PURPOSE: To easily produce high quality case hardened parts made of steel by subjecting a steel stock for case hardening to high velocity hot forging into a preformed body, finishing the above forging at the prescribed temp., subjecting the above preformed body to warm forging into the prescribed shape at low draft, and then performing case hardening treatment.

CONSTITUTION: High velocity hot forging is applied to a steel stock for case hardening to form it into a preformed body having a shape near to the prescribed shape. It is preferable that this steel stock has a composition containing, by weight, ≤0.25% C, ≤1.0% Si, ≤1.0% Mn, and 0.5-1.5% Cr as essential components, further containing Ni, Mo, W, V, Nb, Ti, Al, N, etc., as optional additive components, and having the balance Fe with impurities. Further, proper temp. at the above hot forging is 1100-1250°C. This hot forging is finished at the hot forging finishing temp. where the initial crystal grain size becomes increased. By the above procedure, the preformed body can be provided with a hardness of HRB 80 to 95. Then, warm forging is applied to the preformed body at 700-900°C at low draft to form it into the prescribed shape, followed by case hardening treatment. By this method, the case hardened parts made of steel free from strain can be obtained.