PURPOSE: To form a driving axle having a high load bearing capability by forging an alloy steel consisting of C, Mn, Si, Cr, Fe, etc., to the axle of the prescribed man. main body diameter, then immediately subjecting the axle to high-frequency hardening.

CONSTITUTION: The axle which has the min. main body diameter of 1.70in and is provided with splines and flanges respectively at both ends is formed by forging the alloy steel contg. 0.40 to 0.48% C, 1.35 to 1.61% Mn, 0.16 to 0.30% Si and 0 to 0.20% Cr and if necessary, contg. 0.025 to 0.05% Al and/or 0 to 0.15% Cu, 0.020 to 0.20% Ni, 0 to 0.15% Mo, 0.020 to 0.045% S, ≤0.035% P, etc., and consisting of the balance essentially Fe. Both ends are further machined to a finish shape and size. The axle is then subjected to the high-frequency hardening without the treatment of annealing or normalizing after the forging and is thereafter subjected to tempering. As a result, the axle having the main body diameter of 1.70 to 2.05 in and the load bearing capability of 30000 to 44000lbs is obtd.