Nippon Steel Corporation

Nippos Steel Corporation

Shingo Fujinaka

Yuri Toda

Daisuke Maeda

Kazuo Hikida

Genki Abukawa

Tomohito Tanaka

Kodai Murasawa

This hot-stamping formed body includes, as a chemical composition, by mass %: C: 0.15% or more and 0.50% or less; Si: 0.10% or more and 3.00% or less; Mn: 0.10% or more and 3.00% or less; P: less than 0.10%; S: less than 0.10%; N: less than 0.10%; Ti: 0.020% or more and 0.150% or less; B: 0.002% or more and 0.010% or less; optionally Al, Cr, Mo, Co, Ni, Cu, V, W, Ca, Mg, and REM; and a remainder including Fe and impurities, in which a microstructure of the hot-stamping formed body includes, by volume fraction, 85% or more of martensite and less than 15% of retained austenite, and in the microstructure, a standard deviation of a frequency distribution of nanohardnesses is 0.70 GPa or less, and an average grain size is 4.0 μm or less.

Hot-stamping formed body

A hot stamped body with high strength, good bendability and crack propagation resistance, consisting of: in mass %, C: 0.06% or more to less than 0.20%, Si: 0.010-1.00%, Mn: 0.80-2.00%, P: 0.100% or less, S: 0.010% or less, Al: 0.010-0.500%, N: 0.010% or less, Nb: more than 0.020% to 0.10% or less, Ti: 0-0.10%, V: 0-0.10%, Cr: 0-0.50%, Mo: 0-1.00%, B: 0-0.0100%, Ni: 0-0.50%, REM: 0-0.0100%, Mg: 0-0.010%, Ca: 0-0.0100%, and Co: 0-2.0%, with the balance: Fe and impurities, wherein a microstructure includes, in area fraction, ferrite: 5-50%, and martensite: 50-95%, a proportion of regions in the martensite where GAIQ values are 35000 or more to less than 45000 is 30 area % or more, and a maximum bending angle α (deg) is 90 or more.

Hot stamped body

A hot stamped body with high strength and good bendability, comprising a chemical composition consisting of: in mass %, C: 0.06% or more to less than 0.20%, Si: 0.010 to 1.00%, Mn: 1.20 to 3.00%, P: 0.100% or less, S: 0.010% or less, Al: 0.010 to 0.500%, N: 0.010% or less, Nb: 0.0010 to 0.020%, Ti: 0 to 0.10%, V: 0 to 0.10%, Cr: 0 to 0.50%, Mo: 0 to 1.00%, B: 0 to 0.0100%, Ni: 0 to 0.50%, REM: 0 to 0.0100%, Mg: 0 to 0.010%, Ca: 0 to 0.0100%, and Co: 0 to 2.0%, with the balance: Fe and impurities, wherein a microstructure includes martensite: 85% or more, a proportion of regions in the martensite where GAIQ values are 35000 or more to less than 45000 is 30 area % or more, and TS×α, is 105000 or more, and α is 75 or more.

A hot-stamping formed body has a predetermined chemical composition, in which an average grain size of prior austenite grains in a microstructure is 5.0 μm or less, and an average Mn concentration at grain boundaries of the prior austenite grains is 1.0 mass % or less. The hot-stamping formed body may be provided with a plating layer on the surface thereof, or may have a softened region in a portion thereof.

These steel sheet for hot stamping and hot-stamping formed body have predetermined chemical composition and metallographic structures, and, in textures of a surface layer region and an inside region, ratios between a pole density of an orientation group consisting of {001}<1-10> to {001}<−1-10> and a pole density of an orientation group consisting of {111}<1-10> to {111}<−1-12> are controlled.

Steel sheet for hot stamping and hot-stamping formed body

This hot-stamping formed body has a predetermined chemical composition and has a metallographic structure consisting of, by area ratio, a total of 10% to 30% of ferrite and granular bainite and a remainder in microstructure consisting of one or more of martensite, bainite, and tempered martensite, and, in textures of a surface layer region and an inside region, ratios between a pole density of an orientation group consisting of {001}<1-10> to {001}<−1-10> and a pole density of an orientation group consisting of {111}<1-10> to {111}<−1-12> are controlled.

A hot stamped article having excellent shock absorption having a predetermined chemical composition, having a microstructure containing prior austenite having an average grain size of 3 &#x3bc;m or less and further containing at least one of lower bainite, martensite, and tempered martensite in an area ratio of 90% or more, and having a grain boundary solid solution ratio Z defined by Z=(mass % of one or both of Nb and Mo at grain boundaries)/(mass % of one or both of Nb and Mo at time of melting) of 0.3 or more.

Hot stamped article

A hot-stamping formed body has a predetermined chemical composition and a microstructure including, by area ratio, 90% to 100% of martensite and 0% to 10% of a remainder in the microstructure. In the microstructure, a region in which an average GAIQ value in a unit grain is 60,000 or more is 30 area % or more, and a number density of carbides having a circle equivalent diameter of 0.20 &#x3bc;m or more is 50/mmor less.

A steel sheet for hot stamping use used as a material for a hot stamped article excellent in strength or bending deformability, having a predetermined chemical composition, having a microstructure containing at least one of lower bainite, martensite, and tempered martensite in an area ratio of 90% or more, having an X-ray random intensity ratio of {112}&#x3c;111&#x3e; of the crystal grains forming the above lower bainite, martensite, or tempered martensite of 2.8 or more, having a number density of grain size 50 nm or less cementite or epsilon carbides in the microstructure of 1&#xd7;10/cmor more, and having a grain boundary solid solution ratio Z defined by Z=(mass % of one or both of Nb and Mo at grain boundaries)/(mass % of one or both of Nb and Mo at time of melting) of 0.4 or more.

Steel sheet for hot stamping use

A hot stamped article excellent in strength having a predetermined composition, having an average crystal grain size of prior austenite of 3 &#x3bc;m or less, containing at least one of lower bainite, martensite, and tempered martensite in an area rate of 90% or more, and having a grain boundary solid solution ratio Z, defined by Z=(mass % of one or both of Nb and Mo at the grain boundaries)/(mass % of one or more of Nb and Mo at time of dissolution) of 0.3 or more.

A hot stamped article of high strength steel sheet excellent in bending deformability having a predetermined chemical composition, having an area rate of 90% or more of the microstructures of the steel sheet comprised of one or more of lower bainite, martensite, and tempered martensite, and having a ratio of the length of grain boundaries with a rotational angle about a rotational axis of the &#x3c;011&#x3e; direction of the crystal grains of the lower bainite, martensite, and tempered martensite of 15&#xb0; or more with respect to the length of grain boundaries with a rotational angle of 5&#xb0; to 75&#xb0; of 80% or more.

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Tokyo, Japan

Shingo Fujinaka