ArcelorMittal S.A.
A MANUFACTURING PROCESS OF PRESS HARDENED PARTS WITH HIGH PRODUCTIVITY

Abstract:

A process for manufacturing a non-stamped prealloyed steel coil, sheet or blank, comprising the following successive steps of: providing a non-stamped precoated steel coil, sheet or blank composed of a steel substrate covered by a precoating of aluminum, or aluminum-based alloy, or aluminum alloy, wherein the precoating thickness is comprised between 10 and 35 micrometers on each side of the steel coil, sheet or blank, then heating the non-stamped steel coil, sheet or blank in a furnace under an atmosphere containing at least 5% oxygen, up to a temperature .theta..sub.1 comprised between 750 and 1000.degree. C., for a duration t.sub.1 comprised between t.sub.1min and t.sub.1max, wherein: t.sub.1min=23500/(.theta..sub.1-729.5) and t.sub.1max=4.946.times.10.sup.41.times..theta..sub.1.sup.-13.08, t.sub.1 designating the total duration in the furnace, .theta..sub.1 being expressed in .degree. C. and t.sub.1min and t.sub.1max being expressed in seconds, then cooling the non-stamped steel coil, sheet or blank at a cooling rate V.sub.r1 down to a temperature .theta..sub.i, then maintaining the non-stamped steel coil, sheet or blank at a temperature .theta..sub.2 comprised between 100 and 500.degree. C., for a duration t.sub.2 comprised between 3 and 45 minutes, so to obtain a diffusible hydrogen less than 0.35 ppm.