Forging is a bulk deformation process in metal working commonly employed in the manufacture of metallic materials prostheses. Depending on the compressive loads applied to the material, structures (grain sizes) are formed which increase its strength. By forging an ASTM F138 stainless steel, the heating of material in a suitable temperature is of fundamental importance to be formed without the presence of folds arising from the process and as a result we can obtain a proper microstructure. This work aims to define the accurate temperature in relation to the strain rate applied in the hot die forging process. Besides, it is used a closed-die forging in which cavity has different thickness that stimulates the profile of an orthopedic plate. Four ranges of temperature used in the process vary between 1000 and 1200 ??C, with a strain rate ranging from 400 to 600 s???1.Results demonstrate that there is a transitional temperature close to 1050 ??C, where temperatures of 1000???1040 ??C provide satisfactory grain size and temperatures of 1100 and 1200 ??C, showed limitations in grain size, greater than those recommended by ASTM F 621.