Forging method forged product and forging apparatus

A forging method for upsetting a diameter expansion scheduled portion of a bar-shaped raw material using an upsetting apparatus equipped with a fixing die for fixing the bar-shaped raw material, a guide having an insertion passage for inserting and holding the raw material in a buckling preventing state, and a punch for axially pressing the raw material inserted in and held by the insertion passage of the guide,

• the forging method comprising:
• inserting the diameter expansion scheduled portion of the raw material fixed to the fixing die with the diameter expansion scheduled portion protruded from the fixing die into the insertion passage of the guide;
• and
• moving the guide in a direction opposite to a moving direction of the punch while axially pressing the raw material with the punch by moving the punch in a state in which a part of a peripheral surface of an exposed portion of the raw material exposed between the guide and the fixing die is restrained or an entire peripheral surface of the exposed portion of the raw material is not restrained, to thereby execute upsetting of the diameter expansion scheduled portion of the raw material,
• wherein the upsetting is executed so that, in the case of t0<T, G satisfies a relational expression of:
• (L−X)/[(l0−L)/P−t0]≦G≦P(X1−X)/(l0−X1−Pt0),
• where P is an average moving speed of the punch from initiation of a movement thereof, G is an average moving speed of the guide from initiation of the movement thereof, X0 is a buckling limit length at the cross-sectional area of the raw material before the upsetting, X1 is a buckling limit length at the cross-sectional area of an enlarged diameter portion of the raw material after the upsetting, X is an initial clearance between the guide and the fixing die (O≦X≦X0), t0 is a time lag from the initiation of the movement of the punch to the initiation of the movement of the guide (0≦t0), L is a length of the enlarged diameter portion of the raw material after the upsetting, l0 is a length of the raw material in the state prior to the upsetting required for the enlarged diameter portion, and T is upsetting time from the initiation of the movement of the punch.