High strength steel sheet and method for manufacturing the same

A high-strength steel sheet having a composition comprising:

• C:
• 0.09% to 0.17%, by mass %;
• Si:
• 0.6% to 1.7%, by mass %;
• Mn:
• 3.5% or less, by mass %;
• P:
• 0.03% or less, by mass %;
• S:
• 0.005% or less, by mass %;
• Al:
• 0.08% or less, by mass %;
• N:
• 0.006% or less, by mass %;
• Ti:
• 0.05% or less, by mass %;
• B:
• 0.0002% to 0.0030%, by mass %;
• and
• Fe and inevitable impurities,
• wherein:
• the steel sheet has a microstructure containing:
• less than 20% (including 0%) of a ferrite phase,
• 75% or more of a tempered martensite phase, which has a Vickers hardness of 280 to 340,
• 10% or less (including 0%) of an untempered martensite phase, and
• 2% or more and less than 5% of a retained austenite phase each phase expressed in terms of area fraction, and
• the steel sheet has a tensile strength in a range of from 950 MPa to 1,120 MPa.