An embodiment of the present invention provides a steel plate for a pressure vessel having excellent hydrogen-induced cracking resistance and a method of manufacturing same, the steel plate comprising, in weight %, 0.2 to 0.3% of carbon (C), 0.05 to 0.50% of silicon (Si), 0.1% to 0.5% (exclusive) of manganese (Mn) , 0.005 to 0.1% of aluminum (Al), 0.010% or less of phosphorus (P) , 0.0015% or less of sulfur (S), 0.001 to 0.03% of niobium (Nb), 0.001 to 0.03% of vanadium (V) , 0.001 to 0.03% of titanium (Ti), 0.01 to 0.20% of chromium (Cr), 0.01 to 0.15% of molybdenum (Mo) , 0.01 to 0.50% of copper (Cu) , 0.05 to 0.50% of nickel (Ni), 0.0005 to 0.0040% of calcium (Ca), and the balance of Fe and other inevitable impurities, wherein the average grain size of ferrite is 5-20 μm.

A roll-bonded clad metal sheet and a method for producing a roll-bonded clad metal sheet is provided. The roll-bonded clad sheet includes a metallic base material layer and a metallic cladding material layer which are joined to one another by a metallurgical bond. The metallic cladding material layer includes a nickel-based material whose chemical composition includes, in % by mass, a proportion of more than 50% of Ni and a proportion of 3.1% of Nb. The metallurgical bond is obtained by a thermomechanical rolling process including a first rolling phase for prerolling, a second rolling phase for final forming and a cooling time between the first rolling phase and the second rolling phase, wherein a final rolling temperature of the second rolling phase is set to a value equal to or less than 880° C.

The present invention provides a steel material which has a plate shape and achieves both high strength and high rigidity by imparting large nonuniform deformation to the steel material utilizing rolling using a large-diameter work roll. The steel plate according to an embodiment of the present invention is produced by performing rolling using a rolling mill having a work roll diameter of 650 mm or more in a warm temperature region so that a nonuniform metallographic structure is formed in a plate thickness direction and thus the steel plate of the present invention is a high-strength and high-rigidity steel plate in which a yield strength is 580 MPa or more and a Young's modulus at a plate thickness center portion or a surface layer portion is 210 GPa or more and a difference in Young's moduli at the plate thickness center portion and the surface layer portion is 5 GPa or more in a case in which a tensile direction in a tensile test is at least any one of a rolling direction, a plate width direction, or a direction forming an angle difference of 45 degrees from the rolling direction and the plate width direction.

The invention describes a two-phase steel comprising 8-12 wt. % Mn, 0.3-0.6 wt. % C, 1-4 wt. % Al, 0.4-1 wt. % V, and a balance of Fe. The steel has martensite and retained austenite phases, and may include vanadium carbide precipitations. A method for making the two-phase steel involves the steps of (a) hot rolling the ingots of the composition to produce a plurality of thick steel sheets, (b) treating the steel sheets by an air cooling process, (c) warm rolling the steel sheets at a temperature in the range of 300-800° C. with a thicknesses reduction of 30-50%, (d) annealing the steel sheets a first time at a temperature in the range of 620-660° C. for 10-300 min, (e) cold rolling the steel sheets at room temperature with a thickness reduction of 10-30% to generate hard martensite, and (f) annealing the steel sheets a second time at a temperature in the range of 300-700° C. for 3-60 min to facilitate the partitioning of carbon and release the residual stress n martensite.

An ultra-thick steel excellent in brittle crack arrestability according to an aspect of the present invention comprises, by weight, C: 0.02-0.07%, Mn: 1.8-2.2%, Ni: 0.7-1.2%, Nb: 0.005-0.02%, Ti: 0.005-0.02%, Cu: 0.1-0.4%, P: 0.01% or less, S: 0.004% or less, and the balance of Fe and inevitable impurities, wherein crystal grains that have a high angle grain boundary of 15 degrees or more, as measured by EBSD, may have an average grain size of 15 μm or less in the t/4−(3*t)/8 region (wherein t represents a thickness of the steel, the same below).

A hot dip galvanized steel sheet and hot dip galvannealed steel sheet improved in uniform ductility and local ductility, yield strength and tensile strength, and low temperature impact property, characterized by having a predetermined chemical composition, having a metal structure containing, by volume %, retained austenite: over 5.0% and tempered martensite: over 5.0%, having retained austenite containing C: 0.85 mass % or more, and having a ratio [C].sub.γgb/[P].sub.γgb of an amount of segregation of C (number of atoms/nm.sup.2): [C].sub.γgb to an amount of segregation of P (number of atoms/nm.sup.2): [P].sub.γgb at prior austenite grain boundaries of 4.0 or more.

The present invention relates to steel used for members of chassis parts and wheel discs of commercial vehicles, or the like and, more specifically, to a high-strength steel with excellent durability and a method for manufacturing same.

An aspect of the present invention relates to a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al:

0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.4≤0.4*Cr+Si≤3.2 (wherein element symbols denote measurements of respective element contents by weight

The present invention relates to a non-magnetic austenitic stainless steel material having a component composition containing, in terms of mass percent, C: <0.10%, Si: <0.3%, Mn: more than 4.5% to less than 10.0%, P: <0.05%, S: <0.0020%, Ni: 9.0% to 15.0%, Cr: 17.0% to 25.0%, Mo: 3.0% to 7.0%, and N: 0.3% to 0.6%, with the balance being Fe and unavoidable impurities; satisfying (40[N]+1.2[Cr]+0.07exp(0.3[Ni]+0.3[Cu]))×1.5[Mo]{circumflex over ( )}(−0.18)≤60, in which [M] represents a content of an element M in terms of mass %; having an austenite single phase structure; having a critical pitting temperature of 50° C. or higher; and having a 0.2% proof stress of 970 MPa or more.

An ultra-strong, ductile and cheap medium manganese steel comprises in percentage by mass: 8-12 wt. % Mn, 0.2-0.4 wt. % C, 1-3 wt. % Al, 0.05-0.39 wt. % V, and the balance of Fe. The manufacturing method of the ultra-strong and ductile medium manganese steel includes the steps of: (a) hot rolling an ingot at 900-1200° C. into a steel sheet (or plate, or bar); (b) air cooling or water quenching the steel sheet to room temperature or warm rolling temperature, (c) warm rolling the steel sheet at 350-750° C. with 30-60% thickness reduction; (d) air cooling or water quenched the steel sheet to room temperature; (e) annealing the steel sheet at 600-650° C. for 0-300 minutes and (f) air cooling or water quenched the sheet to room temperature.