摘要:
High-strength parts and a method for producing them can be provided, where such parts exhibit hydrogen embrittlement resistance and strength after high-temperature forming. For example, the atmosphere in a heating furnace can contain less than about 10% hydrogen and/or have a dew point of about 30° C. or less. The amount of hydrogen penetrating a steel sheet during heating can thereby be reduced. After forming, quench hardening in a die assembly and post-working can be performed. Post-working can include shearing followed by re-shearing or compression forming; punching with a cutting blade having a continuously reduced base width; punching with a tool having a curved blade and a protrusion at the tip of the cutting blade, where the curved blade may include a shoulder portion of given radius and/or angle; fusion cutting; etc. Tensile residual stresses after punching can be reduced and resistance to hydrogen embrittlement can be improved.
摘要:
In a hot-rolled sheet, an average value of pole densities of an orientation group {100} to {223} , which is represented by an arithmetic mean of pole densities of orientations {100} , {116} , {114} , {112} , and {223} in a thickness center portion of a thickness range of ⅝ to ⅜ from a surface of the steel sheet, is 1.0 to 6.5 and a pole density of a crystal orientation {332} is 1.0 to 5.0; and a Lankford value rC in a direction perpendicular to a rolling direction is 0.70 to 1.10 and a Lankford value r30 in a direction that forms 30° with respect to the rolling direction is 0.70 to 1.10.
摘要:
A hot-rolled steel sheet has an average value of the X-ray random intensity ratio of a {100} to {223} orientation group at least in a sheet thickness central portion that is in a sheet thickness range of ⅝ to ⅜ from a steel sheet surface of 1.0 to 6.0, an X-ray random intensity ratio of a {332} crystal orientation of 1.0 to 5.0, rC which is an r value in a direction perpendicular to a rolling direction of 0.70 to 1.10, and r30 which is an r value in a direction that forms an angle of 30° with respect to the rolling direction of 0.70 to 1.10.
摘要:
In a hot-rolled sheet, an average value of pole densities of an orientation group {100} to {223} , which is represented by an arithmetic mean of pole densities of orientations {100} , {116} , {114} , {112} , and {223} in a thickness center portion of a thickness range of ⅝ to ⅜ from a surface of the steel sheet, is 1.0 to 6.5 and a pole density of a crystal orientation {332} is 1.0 to 5.0; and a Lankford value rC in a direction perpendicular to a rolling direction is 0.70 to 1.10 and a Lankford value r30 in a direction that forms 30° with respect to the rolling direction is 0.70 to 1.10.
摘要:
A hot-rolled steel sheet has an average value of the X-ray random intensity ratio of a {100} to {223} orientation group at least in a sheet thickness central portion that is in a sheet thickness range of ⅝ to ⅜ from a steel sheet surface of 1.0 to 6.0, an X-ray random intensity ratio of a {332} crystal orientation of 1.0 to 5.0, rC which is an r value in a direction perpendicular to a rolling direction of 0.70 to 1.10, and r30 which is an r value in a direction that forms an angle of 30° with respect to the rolling direction of 0.70 to 1.10.
摘要:
A hot-rolled steel sheet satisfies that average pole density of orientation group of {100} to {223} is 1.0 to 5.0 and pole density of crystal orientation {332} is 1.0 to 4.0. Moreover, the hot-rolled steel sheet includes, as a metallographic structure, by area %, ferrite and bainite of 30% to 99% in total and martensite of 1% to 70%. Moreover, the hot-rolled steel sheet satisfies following Expressions 1 and 2 when area fraction of the martensite is defined as fM in unit of area %, average size of the martensite is defined as dia in unit of μm, average distance between the martensite is defined as dis in unit of μm, and tensile strength of the steel sheet is defined as TS in unit of MPa. dia≦13 μm (Expression 1) TS/fM×dis/dia≧500 (Expression 2)
摘要:
This high-strength steel sheet includes: in terms of percent by mass, 0.03 to 0.10% of C; 0.01 to 1.5% of Si; 1.0 to 2.5% of Mn; 0.1% or less of P; 0.02% or less of S; 0.01 to 1.2% of Al; 0.06 to 0.15% of Ti; and 0.01% or less of N; and contains as the balance, iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, and a ratio between the tensile strength and a yield strength is in a range of 0.80 or more, a microstructure includes bainite at an area ratio of 40% or more and the balance being either one or both of ferrite and martensite, a density of Ti(C,N) precipitates having sizes of 10 nm or smaller is in a range of 1010 precipitates/mm3 or more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 20 μm from a surface to a hardness (Hvc) at a center of a sheet thickness is in a range of 0.85 or more.
摘要:
This high-strength steel sheet includes: in terms of percent by mass, 0.03 to 0.10% of C; 0.01 to 1.5% of Si; 1.0 to 2.5% of Mn; 0.1% or less of P; 0.02% or less of S; 0.01 to 1.2% of Al; 0.06 to 0.15% of Ti; and 0.01% or less of N; and contains as the balance, iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, and a ratio between the tensile strength and a yield strength is in a range of 0.80 or more, a microstructure includes bainite at an area ratio of 40% or more and the balance being either one or both of ferrite and martensite, a density of Ti(C,N) precipitates having sizes of 10 nm or smaller is in a range of 1010 precipitates/mm3 or more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 10 μm from a surface to a hardness (Hvc) at a center of a sheet thickness is in a range of 0.85 or more.
摘要:
This high-strength hot-rolled steel sheet having excellent local deformability contains, in mass %, C: 0.07% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of 5/8 to 3/8 in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100} to {223} orientation group is 4.0 or less, and a pole density of the {332} crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 10 μm or less.
摘要:
This high-strength cold-rolled steel sheet contains, in mass %, C: 0.02% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; in which Si+Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of ⅝ to ⅜ in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100} to {223} orientation group is 4.0 or less, and a pole density of the {332} crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 7 μm or less.