# US 12,180,556 B2 · Hot rolled steel sheet having excellent crashworthiness and method for manufacturing same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,180,556 B2 - Document ID: US12180556B2 - Status: Granted - Kind: B2 - Application number: 18/025,836 - Filed: 2021-09-13 - Published: 2023-11-16 - Granted: 2024-12-31 - Earliest claimed: 2020-09-22 - Assignees: Posco - Applicants: Posco Co., Ltd - Inventors: Tae-Jin Song; Sung-Il Kim; Chang-Sik Choi - Web page: https://patentgrep.com/patent/US12180556B2 ## CPC - C21D 1/02: Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation - C21D 8/0226: {Hot rolling} - B32B 15/013: {one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium} - C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) - C21D 1/19: by interrupted quenching - C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence) - C21D 8/0247: characterised by the heat treatment - C21D 8/0263: {following hot rolling} - C21D 8/0273: {Final recrystallisation annealing} - C21D 9/46: for sheet metals - C22C 38/001: {containing N} - C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium - C22C 38/14: containing titanium or zirconium - C22C 38/22: with molybdenum or tungsten - C22C 38/26: with niobium or tantalum - C22C 38/28: with titanium or zirconium - C22C 38/38: with more than 1.5% by weight of manganese - C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur - C23C 2/0224: {Two or more thermal pretreatments} - C23C 2/06: Zinc or cadmium or alloys based thereon - C23C 2/40: Plates; Strips - C23G 1/00: Cleaning or pickling metallic material with solutions or molten salts (with organic solvents C23G5/02) - C21D 2211/001: Austenite - C21D 2211/002: Bainite - C21D 2211/005: Ferrite - C21D 2211/008: Martensite - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM - C22C: ALLOYS (treatment of alloys C21D, C22F) - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) - C23G: CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS ## Abstract Provided are a hot rolled steel sheet having excellent crashworthiness and a method for manufacturing same. The hot rolled steel sheet of the present invention contains, in weight %, 0.05-0.13% of carbon (C), 0.2-2.0% of silicon (Si), 1.3-3.0% of manganese (Mn), 0.01-0.1% of aluminum (Al), 0.001-0.05% of phosphor (P), 0.001-0.05% of sulfur (S), 0.001-0.02% of nitrogen (N), and the balance being Fe and other inevitable impurities, and has a steel microstructure comprising, in area %, 55% or more of bainitic ferrite, 10% or more of a martensite/austenite composite phase (MA), the sum of the bainitic ferrite and the martensite/austenite composite phase (MA) being 95% or more, and the remaining total being less than 5% of granular ferrite, retained austenite, and carbides. ## Claims ### Claim 1 A high-strength hot rolled steel sheet having an excellent yield strength comprising, by weight: 0.05 to 0.13% of carbon (C), 0.2 to 2.0% of silicon (Si), 1.3 to 3.0% of manganese (Mn), 0.01 to 0.1% of aluminum (Al), 0.001 to 0.05% of phosphorus (P), 0.001 to 0.05% of sulfur(S), and 0.001 to 0.02% of nitrogen (N), with a balance of Fe and other inevitable impurities, wherein a steel microstructure includes, by area: 55% or more of bainitic ferrite and 10% or more of a martensite/austenite (MA) composite phase, the sum of the bainitic ferrite and the martensite/austenite (MA) composite phase being 95% or more and the remaining total being less than 5% of granular ferrite, residual austenite, and carbides, in the bainitic ferrite, an area fraction of bainitic ferrite having an intragrain orientation difference of 1.5° or more and 10.5° or less is 55% or more of the total area of the bainitic ferrite, and the martensite/austenite (MA) composite phase has an average particle diameter of 2.0 μm or less and an average interval of 0.3 μm or more. ### Claim 2 (depends on 1) The high-strength hot rolled steel sheet having an excellent yield strength of claim 1, further comprising one or more of, by weight: 0.01 to 2.0% of chromium (Cr), 0.01 to 2.0% of molybdenum (Mo), 0.01 to 0.2% of titanium (Ti), and 0.01 to 0.1% of niobium (Nb). ### Claim 3 (depends on 1) The high-strength hot rolled steel sheet having an excellent yield strength of claim 1, wherein the martensite/austenite (MA) composite phase has an area fraction of 10 to 45%. ### Claim 4 (depends on 1) The high-strength hot rolled steel sheet having an excellent yield strength of claim 1, wherein the hot rolled steel sheet has yield strength of 750 MPa or more, a tensile strength of 950 MPa or more, an elongation of 8% or more, a hole expandability of 25% or more, and a difference in elongations measured in a vertical rolling direction and a parallel rolling direction of 3% or less. ### Claim 5 A method for manufacturing a high-strength hot rolled steel sheet having an excellent yield strength, the method comprising: heating a steel slab including, by weight: 0.05 to 0.13% of carbon (C), 0.2 to 2.0% of silicon (Si), 1.3 to 3.0% of manganese (Mn), 0.01 to 0.1% of aluminum (Al), 0.001 to 0.05% of phosphorus (P), 0.001 to 0.05% of sulfur(S), and 0.001 to 0.02% of nitrogen (N), with a balance of Fe and other inevitable impurities at 1100 to 1350° C.; finish hot rolling the heated steel slab while controlling the sum of reduction amounts of final two rolling passes to 10 to 40% in which FDT (° C.) which is a temperature of a hot rolled sheet immediately after the finish hot rolling satisfies the following Relations 1 and 2 at a temperature between 750° C. and 1150° C.; first cooling the hot rolled steel sheet to a temperature of T1 defined in the following Relation 3 or lower between Ms and 520° C. at a cooling rate of 50° C./s or more, and then, second cooling the steel sheet to a coiling temperature between T1 and Ms-50° C. at a cooling rate of 50° C./s or less; and finally cooling the hot rolled steel sheet coiled after the second cooling to room temperature: [Relation 1] FDT ≥Tnr−50° C. wherein Tnr is a temperature at which recrystallization delay starts with Tnr=795+88×[C]+45×[Mn]+23×[Cr]+760×[Ti]+480×[Nb]−80×[Si], and each element refers to % by weight thereof, [Relation 2] Du=3.7+0.36×[C]−1.21×[Si]−0.23×[Mn]+0.19×[Cr]−41.63×[Ti]−54.44×[Nb]+0.049×[FDT-773]≤10, wherein Du is an indicator showing an effective crystal grain size of austenite immediately before the first cooling after the finish hot rolling, and each element refers to % by weight thereof, k ⁡ ( t ) = 2 ⁢ 0 D u ⁢ exp ⁢ { - ( T 1 + 2 ⁢ 73 - T D 1 ⁢ 1 ⁢ 2 ) 1.92 } ≥ 7. × 10 - 3 [ Relation ⁢ 3 ] wherein TD=820−290×[C]−90×[Mn]−70×[Cr]−62×[Mo]−35×[Si], and each element refers to weight contents thereof, wherein Ms is a temperature at which martensite production starts by cooling with Ms=550−330×[C]−41×[Mn]−20×[Cr]−10×[Mo]+30×[A1]−20×[Si], in ° C., and each element refers to % by weight thereof. ### Claim 6 (depends on 5) The method for manufacturing a high-strength hot rolled steel sheet having an excellent yield strength of claim 5, wherein the hot rolled steel sheet further includes one or more of, by weight: 0.01 to 2.0% of chromium (Cr), 0.01 to 2.0% of molybdenum (Mo), 0.01 to 0.2% of titanium (Ti), and 0.01 to 0.1% of niobium (Nb). ### Claim 7 (depends on 5) The method for manufacturing a high-strength hot rolled steel sheet having an excellent yield strength of claim 5, further comprising: pickling and oiling the finally cooled steel sheet. ### Claim 8 (depends on 5) The method for manufacturing a high-strength hot rolled steel sheet having an excellent yield strength of claim 5, further comprising: after the pickling, heating the finally cooled steel sheet to a temperature within a range of 400 to 750° C. to perform hot dip galvanizing.