Iron-type golf club head

Abstract

An iron-type golf club head comprises a face portion and a hosel portion which are integrally formed by forging or casting soft iron. The face portion has a face hardness hf (HV) which is defined by Vickers hardness at a depth of 4 mm from the hitting surface at a main impact point. The hosel portion has a reference hosel outer peripheral portion defining a hosel hardness hh (HV) which is an average value of Vickers hardness measured at positions around the hosel axis, and at a depth of 1 mm from the outer surface thereof. The hosel hardness hh is higher than the face hardness hf.

1 . An iron-type golf club head comprising:
 a face portion having a hitting surface; and   a hosel portion continuous to the face portion on a heel-side thereof, wherein   the face portion and the hosel portion are made of soft iron,   the face portion and the hosel portion are integrally formed by forging or casting the soft iron,   the hitting surface has a main impact point which is defined as being positioned at the center in a toe-heel direction of the hitting surface and 12 mm above the lowermost end of the hitting surface along the hitting surface in a reference state in which the golf club head is set on a horizontal plane at its lie angle and loft angle,   the face portion has a face hardness hf (HV) which is defined by Vickers hardness measured at a depth of 4 mm from the hitting surface at the main impact point,   the hosel portion has a reference hosel outer peripheral portion which is defined as extending in the circumferential direction of the hosel portion at a position downward from an upper end of the hosel portion by 30 mm along the direction of a hosel axis,   when positions on the reference hosel outer peripheral portion are expressed as angles around the hosel axis on the basis that the most heel side is 0 degrees, the most rear side is 90 degrees, the most toe side is 180 degrees, and the most face side is 270 degrees, the hosel portion has a hosel hardness hh (HV) which is an average of Vickers hardness values at positions of 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees around the hosel axis, and   the Vickers hardness values are values measured at a depth of 1 mm from the outer surface of the hosel portion at the reference hosel outer peripheral portion,   wherein
 the hosel hardness hh is higher than the face hardness hf. 
   
     
     
         2 . The iron-type golf club head according to  claim 1 , wherein
 the soft iron has a carbon content of not more than 0.20% by weight.   
     
     
         3 . The iron-type golf club head according to  claim 1 , wherein
 the soft iron has a carbon content of not more than 0.15% by weight.   
     
     
         4 . The iron-type golf club head according to  claim 1 , wherein
 the face hardness hf is less than 130 (HV) and the hosel hardness hh is 130 to 190 (HV).   
     
     
         5 . The iron-type golf club head according to  claim 1 , wherein
 the ratio hh/hf of the hosel hardness hh to the face hardness hf is not less than 1.10.   
     
     
         6 . The iron-type golf club head according to  claim 1 , wherein
 the face portion and the hosel portion are integrally formed by forging, and   the hosel portion has a metal structure such that crystal grains of at least a part of the soft iron in the reference hosel outer peripheral portion are finer than crystal grains of the soft iron at the main impact point.   
     
     
         7 . The iron-type golf club head according to  claim 1 , wherein
 the hosel portion has a heat-treated metal structure in the reference hosel outer peripheral portion.   
     
     
         8 . An iron-type golf club head comprising:
 a face portion having a hitting surface; and   a hosel portion continuous to the face portion on a heel-side thereof,   the face portion and the hosel portion integrally formed by forging or casting one kind of soft iron,   
       wherein
 a hosel hardness hh is higher than a face hardness hf, 
 
       wherein
 the face hardness hf (HV) is defined by Vickers hardness measured at a depth of 4 mm from the hitting surface at a main impact point of the hitting surface, 
 the main impact point is defined as being positioned at the center in a toe-heel direction of the hitting surface and 12 mm above the lowermost end of the hitting surface along the hitting surface in a reference state of the golf club head defined as being set on a horizontal plane with its lie angle and loft angle, 
 the hosel hardness hh (HV) is defined by an average value of Vickers hardness measured at a depth of 1 mm from the outer surface of a reference hosel outer peripheral portion of the hosel portion at at least eight equiangular positions around the hosel axis, and 
 the reference hosel outer peripheral portion is defined as extending in the circumferential direction of the hosel portion around the hosel axis at a position downward from an upper end of the hosel portion by 30 mm along the direction of the hosel axis. 
 
     
     
         9 . A method for manufacturing an iron-type golf club head,
 the iron-type golf club head comprising a face portion having a hitting surface, and a hosel portion continuous to the face portion on a heel-side thereof,   the hitting surface having a main impact point defined as being positioned at the center in a toe-heel direction of the hitting surface and 12 mm above the lowermost end of the hitting surface along the hitting surface in a reference state in which the golf club head is set on a horizontal plane at its lie angle and loft angle,   the face portion having a face hardness hf (HV) defined by Vickers hardness at a depth of 4 mm from the hitting surface at the main impact point,   the hosel portion having a reference hosel outer peripheral portion defined as extending in the circumferential direction of the hosel portion at a position downward from an upper end of the hosel portion by 30 mm along the direction of a hosel axis, and   the reference hosel outer peripheral portion having a hosel hardness hh (HV) which is an average value of Vickers hardness at positions of 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees when positions on the reference hosel outer peripheral portion are expressed as angles around the hosel axis on the basis that the most heel side is 0 degrees, the most rear side is 90 degrees, the most toe side is 180 degrees, and the most face side is 270 degrees, and the Vickers hardness is measured at a depth of 1 mm from the outer surface of the hosel portion at reference hosel outer peripheral portion, wherein the hosel hardness hh is higher than the face hardness hf,   the method comprising:
 a casting process in which the face portion and the hosel portion are integrally formed by casting soft iron; and 
 a heat treatment process in which the hosel portion is locally heated in the reference hosel outer peripheral portion by a local heating device, whereby the reference hosel outer peripheral portion has a heat-treated metal structure having increased hardness to achieve the hosel hardness higher than the face hardness. 
   
     
     
         10 . The method according to  claim 9 , wherein
 the local heating device is an induction heating device and/or a laser heating device.   
     
     
         11 . The method according to  claim 10 , wherein
 the soft iron has a carbon content of not more than 0.20% by weight.   
     
     
         12 . The method according to  claim 10 , wherein
 the face hardness hf is less than 130 (HV) and the hosel hardness hh is 130 to 190 (HV).   
     
     
         13 . The method according to  claim 12 , wherein
 the ratio hh/hf of the hosel hardness hh to the face hardness hf is not less than 1.10.