Steel sheet including a multilayer coating and methods
A steel sheet is provided. The steel sheet includes a multilayer coating including at least one zinc-based layer being 0.1% to 20% magnesium by weight which is covered by a fine temporary protective layer of 5 to 100 nm. The fine temporary protective layer is composed of metal or metal oxide selected from the group consisting of aluminum, chromium, aluminum oxides AlOx, with x being strictly between 0.01 and 1.5 and chromium oxides CrOy, with y being strictly between 0.01 and 1.5. The at least one zinc-based layer is not alloyed with the temporary protective layer. Manufacturing methods for a sheet and part are also provided.
1. A steel sheet with a multilayer coating comprising:
at least one zinc-based layer including from 0.1% to 20% magnesium by weight; and
a temporary protective layer covering the at least one zinc-based layer, the temporary protective layer being between 5 and 100 nm and consisting of metal or metallic oxide selected from the group consisting of aluminum, chromium, aluminum oxides AlOx, x being from 0.01 to 1.5, and chromium oxides CrOy, y being from 0.01 to 1.5,
the at least one zinc-based layer not being alloyed with the temporary protective layer.
2. The steel sheet according to claim 1 , wherein the multilayer coating further comprises:
a second zinc-based layer of less than 0.05% magnesium by weight, covered by the at least one zinc-based layer, which is covered by the temporary protective layer, the at least one zinc-based layer not being alloyed with the temporary protective layer or the second zinc-based layer.
3. The steel sheet according to claim 2 , wherein the at least one zinc-based layer and the second zinc-based layer-further include from 0.1% to 10% aluminum by weight.
4. The steel sheet according to claim 1 , wherein the at least one zinc-based layer is formed from Zn 2 Mg.
5. The steel sheet according to claim 1 , wherein the temporary protective layer is formed from aluminum.
6. The steel sheet according to claim 1 , wherein the temporary protective layer has a thickness between 5 and 50 nm.
7. The steel sheet according to claim 1 , wherein the at least one zinc-based layer is 0.1% to 10% aluminum by weight.
8. A sheet manufacturing method comprising the steps of:
forming the multilayer coated steel sheet according to claim 1 by:
supplying a bare steel sheet;
applying the at least one zinc-based layer to the bare steel sheet; and
depositing the temporary protective layer over the at least on zinc-based layer by vacuum deposition.
9. The manufacturing method according to claim 8 , wherein the at least one zinc-based layer is applied by vacuum deposition.
10. A manufacturing method for a part from the steel sheet according to claim 1 , comprising the steps of:
coating the steel sheet with a lubricating oil in an amount less than or equal to 1 g/m 2 ;
forming the sheet by drawing; and
subjecting the steel sheet to alkaline degreasing.
11. A steel sheet with a multilayer coating consisting of:
at least one zinc-based layer including 0.1% to 20% magnesium by weight, covered by a temporary protective layer of between 5 and 100 nm consisting of metal or metal oxide selected from the group consisting of aluminum, chromium, aluminum oxides AlOx, x being strictly between 0.01 and 1.5, and chromium oxides CrOy, y being strictly between 0.01 and 1.5, with the at least one zinc-based layer not being alloyed with the temporary protective layer.