Cryogenic treatment of martensitic steel with mixed hardening

摘要

The invention relates to a method for producing martensitic steel that comprises a content of other metals such that the steel can be hardened by an intermetallic compound and carbide precipitation, with an Al content of between 0.4% and 3%, comprising the following steps:(a) heating the entirety of the steel above its austenizing temperature,(b) cooling said steel approximately to ambient temperature,(c) placing said steel in a cryogenic medium.;The temperature T₁ is substantially lower than the martensitic transformation temperature Mf, and the time t during which said steel is kept in said cryogenic medium at a temperature T₁ from the moment when the hottest part of the steel reaches a temperature lower than the martensitic transformation temperature Mf is at least equal to a non-zero time t₁, the temperature T₁ (in ° C.) and the time t₁ (in hours) being linked by the equation T₁=ƒ(t₁), the first derivative of the function ƒ relative to t, ƒ′(t), being positive, and the second derivative of ƒ relative to t, ƒ″(t), being negative.