composition, by analysis, is as follows: chromium 2l to 23 percent, molybdenum 5 to 8 percent, copper 4 to 7 percent, iron up to 8 percent, manganese` l to 1.5 percent, carbon 0.18 to 0.22 percent, silicon 4.5 to 6.5 percent, boron 0.025 to 0.20 percent, and the balance essentially nickel (50.0 to 66.5 percent) except for an extremely small amount of residual elements and concomitant impurities generally present in prior art nickel alloys (less than 0.25 percent). Particularly desirable results in intermediate and concentrated reducing-acid media at elevated temperatures are obtained with a preferred alloy composition by analysis as follows: chromium 22.5 percent, molybdenum 6.4 percent, copper 6.5 percent, iron up to 8 percent, manganese 1.25 percent, carbon 0.2 percent, silicon 5 percent, boron 0.05 percent, and the balance vessentially nickel, except for residual amounts of impurities generally found in conventional nickel "alloys (less than 0.25r percent). Such an alloy gives maximum corrosion'resistance at a readily machinable hardness level.

The following table gives examples of alloys Withinthe series covered by this invention and alloys consisting essentially of an aforementioned known alloy with additions of silicon and/ or boron in certain amounts with one or both outside the amounts of silicon and boron in the alloys of this invention, the tablegiving a comparison of the corrosion resistance and hardness thereof.

Composition, Percent By Weight Cu Fe Mn C Si Analysesofcommercialalloystowhlchboronwasadde Corrosion Rates-Inches Per Year at Temperatures of 90 (ZL-100 C.

Alloy No. BEN

60% (i5-70% 78% 85% 93% Conc. H1804 H1804 H2804 H2804 H2804 H3804 H1804 Corrosion resistance of cast and cast-machined alloys of the invention were determined by immersion of alloy samples in aqueous solutions of various acid concentrations at dierent temperatures. The alloy samples were supported on glass supports in the acid solutions. After each 48-hour period of immersion, each sample was removed, rinsed with distilled water, rinsed with acetone, and then oven-dried. Loss of weight of a sample was converted to the calculated reduction in thickness which a large casting would undergo underl similar conditions in a one-year period. Data obtained are reported in inches of penetration per year (i.p.y.) on the basis of the average of replicate samples for three 48-hourrperiods of immersion.

From test data of the nature as reported in the table, it has been found with the aforementioned prior art nickel alloys containing a fraction of one percent of silicon, that hardness increases while corrosion resistance is deleteriously changed upon addition of small amounts of boron thereto. In such low-silicon-content alloys, inclusion therein of a small amount of boron and increasing of this boron content stepwise, -in amounts up to about 0.75 percent, results in an inferior corrosion resistance. This inferior corrosion resistance of such alloys is readily apparent with corrosive environments of 50 to 98 percent sulfuric acid concentrations at elevated temperatures of 90 to 100 C. If, in the aforementioned known nickel alloys there are included, according to this invention, a silicon content of about 2 percent and a boron content of 0.025 to 0.05 percent, a significant increase in hardness is obtained. This hardness increase appears to be due partly to solid-solution hardening of the matrix, which strengthens the matrix, and partly to an increase from a second phase. 'Ihis increased hardness from the second phase possibly may be occasioned by a reduction in the solubility of carbon in the matrix from the increased silicon and is accompanied by a formation in the second phase of a Chinese script configuration. If, in these nickel alloys containing about 2 percent silicon, the boron is increased to 0.10 percent, there is a marked drop in hardness. Microstructure of these alloys indicates the appearance of a third phase closely associated with the second phase. If, in these nickel alloys containing about 2 percent silicon, the boron is increased to 0.20 percent, hardness values in the order of those at the previously mentioned 0.05 percent boron level are obtained. These 2 percent silicon-0.2 percent boron content nickel alloys exhibit a corrosion resistance, in 50 to 98 percent sulfuric acid concentrations at 90 to 100 C., substantially superior to the aforementioned known nickel alloys. A further increase in boron content to about 0.4 to 0.5 percent in these 2 percent silicon-nickel alloys results in an additional marked increase in hardness but slightly reduced resistance to corrosion which can be overcome by increasing the silicon content to 4. to 6.5 percent. Further increases in boron content above 0.515 percent does not appreciably increase the hardness in these 2 percent silicon-nickel alloys. If, in the aforementioned known nickel alloys, there are included silicon contents ranging from 1.5 percent to about 7.5 percent and boron contents ranging from 0.025 percent to about 0.55 percent, further increases in hardness are noted with various hardness readings indicating the increases primarily in the matrix at a constant boron level and increasing silicon levels Within these ranges. Corrosion resistance of such nickel alloys containing from 1.5 to about 7.5 percent silicon and 0.025 to about 0.55 percent boron at the lower silicon and boron levels within these ranges is substantially equivalent to, and at the higher silicon and boron levels within these ranges, is superior to the aforementioned known nickel alloys. At still higher boron and silicon contents (i.e. boron greater than about 0.55l percent and silicon greater than about 7 .5 percent) for the aforedescribed known nickel alloys somewhat higher hardness values are obtained. However, at still higher boron and silicon contents the alloys have an excessive brittleness as evidenced by a heat checking or cracking tendency upon cutting with an abrasive saw and by a cracking or fracturing of specimens subjected to the Brinell hardness test. These alloys with these high boron and silicon contents, because of excessive brittleness, are of extremely limited utility and generally are not satisfactory for most applications in the chemical processing industry.

The alloys of this invention have a desirable corrosion resistance of at least 0.020 inch per year in hot 93% sulfuric acid at temperatures up tov C. Furthermore, these alloys have a desirable hardness ranging from 200 to 400 Brinell. These alloys also have good mechanical strength in the range of 70,000 to 80,000 pounds per square inch.

The graph shown in the accompanying drawing compares the elect of silicon on the corrosion resistance and the hardness of alloys which have a boron content of 0.025 to 0.12 which is within the preferred range according to this invention. These alloys had a base composition of:

The corrosion values were determined by immersion in ,Y Y,

sulfuric acid at 100 C.

this invention provides a series 5f-nickel base alloys containing silicon and boron in such related amounts that A,

the resultant hardness of any alloy within such series may M Copper be predetermined and thus a Av vide range of alloys ofi.; Y varied hardness, all possessing good corrosion resistance -Y in both oxidizing and reducingmedia carijbelmadefcon-j sequently increasing the utility of the alloysYforYvaried industrial apparatus. The alloys of this linlllention also possess good mechanical strength, wear resistance, resistance to gall-ing, non-sparking qualitiesgg'ood machinability, good Weldability, and other desirable properties.

From the foregoing description of the inventionandd specic embodiments thereof, it is believed-apparent that the invention may be embodied in otherlspeciiic lforms l 1. A nickel base alloy containing about 19 to 26 percent chromium, 5 to 9 percent molybdenum, 4 to 7 percent copper, up to 10 percent iron, up to 1.5 percent manganese, up to 0.3 percent carbon, 1.5 to 7.5 percent silicon, 0.025 to 0.55 percent boron, andthe balance' substantially nickel characterized by high corrosion resistance and high hardness without brittleness.

2. A nickel base alloy consisting of 19 to 26 percent chromium, 5 to 9 percent molybdenum, 4 to 7 percent coppergup to 10 percent iron, up to 1.5 percent manganese, up to 0.3 percent carbon, 1.5 to 7.5 percent silicon, 0.025 to 0.55 percent boron, and the balancenickel eX- cept for residual elements and impurities -in a total amount less than 0.25 percent. Y

8 3. An alloy in percent by( weight consisting essentially of: r

K Y Y p VPercent Chromium n Y 1910 Y26 Molybdenum 5 t0 9 4 to 7 Y Y Iron Up to 10\ Manganese Y Y Y YYUp t0 1.5 Carbon Upto 0.3V Silicon Y Y1.5 to 7.5 Boron 0.025 to 0.55 Nickel Y Balance 4. An alloy in percent by w ight consistingessentially of:

- Y Y Y Percent Chromiumui. .l. v21.to23 Molybdenum Y 5 t0 8 Copper 4 to 7V Y Iron Y Y Up to 8 Manganese 1 to 1.5 Carbon 0.18 to 0.22. Silicon 4.5 to 6.5 Boron 0.025 to 0.20 Nickel Balance f 5. An alloy in percent by weight consisting essentially o Percent Chromium 22.5 Molybdenum 6.4 Copper 6.5 Iron Up to 8 Manganese 1.25 Silicon ,Y 5 Boron 0.05

Nickel Balance References Cited in the le of this patent UNITED STATES PATENTS Jackson et al. May 20, 1952

Claims (1)

1. A NICKEL BASE ALLOY CONTAINING ABOUT 19 TO 26 PERCENT CHROMIUM, 5 TO 9 PERCENT MOLYBDENUM, 4 TO 7 PERCENT COPPER, UP TO 10 PERCENT IRON, UP TO 1.5 PERCENT MANGANESE, UP TO 0.3 PERCENT CARBON, 1.5 TO 7.5 PERCENT SILICON, 0.025 TO 0.55 PERCENT BORON, AND THE BALANCE SUBSTANTIALLY NICKEL CHARACTERIZED BY HIGH CORROSION RESISTANCE AND HIGH HARDNESS WITHOUT BRITTLENESS.

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