PURPOSE: To enable extend forging of a large steel material using a press of relatively small capacity in a process that performs extend forging of axially symmetrical steel material between upper and lower anvils, by making sectional form perpendicular to the direction of extend forging rectangular during the stage of extend forging.
CONSTITUTION: When extend forging a steel material 3 between upper and lower anvils 1, 2, extend forging is started in a state that the sectional form perpendicular to the direction of extend forging is, for instance, nearly circular. Then, in an optional stage during the stage of extend forging, the sectional form perpendicular to the direction of extend forging is made rectangular or nearly rectangular, and the ratio of longer side to shorter side is made 1.4 or more. The material is then extend forged to desired final form such as square, octagon etc. of axial symmetry. By this way, the height H of the steel material when it is rectangular can be made small, and W/H can be made large without enlarging the width W of anvils 1, 2. Accordingly, internal cavities of a large-sized steel material can be pressure welded, and a formed product free from deffects can be obtained.
KANO SHIYOUICHI
MORIYA HIROAKI
