The present invention relates to steel used for a sash component and the like of a vehicle and, more specifically, to a hot-rolled steel sheet having excellent durability and a method for manufacturing same, the hot-rolled steel sheet having no cracks formed on a material and a welding heat-affected zone (HAZ) even after pipemaking and molding due to a smaller decrease in the strength of the welding heat-affected zone formed during electric resistance welding in comparison with the strength of the material (base material).

The present invention relates to steel used for a sash component and the like of a vehicle and, more specifically, to a hot-rolled steel sheet having excellent durability and a method for manufacturing same, the hot-rolled steel sheet having no cracks formed on a material and a welding heat-affected zone (HAZ) even after pipemaking and molding due to a smaller decrease in the strength of the welding heat-affected zone formed during electric resistance welding in comparison with the strength of the material (base material).

The present invention relates to a steel for mold, containing: 0.28 mass %≤C≤0.65 mass %, 0.01 mass %≤Si≤0.30 mass %, 1.5 mass %≤Mn≤3.0 mass %, 0.5 mass %≤Cr≤1.4 mass %, 1.9 mass %≤Mo+W/2≤4.0 mass %, 0.2 mass %≤V≤1.0 mass %, and 0.01≤N≤0.10 mass %, with the balance being Fe and inevitable impurities, in which, in a state after quenching and tempering, the steel has: a (Mo, W) carbide having a diameter of 0.2 μm or less being in an amount of 1.2 mass % or more, a ratio (mass ratio) of the amount of the (Mo, W) carbide to an amount of a Cr carbide being 11 or more, and a hardness change of 15 HRC or less.

The present invention relates to a steel for mold, containing: 0.28 mass %≤C≤0.65 mass %, 0.01 mass %≤Si≤0.30 mass %, 1.5 mass %≤Mn≤3.0 mass %, 0.5 mass %≤Cr≤1.4 mass %, 1.9 mass %≤Mo+W/2≤4.0 mass %, 0.2 mass %≤V≤1.0 mass %, and 0.01≤N≤0.10 mass %, with the balance being Fe and inevitable impurities, in which, in a state after quenching and tempering, the steel has: a (Mo, W) carbide having a diameter of 0.2 μm or less being in an amount of 1.2 mass % or more, a ratio (mass ratio) of the amount of the (Mo, W) carbide to an amount of a Cr carbide being 11 or more, and a hardness change of 15 HRC or less.

Disclosed is an austenitic stainless steel having an increased yield ratio. The disclosed austenitic stainless steel is characterized by comprising, in percent by weight (wt %), 0.1% or less (exclusive of 0) of C, 0.2% or less (exclusive of 0) of N, 1.5 to 2.5% of Si, 6.0 to 10.0% of Mn, 15.0 to 17.0% of Cr, 0.3% or less (exclusive of 0) of Ni, 2.0 to 3.0% of Cu, and the remainder of Fe and other inevitable impurities, and satisfying Expressions (1) and (2) below.

3.2≤5.53+1.4Ni−0.16Cr+17.1(C+N)+0.722Mn+1.4Cu−5.59Si≤7  Expression (1):

551-462(C+N)−9.2Si−8.1Mn−13.7Cr−29(Ni+Cu)≤110  Expression (2): wherein C, N, Si, Mn, Cr, Ni, and Cu indicate the content (wt %) of respective elements.

Provided are thick hot-rolled composite-phase steel having excellent durability and a manufacturing method therefor. The thick composite-phase steel having excellent durability according to the present invention comprises, by wt %, C: 0.05 to 0.15%, Si: 0.01 to 1.0%, Mn: 1.0 to 2.3%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.07%, Ti: 0.005 to 0.11%, Fe, and inevitable impurities, and has a mixed phase of ferrite and bainite as a base structure, wherein, in the base structure, the area fraction of each of a pearlite phase and a martensite and austenite (MA) phase is less than 5%, and the area fraction of a martensite phase is less than 10%.

Provided are thick hot-rolled composite-phase steel having excellent durability and a manufacturing method therefor. The thick composite-phase steel having excellent durability according to the present invention comprises, by wt %, C: 0.05 to 0.15%, Si: 0.01 to 1.0%, Mn: 1.0 to 2.3%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.07%, Ti: 0.005 to 0.11%, Fe, and inevitable impurities, and has a mixed phase of ferrite and bainite as a base structure, wherein, in the base structure, the area fraction of each of a pearlite phase and a martensite and austenite (MA) phase is less than 5%, and the area fraction of a martensite phase is less than 10%.

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.

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 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.