Abstract: The high-strength galvanized steel sheet having excellent formability has a component composition containing, on the basis of mass percent, 0.05 to 0.2% C, 0.5 to 2.5% Si, 1.5 to 3.0% Mn, 0.001 to 0.05% P, 0.0001 to 0.01% S, 0.001 to 0.1% Al, and 0.0005 to 0.01% N, the balance being Fe and incidental impurities; and the steel sheet has a microstructure including a ferritic phase and a martensitic phase including a tempered-martensitic phase, the ferritic phase having an area fraction of 30% or more relative to an entirety of the microstructure, the martensitic phase having an area fraction of 30 to 50% relative to the entirety of the microstructure, and the tempered-martensitic phase having an area fraction of 70% or more relative to an entirety of the martensitic phase.

Abstract: A high-strength galvanized steel sheet with excellent formability and shape fixability and a method for manufacturing the high-strength galvanized steel sheet.

Abstract: A method of manufacturing a high-strength galvanized steel sheet includes hot-rolling a slab to form a steel sheet; during continuous annealing, heating the steel sheet to a temperature of 750° C. to 900° C. at an average heating rate of at least 10° C./s at a temperature of 500° C. to an A1 transformation point; holding that temperature for at least 10 seconds; cooling the steel sheet from 750° C. to a temperature of (Ms point—100° C.) to (Ms point—200° C.) at an average cooling rate of at least 10° C./s; reheating the steel sheet to a temperature of 350° C. to 600° C.; holding that temperature for 10 to 600 seconds; and galvanizing the steel sheet.

Abstract: The present invention provides a high-strength galvanized steel sheet having excellent ductility, stretch flangeability, and fatigue resistance, and a method for manufacturing the same. A high-strength galvannealed steel sheet having excellent formability and fatigue resistance is characterized in that the steel sheet is composed of steel having a composition containing, by % by mass, C: 0.05% to 0.3%, Si: 0.5% to 2.5%, Mn: 1.0% to 3.5%, P: 0.003% to 0.100%, S: 0.02% or less, Al: 0.010% to 0.1%, and the balance including iron and unavoidable impurities, and the steel sheet has a microstructure containing 50% or more of ferrite, 5% to 35% of martensite, and 2% to 15% of pearlite in terms of an area ratio, the martensite having an average gain size of 3 ?m or less and an average distance of 5 ?m or less between adjacent martensite grains.

Abstract: There is provided a high-strength galvanized steel sheet including, on a mass percent basis, C: more than 0.060% and 0.13% or less, Si: 0.01% or more and 0.7% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.100% or less, S: 0.010% or less, sol.Al: 0.005% or more and 0.100% or less, N: 0.0100% or less, Nb: 0.005% or more and 0.10% or less, Ti: 0.03% or more and 0.15% or less, and the balance comprising Fe and incidental impurities, satisfying the relationship of (Nb/93+Ti*/48)/(C/12)>0.08 (wherein Ti*=Ti?(48/14)N?(48/32)S). The high-strength galvanized steel sheet has a structure including ferrite and martensite. The ferrite has an average grain diameter of 15 ?m or less and an area percentage of 80% or more. The martensite has an area percentage of 1% or more and 15% or less.

Abstract: A galvanized steel sheet has a composition containing, by mass %, C: 0.05% or more and 0.5% or less, Si: 0.01% or more and 2.5% or less, Mn: 0.5% or more and 3.5% or less, P: 0.003% or more and 0.100% or less, S: 0.02% or less, Al: 0.010% or more and 0.5% or less, B: 0.0002% or more and 0.005% or less, Ti: 0.05% or less, a relationship of Ti>4N being satisfied, and the balance comprising Fe and inevitable impurities, and a microstructure containing 60% or more and 95% or less of tempered martensite in terms of area ratio and 5% or more and 20% or less of retained austenite in terms of area ratio, or further containing 10% or less (including 0%) of ferrite in terms of area ratio and/or 10% or less (including 0%) of martensite in terms of area ratio, the tempered martensite having an average grain diameter of 5 ?m or less.

Abstract: A method of manufacturing a high strength steel sheet having excellent formability suitable for the material of an automotive part has a tensile strength (TS) of 980 MPa or more and total elongation (EL) is 25% or more. A steel slab has a chemical composition containing C: 0.03% to 0.35%, Si: 0.5% to 3.0%, Mn: 3.5% to 10.0%, P: 0.100% or less, S: 0.02% or less, and the remainder includes Fe and incidental impurities on a percent by mass basis is hot-rolled, a heat treatment is performed, in which an achieved temperature of Ac1 to Ac1+100° C. is held for 3 minutes or more, subsequently, cold rolling is performed at a rolling reduction of 20% or more and, annealing is performed, in which an achieved temperature of Ac1?30° C. to Ac1+100° C. is held for 1 minute or more.

Abstract: A hot rolled steel sheet having a chemical composition containing, by mass %, C: 0.04% or more and 0.20% or less, Si: 0.7% or more and 2.3% or less, Mn: 0.8% or more and 2.8% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.1% or less, N: 0.008% or less, and the balance being Fe and inevitable impurities. The microstructure of the hot rolled steel sheet includes ferrite and pearlites, in which the area ratio of the ferrite is 75% or more and less than 95%, the mean grain size of the ferrite is 5 ?m or more and 25 ?m or less, the area ratio of pearlite is 5% or more and less than 25%, the mean grain size of pearlite is 2.0 ?m or more, and the mean free path of pearlite is 5 ?m or more.

Abstract: The present invention provides a high-strength steel sheet having a tensile strength of 980 MPa or more and also excellent bending property stably over the entire steel sheet, due to a predetermined chemical composition in combination with a specific microstructure wherein an average crystallized grain diameter of ferrite phase is 10 ?m or less, a volume fraction of ferrite phase is within the range from 30% to 70%, a volume fraction of the total of martensite and retained austenite phases is 10% or less, and a ratio of interphases each having an interphase nano-hardness difference within 4 GPa is 90% or more.

Abstract: A formable galvanized steel sheet includes, in terms of % by mass, 0.05 to 0.3% of C, 0.01 to 2.5% of Si, 0.5 to 3.5% of Mn, 0.003 to 0.100% of P, 0.02% or less of S, 0.010 to 1.5% of Al, and 0.01 to 0.2% in total of at least one element selected from Ti, Nb and V, the remainder being Fe and unavoidable impurities, having a microstructure composed of, in terms of area fraction, 20 to 87% of ferrite, 3 to 10% in total of martensite and residual austenite, and 10 to 60% of tempered martensite, and a second phase composed of the martensite, residual austenite, and tempered martensite having an average crystal grain diameter of 3 ?m or less, and having a ratio of absorption energy AE to tensile strength TS (AE/TS) not less than 0.063.

Abstract: A high strength galvanized steel sheet having a TS of 780 MPa or more and exhibiting excellent stretch frangeability and bendability and a method for manufacturing the same are provided. The component composition contains C: 0.05% to 0.15%, Si: 0.8% to 2.5%, Mn: 1.5% to 3.0%, P: 0.001% to 0.05%, S: 0.0001% to 0.01%, Al: 0.001% to 0.1%, N: 0.0005% to 0.01%, Cr: 0.1% to 1.0%, Ti: 0.0005% to 0.1%, B: 0.0003% to 0.003%, and the remainder composed of iron and incidental impurities, on a percent by mass basis. The microstructure includes 30% or more of ferrite phase and 30% or more, and 70% or less of martensite phase on an areal fraction basis, wherein regarding the above-described martensite phase, the proportion of a tempered martensite phase is 20% or more relative to the whole martensite phase and the proportion of a martensite phase having a grain diameter of 1 ?m or less is 10% or less relative to the whole martensite phase.

Abstract: A high strength galvanized steel sheet excellent in coating adhesiveness is made from a base material that is a high strength steel sheet containing Si, Mn, and Cr. A method includes performing an oxidation treatment on steel containing Si, Mn, and Cr in an oxidation furnace under the condition that a selected exit temperature T, reduction annealing and a galvanizing treatment, or optionally, further an alloying treatment under conditions that heating is performed at a temperature of 460° C. or higher and 600° C. or lower for an alloying treatment time of 10 seconds or more and 60 seconds or less.

Abstract: Provided are a high-strength hot-dip galvanized steel sheet having excellent formability and a tensile strength of 440 MPa or more and a method for manufacturing the same. A steel sheet has a microstructure containing a ferrite phase having an area fraction of 60% or more, a pearlite phase having an area fraction of 20% to 30%, and a bainite phase having an area fraction of 1% to 5%, the area fraction of a cementite phase present in a grain of the ferrite phase being 5% or less. Upon manufacture, a hot-rolled sheet or a cold-rolled sheet is heated to a temperature of 650° C. or higher at an average heating rate of 10° C./s or more, is held at a temperature of 700° C. to (Ac3-5)° C. for ten seconds or more, is cooled to a temperature of 300° C. to 500° C. at an average cooling rate of 10° C./s to 200° C./s, is held at a temperature of 300° C. to 500° C. for 30 seconds to 300 seconds, and is then hot-dip galvanized.

Abstract: The present invention provides a high-strength galvanized steel sheet having excellent ductility, stretch flangeability, and fatigue resistance, and a method for manufacturing the same. A high-strength galvannealed steel sheet having excellent formability and fatigue resistance is characterized in that the steel sheet is composed of steel having a composition containing, by % by mass, C: 0.05% to 0.3%, Si: 0.5% to 2.5%, Mn: 1.0% to 3.5%, P: 0.003% to 0.100%, S: 0.02% or less, Al: 0.010% to 0.1%, and the balance including iron and unavoidable impurities, and the steel sheet has a microstructure containing 50% or more of ferrite, 5% to 35% of martensite, and 2% to 15% of pearlite in terms of an area ratio, the martensite having an average gain size of 3 ?m or less and an average distance of 5 ?m or less between adjacent martensite grains.

Abstract: A high strength galvanized steel sheet with excellent workability, having a component composition containing C: 0.04% or more, and 0.15% or less, Si: 0.7% or more, and 2.3% or less, Mn: 0.8% or more, and 2.2% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.1% or less, N: 0.008% or less, and the remainder composed of iron and incidental impurities on a percent by mass basis, and a microstructure including 70% or more of ferrite phase, 2% or more, and 10% or less of bainite phase, and 0% or more, and 12% or less of pearlite phase on an area fraction basis and 1% or more, and 8% or less of retained austenite phase on a volume fraction basis, wherein an average crystal grain diameter of ferrite is 18 ?m or less and an average crystal grain diameter of retained austenite is 2 ?m or less.

Abstract: A method of manufacturing a high strength galvanized steel sheet has a first heating step including heating to 400° C. to 750° C. in an atmosphere containing O2: 0.1 to 20 percent and H2O: 1 to 50 percent and heating to 600° C. to 850° C. in an atmosphere containing O2: 0.01 to less than 0.1 percent and H2O: 1 to 20 percent is applied to a steel sheet, a second heating step includes holding the steel sheet in an atmosphere containing H2: 1 to 50 percent and having a dew point of 0° C. or lower at 750° C. to 900° C. for 15 to 600 s, cooling to a temperature of 450° C. to 550° C., and holding is performed at that temperature for 10 to 200 s, and a galvanization treatment is applied.

Abstract: A high-strength hot-rolled steel sheet has a tensile strength (TS) of 540 to 780 MPa, only small variations in strength, and excellent uniformity in strength using a general-purpose Ti-containing steel sheet, which is inexpensive. The high-strength hot-rolled steel sheet includes, on a mass percent basis, 0.05%-0.12% C, 0.5% or less Si, 0.8%-1.8% Mn, 0.030% or less P, 0.01% or less S, 0.005%-0.1% Al, 0.01% or less N, 0.030%-0.080% Ti, and the balance being Fe and incidental impurities. The microstructure have a bainitic ferrite fraction of 70% or more, and the amount of Ti present in a precipitate having a size of less than 20 nm is 50% or more of the value of Ti* calculated using formula (1): Ti*=[Ti]?48/14×[N] (1) where [Ti] and [N] represent a Ti content (percent by mass) and a N content (percent by mass), respectively, of the steel sheet.

Abstract: A high strength galvanized steel sheet has a TS of 590 MPa or more and excellent processability. The component composition contains, by mass %, C: 0.05% to 0.3%, Si: 0.7% to 2.7%, Mn: 0.5% to 2.8%, P: 0.1% or lower, S: 0.01% or lower, Al: 0.1% or lower, and N: 0.008% or lower, and the balance: Fe or inevitable impurities. The microstructure contains, in terms of area ratio, ferrite phases: 30% to 90%, bainite phases: 3% to 30%, and martensite phases: 5% to 40%, in which, among the martensite phases, martensite phases having an aspect ratio of 3 or more are present in a proportion of 30% or more.

Abstract: A high strength steel sheet including, by mass, C: 0.03% or more and 0.25% or less, Si: 0.4% or more and 2.5% or less, Mn: 3.5% or more and 10.0% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 2.5% or less, N: 0.008% or less, Si+Al: 1.0% or more, the balance being Fe and inevitable impurities. The area ratio of ferrite is 30% or more and 80% or less, the area ratio of martensite is 0% or more and 17% or less, the volume fraction of retained austenite is 8% or more, and the average grain size of retained austenite is 2 ?m or less.

Abstract: A high-strength galvanized steel sheet with high yield ratio having excellent ductility and stretch flange formability, the steel sheet having a chemical composition containing, by mass %, C: 0.04% or more and 0.13% or less, Si: 0.9% or more and 2.3% or less, Mn: 0.8% or more and 2.4% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 0.1% or less, N: 0.008% or less, and the balance being Fe and inevitable impurities and a microstructure including, in terms of area ratio, 94% or more of a ferrite phase and 2% or less of a martensite ferrite phase, wherein mean grain size of ferrite is 10 ?m or less, Vickers hardness of ferrite is 140 or more, mean grain size of carbide particles existing at grain boundaries of ferrite is 0.5 ?m or less, and aspect ratio of carbide particles existing at the grain boundaries of ferrite is 2.0 or less.