Method of treating a steel

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.

1 . A method of treating a steel comprising, 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 comprising:
 subjecting the steel to solutionizing heat treatment at a temperature lying in the range 950° C. to 1100° C.;   subjecting the steel to quenching treatment, performed after the solutionizing heat treatment;   placing the steel in a cryogenic enclosure after the quenching treatment;   cooling the inside of the cryogenic chamber in which the steel is present, the cooling being taken down 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.   
     
     
         2 . The method according to  claim 1 , wherein the time duration between the end of the quenching treatment and the beginning of the cryogenic treatment is less than or equal to 2 hours. 
     
     
         3 . The method according to  claim 2 , wherein the time duration between the end of the quenching treatment and the beginning of the cryogenic treatment is less than or equal to 1 hour. 
     
     
         4 . The method according to  claim 1 , wherein the duration of the cryogenic treatment is greater than or equal to 1 hour. 
     
     
         5 . The method according to  claim 1 , further comprising subjecting the steel to tempering treatment performed after the cryogenic treatment. 
     
     
         6 . The method according to  claim 1 , wherein the treated steel constitutes an aircraft landing gear part. 
     
     
         7 . The method according to  claim 1 , wherein the steel constitutes a part of weight greater than or equal to 10 kg. 
     
     
         8 . The method according to  claim 1 , wherein, during the quenching treatment, the steel is cooled to an end-of-quenching temperature that is less than or equal to 71° C.