Abstract: A steel composition includes, in wt. %: C: 0.25-0.35; Si: 0.20-0.35; Mn: 0.40-0.60; Cr: 1.20-1.70; Ni: 1.40-1.90; Mo: 0.15-0.25; Al: 0.015-0.035; Nb: 0.001-0.040; V: 0.001-0.060; N: 0.0030-0.0120; Ca: 0.0010-0.0030; and Fe. The wrought article made from this composition has a balanced set of mechanical properties including strength, ductility and toughness including resistance to fatigue crack propagation.

Abstract: Hybrid propulsion system comprising an internal-combustion engine (1) rotatably connected to a reversible electrical machine (2), a rechargeable battery (3), an electric driving motor (7), control apparatus (8) commanding first switching device (4, 5) for selectively connecting the battery (3) to the electric driving motor (7) and/or the reversible electrical machine (2). When the electric driving motor (7) is supplied with the current flowing in from the battery (3), said control apparatus (8) monitor the voltage at the poles (3P, 3N) of the battery (3). When the motor (7) is at least partially supplied with the current generated by the reversible electrical machine (2), owing to the latter being driven rotatably by the internal-combustion engine (1), the same control apparatus (8) monitor the voltage at the poles (2P, 2N) of the reversible electrical machine (2).