Steel sheet and high strength press hardened steel part having excellent bending and method of manufacturing the same

A process for manufacturing a steel sheet, comprising the following successive steps:

• providing a liquid steel having a chemical 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;
• casting said liquid steel to obtain a semi-product able to be hot-rolled;
• hot rolling the semi-product at a finish hot rolling temperature comprised from 800° C. to 950° C.;
• and
• coiling the hot rolled steel sheet at a coiling temperature Tcoil lower than 670° C. to obtain a coiled steel sheet,
• the obtained steel sheet having a microstructure in surface fraction comprising from 75% to 90% of ferrite, a rest being comprised of Fe3C and hard phases made of martensite and/or bainite,
• said steel sheet comprising from a bulk to a surface of the steel sheet:
• the bulk representing 80% of the steel sheet thickness,
• 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, a density of TiN/Ti(C,N) inclusions in said skin being strictly lower than 240 particles/mm2 and a clustering index of MnS inclusions in said skin being strictly lower than 110 μm/mm2.