US3008822A - Nickel-base alloys - Google Patents

Description

Un d Sta s a e- Q fiw Patented Nov. 14,, 1961 v 3,008,822 NICKEL-BASE ALLOYS Walter K. Boyd and Merritt E. Langston, Columbus, Ohio, and ThomasE. Johnson, Milwaukee, Wis; said Walter K..Boyd and Merritt E. Langston assignors to Battelle Memorial Institute, Columbus, Ohio, :1 corporation of Ohio; said Johnson assignor to Stainless Foundry & Engineering, Inc., Milwaukee, Wis., a corporation of Wisconsin I No Drawing. Filed July 30, 1959, Ser. No. 830,473

' r 2 Claims. (Cl. 75-171) 7 This invention relates to nickel-base alloys. More particularly, the invention relates to nickel-base alloys composed primarily of nickel, but including a substantial amount of chromium and smaller amounts of other elements. These alloys exhibit remarkable resistance to corrosion. g I

Nickel alloys have been, and are presently, used in the chemical processing industry for corrosion-resistant applications. In this industry, in handling chemicals and solutions of corrosive materials, such as acids, alkalis, and the like, particularly at elevated temperatures, it is highly desirable that equipment in contact with the corrosive environments be of a material possessing a high resistance to corrosion. For example, nickel alloys are used for equipment, such as pumps, impellers, shafts, cellophane hopper lips or blades, valves, pipes, bearings, pipe fitfingavessels, tanks, and the like in this industry. However, the nickel alloys presently employed in these applications have a limited range of practical utility. For example, nickel alloys suitable for use at either a low or a high concentration of acid ordinarily are not satisfactory at an intermediate concentration of acid. Likewise, nickel alloys suitable at low temperatures are not too satisfactory at high temperatures. 7 V g It is an object of the invention to provide new nickelbase alloys exhibiting a remarkable resistance to corrosion. It is a further object to-provide new nickel-base alloys exhibiting superior corrosion-resistant properties over a broadrange of temperature and concentration of corrosive media, which alloys are of great value to the chemical processing industry. It is still afurther object In accordance with theinvention, the nickelabase alloys consist essentially of 26 .to 30'pe'rcent chromium,

' included in the alloys.

7.5 to 9.0 percent molybdenum, 4 to 6.5 percent copper, and the balance -essentially nickel. Generally up to 1.6

percent manganese, up to 2.0 percent iron, up to 2.0

percent silicon, and up to 0.06 percent carbon, also are Titanium may be added to these nickel-base alloys and may be present in residual amounts up to a maximum of 0.25 percent. Small or residual amounts of other elements and/or concomitant impurities (i.e., sulfur, phosphorus, etc.) generallyfound in nickel alloys up to 0.15 percent also may be present. In the application and claims, unless expressly stated otherwise, all parts and percents are expressed as parts and percents by Weight.

The nickel-base alloys of the invention have constituent-s upon analysis (percent by weight) falling the following broad, preferred, and optimum ranges:

Table I Amount, percent'by weight The broad range of compositions in Table I sets forth the alloys providing improved corrosion resistance over broad ranges of temperature and corrosive material concentration for many corrosive materials. The preferred range of'compositions in Table I sets forth .the preferred alloys providing corrosion resistance superior to known alloys presently used in the chemical processing industry.

to provide alloys, composed primarily of nickel, but ineluding a substantial amount of chromium and smaller amounts of other elements, which alloys are characterized by exceptional corrosion resistance to concentrated acid at elevated temperatures. It is another object to provide alloys of the character described herein, which The optimum range of compositions in Table I sets forth the alloys providing optimum corrosion resistance to concentrated sulfuric acid at elevated temperatures.

The alloys of the invention may be prepared by present day melt procedures for nickel alloys. One method of preparation is as follows: An induction furnace is charged with a suitable grade of commercially pure nickel. Grades of nickel, such as nickel scrap, electrolytic nickel, powdered nickel briquettes, nickel powder, or nickel shot maybe used. After the furnace charged and the nickel brought to a molten state,the' molten nickel is preferably protected by a slag of any known type suitable for nickel alloys. Depending greatly on the particular grade of nickel being used and its carbon content, a carbon boil may be used to adjust the carbon temperatures where present nickel alloys find limited application because of the high corrosion-rates, of the prior art alloys. The nickel-base alloys of the invention also possess other desirable physical characteristics essential to their .being used inequipment for'the chemicalprocessing industry. V I

For their greatest utility, the nickel-base alloys of the invention usually are employed in the cast form. This cast form is capable of being readily machined and welded. Additionally, these nickel-base alloys possess a degree of hot and cold workability that permits at least a limited forgeability, rolling, swaging, and the like.

content of the alloy. Chromium and molybdenum in the required amounts are then added. When the mass is again molten, the requisite amount of copper is added. Preferably the constituents, which are added, are for practical purposes in at least a commercially pure state, to avoid introduction of unwanted constituents or too much of essential constituents. Preferably, to minimize chromium losses, a-si1itable conventional reducing agent is added to the slag. When the molten mass reaches a desired pouring temperature, generally a temperature between 2750 to 2950? F., at suitable scavenger ofthe desired type is added. The scavenger may contain mam ganese, silicon, and*titanium,iandis capable of elimi. nating oxides and gases, and reducing the sulfur level,

. while bringing the manganese, silicon, 'andtitanium to within the constituent amounts of the composition ranges of the alloys of the invention. Then the molten mass is quickly cast or poured into suitable forms or molds;

As specific-examples of alloys of the invention,v which have been prepared and which have been shown to provide the advantages of the invention, the following compositions by analysis are illustrative:

1 Less than 0.1% titanium, less than 0.005% sulfur, less than 0.005% phosphorus, with the balance essentially nickel.

To evaluate corrosion resistance of the nickel-base alloys, cast and machined samples of various alloys were immersed in aqueous solutions of various acid concentrations at several temperatures. These 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 under similar conditions in a one-year period. Data obtained are reported as the average of replicate samples for three 48-hour periods ofimmersion. Data are reported as corrosion rate in inches of penetration per year (I.P.Y.), a well-recognized manner of presenting and evaluating corrosion re- The alloys of the invention upon exposure to sulfuric acid concentrations of less than 65' percent 'and/or'tem peratures less than 90 C. exhibit lower corrosion rates (i.e. smaller losses in inches of penetration per year) than obtained at the higher acid concentrations and higher temperatures, illustrated inTable HI.

The alloys of the inventiongalso exhibit remarkable corrosion resistance to manyother corrosive media at both high and low concentrations and temperatures. For example, alloy No. A of Table II in 25% boiling'm'tric acid had a loss of 0.010 I.P.Y. (inches of penetration ,per year). A commercial nickel alloy, presently widely used in the chemical processing industry, for comparison purposes had a corrosion rate of 0.197 I.P.Y. in 25% boiling nitric acid. Equipment made from alloy compositionsof the invention has exhibited exceptional utility in corrosive media in the chemical processing industry. While the ultimate service life for equipment made of alloy compositions of the invention has not been completely determined, to date the service life of the alloy compositions of the invention has been found to be at least equal to and in most instances superior to commercially available nickel alloy compositions. With the alloy compositions of the invention there has beenobtained a service life of three to four or more times that obtained with many conventionally used nickel alloys. a

For comparison purposes, Table IV presents typical results of conventional nickel alloys .(alloysNo. 6.07 and N0. 593) subjected to the same corrosive media test to whichthe alloys of the invention were exposed. Table IV also presents a number of illustrative, experimental alloys having amounts of constituents falling outside the constituent ranges of them'ckl-base alloys of the invention with results of these corrosive media tests illustrating" that these alloys do not possess thesuperior corrosionre sistance .found in the alloys of the invention.

Table IV 2 Composition (percent) Loss inlnches of penetration per-year'(I.P.Y.)at 90C.

Alloy No.

' Sulfuric Acid Concentration Or Mo Cu Mn Fe S1 0 N1 22. 30 5. 6. 22' 1.25 0. 98 0. 92 0. 05 62.70 0. 063 0. 022 0. 01 2 22. 38 6.00 6. 56 '0. 99 6.39 '0. 99 0. 25 56. 85 0; 096' 0.051 0. 020 22. ,3. 80 i 6.18 1. 22 1. 45 0. 73 0. 05 balance 0.050 0.019 0. 012 22. 40 5. 00 '6. 20 l. 26 1. 26 0. 72 0. 03 balance '0. 033' 0. 018 0.012 21. 78 5. 45 6; 25 1. 22 1.70 1. 86 0. 05 balance. -0. 034 0. 013 0.008 22. M30 6. 20. 1. 20 1. 20 0.05 0.05 balance 0. 031 0. 016 0. 009 22. 20 12.10 4. 28 1. 28 1. 37 0.60 0. 05 58. 00 0.022 -0. 015' 0.008 22. 45 12. 10 6. 36 l. 30 1.45 0:56 0. 05 55. 0. 031' 0. 014- 0. 008 22. 63 12. 10 7. 24 1.29 1.48 0.03 0. 05 54. 46 0.022 0. 014' 0. 010 21. 50 13.50 6. 76 1. 15 1. 73 0.70 r 0. 05- 55. 50 '0. 029 05012 0.006

sistance of metals. A corrosion rate of 0.020 I.P.Y. generally is considered the maximum tolerable rate in industrial usage.

Table III represents results of some tests of alloys of this invention upon being exposed to corrosive sulfuric acid media:

Table III Loss in inches of enetratlon per year (I.P.Y.? at 90 C.

One of the outstanding advantages provided .bythe alloys of the: invention is a significant superiority at intermediate ranges of acid concentration at elevated temperatures over prior art alloys; A comparison of the corrosion rates of the .priorart alloys (No. .607 and No.

593) of Table IV with thecorrosion ratesof the alloys of the invention of Table III illustrates this advantage. For example, prior art alloys No. 607 and No. 593 (Table IV) had corrosion rates of 0.063 I.P.Y. and 0.096 I.P.Y., respectively, in a 65% sulfuric acid concentration at C. In comparison therewith, alloy A (Table III) of-the invention had a corrosion rate of 0.015v I.P.Y.at the same conditions or asuperior corrosion rate for the alloy of the invention of about one-fourth to one-sixth that for conventionally employed prior art alloys.

From test data of the natureas reported in Table IV for experimental alloys it has been found that chromium contents-of less than 26% generally provide corrosion rates inferiorto those exhibited by the: alloys of the invention whether the molybdenum contents are vabove or below or within the contents specified for the alloys of the invention. Nickel alloys having chromium contents larger than 30% are more diflicult to machine and weld than the alloys of the invention. These higher chromium alloys also are more expensive. Any slight benefit in corrosion rates that may be realized from chromium contents in excess of 30% does not offset the increased cost and other resultant disadvantages. Generally it has been found that the chromium content may range from 26 to 30% with advantages and improvements of the invention being obtainable. Within this broad range of chromium, a preferred range of 27.5 to 30% of chromium generally provides a corrosion resistance superior to known alloys at one or more acid concentrations, and an optimum range of 28.5 to 29.5% chromium provides the optimum corrosion resistance to concentrated sulfuric acid at elevated temperatures. It also has been found in nickel-base alloys of a standard chromium content that increasing the molybdenum content generally results in an improvement in corrosion properties. In the alloys of the invention these corrosion resisting benefits are at a maximum over a molybdenum content broad range of 7.5 to 9.0%. Molybdenum contents above and below this broad range provide no appreciable improvement in corrosion resistance. Within this broad range of 7.5 to 9.0% molybdenum; a preferred and superior corrosion resistance is obtained from 8.5 to 9.0% molybdenum, with this range of molybdenum also providing the optimum corrosion resistance to concentrated sulfuric acid at elevated temperatures.

Similarly in nickel-base alloys of a standard chromium content it has been found that the copper level may vary from 4 to 6.5% with the improved corrosion benefits of the invention being obtainable. Copper levels above and below this broad range of 4 to 6.5% generally show little or no improvement in corrosion resistance over known alloys. Somewhat narrower ranges of 5 to 6% and 5.25 to 5.75% of copper have been found to provide preferred and optimum benefits respectively. In addition to the principal elements of nickel, chromium, molybdenum, and copper, the alloys of the invention may comprise other elements in limited amounts. Some carbon, iron, silicon and other concomitant impurities (i.e. sulfur, phosphorus, etc.) are residual elements and generally unavoidable, out are kept as low as economically practical within good melting practice and should be within the ranges set forth in Table I if results of the invention are to be obtained. Generally, the lower the level of such elements in the alloys the better the corrosion resistance, with larger amounts being deleterious and not desirable to impart a beneficial corrosion resistance. Theinclusion in the alloys of manganese and titanium within the limited amounts specified in Table 1 has been found to be desirable from a metallurgical standpoint.

From the foregoing description and specific embodiments thereof, it is believed apparent that the invention may be embodied in other specific forms without departing from the true spirit, scope, and essential characteristics of the invention. Hence, in the present invention it is intended to be limited only to the extent as set forth in the appended claims and it is intended to embrace within these claims all modifications and variations as fall within the meaning and purview and range of equivalency of these claims.

What is claimed is: I

1. An alloy characterized by exceptional corrosion resistance to high concentration of acid at elevated temperatures, the alloy in percent by weight consisting essentially of:

Chromium 27.5-30 Molybdenum 8.5-9.0 Copper 5-6 Manganese 1.01.5 Iron Up to 1.5 Silicon 0.5-1.0 Carbon 0.04 up to 0.06 Titanium Up to 0.25 Nickel Balance 2. An alloy characterized by exceptional corrosion resistance to high concentration of sulfuric acid at elevated temperatures, the alloy in percent by weight consisting essentially of:

References Citedin the file of this patent UNITED STATES PATENTS Parr Oct. 27, 1914 Jackson et al. May 20, 1952

Claims (1)

1. AN ALLOY CHARACTERIZED BY EXCEPTIONAL CORROSION RESISTANCE TO HIGH CONCENTRATION OF ACID AT ELEVATED TEMPERATURES, THE ALLOY IN PERCENT BY WEIGHT CONSISTING ESSENTIALLY OF: