ArcelorMittal S.A.
Manufacturing process of hot press formed aluminized steel parts

Abstract:

A manufacturing process of a press hardened coated part including providing a furnace containing N zones, each furnace zone being respectively heated at a setting temperature .THETA..sub.1F, .THETA..sub.2F, . . . .THETA..sub.iF, . . . , .THETA..sub.NF, including: providing a steel sheet with thickness th between 0.5 and 5 mm, the steel sheet covered by an aluminium alloy precoating with a thickness between 15 and 50 .mu.m, the emissivity coefficient being equal to 0.15(1+.alpha.), .alpha. being between 0 and 2.4, then cutting the steel sheet to obtain a precoated steel blank, then placing the precoated steel blank in furnace zone 1 for a duration t.sub.1 between 5 and 600 s, wherein .THETA..sub.1F and t.sub.1 are such that: .THETA..sub.1Fmax>.THETA..sub.1F>.THETA..sub.1Fmin then transferring the precoated steel blank in the furnace zone 2 heated at a setting temperature .THETA..sub.2F=.THETA..sub.1B and maintaining isothermally the precoated steel blank for a duration t.sub.2, then transferring the precoated steel blank in further zones (3, . . . i, . . . , N) of the furnace, so to reach a maximum blank temperature .THETA..sub.MB between 850.degree. C. and 950.degree. C., the average heating rate V.sub.a of the blank between .THETA..sub.2F and .THETA..sub.MB being between 5 and 500.degree. C./s, then hot forming the heated steel blank so as to obtain a part, then cooling the part to obtain martensite or bainite.