HARDENED MARTENSITIC STEEL HAVING A LOW COBALT CONTENT, PROCESS FOR MANUFACTURING A PART FROM THIS

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Hardened martensitic steel having a low cobalt content, process for manufacturing a part from this steel, and part thus obtained. The steel is characterized in that its composition is, in percentages by weight : C = 0.18–0.30%; Co = 1.5 - 4%; Cr = 2–5%; Al = 1–2%; Mo + W/2 = 1–4%; V = traces - 0.3%; Nb = traces - 0.1%; B = traces – 30 ppm; Ni = 11–16%, where Ni ≥ 7 + 3.5 Al; Si = traces - 1.0%; Mn = traces - 4.0%; Ca = traces - 20 ppm; rare earths = traces – 100 ppm; if N ≤ 10 ppm, Ti + Zr/2 = traces – 100 ppm, where Ti + Zr/2 ≤ 10N; if 10 ppm < N ≤ 20 ppm, Ti + Zr/2 = traces – 150 ppm; O = traces – 50 ppm; N = traces – 20 ppm; S = traces – 20 ppm; Cu = traces – 1%; P = traces – 200 ppm, the balance being iron and inevitable impurities resulting from the smelting. Process for manufacturing a part from this steel, and part thus obtained.