The invention belongs to the formation field of
metal materials and relates to a
deep hole extrusion forming process of medium-carbon low-
alloy structural steel. When a punch head extrudes downwards, the upper end of a blank keeps still, the lower end of the blank is extruded downwards along the
barrel wall of a die, one or more punch heads are adopted to extrude according to the forming requirement of a
deep hole, and the sizes of the punch head, the die and the initial blank and the relation among the punch head, the die and the initial blank meet the following forming conditions: the
diameter of the punch head is d, and the initial length L1 of the blank is (1.5-6) d; the initial
diameter of the blank is same as the inner
diameter of the upper part of the die, and the size range of the initial diameter of the blank is greater than d+10 millimeters and less than 2d; a single-side gap between the punch head and the inner diameter of the upper part of the die is greater than 5 millimeters; an annular gap is arranged between the
caliber D2 of a next-stage stair on the inner wall of the die and the punch head, and the single-side width of the annular gap is greater than 1
millimeter and less than 0.4d; the annular area of the next-stage stair on the inner wall of the die is 39% greater than the sectional area of the punch head; and the head of the punch head is in a 15-degree
conical surface shape, the most front end of the head of the punch head is a circular-arc surface, and the length of the head of the punch head is (0.8-1) d. The invention can obtain better strength than
tempering heat treatment and flexible comprehensive mechanical properties.