摘要:
A method of producing a hot-rolled steel sheet and a method for producing a cold-rolled full hard steel sheet are provided. The methods comprising heating a steel slab having a composition containing, in terms of mass %, C: 0.010% or more and 0.150% or less, Si: 0.20% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.0500% or less, Al: 0.001% or more and 0.100% or less, N: 0.0100% or less, and the balance being Fe and unavoidable impurities, in which 0.002%≤[%P]+[%S ]≤0.070% ([%M] denotes a content (mass %) of M element in steel) is satisfied.
摘要:
A high-strength steel sheet for warm working having excellent warm workability, and a method for manufacturing the steel sheet. The steel sheet has a chemical composition including, by mass %, C: 0.05% to 0.20%, Si: 3.0% or less, Mn: 3.5% to 8.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.01% to 3.0%, N: 0.010% or less, one or more selected from Nb: 0.005% to 0.20%, Ti: 0.005% to 0.20%, Mo: 0.005% to 1.0%, and V: 0.005% to 1.0%. The steel sheet has a microstructure including, in terms of area ratio, 10% to 60% of retained austenite, 10% to 80% of ferrite, 10% to 50% of martensite, and 0% to 5% of bainite, in which a C content in the retained austenite is less than 0.40 mass % and the average crystal grain diameter of the retained austenite, the martensite, and the ferrite is 2.0 μm or less.
摘要:
A high-strength steel sheet having a composition containing C: 0.09% to 0.17%, Si: 0.6% to 1.7%, Mn: 3.5% or less, P: 0.03% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.006% or less, Ti: 0.05% or less, and B: 0.0002% to 0.0030% on a mass basis, the remainder being Fe and inevitable impurities. The steel sheet also has a microstructure containing less than 20% (including 0%) of a ferrite phase, 75% or more (including 100%) of a tempered martensite phase, 10% or less (including 0%) of an untempered martensite phase, and less than 5% (including 0%) of a retained austenite phase in terms of area fraction. The tempered martensite phase has a Vickers hardness of 280 to 340 and a tensile strength of 950 MPa to 1,120 MPa.
摘要:
A high-strength steel includes a steel structure with: in area fraction, 60.0% to less than 90.0% of ferrite, 0% to less than 5.0% of unrecrystallized ferrite, 2.0% to 25.0% of martensite, 0% to 5.0% of carbide, and 0% to 3.0% of bainite; in volume fraction, more than 7.0% of retained austenite; in a cross-sectional view of 100 μm×100 μm, a value obtained by dividing number of retained austenite that are not adjacent to retained austenite whose crystal orientations are different by a total number of retained austenite being less than 0.80, an average crystal grain size of the ferrite being 6.0 μm or less, an average crystal grain size of the retained austenite being 3.0 μm or less, and a value obtained by dividing, by mass %, an average content of Mn in the retained austenite by an average content of Mn in steel being 1.50 or more.
摘要:
A steel sheet, a plated steel sheet, and methods for producing a hot-rolled steel sheet, a cold-rolled full hard steel sheet, and a steel sheet. The steel sheet has a specified composition and a microstructure including 0 to 80% of polygonal ferrite and 20 to 100% of a total of martensite, bainite, and residual austenite in terms of an area ratio within 20 μm of the steel sheet surface. The content of Mn in martensite present within 20 μm of the steel sheet surface ([Mn]SM) and the content of Mn in a bulk ([Mn]B) satisfy [Mn]SM/[Mn]B≤1.5. At a location 300 μm from the steel sheet surface, an area ratio of the martensite is in a range of 20 to 50%.
摘要:
A high strength hot rolled steel sheet with good formability, which has good magnetic properties, excellent punchability, and a tensile strength of 780 MPa or more. The high strength hot rolled steel sheet having a chemical composition containing C: 0.070% to 0.140%, Si: 0.10% to 1.00%, Mn: 1.00% to 1.80%, P: 0.050% or less, S: 0.0050% or less, N: 0.0080% or less, Al: 0.010% to 0.100%, Ti: 0.050% to 0.150%, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and 95% or more of bainite microstructure on a volume fraction basis, wherein carbides constituting 80% or more of total precipitation carbides are dispersed at grain boundaries of bainitic ferrite constituting the bainite microstructure and 80% or more of total precipitation carbides have particle grain sizes of 20 to 300 nm.
摘要:
A high-strength steel sheet includes a steel structure with: ferrite being 35% to 80% and tempered martensite being greater than 5% and 20% or less in terms of area fraction; retained austenite being 8% or more in terms of volume fraction; an average grain size of: the ferrite being 6 μm or less; and the retained austenite being 3 μm or less; a value obtained by dividing an area fraction of blocky austenite by a sum of area fractions of lath-like austenite and the blocky austenite being 0.6 or more; a value obtained by dividing, by mass %, an average Mn content in the retained austenite by an average Mn content in the ferrite being 1.5 or more; and a value obtained by dividing, by mass %, an average C content in the retained austenite by an average C content in the ferrite being 3.0 or more.
摘要:
Disclosed is a hot-pressed member that can exhibit very high tensile strength after hot pressing as high as TS: 1780 MPa or more, and excellent indentation peeling strength at projection welds by properly adjusting its chemical composition and its microstructure such that a prior austenite average grain size is 7 μm or less within a range of 50 μm or less in a thickness direction from a surface of the member, a volume fraction of martensite is 90% or more, and an average intergrain distance of Nb and Ti carbonitrides having a grain size of less than 0.10 μm within a depth range of 20 μm to 100 μm in the thickness direction from the surface of the member is 5 μm or less.
摘要:
A steel sheet having excellent fatigue resistance as a material for automobile parts and a TS of 590 MPa or more, and a method for producing the same. The steel sheet having a specified chemical composition and a microstructure of 50% or more and 90% or less of martensite, 10% to 50% of ferrite and bainite in total, in terms of an area ratio, and an average concentration of solute Mn in ferrite in a region from a surface of a base steel to a depth of 0.5 μm is 60% or more relative to an average concentration of solute Mn in ferrite at a location of ¼ in the thickness of the steel sheet.
摘要:
To provide a high-strength steel sheet with excellent ductility and hole expansion formability, a yield ratio of less than 68%, and a tensile strength of 980 MPa or more, by having a predetermined chemical composition and a microstructure where ferrite is 15% or more and 55% or less and martensite is 15% or more and 30% or less in area ratio, retained austenite is 12% or more in volume fraction, the average grain size of ferrite, martensite and retained austenite is 4.0 μm or less, 2.0 μm or less and 2.0 μm or less respectively, the average aspect ratio of crystal grain of ferrite, martensite and retained austenite is each more than 2.0 and 15.0 or less, and the value obtained by dividing the Mn content (mass %) in retained austenite by the Mn content (mass %) in ferrite is 2.0 or more.