Hot-rolled high-strength roll-formable steel sheet with excellent stretch-flange formability and a method of producing said steel
AssigneeTata Steel Ijmuiden B.V.
InventorsRolf Arjan Rijkenberg, Maxim Peter Aarnts
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Abstract
A hot-rolled high-strength steel strip or sheet with excellent roll-forming characteristics and excellent stretch-flange formability suitable for automotive chassis part or the like and, more particularly, to a high-strength steel strip or sheet with tensile strength of 780 MPa or higher, or preferably 950 MPa or higher, with an excellent combination of total elongation, stretch-flange formability and fatigue resistance and to a method of manufacturing the steel strip or sheet, and to the use of the strip or sheet in a part.
Claims20
A high-strength hot-rolled steel strip or sheet with a tensile strength of 780 MPa or higher with continuous yielding behaviour, consisting of (in wt %):
- between 0.08 and 0.14% C.;
- between 1.0 and 2.0% Mn;
- between 0.05 and 0.45% Mo;
- between 0.10 and 0.40% V;
- optionally one or more of
- at least 0.1 and/or at most 1.2% Cr;
- at least 0.01 and/or at most 0.14% Ti;
- at least 0.05 and at most 0.5% Si;
- at least 0.01 and at most 0.10% Nb;
- at most 0.04% P;
- at most 0.008% S;
- at most 0.1% Al_sol;
- at most 0.020% N;
- at most 0.003% B;
- optionally Ca in an amount consistent with a calcium treatment for inclusion control;
- balance Fe and inevitable impurities;
- wherein the steel strip or sheet has a microstructure that contains a matrix consisting of a mixture of at most 60 vol. % polygonal ferrite (PF) and at least 40 vol. % bainitic ferrite (BF) and between at least 0.8 vol. % and at most 5 vol. % of Σ(martensite and retained-austenite), wherein the PF and BF is precipitation-strengthened with fine composite carbides and/or carbo-nitrides of V and/or of Mo and optionally of Ti and/or of Nb.
A coated high-strength steel strip or sheet consisting of:
- a zinc-based coating on an upper and/or lower surface of:
- a strip or sheet with a tensile strength of 780 MPa or higher with continuous yielding behaviour, consisting of (in wt %):
- between 0.08 and 0.14% C;
- between 1.0 and 2.0% Mn;
- between 0.05 and 0.45% Mo;
- between 0.10 and 0.40% V;
- optionally one or more of
- at least 0.1 and/or at most 1.2% Cr;
- at least 0.01 and/or at most 0.14% Ti;
- at least 0.05 and at most 0.5% Si;
- at least 0.01 and at most 0.10% Nb;
- at most 0.04% P;
- at most 0.008% S;
- at most 0.1% Al_sol;
- at most 0.020% N;
- at most 0.003% B;
- optionally Ca in an amount consistent with a calcium treatment for inclusion control;
- balance Fe and inevitable impurities;
- wherein the steel strip or sheet has a microstructure that contains a matrix consisting of a mixture of at most 60 vol. % polygonal ferrite (PF) and at least 40 vol. % bainitic ferrite (BF) and between at least 0.8 vol. % and at most 5 vol. % of Σ(martensite and retained-austenite), wherein the PF and BF is precipitation-strengthened with fine composite carbides and/or carbo-nitrides of V and/or of Mo and optionally of Ti and/or of Nb.
Dependencies are inferred from the claim text.