The invention relates to steel which is characterized by the following composition as expressed in percentages by weight: —C=0.18 0.30%, —Co=5-7%, —Cr=2-5%, —Al=1-2%, —Mo+W/2=1-4%, —V=trace 0.3%, —Nb=trace 0.1%, —B=trace—50 ppm, —Ni=10.5-15% with Ni≧7+3.5 Al, —Si=trace 0.4%, —Mn=trace 0.4%, —Ca=trace—500 ppm, —Rare earths=trace—500 ppm, —Ti=trace—500 ppm, —O=Trace—200 ppm if the steel is obtained by means of powder metallurgy or trace—50 ppm if the steel is produced in air or under a vacuum from molten metal, —N=trace—100 ppm, —S=trace—50 ppm, —Cu=trace—1%, and —P=trace—200 ppm, the remainder including iron and the inevitable impurities resulting from production. The invention also relates to a method of producing a part from said steel and to the part thus obtained.