Abstract: In order to sharpen and harden a corner portion of a score line edge portion of an iron golf club having a plurality of score lines on a face surface within a prescribed range, heat input is implemented on an edge portion of a groove through laser irradiation after the groove is machined and, as a result, the edge portion is hardened and melted to form a rounded corner R. The hardness is set at a Vickers hardness value (HV) of at least 350. The corner R forms a part of a contour line of the edge portion and this contour line is formed to exist between a first circle that contacts the face surface and a side surface of the groove and has a radius of 0.010 inches (0.254 millimeters) and a second circle that is concentric with the first circle and has a radius of 0.011 inches (0.2794 millimeters).

Abstract: In order to sharpen and harden a corner portion of a score line edge portion of an iron golf club having a plurality of score lines on a face surface within a prescribed range, heat input is implemented on an edge portion of a groove through laser irradiation after the groove is machined and, as a result, the edge portion is hardened and melted to form a rounded corner R. The hardness is set at a Vickers hardness value (HV) of at least 350. The corner R forms a part of a contour line of the edge portion and this contour line is formed to exist between a first circle that contacts the face surface and a side surface of the groove and has a radius of 0.010 inches (0.254 millimeters) and a second circle that is concentric with the first circle and has a radius of 0.011 inches (0.2794 millimeters).