Abstract: A method of treating a steel including, in percentages by weight: 0.2% to 0.33% carbon, 4% to 8% cobalt, 7% to 11% nickel, 0.8% to 3% chromium, 0.5% to 2.5% molybdenum, 0.5% to 5.9% tungsten, 0.05% to 0.2% vanadium, and not more than 0.02% titanium, the balance being constituted by iron and inevitable impurities, the method including subjecting the steel to solutionizing heat treatment at a temperature from 950° C. to 1100° C.; then subjecting the steel to quenching treatment; then placing the steel in a cryogenic enclosure; cooling the inside of the cryogenic chamber in which the steel is present to a treatment temperature less than or equal to ?73° C.; and subjecting the steel to cryogenic treatment while the treatment temperature is maintained inside the enclosure, the time duration between the end of the quenching treatment and the beginning of the cryogenic treatment being less than or equal to 4 hours.