Granted Patent B2

US 12,509,742 · App. 17/436,348 · Granted Dec 30, 2025

Inventors: Sung-Il Kim (Gwangyang-si, KR); Chan-Woo Bang (Gwangyang-si, KR)

Assignee: POSCO CO., LTD

C21D9/46C21D6/002C21D6/005C21D6/008C21D8/0205C21D8/0226C21D8/0236C22C38/001C22C38/002C22C38/02C22C38/06C22C38/26C22C38/28C22C38/32C22C38/38C21D2211/002C21D2211/008

Abstract

Claims (47)

1 . A steel sheet having excellent shear workability, the steel sheet comprising, by weight %,

carbon (C): 0.06 to 0.14%,

silicon (Si): 0.1 to 0.8%,

manganese (Mn): 1.8 to 2.2%,

chromium (Cr): 0.005 to 0.8%,

phosphorus (P): 0.001 to 0.05%,

sulfur (S): 0.001 to 0.01%,

aluminum (Al): 0.01 to 0.1%,

nitrogen (N): 0.001 to 0.01%,

titanium (Ti): 0.01 to 0.06%,

niobium (Nb): 0.005 to 0.06%,

boron (B): 0.0003 to 0.0050%, and

a balance of iron (Fe) and unavoidable impurities,

wherein the steel sheet has a microstructure that includes:

a bainite phase in an area fraction of 80% or more,

a martensite phase in an area fraction of 10% or less, and

at least one of a retained austenite phase, a ferrite phase, and a pearlite phase as a remainder,

wherein a maximum length of cracks formed during a shearing process is 0.1 mm or less,

wherein the steel sheet has tensile strength of 1350 MPa or more and a Vickers hardness value of 360 Hv or more.

2 . The steel sheet of claim 1 , wherein the steel sheet includes pearlite including carbides, each having an equivalent circular diameter of 0.1 μm or more, in an area fraction of less than 5%.

3 . A method for manufacturing a steel sheet having excellent shear workability, the method comprising:

heating a steel slab including, by weight %,

carbon (C): 0.06 to 0.14%,

silicon (Si): 0.1 to 0.8%,

manganese (Mn): 1.8 to 2.2%,

chromium (Cr): 0.005 to 0.8%,

phosphorus (P): 0.001 to 0.05%,

sulfur (S): 0.001 to 0.01%,

aluminum (Al): 0.01 to 0.1%,

nitrogen (N): 0.001 to 0.01%,

titanium (Ti): 0.01 to 0.06%,

niobium (Nb): 0.005 to 0.06%,

boron (B): 0.0003 to 0.0050%, and

a balance of iron (Fe) and unavoidable impurities;

finish-rolling the heated steel slab within a temperature range of 800 to 1150° C. to manufacture a hot-rolled steel sheet;

cooling the hot-rolled steel sheet, and then coiling the cooled hot-rolled steel sheet; and

cold-rolling the coiled hot-rolled steel sheet to manufacture a cold-rolled steel sheet,

wherein the cooling is performed at an average cooling rate CR Min (C/s), obtained by Relation Expression 1 below, or higher, and is performed to a temperature between CT Min (° C.) and CT Max (° C.) obtained by Relational Expression 2 below,

CR Min =190−(105×[C])+(35×[Si])−(58×[Mn])−(46×[Cr])+(15×[Ti])+(50×[Nb])−(150×[B])  [Relational Expression 1]

CT Max =510−(120×[C])+(30×[Si])−(25×[Mn])−(22×[Cr])+(8.5×[Ti])+(14×[Nb])+(805×[B])

CT Min =420−(45.3×[C])+(16×[Si])−(21×[Mn])−(18×[Cr])  [Relational Expression 2]

where each element denotes a content by weight %, and

wherein an increase of strength by the cold rolling (reduction ratio, %) is 6 MPa/1% or more.

4 . The method of claim 3 , wherein the heating of the steel slab is performed within a temperature range of 1100 to 1350° C.

5 . The method of claim 3 , wherein the cold-rolling is performed at a cold reduction ratio of 60 to 80%.

6 . The steel sheet of claim 1 , comprising, by weight %, chromium (Cr): 0.3 to 0.8%.

7 . The steel sheet of claim 1 , comprising, by weight %, titanium (Ti): 0.01 to 0.04%.

Assignments (3)

Priority Claims (1)

Continuity (1)

References Cited (36)