US3892541A - Highly castable, weldable, oxidation resistant alloys - Google Patents

Abstract

Special highly castable and weldable heat resistant alloys containing nickel, manganese, silicon, chromium, carbon, iron, boron and molybdenum afford high temperature oxidation resistance and characteristics which render the alloys particularly suitable for the casting of thin section components for use at elevated temperatures under oxidizing conditions.

Description

" United States Patent Forbes Jones et a].

[4 1 July 1, 1975 HIGHLY CASTABLE, WELDABLE,

OXIDATION RESISTANT ALLOYS Inventors: Robin Mackay Forbes Jones,

Suffern, N.Y.; Walter Adrian Petersen, Ridgewood, NJ.

- Assignee: The International Nickel Co., Inc.,

New York, NY.

Filed: Dec. 13, 1974 Appl. No.: 532,330

Related U.S. Application Data Continuation-impart of Ser. No. 384,799, Aug. 2, 1973, abandoned.

U.S. Cl. 29/l96.1; 75/122; 75/128 A; 75/128 C; 75/128 F; 75/128 W;

Int. CL? B23? 3/00; C22C 19/05; C22C 38/44; C22C 38/54 Field of Search 75/134 F, 122, 171, 128 A, 75/128 C, 128 R128 W; 29/l96.1

[56] References Cited UNITED STATES PATENTS 2,938,786 5/1960 Johnson 75/171 3,758,296 9/1973 Johnson 75/122 Primary Examiner-L. Dewayne Rutledge Assistant ExaminerArthur J. Steiner Attorney, Agent, or FirmEwan C. MacQueen; Raymond J. Kenny [5 7 ABSTRACT 11 Claims, No Drawings HIGHLY CASTABLE, WELDABLE, OXIDATION RESISTANT ALLOYS The present invention is a continuation-in-part of application Ser. No. 384,799 filed Aug. 2, 1973, now abandoned, and relates to heat-resistant alloys having excellent castability and weldability and high temperature oxidation resistance.

It is well known that many industrial processes and applications require heat resistant components of intricate design. To produce such components, the alloy should be highly castable; however, to be commercially useful in respect of any number of applications, the alloy must also be capable of offering good weldability characteristics to permit, for example, fabrication of the components into larger, more complex units and, more importantly, for the joining of the components to other parts of an assembly.

One application requiring alloys having both high castability and weldability is static components in vehicular turbines, e.g., shrouds and the dome and plenum chambers. These components are commonly manufactured by special casting techniques and/or sheet fabrication, extremely expensive procedures adding greatly to cost. In this connection and desirably, such components should be capable of being cast in conventional sand molds, and, in particular, in thin section sand molds. And, more importantly, the component should be weldable since this allows the component to be assembled to the other parts of the vehicular turbine. Additionally, welding also allows for the fabrication of several small components into one large unit and for repairing of casting defects or even service damage.

But bringing these two properties, castability and weldability, together in one heat-resistant alloy, particularly of the nickel-base type, is beset with difficulty since one property is often achieved at the expense of the other. To explain, weldable heat resistant alloys and, in particular, heat-resistant nickel alloys containing high amounts of chromium, are known to have relatively poor casting properties, forming folds, cold shuts and misruns, especially when cast into thin sections. Attempts to improve casting properties have invariably led to a decrease in weldability. However, improved castability properties have been recently achieved through the judicious use of both silicon and boron in at least nickel-containing stainless steels. However, weldability was such that brazing was recommended. Now, as is well known in the art, silicon and boron are considered to be among the most detrimental performers in terms of weldability considerations with regard to high nickel, chromium-containing alloys. Notwithstanding this and as will be demonstrated herein, these constituents, we have found, can be used to their advantage but while simultaneously achieving outstanding weldability.

We have now discovered a new alloy providing a new combination of characteristics, especially excellent castability and weldability, notwithstanding the pres ence of relatively high amounts of the normally weldcracking promoters, silicon and boron, and this has been accomplished while obtaining good oxidation resistance and other properties at high temperature.

It is an object of the invention to provide an alloy having a combination of characteristics including excellent castability and weldability and resistance to oxidation at high temperatures.

Another object of the invention is to provide oxidation-resistant cast alloy products and articles, including products and articles for use as static components in vehicular turbines.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention is directed to an alloy containing (by weight) up to about 1.4 percent carbon, up to about 8.5 percent molybdenum, the carbon and molybdenum being specially correlated as detailed herein, from about 1.5 to about 4 percent silicon, up to about 4.5 percent manganese, from about 16 to about 30 percent chromium, up to about 50 percent iron, from about 0.1 to about 1 percent boron, and the balance essentially nickel, in an amount preferably at least about 35 percent, the nickel being further correlated such that for molybdenumfree alloys or those containing less than about 2 percent molybdenum, the nickel content should be maintained below about 49 percent and preferably less than about 45 percent. As will be understood by those skilled in the art, the use of the expression balance essentially in referring to the nickel content of the alloys does not exclude the presence of other elements commonly present as incidental constituents and impurities.

Carbon has been found to contribute to the elevated temperature strength of the alloy and molybdenum to contribute to the stress-rupture strength and ductility of the alloy; however, both elements have a detrimental effect on weldability. In order to weld the alloy, carbon and molybdenum must be correlated according to the following relationship:

wherein %Mo and %C are in terms of weight percent. Alloys with a calculated carbon and molybdenum level above about 8.5 exhibit heat-affected-zone cracking and cannot be welded. Alloys which exhibit heataffected-zone cracking may be weldable under certain conditions, e.g., thin, unrestrained sections, special welding techniques, etc., but are not considered to be within the purview of this invention. Alloys in accordance with the foregoing relationship, however, are weldable and, as will be appreciated by those skilled in the art, alloys exhibiting only weld cracking may be welded using special filler wires. It is preferred, however, that matching filler wires be employed. It has been found that molybdenum and carbon correlated according to the following relationship:

will result in alloys having these preferred welding characteristics. In striving for an optimum combination of properties, e.g., stress-rupture strength, weldability, etc., it is preferred that molybdenum in accordance with the foregoing relationships be present in the alloy in amounts of at least about 3 percent, and advantageously, about 6 percent.

Silicon and boron are essential for their beneficial effect on castability. Silicon and boron reduce the melting point of the alloy improving fluidity and also alter the chemical composition of the oxide film on the surface of the molten metal minimizing the formation of casting defects such as folds. Silicon and boron also contribute to the oxidation resistance of the alloy.

3 However, the exact mechanism which will explain the theoretical considerations as to why the alloy is weldable, given the high levels of silicon and boron, is not presently at hand.

While alloys containing silicon above about 1 percent may be welded, the castability of the alloy requires that the level of silicon be at least about 1.5 percent and preferably 2 to 2.5 percent. Alloys with silicon levels above about 4 percent are extremely brittle and an upper limit of about 3.5 percent is preferred.

The level of boron in the alloy is dependent on the carbon and molybdenum content. For alloys without molybdenum, boron levels below about 0.1 percent and above about 0.5 percent are deemed to have a detrimental effect on weldability. An upper level of about 0.4 percent is preferred. Alloys containing molybdenum and which have carbon levels below about 0.05 percent, are weldable at boron levels from about 0.] to about 1 percent and greater. It is expected though that at the higher boron levels, the ductility of the alloy would be unsatisfactory and an upper level of about 0.5 percent boron is considered more useful. For castability however, it is preferred that the alloys contain boron in an amount of at least 0.2 percent and, advantageously, about 0.3 percent.

Nickel contributes tothe elevated temperature oxidation resistance of the alloy and suppresses the embrittling sigma-forming tendencies of silicon, manganese and chromium. While the nickel content might be extended down to say, 20 percent, given the chemistry of the other constituents, such alloys tend to be brittle in the as-cast condition and also exhibit severe cracking in the weld heat-affected-zone. In any case it is most preferred that the nickel level not fall below 30 percent and it is of marked benefit that the nickel be about 35 percent or more. The upper limit for nickel is dependent on its effect on weldability and for molybdenumfree alloys or those containing less than about 2 percent molybdenum, the nickel content should be maintained below about 49 percent and preferably less than about 45 percent. Alloys containing molybdenum above this level, however, may contain nickel in amounts up to about 65 percent, but preferably, about 55 percent.

Chromium is essential in the alloy for oxidation resistance and should be maintained at levels of at least about 16 percent and preferably from about 19 to about 24 percent. Also, at the lower limit for chromium, weldability was found to be detrimentally affected in that the weldment was susceptible to weld and heat-'affected-zone cracking. Chromium may be present in amounts up to about 30 percent. At levels above about 30 percent, it is suspected that a deleterious intermetallic compound, sigma phase, would form, thereby embrittling the alloy.

Iron in amounts up to about 50 percent, but most advantageously at least percent, e.g., percent, can be incorporated in the alloy without materially affecting the properties. Alloys containing less than about 10 percent iron in the thicker sections, e.g., one-half inch or more, tend to be susceptible to heat-affected-zone cracking during the welding operation. This range of iron contents also enables use of less expensive raw materials, e.g., ferrochrome insteaad of electrolytic chromium, thereby resulting in a significant cost savings.

Manganese contributes to castability and also counteracts the detrimental effect of sulfur. Manganese above about 4.5 percent has a detrimental effect on weldability however, and a level from about 0.2 to about 0.8 percent for alloys containing molybdenum and from about 0.5 to about 3 percent for alloys without molybdenum is preferred.

Solid solution strengtheners such as 'columbiummay also be incorporated in the alloy to improve elevated temperature properties; columbium at levels up to about 2.2 percent has been found to produce beneficial effects in this regard. Columbium, however, appears to have a detrimental effect on the ductility and any benefit to strength must be offset by the decrease in the duetility of the alloy. Aluminum or other suitable deoxidation elements may be added to the alloy; it is expected though that the castability of the alloy would deteriorate if the aluminum content exceeded about 0.5 percent. Consistent with good steelmaking practice, other additives, such as desulfurizing agents and the like, may also be added to the melt. The phosphorus and sulfur levels may have an influence on hot-tearing resistance and weldability and should be maintained at levels less than about 0.04 percent. However, copper adversely affects weldability. It is an unnecessary constituent but if present should be less than about 2 percent and preferably should not exceed 1 percent.

In accordance with the invention, preferred alloys contemplated herein contain (by weight) from about 0.005 to about 0.04 or 0.05 percent carbon, from about 5 to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about 19 to about 24 percent chromium, up to about 30 percent and particularly from 10 or 15 to 30 percent, iron, from about 0.1 to about 0.5 percent boron, and the balance essentially nickel.

Other preferred alloys in accordance with the invention contemplated herein contain (by weight) from about 0.8 to about 1.2 percent carbon, from about 2.5 to about 3.5 percent silicon, from about 0.5 to about 3.0 percent manganese, from about 19 to about 23 percent chromium, from about 30 to about 47 percent iron, from about 0.2 to about 0.4 percent boron, and the balance essentially nickel.

For the purpose of giving those skilled in the art a better understanding of the invention, the following examples are given:

EXAMPLE I Table I sets forth the compositions of Alloys 1 through 16 which are examples of alloys within the invention and Alloys A through E which are outside the invention. The series of alloys was air-induction melted using a magnesia crucible. Electrolytic nickel, electrolytic manganese and Armco iron were charged into the furnace and heated to 2,850F. Molybdenum pellets were then added followed by silicon-manganese (18 percent silicon, 62 percent manganese, balance iron), electrolytic chromium (Alloy No. l was prepared using ferro-chromium containing about percent chromium), boron in the form of ferro-boron or nickelboron (23 percent and 18 percent boron, respectively), electrolytic manganese and metallic silicon. Columbium, in the form of columbium pellets was also added to Alloy No. 5. The melts were then deoxidized with 0.1 percent aluminum and poured at 2,650F. into green sand Chinese Puzzle pattern molds and green sand single keel block rectangular plate molds having the dimensions: (1) inch X l% inches X 12 /2 inches,

(2) A: inch X 2 inches X 12 inches and (3) 1 inch X 3 inches X 12 inches. The castings were then shaken from the molds, sandblasted and examined visually for defects, such as folds.

It should be noted that the Chinese Puzzle pattern molds are designed to test castability characteristics such as the ability of a molten metal to run through the passages of a complex mold with abrupt changes in flow direction that are conducive to turbulence, and comprise a number of partially adjoining rectangular cavities of about three-sixteenths inch thickness. The Chinese Puzzle pattern demands more of a melt than simply the capability to remain fluid over the course of a long run, such as in a fluidity spiral, but requires many TABLE I as evidenced by the Chinese Puzzle castings which were filled completely without evidence of folds or cold-shuts. In contrast, Alloy B, whichis similar in composition to a well known commercial alloy, had unsatisfactory castability under the same conditions in that numerous folds and poor definition at the corners resulted.

Test specimens of Alloys 1, 2, 5 and B were machined from the castings (Mold Nos. 1 and 2) and tested at room and elevated temperatures for mechanical properties using a standard testing procedures. As can be seen from the results shown here'inbelow in Table 11, the alloys of the invention exhibit satisfactory tensile properties in both the as-cast and heat treated Compositions of Cast Alloys, Weight Percent Alloy C Si Mn Ni Cr Mo Fe B Al Other No. 7: 7r 7: 72 7r 7: 7r 7r 7:

1 0.040 3.5 0.5 Bal. 23.9 6.0 30.15 0.35 087 2 0.014 3.1 0.27 Bal. 23.9 6.1 19.3 0.30 0.09 3 0.017 3.2 0.27 Bal. 24.1 6.0 19.3 0.32 0.11 4 0.55 2.8 0.57 Bal. 20.3 3.0 19.0 0.31 5 0.02 2.05 N.A. Bal. 20.8 7.9 0.089 0.27 0.080 2.2 Cb 6 0.017 2.6 0.53 Bal. 21.9 3.0 19.0 0.31 7 0.010 2.8 0.57 Bal. 21.9 1.0 19.0 0.31 8 0.015 2.9 1.85 Bal. 20.9 6.2 19.9 0.30 9 0.011 2.9 4.3 Bal. 20.7 6.3 19.6 0.30 10 0.028 2.9 0.6 Bal. 21.2 6.2 19.9 0.90 11 0.024 2.8 0.23 Bal. 20.5 6.3 18.5 0.18 Cu 12 0.022 3.2 0.25 Bal. 21.9 6.3 18.5 0.38 0.12 13 0.017 3.2 0.22 Bal. 21.0 6.0 15.0 0.25 0.085 14 0.010 3.2 0.26 Bal. 22.6 6.0 18.9 0.31 0.11 15 0.015 3.1 0.22 Bal. 20.5 6.0 5.2 0.28 0.060 16 0.019 3.2 0.22 Bal. 20.5 6.0 9.2 0.35 0 070 A 0.55 3.0 0.48 Bal. 20.0 7.0 19.0 0.31 B 0.005 1.2 0.29 Bal. 22.9 9.2 18.9 N.A. 0.09 C 0.013 2.8 0.23 Bal. 20.5 6.3 18.4 0.20 0.10 1.9 Cu D 0.011 3.3 0.23 Bal. 20.5 6.1 19.0 0.38 0.073 3.9 Cu E 0015 3.3 0.23 Bal. 20.5 6.1 19.4 0.40 0.077 5.9 Cu

N.A. No! Added.

sharp changes in flow direction with the flow meeting and merging with itself, filling of many corners and flow through and filling of large thin flat surfaces, e.g., l /2 inches square by 3/16 inch thick.

The alloys of the invention had excellent castability TABLE II Tensile Properties of Cast Alloys Alloy Mold Test Yield Tensile No. Condition No. Temp., Strength Strength Elong, R.A.,

F. psi psi 7: 71

1 As Cast 2 37,400 77,100 18.0 26.0

1 hr. at 2200F.,AC 2 As Cast 2 70 39,800 85,800 15.0 17.0 39.800 78,800 11.0 14.0 2 As Cast 2 70 38,300 83,500 16.6 22.0 40,200 83,900 16.5 13.0 5 As Cast 2 70 46,900 72,700 4.0 7.0 46,300 75,000 5.0 5.5 5 As Cast 2 70 44,100 85,000 10.0 13.0

1 hr. at 44.900 92,600 15.0 17.5 I 2200F.,AC 5 As Cast 2 1200 32,100 70,900 13.0 12.0 5 As Cast 2 1400 31,600 67,600 19.0 15.0 5 As Cast 2 1600 29,900 64,600 30.0 37.5 B As Cast 2 70 35,300 72,500 38.0 39.0 36,000 74,700 40.0 34.5 B As Cast 2 70 36,300 68,900 32.5 35.0 38.300 80.600 45.5 51.0

AC Air Cooled R.A. Reduction of Area The oxidation resistance of the alloys were compared with commercial alloys by cyclically testing specimens in an airpercent water atmosphere at l, 000F., using a 24 hour cycle period. The airwater mixture was flowing at 250 cc/min. over the specimens. which were machined from the castings to a size of 0.3 inch diameter X 0.75 inch long. At the end of each test period, the specimens were removed to cool in air. The specimens were then lightly desealed to remove the oxide formed and the weight change of the specimens was measured. Desealing of all the test specimens was done with an S. S. Whiteprecision abrasive cleaning unit using 50 micron alumi na propelled by dry CO A total of 500 hours exposure was employed. The 500 hour exposure weight change results shown hereinbelow in Table 111 evidence the excellent oxidation resistance of the alloys of the invention as compared with commercial composition Alloy B and commercially'obtained alloys Type 310 stainless Steel and HK-40.

TABLE 111 Results of Oxidation Tests To test the weldability of the alloys of the invention, comparative tests were performed by using a Bead-on- Plate test, by welding /2 inch butt joints and by welding 1 inch butt joints. As is known, the Bead-on-Plate test is primarily a screening test, the butt-weld being an actual welded joint which shows the ability of the metal to be welded.

affected-zone cracking and Alloys D and E exhibited severe weld and heat-affected-zone cracking. Alloy A violates the above-described carbon-molybdenum relationship. Alloy 8 had very slight heat-affected-zone cracking in one test specimen but the other specimen showed none, indicating, as will be appreciated by those skilled in the art, a satisfactory base plate material. Alloys 6 and 7, which are below the required value of the carbon-molybdenum weldability relationship, exhibited severe weld cracking, indicating the need for a special filler metal, e.g., a filler made from Alloy 3. The same applies to Alloy 9, an alloy relatively high in manganese, i.e., 4.3 percent, and which exhibited severe weld cracking.

Alloys D and E which are outside of the invention and contained 3.9 and 5.9 percent copper, respectively, exhibited severe weld and heat-affected-zone cracking. This is in contrast to the freedom from weld and heat-affected-zone cracking in the bead-on-plate test exhibited by Alloy No. l l which contained 0.9 percent copper and by Alloy C which contained 1.9 percent copper.

With regard to butt-weld tests, restrained /2-in :h thick butt-welds were prepared in the various baseplate compositions as described in Table V by manual gas-tungsten arc welding. The base plate was prepared with a 60 V-bevel edge preparation, 3/32-inch root face and l/l6-inch root space. Direct-current-straightpolarity was used with an amperage between about l 80 and 220 and a voltage of about 16 volts. Argon shielding at a rate of about 25 cubic feet per hour and manual welding at a rate of approximately 2 to 2.5'inch/min. were employed. Approximately 8 to 10 passes were needed to fill these joints. After welding, /z-ineh wide transverse slices (containing base plate, heat-affectedzone and weld deposit approximately to about 75 percent weld deposit) were cut from the weldment. Approximately eight slices from each weld were ground, polished, etched with Lepitos reagent and examined for defects at 10X. The compositions of the tiller metals used are given hereinbelow in Table IV, and the baseplate and filler metal data in Table V.

TABLE IV Compositions of Filler Metals Filler Metal C Si Mn Ni Cr Mo Fe B Other (Alloy No.) 7! 1 7r 7! 72 7c 71 7: 71

I 0.007 0.32 0.26 Bal. 21.8 6.0 19.4 0.13 11 0.007 0.30 0.29 Bal. 22.6 6.0 19.1 0.29 111 0.031 0.28 0.22 Bal. 21.0 6.1 19.7 0.23 17 0.023 2.90 0.31 13211. 21.6 6.2 18.5 0 35 F* 0.05 0.40 0.3 61.0 21.5 9.0 4.0 Cb+Ta 3.6 G* 0.10 0.50 0.50 Bal. 22.0 9.0 18.5 W 06 "A Commercial Filler Metal The Bead-on-Plate tests were performed on the cast TABLE V pieces by grinding the surface and welding a single bead with an automatic gas tungsten arc welding ma- Vamch Butt 101MB chine using argon shielding, 250 amperes, l 1 volts, dirweld Alloy Finer Mam ect-current-stralght-polarity and a travel speed of 16 N0 N0. (Alloy No.) inches per minute. No filler metal was used in the as 4 D welded bead. The weld beads were examined for crack- 6 D ing under a microscope at 10X. Alloys 1 through 15 3 7 D (within the invention) exhibited no heat-affected-zone 2 cracking, whereas Alloy A exhibited severe heat- TABLE V-Continued /2-inch Butt .loints Weld Alloy Filler Mctal No. No. (Alloy N0.)

6 l l 7 2 G 8 2 F 9 l 1 ll 10 C II The /2-inch joint, No. 9 in Table V, in Alloy No. l 1 containing 0.9 percent copper made with the special composition filler No. II was found to be entirely free from weld and heat-affected cracking. However, a similar weld, No. 10, in the 1.9 percent copper Alloy C, showed heat-affected-zone cracking. These results, together with the results of the Bead-on-Plate tests, show that the alloys of this invention can tolerate a small copper addition such as that resulting from the use of copper-containing scrap in the preparation of the charge and that large additions of copper must be avoided in order to retain the desirable weldability characteristic.

All the other /z-inch welds were satisfactory and exhibited freedom from heat-affected-zone and weld cracking, except Alloys 2, 4 and 7 which had very slight weld cracking, less than about one crack per section. As will be appreciated by those skilled in the art, this amount of weld cracking is not considered detrimental and meets the requirements as set forth in Military Specification MIL-E-2l562B(SHlPS). The results also indicate the ability of the alloy to be welded with both matching and non-matching filler wires.

In order to further demonstrate the weldability of the alloys of this invention, butt-welds were prepared in 1- inch thick plates prepared from No. 3 rectangular plate mold castings having a single U-groove joint preparation. This preparation consisted of a bevel blended to a 3/32inch root face by a At-inch radius. Two plates with such edge preparation were separated by l/16- inch and clamped to a 3-inch thick cast iron platen for welding tests. Gas tungsten-arc welding was used manually at a travel speed of about 2 to about 2.5- inch/min., about l6 volts, about 180 to 200 amperes direct-current-straight-polarity and argon shielding at about cubic feet per hour. Also, gas metal-arc welding was used automatically at a travel speed of about 10 inches per minute, about 33 volts, about 300 amperes direct-current-reverse-polarity, with 0.062-inch diameter wire and argon shielding at about 40 cubic feet per hour. After welding, transverse slices were prepared and examined as previously described for the /2-inch welds.

The l-inch thick weld No. l l was prepared with the manual gas tungsten-arc process using filler wire of the same composition as the alloy of this invention, e.g., matching composition filler wire. This wire was prepared by casting A-inch dia. rods which were centerless ground to 5/32-inch dia., a suitable form for gas tungsten-arc welding. The joint required 17 passes for completion. A total of 13 polished and etched transverse faces were examined at 10X and found to be entirely free from weld and heataffected'zone cracking.

A similar l-inch thick gas tungsten-arc weld, No. 12 in Table VI, was prepared with a special composition wrought filler wire, identified as III, in base plate 13 containing 15.0 percent iron. This joint was completed in 21 passes and transverse slices were entirely free from weld and heat-affected-zone cracking.

A third l-inch thick weld, No. 13 in Table VI, was prepared with the special wrought filler composition, I, using the gas metal-arc welding process. This 8-pass weld in Alloy 14 was entirely free from weld and heat affected-zone cracking. It is generally known in the Welding Industry that the automatic gas metal-arc process provides conditions significantly more severe than those imposed by the manual gas tungsten-arc welding process and accordingly, further support is provided for the exceptional weldability of the alloy of this invention.

Weld Nos. 14 and 15 in Table V] were l-inch thick butt-joints in base alloys 15 and 16 which contained 5.2 percent and 9.2 percent iron, respectively. Both joints were completed in 21 passes using the manual gas tungsten-arc welding process. Microscopic examination of transverse slices, cut from these welds, showed the presence of cracks within the heat-affected zone of both. This behavior is distinctly different from the behavior shown previously for weld Nos. 1 l, 12 and 13 of this invention. As previously mentioned herein, alloy with less than about 10 percent iron tend to exhibit susceptibility to cracking in the heat-affected zone in thick sections. It is most beneficial that the alloys of this invention contain more than 10 percent iron to minimize susceptibility to heat-affected-zone cracking.

To test the stress-rupture properties of the alloys, the transverse slices from the butt welds described hereinabove were machined into test bars containing weld metal, heat-affected zone and base metal (approximately 50 percent to about percent weld deposit). The stress-rupture properties were then measured at l,600F. using standard testing procedures. The results shown hereinbelow in Table VII reflect the excellent stress-rupture properties of the alloys of the invention and show that sound welds are produced without degrading the base metal properties.

A comparison of welds 2 and 3 in Alloys 6 and 7 demonstrate the beneficial effect of molybdenum on the stress-rupture life of the alloy. Alloys 6 and 7 are comparable in composition except for the molybdenum contents which are 3 percent and 1 percent, respectively.

TABLE V11 TABLE VIII-Continued Stress-Rupture Properties of Welds Weld Base Filler No. Alloy Metal No. Alloy Stress Life Elong.. R.A.. Fracture No. psi hrs. 72 (1") '71 Location 4 3 3 10.000 23.1 30.0 52.5 Base 8.000 139.9 20.0 51.7 Base 6,000 496.6 7.0 2.5 Weld 5 3 11 8.000 56.5 26.0 54.3 Base 6.000 692.5 24.0 53.0 Base 10.000 21.0 26.0 61.5 Base 8 2 F 8.000 106.0 23.0 61.0 Base 6,000 378.3 29.0 52.8 Base 10.000 10.7 19.0 47.3 Base 1 4 D 8,000 66.2 18.0 25.5 Base 6,000 317.6 8.0 17.0 Base 10.000 52.1 12.0 29.0 Base 2 6 8.000 154.3 8.0 24.4 Base 6.000 456+ 3 7 D 8.000 17.6 21.0 37.8 Base 6.000 48.5 18.0 40.3 Base 10.000 13.6 21.0 58.6 Base 13 14 1 8.000 75.7 11.0 35.3 Base 6.000 835.7 11.0 19.0 Base EXAMPLE 11 Table V111 sets forth the compositions of Alloys 18 through 29, alloys within the invention, and Alloys H through R, alloys outside the invention, having been prepared and cast following the procedures described in Example I except that molybdenum was not added to the melts. Alloy 25 was not cast into molds 1, 2 and 3 but was cast into a similar mold (double keel) having the dimensions 1 inch X 1% inches X 7% inches (Mold No. 4). The alloys of the invention had excellent castability as evidenced by the Chinese Puzzle castings which were filled completely without evidence of folds or cold shuts. In contrast, a commercial composition HU Alloy having the nominal composition (in weight percent) 0.45 percent carbon, 1.6 percent manganese, 1.6 percent silicon, 20.7 percent chromium, 38.8 percent nickel, balance iron exhibited folds when poured at the same temperature and, when the pouring temperature was increased to eliminate the folds, other defects such as hot tears and solidification shrinkage appeared.

TABLE VIII Compositions of Cast Alloys. Weight Percent Alloy C Si Mn Ni Cr B Al Fe No. 7: 7: 7c 7( 7r 7: 7c 71 18 0.95 3.17 2.09 39.7 19.5 0.27 0.055 Bal. 19 0.97 2.8 2.15 39.7 21.5 0.34 0.040 Bal. 20 0.98 3.02 0.74 38.5 20.1 0.32 0.086 Bal. 21 0.9 2.76 2.28 40.5 20.0 0.13 0.01 8:11. 22 0.91 2.90 1.86 38.8 20.1 0.14 0.063 Ba]. 23 0.90 3.07 1.48 39.9 19.4 0.3 0.08 Ba]. 24 0.80 1.99 2.32 39.9 20.4 0.14 0.04 Ba]. 25 0.98 2.77 2.34 39.7 21.3 0.24 0.13 8:11. 26 1.03 2.90 1.90 41.9 18.6 0.29 0.11 Bal. 27 1.08 3.20 1.80 29.5 21.1 0.24 0.005 Bal. 28 1.01 3.10 1.39 38.5 19.6 0.28 0.12 Bal. 29 1.00 3.12 1.00 38.4 20.0 0.32 0.11 Bal. H 1.50 3.10 1.90 39.7 20.7 0.26 0.005 Bal. 1 1.08 3.00 4.60 39.7 20.6 0.27 0.005 B211. .1 0.97 2.97 2.36 40.4 20.5 0.53 0.10 Bal. K 1.05 2.90 2.00 49.0 19.8 0.26 0.005 Bal. L 1.10 2.90 1.90 38.8 15.7 0.24 0.005 Bal. M 1.09 0.93 1.80 39.8 20.6 0.27 0.039 Bal. N 1.12 3.20 1.80 19.9 21.1 0.26 0.005 B211. 0 0.87 2.90 1.80 39.1 19.7 N.A. 0.068 Bal.

Compositions 01 Cast Alloys. Weight Percent N.A.= Not Added I Test specimens of Alloys 18 and 20 were machined from the castings (Mold Nos. 1 and 2 described hereinabove in Example I) and tested at room and elevated temperatures for mechanical properties using standard testing procedures. Alloy 25 was welded with a matching composition filler wire as a /2-inch butt-weld by manual gas tungsten-arc welding as described hereinabove in Example I. Tensile specimens were machined from the transverse slices of the weldment and contained base plate, heat-affected-zone and weld deposit (about 50 to about percent weld deposit). For comparison purposes also shown hereinbelow in Table 1X are tensile values of commercial alloy (l-lU) obtained from the American Casting Institute Data Sheet for Heat Resistant Type HU, issued March 1957.

Failure outside of weld in base plate Commercial alloy HU Oxidation tests were also conducted in respect of versions of the molybdenum-free alloys of Table V111 as well as a few comparative alloys. The procedures were identical to those described hereinbelow. Specimens were either machined from the castings (as-cast) or from /z-inch butt-welds (as-welded). The as-welded specimens included the base-plate, heat-affected zone and weld deposit (approximately 50 to about 75 percent weld deposit). The results are given in Table X.

As can be seen from the data, the alloys of the invention exhibit excellent oxidation-resistance in both the as-cast and as-welded conditions as compared to commercial alloys. The relatively low oxidation-resistance of Alloy 24 can be attributed to the silicon content which is below the preferred range of the alloy, i.e., 2.5 percent. Alloy 0 demonstrates the effect of not including boron in the alloy as this alloy has a relatively low oxidation resistance.

TABLE x Results of Oxidation Tests Alloy No. Condition Dcscaled Weight Change mg/cm 18 As-Cast 5.95

19 As-Welded 7.04 24 As-Cast 18. 10 -25.72

26 AsWelded 8.42

27 As-Welded 6.50 2 8 As-Welded 5 .79 29 As-Welded 4.77 O As-Cast 18.38 1 8.28

P As-Cast 9.76 (l) Wrought and 5.21

Annealed (2) Wrought and 1 1.7

Annealed l commercially obtained Hustelloy X (2) commercially obtained Type 310 S.S.

To determine weldability behavior, the alloys in Table VIII were tested using the Bead-on-Plate test and several by welding a A a-inch butt-welded joint, as described hereinabove in Example I.

As to the Bead-on-Plate tests, none of the preferred alloys exhibited heat-affected-zone cracking. Alloys H through M, which are outside the invention, showed both severe heat-affected-zone and weld cracking and are thus unsatisfactory as base plate materials. Alloy did not exhibit any heat-affected-zone cracking but exhibited severe weld cracking. Alloys Q and R exhibited weld and heat-affected-zone cracking and this is attributable to a carbon content below the preferred level and a silicon content above the preferred level, respectively.

The /2-inch buttweld joints were made from Alloys 19, 22, and 23 and Alloy N with matching filler wires. None of the joints exhibited weld cracking; however, Alloy N, which is outside the invention, exhibited severe heat-affected-zone cracking. This may be attributed to the low nickel content of 19.9 percent.

To test the stress-rupture properties of the alloys of the invention, specimens of Alloys 19 and 23 were machined and tested (in the as-cast condition) at 1,600F. The results as shown hereinbelow in Table XI indicate the excellent stress-rupture properties of the cast alloy. The stress-rupture life of Alloy 19 at the 8,000 psi stress level is low probably due to a casting defect and should not be regarded as representative of the alloys stress-rupture property.

Transverse slices of a /2-inch butt-weld of Alloy 22 (prepared as described hereinabove) was also tested and, as can be seen from the results, exhibits excellent stress-rupture properties. The weld was prepared using the procedures described hereinabove and the filler wire, identified as I in Table IV, contained 21.8 percent chromium, 19.4 percent iron, 6.0 percent molybdenum, 0.13 percent boron and the balance essentially nickel.

TABLE XI Stress-Rupture Properties The alloys of the invention are especially useful in high temperature oxidizing atmosphere applications. They may be employed in many other applications, including high temperature applications where resistance to corrosion and good creep and rupture properties are required. The alloys are particularly useful as static components in vehicular turbines.

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. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim: v

1. A highly castable and weldable heat resistant alloy affording high temperature oxidation resistance consisting essentially of (by weight) up to about 1.4 percent carbon, less than 8.5 percent molybdenum, the carbon and molybdenum being specially correlated according to the following relationship:

from about 1.5 to about 4 percent silicon, up to about 4.5 percent manganese, from about 16 to about 30 percent chromium, up to about 50 percent iron, from about 0.1 to about 1 percent boron for alloys containing molybdenum and from about 0.1 to about 0.5 percent for alloys without molybdenum, and the balance, in an amount of at least about 35 percent, essentially nickel, the nickel being further correlated such that for alloys not containing molybdenum, the nickel content does not exceed about 49 percent.

2. An alloy in accordance with claim 1 wherein the carbon and molybdenum are correlated according to the following relationship:

3. An alloy in accordance with claim 1 containing from about 0.005 to about 0.05 percent carbon, from about 5 to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about 19 to about 24 percent chromium, up to about 30 percent iron and from about 0.1 to about 0.5 percent boron.

4. An alloy in accordance with claim 3 wherein the carbon and molybdenum are correlated according to the following relationship:

5. An alloy in accordance with claim 1 containing at least about 10 percent iron.

6. An alloy in accordance with claim 1 containing at least about 15 percent iron.

7. An alloy in accordance with claim 1 containing from about 0.005 to about 0.05 percent carbon. from about to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about 19 to about 24 percent chromium, from about to about 30 percent iron and from about 0.1 to about 0.5 percent boron.

8. An alloy in accordance with claim 1 containing from about 0.005 to about 0.05 percent carbon, from about 5 to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about l9 to about 24 percent chromium, from about to about 25 percent iron and from about 0.1 to about 0.5 percent boron.

9. An alloy in accordance with claim 1 containing from about 0.8 to about 1.2 percent carbon, from about 2.5 to about 3.5 percent silicon, from about 0.5 to about 3.0 percent manganese, from about 19 to about 23 percent chromium, from about 30 to about 47 percent iron, and from about 0.2 to about 0.4 percent boron.

10. An alloy in accordance with claim 9 containing less than about 45 percent iron.

11. As a new article of manufacture. a welded assembly of the alloy as set forth in claim 1, exhibiting freedom from cracking in sections of /2-inch and greater thicknesses.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,892,541

DATED July 1, 1975 INVENTOR(S) Robin Mackay Forbes Jones and Walter Adrian Petersen it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 8, for "to" read or line 63, for "insteaad" read instead Col. 5, last column of Table II (R.A. bottom line,

omit l5 O" Col. 12, last column of Table IX, for "R.A. Q 10" read Signed and Sealed this sixteenth Day Of September 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflarenrs and Trademarks

Claims (11)

1. A HIGHLY CASTABLE AND WELDABLE HEAT RESISTANT ALLOY AFFORDING HIGH TEMPERATURE OXIDATION RESISTANCE CONSISTING ESSENTIALLY OF (BY WEIGHT) UP TO ABOUT 1.4 PERCENT CARBON, LESS THAN 8.5 PERCENT MOLYBDENUM, THE CARBON AND MOLYBDENUM BEING SPECIALLY CORRELATED ACCORDING TO THE FOLLOWING RELATIONSHIP:

2. An alloy in accordance with claim 1 wherein the carbon and molybdenum are correlated according to the following relationship: 5.4 <%Mo + 6(%C) <8.5

3. An alloy in accordance with claim 1 containing from about 0.005 to about 0.05 percent carbon, from about 5 to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about 19 to about 24 percent chromium, up to about 30 percent iron and from about 0.1 to about 0.5 percent boron.

4. An alloy in accordance with claim 3 wherein the carbon and molybdenum are correlated according to the following relationship: 5.4 <%Mo + 6(%C) <8.5.

5. An alloy in accordance with claim 1 containing at least about 10 percent iron.

6. An alloy in accordance with claim 1 containing at least about 15 percent iron.

7. An alloy in accordance with claim 1 containing from about 0.005 to about 0.05 percent carbon, from about 5 to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about 19 to about 24 percent chromium, from about 10 to about 30 percent iron and from about 0.1 to about 0.5 percent boron.

8. An alloy in accordance with claim 1 containing from about 0.005 to about 0.05 percent carbon, from about 5 to about 8 percent molybdenum, from about 2 to about 4 percent silicon, from about 0.2 to about 0.8 percent manganese, from about 19 to about 24 percent chromium, from about 15 to about 25 percent iron and from about 0.1 to about 0.5 percent boron.

9. An alloy in accordance with claim 1 containing from about 0.8 to about 1.2 percent carbon, from about 2.5 to about 3.5 percent silicon, from about 0.5 to about 3.0 percent manganese, from about 19 to about 23 percent chromium, from about 30 to about 47 percent iron, and from about 0.2 to about 0.4 percent boron.

10. An alloy in accordance with claim 9 containing less than about 45 percent iron.

11. As a new article of manufacture, a welded assembly of the alloy as set forth in claim 1, exhibiting freedom from cracking in sections of 1/2 -inch and greater thicknesses.