US2782135A

US2782135A - Method for producing articles having high creep resistance

Info

Publication number: US2782135A
Application number: US397050A
Authority: US
Inventors: Richardson Bruce Frederick
Original assignee: Cobalt Chemicals Ltd
Current assignee: Cobalt Chemicals Ltd
Priority date: 1953-12-08
Filing date: 1953-12-08
Publication date: 1957-02-19
Anticipated expiration: 1974-02-19

Description

METHOD FOR PRODUCING ARTICLES HAVING HIGH CREEP RESISTANCE Bruce Frederick Richardson, Ottawa, Ontario, Canada, assignor to Cobalt Chemicals, Limited, Cobalt, Ontario, Canada, a corporation of Canada No Drawing. Application December S, 19:13, Serial No. 397,050

6 Claims. (Cl. 148-115) This invention relates particularly, although not exclusively, to the production of parts for gas turbines, such as turbine blades and the like, which require high strength and high resistance to impact at both low and high temperatures as well as high resistance to corrosion, erosion and fatigue at high temperatures, high resistance to heat shock, and resistance to creep.

Two of the principal problems which have faced manu facturers of gas turbines are (1) the provision of an alloy which possesses satisfactory high temperature properties, and (2) the economical fabrication of the alloy to form the turbine parts, such as by rolling, forging and machining. Various attempts have been made to solve these problems by the provision of various ferrous and non-ferrous alloys containing various combinations of elements and amounts thereof. So far as I am aware all of these various attempts have failed either because the alloy thus provided did not possess one or more of the necessary properties or because the alloy did not possess one or more of these properties to a sufficient degree. Alloys which have combined the desired properties for turbine blades and the like to the best degree have not been forgeable or machinable and have required precision casting which is a slow and expensive method of fabrication. Furthermore, cast metals do not possess the valuable properties which can be imparted to metals by mechanically working them, as by rolling, forging, etc. Alloys which have been forgeable have not possessed other necessary properties to the desired degree, such for example as resistance to creep and erosion.

The present invention is founded, in part, upon the observation that alloys theretofore proposed for turbine blades and the like which possess the greatest resistance to creep and erosion, and which also possess other desired. properties, are those which are not forgeable. The invention also is founded, in part, upon the observation that the presence of a large amount of iron is detrimental in alloys for use at temperatures in excess of 1200 F., such as for turbine blades and the like. As a result of these observations, the idea was conceived that parts for gas turbines or superchargers, such as turbine blades, buckets, vanes, discs and the like, could be produced by selecting a forgeable non-ferrous alloy which possesses some or most of the properties desired and, after mechanically working the alloy to the desired shape, treating it to change its composition to a non-forgeable alloy and impart to its other desired properties without detrimentally affecting the desired properties possessed by the original alloy. Valuable properties also are imparted to the article as a result of the mechanical working. By selecting an alloy having most or all the properties desired in a turbine blade except, for example, high resistance to erosion and creep, a forged turbine blade may be produced having a final hard non-forgeable composition possessing high resistance to erosion and creep as Well as the other properties desired.

As previously pointed out, in general, alloys for turbine blades which have possessed the greatest resistance to creep and erosion and which also have possessed other properties desired are those which have not been readily forgeable. A

States Patent somewhat similar situation exists with respect to some other articles which are not directly related to turbine parts but which require some similar properties, such as great hardness, high strength and high resistance to erosion at elevated temperatures. Thus, the properties desired in certain cutting tools, extrusion dies and the like, are often possessed to the greatest degree by alloys which are not readily forgeable.

' In accordance with one aspect, the present invention contemplates a forged or otherwise mechanically worked non-ferrous article of the type illustrated by gas turbine parts, such as turbine blades, certain cutting tools, extrusion dies and the like, fabricated from a selected forgeable non-ferrous alloy having some of the properties desired and, which after mechanically working to the desired shape, has been treated to change its composition to a non-forgeable alloy and to impart to it other desired properties without detrimentally affecting the desired properties possessed by the original alloy.

When a forged article is desired, 1 have found a suitable alloy for use in the practice of the present invention is an initially forgeable non-ferrous alloy containing by Weight from about 17 to 27 percent chromium, about 5 to 15 percent nickel, about to percent cobalt, not more than about 0.03 percent carbon, about 12 to 18 percent tungsten, and from about 1 to 4 percent titanium together with about 0.25 to 0.75 percent silicon and 0.50 to 1.50 percent manganese, the balance being impurities. Iron may be present as an impurity in an amount not exceeding about 2 percent. in some instances, part or all of the titanium may be replaced by other carbide or nitride forming elements, such as molybdenum, tantalum, columbium, etc., or the latter elements may replace part of the tungsten. By the practice of the present invention, this forgeable non-ferrous article ing, approximately to the shape of the article desired and thus impart to it valuable properties due to the mechanical working. Then it may be machined, if desired, and treated to precipitate hard compounds, as by nitriding, gas carburizing or pack carburizing, and thus change its composition to a non-forgeable alloy and impart to it other desired properties possessed by the original alloy. If desired, the article then may be heat treated at the temperature and for a period of time required to obtain a solid solution of the original alloy after which it is air cooled rapidly to a black color. In some instances, it is desirable finally to age harden the article by heating at a suitable temperature and time, such as about 1,400 F. for about five hours.

For turbine blades and the like I presently prefer to employ a non-ferrous alloy containing by weight carbon as an impurity in amount not exceeding 0.03 percent, about 0.50 percent silicon, about 1.00 percent manganese, about 20 percent chromium, about 10 percent nickel, about 15 percent tungsten, about 2 percent titanium, and the balance cobalt, namely, about 50 percent cobalt, except for impurities. Iron may be present as an impurity in an amount preferably not exceeding about 2 percent.

As further illustrative of the invention, I have forged an alloy of the last mentioned composition in one direction at a temperature of about 2,250 P. to effect a reduction of about 69 percent and form a forged article about one inch wide and two inches long and with a maximum thickness of one quarter inch and having a cross sectional size resembling that of a turbine blade. After forging, the article was pack carburized by heating for about 12 hours at a temperature of 2,150 F. with a conventional carburizing material. The article then was removed and heated in a furnace at about 2,200 F, for about 40 minutes that is, for a time sufficient to obtain a solid solution. It was then rapidly air cooled to a black color. Finally, the article was subjected to an ageing treatment by heating in a furnace at atemperature of about 1,400 Fofor about hours.

The article as forged had a hardness of 29 Rockwell .C and after complete treatment had a hardness of 41 Rockwell C. Microscopic examination indicated complete penetration by carbon throughout the thickness of the article. Thus, by the above treatment, the properties of the original alloy were improved by the forging operation and its composition was converted from a forgeable alloy to a hard erosion resistant alloy in which the titanium and, to some extent some of the tungsten and chromium had combined with carbon to form hard compounds dispersed in a strong matrix comprising essentially cobalt, nickel, chromium and some tungsten.

While the aflinity of carbon or nitrogen for chromium or tungsten usually is not as great as it is for titanium, the expression an element capable of forming hard compounds as used in the appended claims is not intended to exclude chromium or tungsten either with or without such elements as titanium.

The present invention is not limited to the production of a forged or mechanically worked article from an initially forgeable alloy, which after being shaped, is treated to convert the alloy to a non-forgeable composition. In its broader aspect, the invention is applicable for producing articles of the general type previously mentioned from non-ferrous alloys of a non-forgeable composition. Thus, such non-forgeable, non-ferrous alloys may be shaped by casting and then treated in accordance with the invention to improve the properties of the alloy. Such non-forgeable, non-ferrous alloys should contain one or more carbide or nitride forming elements. The cast alloy may be subjected, for example, to a carburizing operation to precipitate therein hard compounds of carbon and one or more of the elements of the original alloy. if desired, the article then may be heat treated as previously described in connection with the treatment of the initially forgeable non-ferrous alloy. One advantage of such treatment of a cast alloy is to impart to the surface layer increased resistance to erosion without changing the characteristics of the core of-the article. if such hard compounds were present in the alloy as cast they would be distributed through the alloy and this, in many instances would not be desirable.

The invention, also is applicable for producing articles from a non-ferrous alloy containing carbide or nitride forming elements which is shaped solely by machining rather than by forging or by forging andmachining. Such articles, after being shaped, may be treated aspreviously described toprecipitate hard-compounds'therein followed, if desired, by heat treatment as previously described.

I claim:

1. '1' he method for producing articles having high strength at high temperatures and high creep resistance which comprises forming a forgeable alloy consisting essentially of primary non-ferrous metals and about 1 to 4 percent by weight of a secondary non-ferrous metal together with about 0.25 to 0.75 percent silicon and about 0.50 to 1.00 percent manganese by weight, said secondary metal having a substantially greater afiinity for a selected non-metallic element than does any one of said primary metals, said primary metalscomprising about 35 to 55 percent cobalt, about 5 to 15 percent nickel, about 17 to 27 percent chromium and. about 12 to 18 percent tungsten each by weight based upon the weight of the alloy, shaping the alloy to a desired shape, and subsequentlytreating the alloy to introducctheselected non-metallic element and form hard compounds of said secondary metal with said non-metallic element dispersed inamatrixcomprising essentially said primary metals thereby imparting high creep resistance to the alloy, said nonametallicclement about 5 to percent nickel, about 17 to 27 percent chromium, and about 12 to 18 percent tungsten each by Weight based upon the weight of the alloy, shaping the alloy to a desired shape, and subsequently subjecting the alloy to a carburizing operation tofo'rm hard carbides of said secondary metal dispersed in a matrix comprising essentially said primary metals thereby imparting high creep resistance to the alloy.

3. The method for producing articles having high strength at high temperatures and high creep resistance which comprises forming a forgeable alloy consisting essentially of about 1 to 4 percent of titanium, about 0.25 to 0.75 percent silicon, about 0.50 to 1.00 percent manganese, about to 55 percent cobalt, about 5 to 15 percent nickel, about 17 to 27 percent chromium and about 12 to 18 percent tungsten each by weight based upon the weight of the alloy, shaping the alloy to a desired shape, and subsequently subjecting the alloy to a carburizing operation to form hard carbides of titanium dispersed in a matrix comprising :essentially cobalt, nickel, tungsten and chromium thereby imparting high creep resistance to the alloy.

4. The method for producing articles having high strength at high temperatures and high creep resistance which comprises forming a forgeable alloy consisting essentially of about 0.50 p,ercent silicon, about 1.00 percent manganese, about 20 percent chromium, about 10 percent nickel, about 15 percent tungsten, about 2 percent titanium and about percent cobalt each by weight basednpon the weight of thealloy, shaping the alloy to a desired shape, and subsequently subjecting the alloy to a carburizing operation to form hard carbides of titanium dispersed in a matrix comprising essentially, cobalt, nickeLtungsten and chromium thereby imparting high creep resistance to the alloy.

5. The method for producing articles having high strength at; high temperatures and high creep resistance which comprises forming a forgeable alloy consisting essentially of primary non-ferrous metals and about 1 to 4 percent by weight ofa secondary non-ferrous metal selected from the group consisting of molybdenum, tantalum, colurnbium and titanium together withabout 0.25 to 0.75. percent silicon and about 0.50 to 1.00 percent manganese by weight, said primary metals comprising about 35 to percent cobalt, about 5 to 15 percent nickel, about 17 to 27 percent chromium and about 12 to 18 percent tungsten-each by weight based upon the weight of the alloy,. shaping the alloy to a desired shape, and subsequently treating the alloy to introduce a non-metallic element selected from, the group consisting of carbon and nitrogen and form hard compounds of said secondary metal with said non-metallic element dispersed in a matrix comprising essentially said primary metals thereby imparting high creep resistance to the alloy.

6..The method asclaimed byclaim 5 wherein said non-metallic element is carbon.

References Cited in the file of this patent UNITED STATES PATENTS 2,242,254 Mansfield -May 20, 1941 2,677,631 -.Gresham et a1 May 4,1954

Claims

1. THE METHOD FOR PRODUCING ARTICLES HAVING HIGH STRENGTH AT HIGH TEMPERATURES AND HIGH CREEP RESISTANCE WHICH COMPRISES FORMING A FORGEABLE ALLOY CONSISTING ESSENTIALLY OF PRIMARY NON-FERROUS METALS AND ABOUT 1 TO 4 PERCENT BY WEIGHT OF A SECONDARY NON-FERROUS METAL TOGETHER WITH ABOUT 0.25 TO 0.75 PERCENT SILICON AND ABOUT 0.50 TO 1.00 PERCENT WEIGHT, SAID SECONDARY METAL HAVING A SUBSTANTIALLY GREATER AFFINITY FOR A SELECTED NON-METALLIC ELEMENT THEN DOES ANY ONE OF SAID PRIMARY METALS, SAID PRIMARY METALS COMPRISING ABOUT 35 TO 55 PERCENT COBALT, ABOUT 5 TO 15 PERCENT NICKEL, ABOUT 17 TO EACH BY WEIGHT BASED UPON THE WEIGHT OF THE ALLOY, SHAPING THE ALLOY TO A DESIRED SHAPE, AND SUBSEQUENTLY TREATING THE ALLOY TO A DESIRED SHAPE, AND SUBSEQUENTLY TREATING THE ALLOY TO INTRODUCE THE SELECTED NON-METALLIC ELEMENT AND FORM HARD COMPOUNDS OF SAID SECONDARY METAL WITH SAID NON-METALLIC ELEMENT DISPERSED IN A MATRIX COMPRISING ESSENTIALLY SAID PRIMARY METALS THEREBY IMPARTING HIGH CREEP RESISTANCE TO THE ALLOY, SAID NON-METALLIC ELEMENT BEING SELECTED FROM THE GROUP CONSISTING OF CARBON AND NITROGEN.