Press hardening method

A press hardening method comprising the following steps:

• A. providing a steel sheet for heat treatment, the steel sheet being uncoated or having an aluminum-based pre-coating as a top surface of the steel sheet;
• B. depositing, (i) directly onto the uncoated steel sheet of step A or (ii) directly onto the aluminum-based pre-coating of step A, a hydrogen barrier pre-coating comprising at least 50% chromium and not comprising nickel with a thickness from 10 to 550 nm;
• C. cutting of the precoated steel sheet to obtain a blank;
• D. heat treating the blank at a furnace temperature from 800 to 970° C., for a dwell time from 1 to 12 minutes, in an atmosphere having an oxidizing power equal or higher than that of an atmosphere consisting of 1% by volume of oxygen and equal or smaller than that of an atmosphere consisting of 50% by volume of oxygen, the atmosphere having a dew point between −30 and +30° C.;
• E. transferring the blank into a press tool;
• F. hot-forming the blank at a temperature from 600 to 830° C. to obtain a part;
• G. cooling of the part obtained in step F) to obtain a microstructure in steel being martensitic or martensito-bainitic or made of at least 75% in terms of volume fraction of equiaxed ferrite, from 5 to 20% in volume of martensite and bainite in amount less than or equal to 10% in volume.