A low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate and a manufacturing method thereof are provided. The dual-phase steel plate has the following chemical composition by mass percentages: C: 0.1%-0.125%, Si: 0.4%-0.8%, Mn: 2.6%-2.9%, Al: 0.01%-0.05%, Nb: 0.01%-0.03%, and Ti: 0.01%-0.03%, the remainder being Fe and unavoidable impurities. By reasonable design of alloy elements and manufacturing processes, the dual-phase steel plate of the invention achieves a strength of 1180 MPa grade at a low cost, obtains a fine and uniform martensite-ferrite dual-phase structure that ensures excellent elongation rate and cold bending performance, and has good formability. The dual-phase steel plate has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing the 90-degree cold bending performance, of 2.5 or less.

Disclosed are a ferritic stainless steel capable of inhibiting high temperature oxidation through generation of an effective oxide scale, and manufacturing method thereof. The ferritic stainless steel excellent in oxidation resistance at high temperature according to an embodiment of the present disclosure includes, in percent (%) by weight of the entire composition, Cr: 10 to 30%, Si: 0.2 to 1.0%, Mn: 0.1 to 2.0%, W: 0.3 to 2.5%, Ti: 0.001 to 0.15%, Al: 0.001 to 0.1%, the remainder of iron (Fe) and other inevitable impurities, and satisfies a following equation (1).
W/(Ti+Al)≥10  (1)

Disclosed are a ferritic stainless steel capable of inhibiting high temperature oxidation through generation of an effective oxide scale, and manufacturing method thereof. The ferritic stainless steel excellent in oxidation resistance at high temperature according to an embodiment of the present disclosure includes, in percent (%) by weight of the entire composition, Cr: 10 to 30%, Si: 0.2 to 1.0%, Mn: 0.1 to 2.0%, W: 0.3 to 2.5%, Ti: 0.001 to 0.15%, Al: 0.001 to 0.1%, the remainder of iron (Fe) and other inevitable impurities, and satisfies a following equation (1).
W/(Ti+Al)≥10  (1)

Provided are a material for hot stamping, and the material includes: a steel sheet including carbon (C) in an amount of 0.28 wt% to 0.50 wt%, silicon (Si) in an amount of 0.15 wt% to 0.70 wt%, manganese (Mn) in an amount of 0.5 wt% to 2.0 wt%, phosphorus (P) in an amount less than or equal to 0.05 wt%, sulfur (S) in an amount less than or equal to 0.01 wt%, chromium (Cr) in an amount of 0.1 wt% to 0.5 wt%, boron (B) in an amount of 0.001 wt% to 0.005 wt%, an additive in an amount less than or equal to 0.1 wt%, balance iron (Fe), and other inevitable impurities; and fine precipitates distributed within the steel sheet. The additive includes at least one of titanium (Ti), niobium (Nb), and vanadium (V), and the fine precipitates include nitride or carbide of at least one of titanium (Ti), niobium (Nb), and vanadium (V) and trap hydrogen.

Provided are a material for hot stamping, and the material includes: a steel sheet including carbon (C) in an amount of 0.28 wt% to 0.50 wt%, silicon (Si) in an amount of 0.15 wt% to 0.70 wt%, manganese (Mn) in an amount of 0.5 wt% to 2.0 wt%, phosphorus (P) in an amount less than or equal to 0.05 wt%, sulfur (S) in an amount less than or equal to 0.01 wt%, chromium (Cr) in an amount of 0.1 wt% to 0.5 wt%, boron (B) in an amount of 0.001 wt% to 0.005 wt%, an additive in an amount less than or equal to 0.1 wt%, balance iron (Fe), and other inevitable impurities; and fine precipitates distributed within the steel sheet. The additive includes at least one of titanium (Ti), niobium (Nb), and vanadium (V), and the fine precipitates include nitride or carbide of at least one of titanium (Ti), niobium (Nb), and vanadium (V) and trap hydrogen.

The present invention relates to a steel for a mold including: on % by mass basis, 0.55% ≤ C ≤ 0.70%; 0.30% ≤ Si ≤ 0.60%; 0.55% ≤ Mn ≤ 1.2%; 5.7% ≤ Cr ≤ 6.9%; 1.2% ≤ Mo + W/2 ≤ 1.6%; 0.55% ≤ V ≤ 0.79%; and 0.005% ≤ N ≤ 0.1%, with the remainder being Fe and inevitable impurities including, Al ≤ 0.020%, Ni ≤ 0.20%, S ≤ 0.0015%, and Cu ≤ 0.10%, and satisfying P1 ≥ 24 and 4.9 ≤ P2 ≤ 7.3, P1 and P2 being a value obtained based on the following formula (1) and (2), respectively, P1 = 45 - 13.6[Si] - 7.0([Mo]+[W]/2) - 12.9[Ni] (1), P2 = 7.4[V] + 15.8[N] + 38.6[Al] (2) in which [M] represents a content of an element M in % by mass basis, and relates to a mold including the steel for a mold.

The austenitic stainless steel containing niobium according to an exemplary embodiment of the present invention includes: 16 to 26 wt. % of chromium (Cr), 8 to 22 wt. % of nickel (Ni), 0.02 to 0.1 wt. % of carbon (C), 0.2 to 1 wt. % of niobium (Nb), 0.015 to 0.025 wt. % of titanium (Ti), 0.004 to 0.01 wt. % of nitrogen (N), and 0.5 to 2 wt. % of manganese (Mn), wherein the austenitic stainless steel containing niobium has an austenitic matrix structure, a fine niobium carbide and a fine titanium nitride are precipitated in the austenitic matrix structure, and the fine niobium carbide is uniformly dispersed in the austenitic matrix structure.

The austenitic stainless steel containing niobium according to an exemplary embodiment of the present invention includes: 16 to 26 wt. % of chromium (Cr), 8 to 22 wt. % of nickel (Ni), 0.02 to 0.1 wt. % of carbon (C), 0.2 to 1 wt. % of niobium (Nb), 0.015 to 0.025 wt. % of titanium (Ti), 0.004 to 0.01 wt. % of nitrogen (N), and 0.5 to 2 wt. % of manganese (Mn), wherein the austenitic stainless steel containing niobium has an austenitic matrix structure, a fine niobium carbide and a fine titanium nitride are precipitated in the austenitic matrix structure, and the fine niobium carbide is uniformly dispersed in the austenitic matrix structure.

The present disclosure relates to an austenitic stainless steel contains C≤0.10 mass %, Si≤0.50 mass %, 3.0≤Mn≤8.0 mass %, P≤0.30 mass %, S≤0.30 mass %, 7.0 Ni≤12.0 mass %, 18.0≤Cr≤28.0 mass %, 1.0≤Mo≤3.0 mass %, 0.03≤V≤0.50 mass %, 0.0003≤B≤0.0300 mass %, 0.0001≤Ca≤0.0300 mass %, 0.35≤N≤0.80 mass %, W≤2.0 mass %, Zr≤0.20 mass %, Cu≤0.5 mass %, Al≤0.10 mass %, and O≤0.050 mass %, with a balance being Fe and unavoidable impurities. The austenitic stainless steel has a number density of coarse alloy carbonitrides of 3×10.sup.5 pieces/mm.sup.2 or less.

Provided herein is a high-strength seamless steel pipe containing a particular chemical composition. The volume fraction of tempered martensite is 90% or more in terms of a volume fraction. The number of nitride inclusions with a particle diameter of 4 μm or more is 50 or less per 100 mm.sup.2, the number of nitride inclusions with a particle diameter of less than 4 μm is 500 or less per 100 mm.sup.2, the number of oxide inclusions with a particle diameter of 4 μm or more is 40 or less per 100 mm.sup.2, and the number of oxide inclusions with a particle diameter of less than 4 μm is 400 or less per 100 mm.sup.2 in a cross section perpendicular to a rolling direction.