Abstract:
A seal ring comprising a chromium and boron containing cast iron alloy composition is disclosed. The cast iron alloy composition comprises each of boron, chromium and silicon in the following amounts: boron up to 1.5 wt. %; chromium from 8 to 14 wt. %; and silicon up to 3.0 wt. %. The seal ring may be produced by melting a cast iron composition further comprising the foregoing alloying elements; pouring the melted alloy into a mold; cooling the melted alloy to form a cast iron seal ring; and separating the cast iron seal ring from the mold. The seal ring is typically used in the undercarriage of earth-working machines, such as in the drive train or power train of such machines.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to seal rings, and more particularly to seal rings comprising chromium and boron containing cast iron that have enhanced performance characteristics, including improved wear and corrosion resistance. 
       BACKGROUND 
       [0002]    Many earth-working machines, such as loaders, tractors, and excavators, operate in extremely adverse environments often exposing the undercarriage components to various abrasive mixtures of water, dirt, sand, rock or chemical elements. Current undercarriage seal rings do not meet the targets for life in lower powertrain applications for mining and quarry products. 
         [0003]    One attempt to produce cast seal rings that have increased performance is described in published U.S. Patent Application No. U.S. 2012/0058710 to Young Jin Ma (“the &#39;710 application”) that published on Mar. 8, 2012. The &#39;710 application discloses a centrifugal casting method that produces a unique alloy microstructure over a traditional shell mold casting method, even if the same alloy cast iron is used. The centrifugal casting method described in the &#39;710 application is not feasible because it requires large amounts of expensive alloying elements to achieve a desired microstructure, including increased amounts of nickel (Ni) for stabilizing an austenite phase, and molybdenum (Mo) for suppressing a martensite phase and unwanted carbides. 
         [0004]    U.S. Pat. No. 3,758,296 (“the &#39;296 patent”) to Thomas E. Johnson describes another example of a corrosion-resistant cast alloy that requires the use of expensive alloying elements, including: 26-48 wt. % of Ni; 30-34 wt. % Cr; and 4.0-5.25 wt. % Mo. While such an allow does achieve increased corrosion resistance, the cost associated with using these alloying elements makes the use of this alloy prohibitive in most commercial applications. 
         [0005]    The disclosed seal ring comprising chromium and boron cast iron is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art. 
       SUMMARY 
       [0006]    In one aspect, the present disclosure is directed to a seal ring including a cast iron composition. The cast iron composition includes B, Cr, and Si in the following amounts: B in an amount up to 1.5 wt. %; Cr in an amount ranging from 8.0 to 14.0 wt. %; and Si in an amount up to 3.0 wt. %. 
         [0007]    In a further aspect, the present disclosure is directed to a method of making a cast iron seal ring. The method may include melting an alloy composition comprising B, Cr, and Si in the following amounts: B in an amount up to 1.5 wt. %; Cr in an amount ranging from 8.0 to 14.0 wt. %; and Si in an amount up to 3.0 wt. %; pouring the melted alloy into a mold; cooling the melted alloy to form a cast iron seal ring; separating the cast iron seal ring from the mold; and machining the seal ring to at least one predetermined tolerance. 
         [0008]    In yet another aspect, the present disclosure is directed to an undercarriage seal ring. The undercarriage seal ring may include a body that is generally cylindrical and extending along a longitudinal axis between a load end and a seal end; a seal flange, the seal flange disposed at the seal end of the body, the seal flange circumscribing the body and projecting radially from the body to a distal perimeter of the seal flange, the seal flange including a sealing face, the sealing face being annular and disposed adjacent the distal perimeter, wherein the seal ring is made from a cast iron composition, comprising: C: 2.8 to 3.6 wt. %; Mn: 0.40 to 1.0 wt. %; Ni: 3.0 to 5.0 wt. %; V: up to 1.0 wt. %; Mo: up to 0.80 wt. %; B: greater than 0 and up to 1.5 wt. %; Cr: from 8.0 to 14.0 wt. %; Si: greater than 0 and up to 3.0 wt. %; P: up to 0.08 wt. %; S: up to 0.2 wt. %; and the balance comprising Fe and incidental impurities. In an embodiment, the cast iron composition has a microstructure comprising more than 50 wt. % of martensite, austenite, and combinations thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an axial end view of a seal ring according to the present disclosure. 
           [0010]      FIG. 2  is an enlarged, fragmentary view of the seal ring of  FIG. 1  corresponding to the location encompassed by circle VI in  FIG. 1 . 
           [0011]      FIG. 3  is an enlarged, cross-sectional view taken along line VII-VII in  FIG. 1 . 
           [0012]      FIG. 4  is a flow chart illustrating steps of an embodiment of a method of making a seal ring as described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    There are disclosed embodiments of boron containing cast iron compositions for seal rings with enhanced performance characteristics, and methods of making such seal rings. In an embodiment, there is disclosed a boron containing cast iron composition comprising each of boron (B), chromium (Cr), and silicon (Si) in the following amounts: B up to 1.5 wt. %, such as an amount ranging from 0.5 to 1.0 wt. %; Cr in an amount ranging from 8.0 to 14 wt. %, such as an amount ranging from 10 to 14 wt. %; and Si in an amount up to 3.0 wt. %, such as an amount ranging from 1.5 to 2.4 wt. %. 
         [0014]    In an embodiment, the alloy also includes carbon (C) in an amount ranging from 2.8 to 3.6 wt. %; manganese (Mn) in an amount ranging from 0.40 to 1.0 wt. %; nickel (Ni) in an amount ranging from 3.0 to 5.0 wt. %; vanadium (V) in an amount up to 1.0 wt. %; molybdenum (Mo) in an amount up to 0.80 wt. %; phosphor (P) in an amount up to 0.08 wt. %; sulfur (S) in an amount up to 0.2 wt. %, with the balance comprising iron (Fe) and incidental impurities. 
         [0015]    In an embodiment, the cast iron composition has a microstructure comprising less than 50 wt. % carbide, such as between 5 to 45 wt. % carbide, or 10 to 40 wt. % carbide, or even 15 to 35 wt. % carbide, or any combination of these ranges, such as 35 to 40 wt. % carbide. 
         [0016]    In an embodiment, the cast iron composition has a microstructure comprising more than 50 wt. % of martensite, austenite and combinations thereof. For example, in various embodiments, the cast iron composition has a microstructure comprising martensite, austenite and combinations thereof in amounts ranging from 50 to 95 wt. %, 55 to 90 wt. %, 60 to 85 wt. %, 70 to 80 wt. %, or any combination of these ranges, such as 80 to 95 wt. %. As described in more detail below, the alloy composition described herein can be heat treated after casting to allow a majority of this phase to comprise martensite. In an embodiment, at least 75 wt. %, such as 80 to 95 wt. % of this phase comprises martensite. In another embodiment, substantially the entire phase, e.g., at least 99% of this phase is martensite. 
         [0017]    In an embodiment, a seal ring can be made from an alloy described herein using any suitable method of making a seal ring, such as mold casting, sand die casting, and centrifugal casting. In embodiments, the seal ring includes a body and a seal flange. The body is generally cylindrical and extends along a longitudinal axis between a load end and a seal end. The seal flange is disposed at the seal end of the cylindrical body. The seal flange circumscribes the body and projects radially from the body to a distal perimeter of the seal flange. The seal flange includes a sealing face which is annular and disposed adjacent the distal perimeter. 
         [0018]    A more detailed description of the body of the seal ring including the steps of an embodiment of a method of making it is provided in the  FIGS. 1-4 . Referring to  FIGS. 1 and 2 , a seal ring  100 , which is an example of an embodiment according to the present disclosure, is shown. The seal ring  100  is in the shape of an annulus. The seal flange  105  includes the sealing face  110 . The sealing face  110  includes the sealing band  115  disposed adjacent the outer perimeter  120  of the seal flange  105  and an inner relieved area  125  disposed between the sealing band  115  (which is shown as a hatched area in  FIGS. 1 and 2  for illustrative purposes) and an inner perimeter  130  of the seal ring  100 . The inner relieved area  125  can be tapered between the sealing band  115  and the inner perimeter  130  such that the inner perimeter  130  is axially displaced from the sealing band  115 . 
         [0019]    Referring to  FIG. 3 , the seal ring  100  includes a cylindrical body  140  and the seal flange  105 . The cylindrical body  140  extends along the longitudinal axis “LA” between the load end  145  and the seal end  150 , which is in opposing relationship to the load end  145 . The cylindrical body  140  includes the inner perimeter  130  which is substantially cylindrical and the majority of the inclined loading surface  155 , which is in outer, radial spaced relationship to the inner perimeter  130 . 
         [0020]    The seal flange  105  is disposed at the seal end  150 . The seal flange  105  projects radially from the cylindrical body  140  to the outer perimeter  120  thereof. The sealing face  110  is disposed on the seal flange  105  and extends radially with respect to the longitudinal axis “LA.” The sealing band  115  can be substantially flat in cross-section between an inner radial edge  135  and the outer perimeter  120  (also shown in  FIG. 2 ). In an embodiment, the sealing band  115  can include an outer relieved area disposed adjacent the outer perimeter  120  that is tapered. 
       Example 
       [0021]    In the Example, seal rings comprising a chromium and boron containing alloy described herein were made and compared to seal rings made with a commercially available alloy. The compositions of the alloys are shown below in Table I. Of note are the higher amounts of chromium and boron, and lower amount of nickel in the disclosed alloy, compared to commercially available alloys. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Alloy Compositions for Testing 
               
             
          
           
               
                   
                   
                 Commercial Alloy 
                 Inventive Alloy 
               
               
                   
                 Element 
                 (wt. %) 
                 (wt. %) 
               
               
                   
                   
               
             
          
           
               
                   
                 Carbon 
                 2.90 
                 3.30 
               
               
                   
                 Silicon 
                 1.90 
                 1.90 
               
               
                   
                 Manganese 
                 0.50 
                 0.60 
               
               
                   
                 Chromium 
                 8.50 
                 12.00 
               
               
                   
                 Nickel 
                 5.50 
                 3.80 
               
               
                   
                 Molybdenum 
                 0.20 
                 0.10 
               
               
                   
                 Vanadium 
                 0.20 
                 0.60 
               
               
                   
                 Phosphor 
                 0.05 
                 0.05 
               
               
                   
                 Sulfur 
                 0.01 
                 0.01 
               
               
                   
                 Boron 
                 0.25 
                 0.75 
               
             
          
           
               
                   
                 Iron 
                 Balance 
               
               
                   
                   
               
             
          
         
       
     
         [0022]    The above alloys were melted in a production furnace and brought to a pour temperature of 1350° C. The melted alloy was used in a static casting process to form seal rings of the same nominal size and geometric configuration. The seal rings were machined to tolerance using production lathes with standard tool inserts and prepared for pressure velocity testing. 
         [0023]    Next, the seal rings were tested for pressure velocity (PV). In these tests, a test fixture design was used that held the seal rings in spatial and orientation relationship as per their ordinary and intended use, including the test fixture providing a predetermined seal gap. The test fixture contained a seal cavity which was filled to a center fill line with oil at ambient temperature. The sealing faces of the contacting seal rings were subjected to an axial pressure, and one seal ring was rotated relative to the other seal ring at an initial rotational velocity. All of the seal rings were subjected to PV testing with the same load and seal gap settings. 
         [0024]    In particular, the testing conditions comprised a faceload of 1.2 N/mm and a cavity pressure of 10.0 KPa. The PV testing, specifically the rotation of the seal ring, was conducted according to the following cycle as set forth below in Table II: 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Cycle for PV Testing 
               
             
          
           
               
                 Point of Cycle 
                 Rotational Speed and Time 
               
               
                   
               
               
                 1 (Start) 
                 0 rpm 
               
               
                 1-2 
                 Accelerate to 50 rpm at 40 rpm/sec 
               
               
                 2-3 
                 Forward Time, 240 sec at 50 rpm 
               
               
                 3-4 
                 Decelerate to 0 rpm at −40 rpm/sec 
               
               
                 4-5 
                 Dwell Time, 60 sec at 0 rpm 
               
               
                 5-6 
                 Accelerate to −50 rpm at −40 rpm/sec 
               
               
                 6-7 
                 Reverse Time, 240 sec at −50 rpm 
               
               
                 7-8 
                 Decelerate to 0 rpm at 40 rpm/sec 
               
               
                 8-9 
                 Dwell Time, 60 sec at 0 rpm 
               
               
                   
               
             
          
         
       
     
         [0025]    The PV testing followed the cycle described in Table II. The seal rings were monitored for failure using a thermocouple configured to detect failures such as scoring, galling, and leaks. Weep was defined by the instant that dyed oil was present at the sealing face. Leak was defined by any amount of oil leaving the sealing region. The PV testing showed that seal rings made from the chromium and boron containing alloys of the present disclosure exhibited the same or better performance (higher PV values) in PV testing as more expensive seal rings made from commercially available, high Ni alloys, including PV values ranging from 600-800 KN/mm-mm/min. 
       INDUSTRIAL APPLICABILITY 
       [0026]    The disclosed chromium and boron containing cast iron alloy for a seal ring, a seal ring for a seal assembly, and a method of making a seal ring may be applicable to the lower powertrain of machines and equipment used in harsh environments, such as mining and quarry products. A seal ring constructed according to principles of the present disclosure generally exhibit improved life, improved scoring pressure velocity, acceptable corrosion resistance, and ease of manufacturing. The seal rings disclosed herein can be offered on new equipment, or can be used to retrofit existing equipment. 
         [0027]    In an embodiment, there is described a method for preparing a seal ring according to the present disclosure. Referring to  FIG. 4 , steps of an embodiment of a method  400  for preparing a seal ring for a seal assembly as disclosed are shown. The seal ring is produced from an alloy following principles of the present disclosure (step  410 ). The seal ring is machined to at least one predetermined tolerance (step  420 ). The sealing face of the seal ring is lapped to define an inner relieved area (step  430 ). The sealing face of the seal ring is lapped to flatten a sealing band (step  440 ). The sealing band is polished (step  450 ). 
         [0028]    The seal ring can be produce in step  410  using any suitable technique, such as by being stamped and formed or cast, for example. In an embodiment, the seal ring is produced by a casting technique, such as by a static mold casting or centrifugal casting. A casting technique includes melting an alloy composition as described herein, e.g., such as an alloy comprising each of B, Cr, and Si in the following amounts B in amounts up to 1.5 wt. %, Cr in amounts ranging from 8.0 to 14.0 wt. %, and Si in amounts up to 3.0 wt. %. 
         [0029]    The method according to this embodiment further comprises pouring the melted alloy into a mold at a temperature ranging from 1370° C. to 1482° C. The melted alloy is then cooled in the mold to form a cast iron seal ring, separating the cast iron seal ring from the mold, and machining the seal ring to at least one predetermined tolerance. 
         [0030]    While not shown in  FIG. 4 , it is understood that the method of preparing a seal ring according to the present disclosure may further comprise a step for heat treating the cast iron seal to change at least one physical or mechanical property of the alloy. For example, the method may comprise heat treating the cast alloy to change the microstructure to comprise a desired carbide phase and one or more desired crystalline phases chosen from martensite and austenite. 
         [0031]    In an embodiment, the method comprises heat treating the cast iron composition to achieve a microstructure comprising less than 50 wt. % carbide, such as between 5 to 45 wt. % carbide, or 10 to 40 wt. % carbide, or even 15 to 35 wt. % carbide, or any combination of these ranges, such as 35 to 40 wt. % carbide. 
         [0032]    In an embodiment, the method comprises heat treating the cast iron composition to achieve a microstructure having at least 50 wt. % of martensite, austenite and combinations thereof. For example, in various embodiments, the method comprises heating treating the cast iron composition to achieve a microstructure comprising martensite, austenite and combinations thereof in amounts ranging from 50 to 95 wt. %, 55 to 90 wt. %, 60 to 85 wt. %, 70 to 80 wt. %, or any combination of these ranges, such as 80 to 95 wt. %. The method comprises heating treating the cast iron composition to achieve a microstructure to achieve primarily martensite, such as at least 75 wt. % martensite, such as 80 to 95 wt. % martensite, or even substantially all martensite, e.g., at least 99% of this phase is martensite. In an embodiment, phase identification can be determined by Scanning Electron Microscopy (SEM) analysis. 
         [0033]    As defined herein, heat treating comprises an annealing step, a tempering step, or both and annealing and tempering step. In an embodiment, the annealing step comprises heating the cast iron seal to a temperature ranging from 700 to 800° C., such as 750° C., for a time ranging from 1 to 3 hours, such as 2 hours, followed by cooling to less than 200° C., such as 150° C. at a rate ranging from 25 to 35° C. per hour, such as 30° C. per hour. In an embodiment, the tempering step comprises heating at a temperature from 200 to 250° C., such as 225° C. for a time ranging from 1 to 3 hours, such as 2 hours. 
         [0034]    Either prior to or after heat treating, the seal ring can be machined as shown in step  420  of  FIG. 4 . In step  420 , the seal ring can be machined by any suitable technique, such as by using a lathe for lathe-turning and/or grinder for grinding operations, for example. The seal ring can be machined such that the thickness of the seal flange is within a predetermined tolerance, the seal ramp angle is within a predetermined tolerance, and other dimensional tolerances are met, for example. In an embodiment, the resulting seal ring has a hardness ranging from 55 HRC to 70 HRC, such as 68 HRC. 
         [0035]    In addition to the hardness properties, the seal ring made according to the present disclosure exhibits a scoring pressure velocity ranging from 300-1000 KN/mm-mm/min, such as from 600 to 800 KN/mm-mm/min. 
         [0036]    In step  430 , the sealing face can be lapped using any suitable technique, such as with a spherical lap, for example, to define the inner relieved area. In step  440 , the sealing face can be lapped using any suitable technique, such as with a flat lap, for example, to flatten the sealing band. In embodiments, the sealing band can be polished in step  440  using any suitable technique. 
         [0037]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed alloy and method of forming the alloy into a finished part without departing from the scope of the disclosure. Alternative implementations will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.