Drill bit for drilling and method for manufacturing same

A method of manufacturing a drill bit for drilling, the method comprising:

• (a) integrally coupling a shank and a diamond tip;
• (b) spraying cooling medium on a surface of the diamond tip immediately after rapidly heating a surface of a body part of the shank up to point Ac3 to point Ac3+200° C. via high-frequency induction heating;
• and
• (c) rapidly cooling the surface of the body part of the heated shank at speed of 20° C./sec or more via forcible cooling,
• the shank comprises a body part connected to a lower end of the diamond tip and having a first thickness, and a screw coupling part integrally connected to a lower end of the body part and having a second thickness smaller than the first thickness;
• hardness of a surface of the body part of the shank has a higher value than hardness of a surface of the screw coupling part of the shank;
• the body part of the shank has 300 Hv or more as hardness to 2 mm from the surface;
• and the shank is cylindrical and an outer surface of the shank has a uniform radius,
• wherein the diamond tip is attached to the upper end of the shank, and the screw coupling part is threaded,
• wherein a heat treatment is performed between the screw coupling part and the diamond tip so that the diamond tip and the screw coupling part are not heat treated,
• wherein the shank includes Si of 0.5 wt % or less, Mn of 0.1 to 2.0 wt %, S of 0.02 wt % or less, P of 0.03 wt % or less, Mo of 0.05 to 0.50 wt %, Cr of 0.1 to 0.5 wt %, B of 0.001 to 0.010 wt %, and Fe and other inevitable impurities.