Golf club and method of producing the same

Abstract

A golf club includes a head formed of metal and having a face with a center having an average crystal grain size smaller at a rear side than at a front side. The face as seen in cross section has a first region having a relatively large average crystal grain size and a second region having a relatively small average crystal grain size. The second region extends from the center at the rear side to a periphery at the front side.

What is claimed is:  
     
         1 . A golf club including a head formed of metal and having a face, wherein said face has a center having an average crystal grain size smaller at a rear side than at a front side.  
     
     
         2 . The golf club of  claim 1 , wherein said average crystal grain size at said front side is 2-100 times said average crystal grain size at said rear side.  
     
     
         3 . The golf club of  claim 1 , wherein said average crystal grain size at said front side is 10-100 times said average crystal grain size at said rear side.  
     
     
         4 . The golf club of  claim 1 , wherein said average crystal grain size at said front side is 50-100 times said average crystal grain size at said rear side.  
     
     
         5 . The golf club of  claim 1 , wherein said average crystal grain size at said rear side is 0.1 μm to less than 50 μm.  
     
     
         6 . The golf club of  claim 1 , wherein said average crystal grain size at said rear side is 0.1 μm to 20 μm.  
     
     
         7 . The golf club of  claim 1 , wherein said average crystal grain size at said rear side is 0.1 μm to 10 μm.  
     
     
         8 . The golf club of  claim 1 , wherein in said face said center is surrounded by a periphery having an average crystal grain size smaller at said front side than at said rear side.  
     
     
         9 . The golf club of  claim 1 , wherein said center has said rear side provided with a protrusion, said protrusion in a vicinity of a surface having a smaller average crystal grain size than said center at said front side.  
     
     
         10 . A golf club including a head formed of metal and having a face, wherein said face has a center and a periphery surrounding said center said center and said periphery each having a first region having a relatively large average crystal grain size and a second region having a relatively small average crystal grain size, said center as seen in cross section having said first region and said second region therein at front and rear sides, respectively, said periphery as seen in cross section having said second region and said first region therein at said front and rear sides, respectively.  
     
     
         11 . The golf club of  claim 10 , wherein said second region is a region in a strip continuously extending from said center at said rear side to said periphery at said front side.  
     
     
         12 . The golf club of  claim 10 , wherein said center has said rear side provided with a protrusion and said second region extends within said protrusion.  
     
     
         13 . A method of producing a golf club, comprising the steps of: 
 forging a metal material to plastically deform said metal material into a plate to allow plastic flow of said metal material in a center at a rear side to be larger than plastic flow of said metal material in said center at a front side; and    mechanically or plastically processing said forged metal material to shape said metal material into a face of a head of the golf club.    
     
     
         14 . The method of  claim 13 , wherein the step of forging includes the step of plastically deforming said metal material to allow said center to have a front side provided with a protrusion to reduce plastic flow of said metal material in said center at said front side.