ArcelorMittal S.A.
A PRESS HARDENING METHOD

Abstract:

A press hardening method includes the following steps providing a carbon steel sheet coated with a barrier pre-coating including nickel and chromium wherein the weight ratio Ni/Cr is between 1.5 and 9, cutting the sheet to obtain a blank, thermal treatment of the blank 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, such atmosphere having a dew point between -30 and +30.degree. C., transfer of the blank into a press tool, hot-forming of the blank to obtain a part, cooling of the part to obtain a microstructure in steel being martensitic or martensito-bainitic or made of at least 75 wt. % of equiaxed ferrite, from 5 to 20 wt. % of martensite and bainite in amount less than or equal to 10 wt. %.