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|1. (WO2017017514) METHOD FOR THE MANUFACTURE OF A HARDENED PART WHICH DOES NOT HAVE LME ISSUES|
MACHADO AMORIM, Tiago
|Title:||METHOD FOR THE MANUFACTURE OF A HARDENED PART WHICH DOES NOT HAVE LME ISSUES|
The present invention relates to a method for the manufacture of a hardened part comprising the following steps: A) the provision of a steel sheet pre-coated with a metallic coating comprising from 2.0 to 24.0% by weight of zinc, from 1.1 to 7.0% by weight of silicon, optionally from 1.1 to 8.0% by weight of magnesium when the amount of silicon is between 1.1 and 4.0%, and optionally additional elements chosen from Pb, Ni, Zr, or Hf, the content by weight of each additional element being less than 0.3% by weight, the balance being aluminum and unavoidable impurities and residuals elements, wherein the ratio Al/Zn is above 2.9, B) the cutting of the coated steel sheet to obtain a blank, C) the thermal treatment of the blank at a temperature between 840 and 950°C to obtain a fully austenitic microstructure in the steel, D) the transfer of the blank into a press tool, E) the hot-forming of the blank to obtain a part, F) the cooling of the part obtained at step E) in order to obtain a microstructure in steel being martensitic or martensito-bainitic or made of at least 75% of equiaxed ferrite, from 5 to 20% of martensite and bainite in amount less than or equal to 10%.