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US 2023/0272500 A1Published application
High-strength steel sheet having excellent formability and method for manufacturing thereof
AssigneePosco
InventorsSung-Kyu KIM, Jun-Ho PARK, Chang-Hyo SEO, Eul-Yong CHOI, Sang-Ho HAN
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Abstract
Provided is a high-strength steel sheet suitable for automobile structural members, etc., and a method for manufacturing same, wherein the high-strength steel sheet has a low yield ratio and high strength and has excellent formability through improvement of ductility that may prevent processing defects such as cracks, wrinkles, or the like, during press forming.
Claims11
A high-strength steel sheet having excellent formability comprising, by weight %:
- 0.05 to 0.15% of carbon (C), 0.5% or less (excluding 0%) of silicon (Si), 2.0 to 3.0% of manganese (Mn), 0.2% or less (excluding 0%) of titanium (Ti), 0.1% or less (excluding 0%) of niobium (Nb), 0.2% or less (excluding 0%) of vanadium (V), 0.5% or less (excluding 0%) of molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), and a remainder of Fe and other unavoidable impurities,
- wherein a microstructure is composed of ferrite with an area fraction of 20 to 45%, and a remainder of martensite and bainite, and
- a fraction of non-recrystallized ferrite, among the ferrite is 25 area% or less, and an average aspect ratio thereof (major axis:
- minor axis) is 1.1 to 2:1.
1 more element
A method for manufacturing a high-strength steel sheet having excellent formability, comprising:
- an operation of heating a steel slab including, by wt%:
- 0.05 to 0.15% of carbon (C), 0.5% or less (excluding 0%) of silicon (Si), 2.0 to 3.0% of manganese (Mn), 0.2% or less (excluding 0%) of titanium (Ti), 0.1% or less (excluding 0%) of niobium (Nb), 0.2% or less (excluding 0%) of vanadium (V), 0.5% or less (excluding 0%) of molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), and a remainder of Fe and other unavoidable impurities,
- an operation of manufacturing a hot-rolled steel sheet by finishing hot rolling the heated slab at an outlet temperature of Ar3 or higher to 1000° C. or lower;
- an operation of coiling the hot-rolled steel sheet in a temperature range of 400 to 700° C.;
- an operation of cooling the hot-rolled steel sheet to room temperature after the coiling operation;
- an operation of manufacturing a cold-rolled steel sheet by cold rolling the hot-rolled steel sheet at a reduction ratio of 40 to 70% after the cooling operation;
- an operation of continuous annealing of the cold-rolled steel sheet;
- an operation of primary cooling the cold-rolled steel sheet to a temperature range of 650 to 700° C. after the continuous annealing operation;
- and
- an operation of secondary cooling the cold-rolled steel sheet to a temperature range of 300 to 580° C. after the primary cooling operation,
- wherein the continuous annealing operation is performed in a facility equipped with a heating section, a soaking section, and a cooling section, and an end temperature in the heating section is higher than an end temperature in the soaking section by 10° C. or higher.
8 more elements
Dependencies are inferred from the claim text.