Abstract: Provided are an ultra-high strength cold-rolled steel sheet whose microstructure has been controlled to have high strength and elongation, and a manufacturing method thereof. In accordance with an embodiment of the present disclosure, the ultra-high strength cold-rolled steel sheet includes: carbon (C): 0.28% to 0.45%; silicon (Si): 1.0% to 2.5%; manganese (Mn): 1.5% to 3.0%; aluminum (Al): 0.01% to 0.05%; chromium (Cr): greater than 0% and 1.0% or less; molybdenum (Mo): greater than 0% and 0.5% or less; a total of niobium (Nb), titanium (Ti) and vanadium (V): greater than 0% and 0.1% or less; phosphorus (P): greater than 0% and 0.03% or less; sulfur (S): greater than 0% and 0.03% or less; and nitrogen (N): greater than 0% and 0.

Abstract: A steel sheet having high strength and high formability according to an aspect of the present invention includes: % by weight, an amount of 0.12-0.22% of carbon (C); an amount of 1.6-2.4% of silicon (Si); an amount of 2.0-3.0% of manganese (Mn); an amount of 0.01-0.05% of aluminum (Al); an amount greater than 0 and less than or equal to 0.05% of the sum of one or more of titanium (Ti), niobium (Nb) and vanadium (V); an amount of 0.015% or less of phosphorus (P); an amount of 0.003% or less of sulfur (S); an amount of 0.006% or less of nitrogen (N); and the reminder of Fe and inevitable impurities, and has a yield strength (YS) of 850 MPa or greater, a tensile strength (TS) of 1180 MPa or greater, an elongation ratio (EL) of 14% or greater, and a hole expansion ratio (HER) or 30% of greater.

Abstract: Disclosed are a hot-dip galvannealed steel sheet with ultra-high strength and high formability, and a manufacturing method therefor. In an exemplary embodiment, a hot-dip galvannealed steel sheet include: a base steel sheet; and a hot-dip galvannealed layer formed on the surface of the base steel sheet. The base steel sheet includes an amount of 0.05 to 0.15 wt % of carbon (C), an amount greater than 0 and less than or equal to 1.0 wt % of silicon (Si), an amount of 4.0 to 9.0 wt % of manganese (Mn), an amount greater than 0 and less than or equal to 0.6 wt % of aluminum (Al), an amount greater than 0 and less than or equal to 0.02 wt % of phosphorus (P) in, an amount greater than 0 and less than or equal to 0.005 wt % of sulfur (S), an amount greater than 0 and less than or equal to 0.006 wt % of nitrogen (N), and the balance of iron (Fe) and other inevitable impurities.

Abstract: Provided herein is a steel sheet having high strength and high formability according to an aspect of the present invention including, % by weight, an amount of 0.05 to 0.15% of carbon (C), an amount greater than 0 and 0.4% or less of silicon (Si), an amount of 4.0-9.0% of manganese (Mn), an amount of greater than 0 and 0.3% or less of aluminum (Al), an amount of 0.02% or less of phosphorus (P), an amount of 0.005% or less of sulfur (S), an amount of 0.006% or less of nitrogen (N), and the remainder of iron (Fe) and other inevitable impurities. The steel sheet has a microstructure consisting of ferrite and residual austenite. The grain size of the microstructure is 3 ?m or less. The steel sheet has a yield strength (YS) of 800 MPa or greater, a tensile strength (TS) of 980 MPa or greater, an elongation (EL) of 25% or greater, and a hole expansion ratio (HER) of 20% or greater.

Abstract: In a localized torsional severe plastic deformation method for conical tube metal, a desired region of a conical tube metal can be subjected to severe plastic deformation using molds in which roughness is formed at predetermined regions. The method includes roughening a predetermined region of each of the molds; sticking the conical tube metal only to the roughened regions of the molds; moving the lower mold toward the upper mold to apply a load to the conical tube metal; and rotating the molds to apply severe plastic deformation to the conical tube metal only at the regions stuck to the roughened regions of the molds.

Abstract: The present invention relates to a torsional severe plastic deformation method for a metal bar to which surface polishing is applied to the metal bar to improve the mechanical properties of the metal bar. According to an embodiment of the present invention, there is provided a torsional severe plastic deformation method for a metal bar, which includes: applying torsion to a metal bar; and removing a surface defect on the surface of the metal bar, the surface defect being caused by the applying of torsion, wherein the removing of the surface defect is carried out in a continuous manner in which the removing of the surface defect is performed together with the applying of torsion or in a discontinuous manner in which the applying of torsion is temporarily stopped and then the applying of torsion is performed, and the removing of a surface defect increases the amount of torsional rotation or the shear strain applied to the metal bar.

Abstract: In a localized torsional severe plastic deformation method for conical tube metal, a desired region of a conical tube metal can be subjected to severe plastic deformation using molds in which roughness is formed at predetermined regions. The method includes roughening a predetermined region of each of the molds; sticking the conical tube metal only to the roughened regions of the molds; moving the lower mold toward the upper mold to apply a load to the conical tube metal; and rotating the molds to apply severe plastic deformation to the conical tube metal only at the regions stuck to the roughened regions of the molds.

Abstract: The present invention relates to a torsional extreme-plastic processing method. In other words, a processing method in which severe plastic deformation based on torsion and compressive force is applied to a material by using a mold to produce miniaturize and nano-size crystal particles in a conic pipe. According to the severe plastic deformation method of the present invention, a punch that matches an inner shape of the conic metal pipe is mounted inside the conic metal pipe, and then a mold that matches an outer shape of the conic metal pipe is mounted outside the conic metal pipe. Thus, microstructures of the conic metal pipe may be ultra-finely crystallized or nano-crystallized through shearing by applying compression and torsion to the conic metal pipe.

Abstract: The present invention relates to a torsional extreme-plastic processing method. In other words, a processing method in which severe plastic deformation based on torsion and compressive force is applied to a material by using a mold to produce miniaturize and nano-size crystal particles in a conic pipe. According to the severe plastic deformation method of the present invention, a punch that matches an inner shape of the conic metal pipe is mounted inside the conic metal pipe, and then a mold that matches an outer shape of the conic metal pipe is mounted outside the conic metal pipe. Thus, microstructures of the conic metal pipe may be ultra-finely crystallized or nano-crystallized through shearing by applying compression and torsion to the conic metal pipe.