Golf club head made of metal

Abstract

A golf club head which includes a ball hitting face having a central portion and a peripheral portion surrounding at least a part of the central portion. The golf club head is made of a metal, and the hardness of the peripheral portion is smaller than the hardness of the central portion. The difference in the hardness between the central portion and the peripheral portion is equal to or greater than 50 in terms of the Vickers hardness, and the width of the peripheral portion of the hitting face is in a range between about 5 and 20 mm.

What is claimed is:  
     
         1 . A golf club head, comprising: 
 a ball hitting face which includes a central portion and a peripheral portion surrounding at least a part of said central portion,    wherein said golf club head is made of a metal, and the hardness of said peripheral portion is lower than the hardness of said central portion.    
     
     
         2 . A golf club head, comprising: 
 a face member forming a ball hitting face, said ball hitting face including a central portion and a peripheral portion surrounding at least a part of said central portion,    wherein said golf club head is manufactured by a method comprising the steps of: 
 forming said face member from a raw material separately from other members used for said golf club head; and  
 subsequently welding said other members to said face member at a periphery of said face member, and  
 said golf club head is made of a metal, and the hardness of said peripheral portion is smaller than the hardness of said central portion.  
   
     
     
         3 . A golf club head according to  claim 1 , wherein 
 the width of said peripheral portion of said hitting face is in a range between about 5 and 20 mm, the width of said peripheral portion being determined by: 
 measuring a hardness distribution of said hitting face from an arbitrary point A on the edge of said hitting face, passing through the center of said hitting face, to a point B on the opposite edge of said hitting face;  
 determining the hardness of said central portion by taking an average of the hardness measured in an area in the vicinity of the center of said hitting face where the difference in hardness in the area is in the range of ±5%;  
 determining the hardness of said peripheral portion in the vicinity of the point A by taking an average of the hardness measured in an area in the vicinity of the point A where the difference in hardness in the area is in the range of ±5%;  
 determining a point of measurement having a value of hardness closest to an mean value between the hardness of said central portion and the hardness of said peripheral portion; and  
 determining the width of said peripheral portion as a distance between the point A and the point of measurement.  
   
     
     
         4 . A golf club head according to  claim 2 , wherein 
 the width of said peripheral portion of said hitting face is a the range between about 5 and 20 mm, the width of said peripheral portion being determined by: 
 measuring a hardness distribution of said hitting face from an arbitrary point A on the edge of said hitting face, passing through the center of said hitting face, to a point B on the opposite edge of said hitting face;  
 determining the hardness of said central portion by taking an average of the hardness measured in an area in the vicinity of the center of said hitting face where the difference in hardness in the area is in the range of ±5%;  
 determining the hardness of said peripheral portion in the vicinity of the point A by taking an average of the hardness measured in an area in the vicinity of the point A where the difference in hardness in the area is in the range of ±5%;  
 determining a point of measurement having a value of the hardness closest to an mean value between the hardness of said central portion and the hardness of said peripheral portion; and  
 determining the width of said peripheral portion which is a distance between the point A and the point of measurement.  
   
     
     
         5 . A golf club head according to  claim 1 , wherein 
 the difference in the hardness between said central portion and said peripheral portion is equal to or greater than 50 in terms of the Vickers hardness, the hardness of said central portion and of said peripheral portion being determined by: 
 measuring a hardness distribution of said hitting face from an arbitrary point A on the edge of said hitting face, passing through the center of said hitting face, to a point B on the opposite edge of said hitting face;  
 determining the hardness of said central portion by taking an average of the hardness measured in an area in the vicinity of the center of said hitting face where the difference in hardness in the area is in the range of ±5%; and  
 determining the hardness of said peripheral portion in the vicinity of the point A by taking an average of the hardness measured in an area in the vicinity of the point A where the difference in hardness in the area is in the range of ±5%.  
   
     
     
         6 . A golf club head according to  claim 2 , wherein 
 the difference in the hardness between said central portion and said peripheral portion is equal to or greater than 50 in terms of the Vickers hardness, the hardness of said central portion and of said peripheral portion being determined by: 
 measuring a hardness distribution of said hitting face from an arbitrary point A on the edge of said hitting face, passing through the center of said hitting face, to a point B on the opposite edge of said hitting face;  
 determining the hardness of said central portion by taking an average of the hardness measured in an area in the vicinity of the center of said hitting face where the difference in hardness in the area is in the range of ±5%; and  
 determining the hardness of said peripheral portion in the vicinity of the point A by taking an average of the hardness measured in an area in the vicinity of the point A where the difference in hardness in the area is in the range of ±5%.  
   
     
     
         7 . A golf club head according to  claim 3 , wherein 
 the difference in the hardness between said central portion and said peripheral portion is equal to or greater than 50 in terms of the Vickers hardness, the hardness of said central portion and of said peripheral portion being determined by: 
 measuring a hardness distribution of said hitting face from an arbitrary point A on the edge of said hitting face, passing through the center of said hitting face, to a point B on the opposite edge of said hitting face;  
 determining the hardness of said central portion by taking an average of the hardness measured in an area in the vicinity of the center of said hitting face where the difference in hardness in the area is in the range of ±5%; and  
 determining the hardness of said peripheral portion in the vicinity of the point A by taking an average of the hardness measured in an area in the vicinity of the point A where the difference in hardness in the area is in the range of ±5%.