# US 9,752,217 B2 · Hot-rolled steel sheet and method of producing the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,752,217 B2 - Document ID: US9752217B2 - Status: Granted - Kind: B2 - Application number: 14/008,205 - Filed: 2012-04-13 - Published: 2014-01-16 - Granted: 2017-09-05 - Earliest claimed: 2011-04-13 - Assignees: Nippon Steel & Sumitomo Metal Corporation - Applicants: Tatsuo Yokoi; Hiroshi Shuto; Riki Okamoto; Nobuhiro Fujita; Kazuaki Nakano; Takeshi Yamamoto - Inventors: Tatsuo Yokoi; Hiroshi Shuto; Riki Okamoto; Nobuhiro Fujita; Kazuaki Nakano; Takeshi Yamamoto - Web page: https://patentgrep.com/patent/US9752217B2 ## CPC - C22C 38/34: with more than 1.5% by weight of silicon - C21D 8/0226: {Hot rolling} - C21D 8/0263: {following hot rolling} - 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 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - C22C 38/08: containing nickel {(C22C38/105 takes precedence)} - C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium - C22C 38/14: containing titanium or zirconium - C22C 38/16: containing copper - C22C 38/28: with titanium or zirconium - C22C 38/38: with more than 1.5% by weight of manganese - C21D 2211/003: Cementite - C21D 2211/004: Dispersions; Precipitations - C22C: ALLOYS (treatment of alloys C21D, C22F) - 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) ## Abstract In a hot-rolled steel sheet, an average pole density of an orientation group {100}<011> to {223}<110>, which is represented by an arithmetic mean of pole densities of orientations {100}<011>, {116}<110>, {114}<110>, {112}<110>, and {223}<110> is 1.0 to 4.0 and a pole density of a crystal orientation {332}<113> is 1.0 to 4.8, in a thickness center portion which is a thickness range of ⅝ to ⅜ from the surface of the steel sheet; an average grain size in the thickness center portion is less than or equal to 10 μm and a grain size of cementite precipitating in a grain boundary of the steel sheet is less than or equal to 2 μm; and an average grain size of precipitates containing TiC in grains is less than or equal to 3 nm and a number density per unit volume is greater than or equal to 1×1016 grains/cm3. ## Claims ### Claim 1 A hot-rolled steel sheet comprising, by mass %, C: a content [C] of 0.02% to 0.07%, Si: a content [Si] of 0.001% to 2.5%, Mn: a content [Mn] of 0.01% to 4%, Al: a content [Al] of 0.001% to 2%, Ti: a content [Ti] of 0.015% to 0.2%, P: a limited content [P] of 0.15% or less, S: a limited content [S] of 0.03% or less, N: a limited content [N] of 0.01% or less, and the balance consisting of Fe and unavoidable impurities, wherein the contents [Ti], [N], [S], and [C] satisfy the following expressions (a) and (b); an average pole density of an orientation group {100}<011> to {223}<110>, which is represented by an arithmetic mean of pole densities of orientations {100}<011>, {116}<110>, {114}<110>, {112}<110, and {223}<110> is 1.0 to 4.0 and a pole density of a crystal orientation {332}<113> is 1.0 to 4.8, in a thickness center portion which is a thickness range of ⅝ to ⅜ from the surface of the steel sheet; an average grain size in the thickness center portion is less than or equal to 10 μm and a grain size of a cementite precipitating in a grain boundary in the steel sheet is less than or equal to 2 μm; and an average grain size of precipitates containing TiC in grains is less than or equal to 3 nm and a number density per unit volume is greater than or equal to 1×1016 grains/cm3, 0%≦([Ti]−[N]×48/14−[S]×48/32) (a) 0%≦[C]−12/48×([Ti]−[N]×48/14−[S]×48/32) (b). ### Claim 2 (depends on 1) The hot-rolled steel sheet according to claim 1, wherein the average pole density of the orientation group {100}<011> to {223}<110> is less than or equal to 2.0 and the pole density of the crystal orientation {332}<113> is less than or equal to 3.0. ### Claim 3 (depends on 2) The hot-rolled steel sheet according to claim 2, further comprising, by mass %, Nb: a content [Nb] of 0.005% to 0.06%, wherein the contents [Nb], [Ti], [N], [S], and [C] satisfy the following expression (c), 0%≦[C]−12/48×([Ti]+[Nb]×48/93−[N]×48/14−[S]×48/32) (c). ### Claim 4 (depends on 2) The hot-rolled steel sheet according to claim 2, further comprising one or two or more selected from the group consisting of, by mass %, Cu: a content [Cu] of 0.02% to 1.2%, Ni: a content [Ni] of 0.01% to 0.6%, Mo: a content [Mo] of 0.01% to 1%, V: a content [V] of 0.01% to 0.2%, Cr: a content [Cr] of 0.01% to 2%, Mg: a content [Mg] of 0.0005% to 0.01%, Ca: a content [Ca] of 0.0005% to 0.01%, REM: a content [REM] of 0.0005% to 0.1%, and B: a content [B] of 0.0002% to 0.002%. ### Claim 5 (depends on 1) The hot-rolled steel sheet according to claim 1, wherein the average grain size is less than or equal to 7 μm. ### Claim 6 (depends on 5) The hot-rolled steel sheet according to claim 5, further comprising, by mass %, Nb: a content [Nb] of 0.005% to 0.06%, wherein the contents [Nb], [Ti], [N], [S], and [C] satisfy the following expression (c), 0%≦[C]−12/48×([Ti]+[Nb]×48/93−[N]×48/14−[S]×48/32) (c). ### Claim 7 (depends on 5) The hot-rolled steel sheet according to claim 5, further comprising one or two or more selected from the group consisting of, by mass %, Cu: a content [Cu] of 0.02% to 1.2%, Ni: a content [Ni] of 0.01% to 0.6%, Mo: a content [Mo] of 0.01% to 1%, V: a content [V] of 0.01% to 0.2%, Cr: a content [Cr] of 0.01% to 2%, Mg: a content [Mg] of 0.0005% to 0.01%, Ca: a content [Ca] of 0.0005% to 0.01%, REM: a content [REM] of 0.0005% to 0.1%, and B: a content [B] of 0.0002% to 0.002%. ### Claim 8 (depends on 1) The hot-rolled steel sheet according to claim 1, further comprising, by mass %, Nb: a content [Nb] of 0.005% to 0.06%, wherein the contents [Nb], [Ti], [N], [S], and [C] satisfy the following expression (c), 0%≦[C]−12/48×([Ti]+[Nb]×48/93−[N]×48/14−[S]×48/32) (c). ### Claim 9 (depends on 8) The hot-rolled steel sheet according to claim 8, further comprising one or two or more selected from the group consisting of, by mass %, Cu: a content [Cu] of 0.02% to 1.2%, Ni: a content [Ni] of 0.01% to 0.6%, Mo: a content [Mo] of 0.01% to 1%, V: a content [V] of 0.01% to 0.2%, Cr: a content [Cr] of 0.01% to 2%, Mg: a content [Mg] of 0.0005% to 0.01%, Ca: a content [Ca] of 0.0005% to 0.01%, REM: a content [REM] of 0.0005% to 0.1%, and B: a content [B] of 0.0002% to 0.002%. ### Claim 10 (depends on 1) The hot-rolled steel sheet according to claim 1, further comprising one or two or more selected from the group consisting of, by mass %, Cu: a content [Cu] of 0.02% to 1.2%, Ni: a content [Ni] of 0.01% to 0.6%, Mo: a content [Mo] of 0.01% to 1%, V: a content [V] of 0.01% to 0.2%, Cr: a content [Cr] of 0.01% to 2%, Mg: a content [Mg] of 0.0005% to 0.01%, Ca: a content [Ca] of 0.0005% to 0.01%, REM: a content [REM] of 0.0005% to 0.1%, and B: a content [B] of 0.0002% to 0.002%. ### Claim 11 A method of producing a hot-rolled steel sheet, the method comprising: heating a steel ingot or a slab including, by mass %, C: a content [C] of 0.02% to 0.07%, Si: a content [Si] of 0.001% to 2.5%, Mn: a content [Mn] of 0.01% to 4%, Al: a content [Al] of 0.001% to 2%, Ti: a content [Ti] of 0.015% to 0.2%, P: a limited content [P] of 0.15% or less, S: a limited content [S] of 0.03% or less, N: a limited content [N] of 0.01% or less, and the balance consisting of Fe and unavoidable impurities, in which the contents [Ti], [N], [S], and [C] satisfy the following expressions (a) and (b), at SRTmin° C., which is a temperature determined according to the following expression (d) and 1150° C., to 1260° C.; performing a first hot rolling in which reduction is performed once or more at a rolling reduction of 40% or higher per pass in a temperature range of 1000° C. to 1200° C.; starting a second hot rolling in a temperature range of 1000° C. or higher within 150 seconds after a finish of the first hot rolling; performing a reduction in the second hot rolling in a temperature range of (T1+30)° C. to (T1+200)° C., wherein a temperature determined by components of the steel sheet according to the following expression (e) is represented by T1° C. so as to obtain a total reduction ratio of 50% or higher, with at least one of a rolling reduction ratio of 30%; performing a third hot rolling in which a total rolling reduction is lower than or equal to 30% in a temperature range of less than (T1+30)° C.; finishing the hot rollings at the Ar3 transformation temperature or higher; performing a primary cooling under conditions of a cooling rate of 50° C./sec or higher, a temperature change of 40° C. or more and 140° C. or less, and a cooling end temperature of (T1+100)° C. or lower such that a waiting time t (second) from a finish of a final pass of a large reduction pass to a start of cooling satisfies the following expression (f), wherein said large reduction pass is defined as a pass of a rolling reduction of 30% or higher in the temperature range of (T1+30)° C. to (T1+200)° C.; performing a secondary cooling at a cooling rate of 15° C./sec or higher within 3 seconds from the finish of the primary cooling; and performing a coiling in a temperature range of 550° C. to lower than 700° C., 0%≦([Ti]−[N]×48/14−[S]×48/32) (a) 0%≦[C]−12/48×([Ti]−[N]×48/14−[S]×48/32) (b) SRTmin=7000/{2.75−log([Ti]×[C])}−273 (d) T1=850+10×([C]+[N])×[Mn]+350×[Nb]+250×[Ti]+40×[B]+10×[0]+100×[Mo]+100×[V] (e) t≦2.5×t1 (f) where t1 is represented by the following expression (g), t1=0.001×((Tf−T1)×P1/100)2−0.109×((Tf−T1)×P1/100)+3.1 (g) where Tf represents a temperature (° C.) after a final reduction at a rolling reduction of 30% or higher, and P1 represents the rolling reduction (%) during the final reduction at a rolling reduction of 30% or higher. ### Claim 12 (depends on 11) The method of producing a hot-rolled steel sheet according to claim 11, wherein the primary cooling is performed between rolling stands and the secondary cooling is performed after passage through a final rolling stand. ### Claim 13 (depends on 12) The method of producing a hot-rolled steel sheet according to claim 12, wherein the waiting time t (second) further satisfies the following expression (h), t1≦t≦2.5×t1 (h). ### Claim 14 (depends on 12) The method of producing a hot-rolled steel sheet according to claim 12, wherein the waiting time t (second) further satisfies the following expression (i), t