A trial on an artificial hip joint stem made of Ni-free Co-29Cr-6Mo alloy was conducted by an isothermal hot semiclosed die forging method. The hot forging conditions (i.e., sample dimensions, forging temperature and stroke-speed) were determined by process simulation using “DEFORM-3D” based on FEM. A prototype stem with a shape designed using a FEM simulator was successfully obtained without surface defects or flaws under the predetermined forging conditions. The microstructure of the obtained stem consisted of mainly the ε (H.C.P.) phase as well as the minor γ (F.C.C.) and σ(CoCr:P42/mnm) phases. In addition, inhomogeneous distributions of the σ phase and grain size could be observed in the microstructure of the stem, resulting from the inhomogeneous distributions of effective strain rate, effective strain and effective stress induced in the stem during the forging process. Thus, Vickers hardness exhibited marked scattering, depending on the position of the stem.
