Steel sheet and high strength press hardened steel part having excellent bending anisotropy and method of manufacturing the same
A steel sheet has a chemical composition including in wt % C: 0.2-0.4%, Mn 0.8-2.0%, Si: 0.1-0.5%, Al: 0.01-0.1%, Ti: 0.01-0.1%, B: 0.0005-0.005%, P≤0.040%, Ca≤0.01%, S≤0.006%, N≤0.01%. The steel sheet includes from the bulk to the surface of the coated steel sheet a bulk and a skin layer occupying the outermost 10% of the thickness on either side of the bulk. The bulk includes an inclusion population in which the sum of clustering indexes of MnS and TiN/Ti(C,N) inclusions is less than or equal to 300 μm/mm 2 . This allows to manufacture hot pressed parts having a tensile strength equal to or greater than 1300 MPa and a bending anisotropy equal to or lower than 7°.
1. A steel sheet made of a steel having a composition comprising, by weight percent:
C: 0.2-0.3%;
Mn: 0.8-2.0%;
Si: 0.1-0.5%;
Al: 0.01-0.1%;
Ti: 0.01-0.1%;
B: 0.0005-0.005%;
P≤0.040%;
Ca≤0.01%;
S≤0.006%;
N≤0.01%;
and comprising optionally:
Cr≤0.4%;
Mo≤0.3%;
Nb≤0.1%;
V≤0.3%;
wherein Cr+Mo+Nb+V≤0.5%,
a remainder of the composition being iron and unavoidable impurities resulting from an elaboration process,
said steel sheet having a microstructure in surface fraction comprising from 75% to 90% of ferrite, a rest being comprised of Fe 3 C and hard phases made of martensite and/or bainite, said steel sheet comprising from a bulk to the surface of the steel sheet:
the bulk representing 80% of a thickness of the steel sheet; and
the bulk being topped by a top skin layer and a bottom skin layer occupying an outermost 10% of the thickness on either sides of the bulk, said bulk comprising an inclusion population wherein a sum of clustering indexes of MnS and TiN/Ti(C,N) inclusions is less than or equal to 300μm/mm 2 .
2. The steel sheet according to claim 1 , wherein:
C: 0.2-0.25%; and/or
Mn: 1.0-1.4%; and/or
Si: 0.1-0.4%; and/or
Al: 0.02-0.06%; and/or
Ti: 0.02-0.06%; and/or
B: 0.002-0.004%; and/or
P≤0.020%; and/or
Ca≤0.005%; and/or
S≤0.005%; and/or
N≤0.008%.
3. The steel sheet according to claim 1 , wherein the steel sheet is coated with a metallic coating comprising at least 50% of Al in weight.
4. The steel sheet according to claim 1 , wherein the steel sheet is coated with a metallic coating comprising at least 50% of Zn in weight.
5. The steel sheet according to claim 1 , wherein the composition further respects the following condition, all elements being expressed in weight %:
(S−Ca*32/40)+(30*Ti*N)≤0.0045.
6. The steel sheet according to claim 2 , wherein the composition comprises, by weight percent, Si: 0.15-0.35%.
7. The steel sheet according to claim 2 , wherein the composition comprises, by weight percent, N≤0.005%.