Patent Publication Number: US-2011076176-A1

Title: Cast compressor articles and methods of forming same

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to cast compressor articles. More particularly, the invention relates to cast airfoils, stators, blades, gas turbines, gas turbine shells, etc, and methods of forming the same. 
     Typically, current compressor articles used in various gas turbines are made of conventional and sometimes slightly modified stainless steels, and formed via a forging process with extensive post process machining to bring the articles to their final shape. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A first aspect of the disclosure provides a method of forming a compressor article comprising: preparing an iron-manganese-aluminum-silicon-carbon (Fe—Mn—Al—Si—C) based alloy; casting the Fe—Mn—Al—Si—C based alloy, wherein a cast has a shape of a compressor article; and performing post-casting finishing thereby forming the compressor article. 
     A second aspect of the disclosure provides a method of forming a compressor article comprising: preparing an iron-manganese-aluminum-silicon-carbon (Fe—Mn—Al—Si—C) based alloy; casting the Fe—Mn—Al—Si—C based alloy, wherein a cast has a shape of a compressor article selected from the group consisting of an airfoil, a stator, a gas turbine, a blade, and a gas turbine shell, and performing post-casting finishing thereby forming the compressor article. 
     A third aspect of the disclosure provides a compressor including a part made of an iron-manganese-aluminum-silicon-carbon (Fe—Mn—Al—Si—C) based alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
         FIG. 1  shows a flow diagram of an embodiment of a method of forming a compressor article, in accordance with the present invention; and 
         FIG. 2  shows a compressor blade in an embodiment of a compressor part, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Current forming processes, such as forging, for compressor articles employ heating and shaping the raw material by suitably applying of compressive forces. Due to the nature of this process, typically extensive machining is involved in post processing to bring the products to their final shapes. The whole process can be very costly, time-consuming, and environmentally unsound. It has been discovered that using a casting process and employing an iron-manganese-aluminum-silicon-carbon (Fe—Mn—Al—Si—C) based alloy, eliminates or minimizes machining, reduces lead time, and reduces the carbon foot print of the process. The cast parts can also be Hot Isostatic Pressed (HIPed) to eliminate/minimize internal voids. It also has been discovered that using the Fe—Mn—Al—Si—C based alloy affords a cost savings in raw material use as compared to materials typically used in current forming processes. 
     Referring to  FIG. 1 , an embodiment of a method of forming a compressor article is shown. The method comprises: a first step S 1 , preparing an iron-manganese-aluminum-silicon-carbon (Fe—Mn—Al—Si—C) based alloy; a second step S 2 , casting the Fe—Mn—Al—Si—C based alloy, wherein a cast has a shape of a compressor article; and a third step S 3 , performing post-casting finishing thereby forming the compressor article. 
     Referring to method step S 1 , preparing an Fe—Mn—Al—Si—C based alloy, in an embodiment of the present invention, the Fe—Mn—Al—Si—C based alloy comprises approximately 54.3%-76.4% Fe, approximately 12%-30% Mn, approximately 5%-12% Al, approximately 0.3%-2.5% Si, and approximately 0.3%-1.2% C. In another embodiment, the Fe—Mn—Al—Si—C based alloy comprises approximately 59.5% Fe, approximately 29.4% Mn, approximately 8.8% Al, approximately 1.3% Si, and approximately 1% C. In another embodiment, the Fe—Mn—Al—Si—C based alloy additionally comprises approximately 0.5%-1% Molybdenum (Mo). 
     The Fe—Mn—Al—Si—C based alloy may be prepared by melting the components of the alloy in an argon atmosphere to minimize oxidation and to form a molten metal Fe—Mn—Al—Si—C based alloy. The process to provide the molten Fe—Mn—Al—Si—C based alloy, as described, is well known in the art and thus, for the sake of brevity, no further description is provided. 
     The prepared Fe—Mn—Al—Si—C based alloy has casting characteristics similar to ductile iron with improved age hardening characteristics. The Fe—Mn—Al—Si—C based alloy possesses low density (6.5-7.2 g/cm 3 ), tensile strength (UTS) from 600 MPa to 2000 MPa, and excellent ductility as great as over 70% strain to failure when solution treated, elongation from 10% to 70%, and yield strength (YS) from 600 to 1000 MPa. The superior fluidity and the age-hardening ability characteristics of the Fe—Mn—Al—Si—C based alloy allow it to be used to produce compressor articles utilizing near-net shape casting processes. Examples of the casting processes are described infra. 
     The Fe—Mn—Al—Si—C based alloy has two major matrix constituents (austenite and ferrite). The two constituents increase the dampening capability of compressor articles formed having the Fe—Mn—Al—Si—C based alloy. Table I compares properties of the Fe—Mn—Al—Si—C based alloy with other alloys typically used in forming processes for compressor articles. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 59.5 Fe—29.4 
                 59.5 Fe—29.4 
                   
                   
                 1.58% Cr— 
                 1.18 Cr— 
               
               
                   
                 Mn—8.8 Al— 
                 Mn—8.8 Al— 
                 304 SS 18%-20% 
                 410 SS 
                 1.54% Ni— 
                 1.11 Mo— 
               
               
                   
                 1.33 Si—1C 
                 1.33 Si—1C 
                 Cr, 8%-10.5% Ni 
                 11.5%-13.5% Cr 
                 0.192 Mo 
                 0.26% V 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 condition 
                 Cast, 
                 Cast, Aged 
                 Forged, 
                 Tempered, Motor 
                 Forged, 
                 Forged, 
               
               
                   
                 Sol&#39;n treated 
                 16 hr @ 550 C. 
                 Annealed 
                 Cold Finished 
                 QTed 
                 QTed 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 UTS (MPa) 
                 871 
                 1210 
                 515 
                 min 
                 825 min 
                 840 
                 814.2 
               
               
                 0.2 YS (MPa) 
                 620 
                 884 
                 205 
                 min 
                 620 min 
                 700 
                 694.14 
               
               
                 % elongation 
                 77 
                 15 
                 40 
                 min 
                  12 min 
                 18.5 
                 20.3 
               
               
                 Hardness (BHN) 
                 272 
                 434 
                 203 
                 max 
                   
                 255 
                 244 
               
               
                   
               
            
           
         
       
     
     Referring to method step S 2 , casting an Fe—Mn—Al—Si—C based alloy wherein the cast has a shape of a compressor article, in an embodiment of the present invention casting is selected from the group consisting of sand casting, investment casting, permanent mold casting, and die casting. The aforementioned casting processes, as described, are well known in the art and thus, for the sake of brevity, no further description is provided. The aforementioned casting processes also are near-net shape processes requiring very little post process machining, if any. In an embodiment of the present invention, the Fe—Mn—Al—Si—C based alloy prepared in method step S 1  is poured into pre-made molds (permanent molds) in the shape of a compressor article. 
     The molds have cavities that match the geometrical shape of the final compressor article. The molds also have a gating system that provides channels to the cavity of the mold. In an embodiment, the cast is in a mold having a geometrical shape selected from the group consisting of an airfoil, a stator, a gas turbine, a blade, and a gas turbine shell. In another embodiment, the Fe—Mn—Al—Si—C based alloy may be cast using a technique not specifically mentioned or later developed techniques appropriate for the alloy to be cast. 
     Referring to method step S 3 , performed post-casting finishing resulting in the formation of the compressor article. In an embodiment of the present invention post-casting finishing includes but is not limited to separating the article from the mold, heat treating the separated article, age hardening the separated article, and process machining. In one embodiment, the cast article is separated from the gating system with saw cuts. The separated article is then solution heat treated to meet mechanical properties pre-selected for the article. Solution heat treatment may be performed at 1,000° C. or above in an atmosphere that prevents decarburization and oxidation. Age hardening may then be performed in a temperature range from approximately 500° C. to 650° C. at a period of time required to obtain a pre-selected mechanical property for the article. In another embodiment, the post casting steps may be performed using a technique not specifically mentioned or later developed techniques appropriate for the post casting treatment of the cast Fe—Mn—Al—Si—C based alloy. 
     The compressor article formed from S 3  includes but is not limited to an airfoil, a stator, a gas turbine, a blade, and a gas turbine shell. The formed article has the characteristics as described in Table I supra as well as comparable oxidation and weldability properties to 304SS (Stainless Steel). The formed article also is 12%-18% lighter than High Strength Lightweight Aluminum (HSLA) steels. The formed article also is less expensive than conventional stainless steel articles which require high chromium additions and expensive nickel additions. 
     Referring to  FIG. 2 , a compressor blade  1  is shown, in an embodiment of a compressor part/article, according to the present invention. In one embodiment, the compressor includes a compressor blade  1  comprising an iron-manganese-aluminum-silicon-carbon (Fe—Mn—Al—Si—C) based alloy. The characteristics, methods of forming, and various embodiments of the Fe—Mn—Al—Si—C based alloy are described supra, and thus, for the sake of brevity, no further description is provided. In one embodiment, the compressor blade  1  is formed via casting. The characteristics, methods of forming, and various embodiments of compressor parts/articles comprising the Fe—Mn—Al—Si—C based alloy are described supra, and thus, for the sake of brevity, no further description is provided. In an embodiment of the present invention, the compressor part(s) is selected from the group consisting of an airfoil, a stator, a gas turbine, a blade, and a gas turbine shell. 
     The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “approximately” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc). 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.