Manufacturing method of steel tube provided with rack-shaped inner wall

The invention relates to a manufacturing method of a steel tube provided with a rack-shaped inner wall. The manufacturing method comprises the following steps: I, raw material preparation; II, heating conducted through an annular furnace; III, hole expanding: after hole expanding is completed, the diameter of the inner bore of a inner bore is 1.27+/-0.3 times over the internal diameter of the en product of the steel tube provided with the rack-shaped inner wall; IV, induction heating: heat preservation is conducted while heating is conducted twice, and direct extrusion is conducted outside the furnace; V, extrusion: the diameter of an extrusion mould is 1.29+/-0.5 times over the external diameter of the steel tube provided with the rack-shaped inner wall, the extrusion break-through force is not more than 48 MN, extrusion is conducted at the extrusion speed of 12.5-18% of 2600mm/s, and the extrusion ratio is 3.90+/-0.5; VI, cold rolling preparation: cold rolling is conducted after heat treatment, straightenin