Abstract: Hardened machined parts are manufactured from rolled or forged steel which consists essentially of 0.05 to 0.15 wt % of C, up to 0.50 wt % of Si, up to 1.5 wt % of Mn, 0.30 to 1.0 wt % of Cr, 0.50 to 1.0 wt % of Mo, one or more of elements selected from the group consisting of 0.10 to 0.40 wt % of V, 0.03 to 0.20 wt % of Ti, 0.03 to 0.20 wt % of Nb and 0.0005 to 0.0050 wt % of B, the balance being Fe, in the following steps: cooling the steel in air from 900.degree. C to 1,000.degree. C; machining the cooled steel; and subjecting the machined steel to a nitriding treatment at 500.degree. to 650.degree. C for 2 to 8 hours.