The invention relates to a tool steel, the composition of which comprises (the percentages being expressed in % by weight): TABLE-US-00001 0.8 .ltoreq. C .ltoreq. 1.5 5.0 .ltoreq. Cr .ltoreq. 14 0.2 .ltoreq. Mn .ltoreq. 3 Ni .ltoreq. 5 V .ltoreq. 1 Nb .ltoreq. 0.1 Si + Al .ltoreq. 2 Cu .ltoreq. 1 S .ltoreq. 0.3 Ca .ltoreq. 0.1 Se .ltoreq. 0.1 Te .ltoreq. 0.1 1.0 .ltoreq. Mo + 1/2W .ltoreq. 4 0.06 .ltoreq. Ti + 1/2Zr .ltoreq. 0.15 0.004 .ltoreq. N .ltoreq. 0.02 the balance of the composition consisting of iron and impurities resulting from the smelting, it being furthermore understood that: 2.5.times.10.sup.-4%.sup.2.ltoreq.(Ti+1/2Zr).times.N, to a process for manufacturing parts made in this steel and to the parts obtained.