| 摘要 |
The invention relates to a rolled steel sheet, for press hardening, the chemical composition of which comprises, the contents being expressed by weight: 0.24% ≤ C ≤ 0.38%, 0.40% ≤ Mn ≤ 3%, 0.10% ≤ Si ≤ 0.70%, 0.015% ≤ Al ≤ 0.070%, 0% ≤ Cr ≤ 2%, 0.25% ≤ Ni ≤ 2%, 0.015% ≤ Ti ≤ 0.10%, 0 % ≤ Nb ≤ 0.060%, 0.0005% ≤ B ≤ 0.0040%, 0.003% ≤ N ≤ 0.010%, 0.0001% ≤ S ≤ 0.005%, 0.0001% ≤ P ≤ 0.025%, it being understood that the titanium and nitrogen contents satisfy: Ti/N > 3.42, and that the carbon, manganese, chromium and silicon contents satisfy: formula (I), the chemical composition optionally comprising one or more of the following elements: 0.05% ≤ Mo ≤ 0.65%, 0,001% ≤ W ≤ 0.30%, 0.0005 % ≤ Ca ≤ 0.005%, the remainder consisting of iron and of unavoidable impurities originating from the production, the sheet containing a nickel content Nisurf at any point of the steel in the region of the surface of said sheet over a depth Δ, such that: Nisurf > Ninom, Ninom denoting the nominal nickel content of the steel, and such that, Nimax denoting the maximum nickel content within Δ: formula (II) and such that: formula (III) the depth Δ being expressed in micrometres, the Nimax and Ninom contents being expressed as weight percentages. |
