A hot-stamping formed body has a predetermined chemical composition and includes microstructure which includes residual austenite of which an area ratio is 10% or more and less than 20%, Among grain boundaries of crystal grains of bainite and tempered martensite a ratio of a length of a grain boundary having a rotation angle in a range of 55° to 75° to a total length of a grain boundary having a rotation angle in a range of 4° to 12°, a grain boundary having a rotation angle in a range of 49° to 54°, and the grain boundary having a rotation angle in, a range of 55° to 75° to the <011> direction as a rotation axis is 30% or more.

A hot-stamping formed body has a predetermined chemical composition and includes microstructure which includes residual austenite of which an area ratio is 10% or more and less than 20%, Among grain boundaries of crystal grains of bainite and tempered martensite a ratio of a length of a grain boundary having a rotation angle in a range of 55° to 75° to a total length of a grain boundary having a rotation angle in a range of 4° to 12°, a grain boundary having a rotation angle in a range of 49° to 54°, and the grain boundary having a rotation angle in, a range of 55° to 75° to the <011> direction as a rotation axis is 30% or more.

Provided according to one preferred aspect of the present invention are austenitic steel material having superb abrasion resistance and toughness, and a method for producing the austenite steel material. The austenitic steel material having superb abrasion resistance and toughness according to one preferred aspect of the present invention comprises, in wt %, 0.6-1.9% carbon (C); 12-22% manganese (Mn); 5% or lower (excluding 0%) chromium (Cr); 5% or lower (excluding 0%) copper (Cu); 0.5% or lower (excluding 0%) aluminum (Al); 1.0% or lower (excluding 0%) silicon (Si); 0.1% or lower (including 0%) phosphorous (P); 0.02% or lower (including 0%) sulfur (S); and the rest in Fe and unavoidable impurities, and has the microstructure comprising, by surface area fraction, 97% or higher (including 100%) austenite and 3% or lower (including 0%) carbide.

The entirety or a part of this hot stamped product includes, as a chemical composition, by mass %, C: 0.001% or more and less than 0.080%, Si: 2.50% or less, Mn: 0.01% or more and less than 0.50%, P: 0.200% or less, S: 0.0200% or less, sol.Al: 0.001% to 2.500%, N: 0.0200% or less, Cr: 0.30% or more and less than 2.00%, and a remainder: Fe and impurities, in which a metallographic structure contains, by vol %, ferrite: more than 60.0%, martensite: 0% or more and less than 10.0%, and bainite: 0% or more and less than 20.0%, a tensile strength is less than 700 MPa, and ΔTS, which is a decrease in the tensile strength after a heat treatment at 170° C. for 20 minutes, is 100 MPa or less.

The present invention relates to a process for forming a metal component (20), the process comprising the steps of heating a metal blank (20) coated with a protective layer; cooling said metal blank (20) in a confined space (14), said cooling involving cooling by means of a gas, the gas being cooled by heat exchange with a cooling surface of a heat sink (22) inside said confined space (14), wherein a low frequency sound wave is provided into said confined space (14) in order to improve heat exchange both between the gas and a cooling surface of the at least one heat sink (22), and between the gas and the metal component (20), wherein the heated coated blank is cooled to a temperature below the melting point of the protective layer, and forming the coated blank to a component. The invention also relates to a production line for performing the process.

The present invention relates to a process for forming a metal component (20), the process comprising the steps of heating a metal blank (20) coated with a protective layer; cooling said metal blank (20) in a confined space (14), said cooling involving cooling by means of a gas, the gas being cooled by heat exchange with a cooling surface of a heat sink (22) inside said confined space (14), wherein a low frequency sound wave is provided into said confined space (14) in order to improve heat exchange both between the gas and a cooling surface of the at least one heat sink (22), and between the gas and the metal component (20), wherein the heated coated blank is cooled to a temperature below the melting point of the protective layer, and forming the coated blank to a component. The invention also relates to a production line for performing the process.

An embodiment of the present invention provides a wire rod and a method of manufacturing same. The wire rod comprises, by weight %, 0.3-0.5 wt % of C, 0.02-0.4 wt % of Si, 1.0-1.5 wt % of Mn, 0.3-0.7 wt % of Cr, 0.003 wt % or less (exclusive of 0 wt %) of B, less than 0.03 wt % (exclusive of 0 wt %) of Ti, 0.03 wt % or less (inclusive of 0 wt %) of P, 0.01 wt % or less (inclusive of 0 wt %) of S, 0.02-0.05 wt % of Al, 0.001-0.01 wt % of N, and the balance being Fe and inevitable impurities, wherein a microstructure is a complex structure having a main phase of ferrite+pearlite, with at least one of bainite or martensite accounting for 5 area % or less (inclusive of 0%), and has a cementite average aspect ratio of 35 or less in an area covering ⅖-⅗ of the diameter.

Provided herein is a high-strength seamless steel pipe, and a method for manufacturing same. A high-strength seamless steel pipe of the present invention has a steel microstructure with a prior austenite grain size of 11.0 or more in terms of a grain size number in compliance with ASTM E112, and has a yield strength of 862 MPa or more and 965 MPa or less.

A steel sheet has a predetermined chemical composition containing, in mass %, C: more than 0.18% and less than 0.30%, Mn: more than 2.50% and 4.00% or less, and other elements. The steel micro-structure at a position at a depth of ¼ of the sheet thickness from the surface in an L cross section of the steel sheet is, in area %, tempered martensite: 25 to 90%, ferrite: 5% or less, retained austenite: 10 to 50%, and bainite: 5% or less. At a position at a depth of ¼ of the sheet thickness from the surface of the L cross section, the proportion of a total area of retained austenite grains having an area of 1 μm.sup.2 or more and having a grain shape circularity of 0.1 or more is less than 50% with respect to the entire area of retained austenite. The steel sheet satisfies the formula C.sub.Mnγ/C.sub.Mnα≥1.2.

A method for producing an austempered steel is provided. The method includes subjecting a steel alloy having a silicon content of 1.5 to 4.4 weight percent and a carbon content of 0.3 to 0.8 weight percent to continuous cooling followed by annealing. The cooling rate is initially sufficiently fast to prevent predominant formation of proeutectoid ferrite or pearlite, while subsequently at intermediate temperatures, the cooling rate is sufficiently slow to allow a transformation of the austenite to mainly ausferrite during cooling. The annealing is able to complete the transformation of carbon enriched austenite to ausferrite and to temper any martensite previously formed. The method results in the cost-efficient production of one or more continuously cooled and annealed austempered steel components or semi-finished products having mainly an ausferritic microstructure.