Twist drill for machining material with chips difficult to break

The invention relates to a twist drill for machining a material with chips difficult to break. A cutter body and a handle are coaxial cylinders with the same central axis as the center. Spiral chip grooves are ground in the cutter body, and solid parts, except the chip grooves, of the cutter body are cutter backs. A rear cutter face is ground at the end face position of the head of the cutter, and main cutting edges are formed by crossed lines of the rear cutter face and the chip grooves. A chip discharging part and an edge part joined with the chip discharging part are formed on the cutter body. Each main cutting edge comprises a first apex angle section, a transition circular arc section and a second apex angle section which are joined in sequence. The double-apex-angle design of the large apex angles and the small apex angles is adopted, and iron chips are deformed twice to achieve the chip breaking effect; centering of a drill bit is facilitated in the machining process through the design of a central small apex angle; circular arc transition is adopted between the large apex angles and the small apex angles, so that stress concentration is reduced, abrasion of the drill bit is slowed down, and the shape of the iron chips can be controlled; the smoothness degree of the hole surface after the material difficult to machine is machined is effectively improved; and due the fact that the chip breaking problem is solved, the iron chips can be smoothly discharged out, and it is avoided that the hole wall is scratched by the iron chips.