US2713538A - Nickel cobalt chromium alloy - Google Patents

Description

July 19, 1955 G. T. HARRIS ETAL 2,713,538

NICKEL COBALT CHROMIUM ALLOY Filed Jan. 24, 1951 5 Sheets-Sheet l IO I2 I4 CARBIDE-FORMING ELEMENTS: PER CENT l EFFECT OF COMPOSITION 0N RUPTURE TIME OF COBALT BASE ALLOYS WITH VrM02Nb= I:|:I- TEST CONDITIONS STRESS I4 TONS/SQ. IN. AT 750 C.

F l G.

9 'n d 'f c. T o O o o o N39 aad Noauvo INVENTORS- GEOFFREY THOMAS HARRIS GHENRY CAVE CHILD MWL/#Mimi ATTORNEYS.

July 19, 1955 G. Tr HARRIS ET AL 2,713,538

NICKEL COBALT CHROMIUM ALLOY Filed Jan. 24, i951 3 Sheets-Sheet 2 EFFECT OF COMPOSITION ON CREEP PROPERTIES FOR COBALT- -BASE-ALLOYS WITH V=Mo=Nb=ll=l AND O25/o CARBON CONTENT.

TIME HOURS 2 4 6 8 IO I2 CARBIDE FORMING ELEMENTS (V+ Mo+ Nb)=PER.CENT.

INVENToRs.

GEoFFREY THoMAs HARRIS F IG. 2. a HENRY cAvE cHlLD bM/L/a/AJ/d/Lu/Z ATTORNEYS.

July 19, 1955 G. T. HARRIS ET AL 2,713,538

I NICKEL COBALT CHROMIUM ALLOY Filed Jan. 24, 1951 3 Sheets-Sheet 5 EFFECT oF coMPoslTloN oN THE RUPTURE TIME Fon coBALT BAsE ALLoYs wlTH v+M+Nb=6% AND @25% cARBoN TEsT coNo|cT|oNs= |4ToNs/so-m. AT 750 c.

Mo# PER CENT 347 TIME (HOURS) T0 RUPTURE |00 u u u IN V EN TORS.

GEOFFREY THOMAS HARRIS a HENRY CAVE CHILD ATTORNEYS.

United States Patent() NICKEL COBALT `CHROMIUM ALLOY Geoffrey Thomas Harris and Henry Cave Child, Shellield, England, assignors to William Jessop & Sons Limited, Sheiield, England, a British company Application January 24, 1951, Serial No. 207,551 2 Claims. (Cl. 7.5--171) This invention is concerned with alloys which have a high degree of resistance to creep at elevated temperatures, and this application is a continuation-impart of our co-pending application Serial No. 9,325, led the 18th of February 1948, now abandoned.

Alloys having as essential constituents carbon, co-

balt, nickel, chromium, carbide-forming elements such as niobium, molybdenum and vanadium, deoxidizing agents such as manganese and silicon, and the remainder iron, are known to possess desirable properties such as, for example, their resistance to creep, when operated under stress at high temperatures.

As a result of experimental research upon alloys having these essential constituents, we have found that such properties are markedly superior when the ratio of carbide-forming elements to carbon in the alloys is carefully balanced and when the optimum ratio of one carbide-forming element to another is used.

Initially our experiments were directed to alloys having cobalt, nickel and iron in the ratio 40:15 :15, with 19% by weight of chromium and the usual small amounts of the deoxidizers manganese and silicon, e. g. 0.8% and 0.3% respectively. The carbon content and the carbide-forming content were varied (the carbide-forming elements vanadium, molybdenum and niobium being used and being in the ratio lzlzl), the carbon content extending upwardly from 0.05% and the carbid'e forming content extending upwardly from 2.7%. Each such alloy was normalized from 1280z C. and the time taken to rupture for each alloy under a stress of 14 tons per square inch at 750 C. was determined.

The results obtained are shown graphically in Figure l ofthe accompanying drawings. It will be seen from this figure that for such alloys the time to rupture under a stress of 14 tons per square inch is dependent on the ratio of carbon to carbide forming elements. For each carbon content there is an optimum content of the carbide forming elements, e. g. at 0.25% carbon there should be a total of 6% of the carbide forming elements. This optimum content of the carbide forming elements varies directly as the carbon content and there is a substantial increase in the fracture time of the optimum alloy as the carbon content is raised.

The next experiments were carried out on similar alloys under similar conditions, but the carbon content was maintained fixed at 0.25%, and the carbide-forming content was varied between about 3.2% and 12%. ln each case the carbide-forming elements vanadium, molybdenum and niobium again were in the ratio l:1:l.

Figure 2 shows the eilect of Varying the carbide-forming content of the alloys upon the creep properties of the alloys, the curves showing the time for 1% creep strain, the time for 1.5% creep strain and the time to fracture. It will be seen from these curves that better creep properties are obtained when the carbide-forming elements are present in an amount between about 5.4% and about 7.5%. l

Further tests under similar conditions were carried 2,713,538 Patented July 19, 1955 ICC out on alloys having 0.25% of carbon and 6% of carbideforming elements, the ratio of one carbide-forming element to another being varied. Figure 3 shows the elect of the varying of the proportions of the individual carbide-forming elements on the rupture time of the alloys, and from the curves obtained it will be seen that, for optimum results:

(a) Vanadium rnust be present in an amount between substantially 1% and substantially 5%;

(b) Molybdenum must be present in an amount between substantially 0.5% and substantially 3%; and

(c) Niobium may be absent but, if present, must not exceed 3%.

Subsequent investigations showed that these relationships generally remain true under different test condi tions of temperature and stress.

Bearing in mind these relationships between the carbide-forming elements themselves and between the percentage of carbon and carbide-forming elements, a larger number of alloys having the same constituents but with the individual contents varied over a narrow range were investigated and we have found that optimum properties are obtained with an alloy which has the following constituents:

Per cent Carbon 0.3 Silicon 0.3 Manganese 0.8 Nickel l2 Chromium 19 Molybdenum 2 Niobium 1.2 Vanadium 2.8 Cobalt 45 Iron (with unavoidable impurities) 16.6

An alloy of this composition was solution treated at l280 C. for l5 minutes followed by quenching in oil.l 'After this treatment bars were aged at a temperature of 750 C. for 46 hours and a typical test gave the following results. Under a stress of 14 tons per square inch at a temperature of 750 C., 1% creep extension was reached in 1340 hours and rupture occurred in 1636 hours, the minimum creep rate being 4.7)(10-6 per hour and the iinal elongation being 4%.

Generally these properties were substantially retained not only by alloys falling within the shaded areas of Figures l and 3, but also by alloys having their essential constituents within the narrow range:

Per cent Carbon 0.25-0.35

Silicon 0.2-0.6

Manganese 0.6-1 Nickel 10-15 Chromium 18-20 Molybdenum 1.8-2.3

Niobium ll.4

Vanadium 2.63.l Cobalt 42-46 Iron (with unavoidable impurities) Remainder It will be appreciated that molybdenum may be replaced wholly, or in part, by tungsten and that niobium is intended not only to mean niobium alone but also to mean niobium in combination with tantalum, the tantalum either being added intentionally or occurring as an impurity, since niobium is rarely, if ever, obtained on a commercial scale free from tantalum. Where niobium is combined with tantalum it is desirable for the proportion of niobium to be at least 0.5

What is claimed is:

l. An alloy consisting of the following elements in about the proportions specified:

Per cent Carbon 0.3 Silicon 0.3 Manganese 0.8 Nickel l2 Chromium 19 Molybdenum 2 Niobiurn with tantalum 1.2 Vanadium 2.8

Cobalt 45 Iron (with unavoidable impurities) 16.6

2. Alloys consisting of the following elements: carbon not exceeding about 0.35%; small amounts of silicon and manganese within about the ranges silicon 0.2 to 0.6% and manganese 0.6 to 1.0%; nickel 10 to 15%; chromium 18 to 20%; and the following three carbideforming elements, namely, molybdenum, niobium and vanadium; cobalt 42 to 46%; and the remainder iron with unavoidable impurities: the combined percentages of the said carbide-forming elements being between i about 5.4% and 7.5%; the individual percentages of the References Cited in the file of this patent UNITED STATES PATENTS 2,246,078 Rohn et al. June 17, 1941 2,513,470 Franks et al. July 4, 1950 2,537,477 Mohling et al. Jan. 9, 1951 FOREIGN PATENTS 510,154 Great Britain July 24, 1939

Claims (1)

1. 2. ALLOYS CONSISTING OF THE FOLLOWING ELEMENT: CARBON NOT EXCEEDING ABOUT 0.35%; SMALL AMOUNTS OF SILICON AND MANGANESE WITHIN ABOUT THE RANGES SILICON 0.2 TO 0.6% AND MANGANESE 0.6 TO 1.0%; NICKLE 10 TO 15% CHROMIUM 18 TO 20%; AND THE FOLLOWING THREE CARBIDEFORMING ELEMENTS, NAMELY, MOLYBDENUM, NIOBIUM AND VANADIUM; COBALT 42 TO 46%; AND THE REMAINDER IRON WITH UNAVOIDABLE IMPURITIES: THE COMBINED PERCENTAGES, OF THE SAID CARBIDE-FORMING ELEMENTS BEING BETWEEN ABOUT 5.4% AND 4.5%; THE INDIVIDUAL PERCENTAGES OF THE SAID CARBIDE-FORMING ELEMENTS BEING MOLYBDENUM BETWEEN ABOUT 1.8 AND 2.3%; VANADIUM BETWEEN ABOUT 2.6 AND 3.1%; AND NIOBIUM BETWEEN ABOUT 1.0 AND 1.4%; THE CARBON CONTENT AND THE CORRESPONDING TOTAL CONTENT OF THE CARBIDE-FORMING CONSTITUENTS FALLING WITHIN THE SHADED AREA OF FIGURE 1 OF THE ACCOMPANYING DRAWINGS.

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