Drill bit having increased resistance to fatigue cracking and method of producing same

Abstract

The present invention relates to a roller cone drill bit that includes a bit body adapted to be rotated about a longitudinal axis, where the bit body has at least one leg depending therefrom, wherein the leg comprises a treated portion that provides a residual compressive stress, and a roller cone rotatably mounted on a journal. The treated portion treatment may comprise one selected from shot peening, laser-shock peening, and hammer peening. Further, the present invention relates to a method of manufacturing a roller cone drill bit that includes inducing a compressive stress, through plastic deformation, in at least a portion of at least one leg depending from a bit body. The inducing a compressive stress may comprise one selected from shot peening, laser-shock peening, and hammer peening.

1 . A roller cone drill bit comprising: 
 a bit body adapted to be rotated about a longitudinal axis, the bit body having at least one leg depending therefrom, wherein the at least one leg comprises a treated portion that provides a residual compressive stress; and    a roller cone rotatably mounted on a journal.    
   
   
       2 . The roller cone drill bit of  claim 1 , wherein a treated portion of the at least one leg comprises a leg backtum face.  
   
   
       3 . The roller cone drill bit of  claim 1 , wherein the treated portion is a plastically deformed area.  
   
   
       4 . The roller cone drill bit of  claim 3 , wherein the plastically deformed area extends inward about 0.035 inch.  
   
   
       5 . The roller cone drill bit of  claim 1 , wherein the treated portion treatment comprises one selected from shot peening, laser-shock peening, and hammer peening.  
   
   
       6 . The roller cone drill bit of  claim 5 , wherein the peening provides 100 percent coverage.  
   
   
       7 . The roller cone drill bit of  claim 1 , further comprising a hardface coating disposed on a region adjacent the treated portion.  
   
   
       8 . The roller cone drill bit of  claim 2 , wherein the treated portion of the leg backturn face of the at least one leg comprises p-features.  
   
   
       9 . The roller cone drill bit of  claim 8 , wherein the p-features comprise inserts.  
   
   
       10 . A method of manufacturing a roller cone drill bit comprising: 
 inducing a compressive stress, through plastic deformation, in at least a portion of at least one leg depending from a bit body.    
   
   
       11 . The method of  claim 10 , wherein the portion comprises a leg backturn surface.  
   
   
       12 . The method of  claim 10 , wherein inducing a compressive stress comprises one selected from shot peening, laser-shock peening, and hammer peening.  
   
   
       13 . The method of  claim 10 , further comprising applying a hardface coating to a region adjacent the treated portion.  
   
   
       14 . The method of  claim 12 , wherein the shot peening comprises shot having a hardness between 45 and 52 Rc.  
   
   
       15 . The method of  claim 12 , wherein the shot peening comprises shot having a size between 10 and 18 mesh.  
   
   
       16 . The method of  claim 10 , wherein the shot peening provides 100 percent coverage.  
   
   
       17 . The method of  claim 10 , wherein the shot peening has a peening intensity between 7 and 9 C.  
   
   
       18 . The method of  claim 10 , wherein the inducing a compressive stress is performed on at least one portion of at least one leg with p-features.