To provide a hydroform process for metallic pipe in which a punch can be pushed in without causing buckling, deformation in end face or crack formation.

The hydroform process comprising the steps of applying a softening treatment as a preceding process of the hydroform to a segment of the metallic pipe where a swelling region is preferred to be formed, and/or applying a hardening treatment as a preceding process of the hydroform to a segment of the metallic pipe where no contribution to the swelling is expected but the bucking is easy to occur due to a axial thrust load of the punch (for example, the end face for axial thrust and a intermediate portion between the swelling region). According to this process, satisfactory punch pushing is attainable without causing the buckling of the pipe, the deformation in the end face or the crack formation.