1. In steels with 0.25–0.35% C and 10–14% Ni the mechanical properties after quenching (cooling in air) are approximately the same as for carbon-free maraging steels: σb=190−200 kg/mm2; δ=10–12%; ψ=45–50%;an=6–7 kg-m/cm2;ap=1.7–2.2 kg-m/cm2. Small cold plastic deformation (2–5%) substantially increases the strength characteristics: ΔσT=50−60 kg/mm2, Δσb=20−30 kg/mm2. 2. The high plasticity and resistance to crack propagation of the steels investigated are due to the fact that nickel increases dislocation mobility and promotes relaxation processes, which are necessary to prevent crack nucleation and propagation and brittle fracture.