# US 2018/0023154 A1 · High-strength galvanized steel sheet and method for manufacturing the same (as amended) > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0023154 A1 - Document ID: US20180023154A1 - Status: Published application - Kind: A1 - Application number: 15/550,172 - Filed: 2016-01-21 - Published: 2018-01-25 - Earliest claimed: 2015-02-13 - Assignees: Jfe Steel Corporation - Applicants: Jfe Steel Corporation - Inventors: Hiroshi Hasegawa; Yoshimasa Funakawa - Web page: https://patentgrep.com/patent/US20180023154A1 ## CPC - C21D 8/0226: {Hot rolling} - C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence) - C21D 8/0236: {Cold rolling} - C21D 9/46: for sheet metals - C22C 38/14: containing titanium or zirconium - C22C 38/38: with more than 1.5% by weight of manganese - C22C 38/58: with more than 1.5% by weight of manganese - C23C 2/02: Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence) - C23C 2/0224: {Two or more thermal pretreatments} - C23C 2/024: {by cleaning or etching} - C23C 2/06: Zinc or cadmium or alloys based thereon - C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath - C23C 2/29: {Cooling or quenching} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - 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) - 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) ## Abstract A high-strength galvanized steel sheet having a chemical composition containing, by mass %, C: 0.07% to 0.25%, Si: 0.01% to 3.00%, Mn: 1.5% to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.01% to 1.50%, N: 0.001% to 0.008%, Ti: 0.003% to 0.200%, B: 0.0003% to 0.0050%, and the balance being Fe and inevitable impurities, in which the relationship Ti>4N is satisfied, and a microstructure including, in terms of area ratio in a cross section located at ¼ of the thickness from the surface of a base steel sheet, a ferrite phase in an amount of 70% or less (including 0%), a bainite phase and a tempered bainite phase in an amount of 20% or less (including 0%) in total, a tempered martensite phase in an amount of 25% or more, and a retained austenite phase in an amount of less than 3% (including 0%), in which the average crystal grain diameter of the tempered martensite phase is 20 μm or less, in which a variation in the Vickers hardness of the tempered martensite phase is 20 or less in terms of standard deviation, and in which the number density of carbides having a minor axis length of 0.05 μm or more in the tempered martensite phase is 3×106 particles/mm2 or less, as well as a method for manufacturing the steel sheet, is disclosed. ## Claims ### Claim at position 1 -6. (canceled) ### Claim 7 A high-strength, galvanized steel sheet having a chemical composition containing, by mass %: C: 0.07% to 0.25%, Si: 0.01% to 3.00%, Mn: 1.5% to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.01% to 1.50%, N: 0.001% to 0.008%, Ti: 0.003% to 0.200%, B: 0.0003% to 0.0050%, and the balance being Fe and inevitable impurities, wherein the relationship Ti>4N is satisfied, and a microstructure including, in terms of area ratio in a cross section located at ¼ of the thickness from the surface of a base steel sheet: a ferrite phase in an amount of 70% or less (including 0%), a bainite phase and a tempered bainite phase in an amount of 20% or less (including 0%) in total, a tempered martensite phase in an amount of 25% or more, and a retained austenite phase in an amount of less than 3% (including 0%), wherein the average crystal grain diameter of the tempered martensite phase is 20 μm or less, wherein a variation in the Vickers hardness of the tempered martensite phase is 20 or less in terms of standard deviation, and wherein the number density of carbides having a minor axis length of 0.05 μm or more in the tempered martensite phase is 3×106 particles/mm2 or less. ### Claim 8 (depends on 7) The high-strength, galvanized steel sheet according to claim 7, the chemical composition further containing, by mass %, at least one group selected from the group consisting of Group A to C: Group A, which contains at least one selected from: Cr: 0.01% to 2.00%, Mo: 0.01% to 2.00%, V: 0.01% to 2.00%, Ni: 0.01% to 2.00%, and Cu: 0.01% to 2.00% Group B, which contains: Nb: 0.003% to 0.200%, and Group C, which contains at least one selected from: Ca: 0.001% to 0.005%, and REM: 0.001% to 0.005%. ### Claim 9 (depends on 7) A method for manufacturing a high-strength, galvanized steel sheet, the method comprising performing the following processes in the following order: a hot rolling process in which, after having performed finish rolling on a slab having the chemical composition according claim 7, cooling is performed such that a total time during which the hot-rolled steel sheet is retained in a temperature range of 600° C. to 700° C. is 10 seconds or less and in which coiling is performed at a coiling temperature of lower than 600° C., a cold rolling process in which cold rolling is performed with a rolling reduction of more than 20%, an annealing process in which heating is performed to an annealing temperature of 750° C. to 950° C. at an average heating rate of 15° C./s or less and in which the heated steel sheet is held at the annealing temperature for 30 seconds or more, a first cooling process in which cooling is performed at an average cooling rate of 3° C./s or more, a galvanizing process in which galvanizing is performed, a second cooling process in which, after having performed cooling to a temperature equal to or higher than the Ms temperature at an average cooling rate of 1° C./s or more, cooling is performed to a temperature of 100° C. or lower at an average cooling rate of 100° C./s or more, and a tempering process in which reheating is performed to a temperature of 350° C. or lower and in which the reheated steel sheet is held at the temperature for 1 second or more. ### Claim 10 (depends on 9) The method for manufacturing a high-strength, galvanized steel sheet according to claim 9, wherein, after having performed galvanizing in the galvanizing process, an alloying treatment is further performed on the galvanizing layer by heating the galvanized steel sheet to a temperature of 460° C. to 600° C. ### Claim 11 (depends on 8) A method for manufacturing a high-strength, galvanized steel sheet, the method comprising performing the following processes in the following order: a hot rolling process in which, after having performed finish rolling on a slab having the chemical composition according claim 8, cooling is performed such that a total time during which the hot-rolled steel sheet is retained in a temperature range of 600° C. to 700° C. is 10 seconds or less and in which coiling is performed at a coiling temperature of lower than 600° C., a cold rolling process in which cold rolling is performed with a rolling reduction of more than 20%, an annealing process in which heating is performed to an annealing temperature of 750° C. to 950° C. at an average heating rate of 15° C./s or less and in which the heated steel sheet is held at the annealing temperature for 30 seconds or more, a first cooling process in which cooling is performed at an average cooling rate of 3° C./s or more, a galvanizing process in which galvanizing is performed, a second cooling process in which, after having performed cooling to a temperature equal to or higher than the Ms temperature at an average cooling rate of 1° C./s or more, cooling is performed to a temperature of 100° C. or lower at an average cooling rate of 100° C./s or more, and a tempering process in which reheating is performed to a temperature of 350° C. or lower and in which the reheated steel sheet is held at the temperature for 1 second or more. ### Claim 12 (depends on 11) The method for manufacturing a high-strength, galvanized steel sheet according to claim 11, wherein, after having performed galvanizing in the galvanizing process, an alloying treatment is further performed on the galvanizing layer by heating the galvanized steel sheet to a temperature of 460° C. to 600° C.