A method of production of a cold rolled and heat treated steel sheet having the following steps: providing a cold rolled steel sheet with a composition with the following elements, expressed in percent by weight: 0.10%≤carbon≤0.6%; 4%≤manganese≤20%; 5%≤aluminum≤15%; 0≤silicon≤2% aluminium+silicon+nickel≥6.5%; and optionally at least one of certain optional elements; a remainder being composed of iron and unavoidable impurities caused by processing; heating the cold rolled steel sheet up to a soaking temperature between 750 and 950° C. during less than 600 seconds, then cooling the sheet down to room temperature; and reheating the steel sheet to a soaking temperature of 150° C. to 600° C. during 10 s to 1000 h, then further cooling the sheet.

Disclosed is a highly anticorrosive martensitic stainless steel having uniformly distributed fine chromium carbide so as to have improved corrosion resistance and being applicable as tableware with suitable hardness when strengthened by heat treatment, and a manufacturing metho therefor.

The highly anticorrosive martensitic stainless steel according to an embodiment of the present disclosure includes, in percent by weight (wt%), 0.14 to 0.21% of C, 0.05 to 0.11% of N, 0.1 to 0.6% of Si, 0.4 to 1.2% of Mn, 14.0 to 17.0% of Cr, 0.2 to 0.32% of C+N, and the balance of Fe and inevitable impurities, has a PREN value, represented by Formula (1), of 16 or more, and has a precipitation temperature of chromium carbide of 950° C. or lower.

A dual-phase stainless steel or dual-phase stainless steel seamless pipe has a certain composition, the dual-phase stainless steel or dual-phase stainless steel seamless pipe having a microstructure containing 20 to 70% austenitic phase and 30 to 80% ferritic phase by volume, the dual-phase stainless steel or dual-phase stainless steel seamless pipe having a yield strength, YS, of 448 MPa or more, and containing oxide inclusions of which oxide inclusions having an average particle diameter of 1 μm or more have a number density of 15/mm.sup.2 or less, and at most 50 mass % of the oxide inclusions having an average particle diameter of 1 μm or more are oxide inclusions containing aluminum.

The present disclosure relates to a high-strength Fe—Cr—Al—Ni multiplex stainless steel and a manufacturing method therefor. The multiplex stainless steel comprises 35 to 67 wt % of iron (Fe), 13 to 30 wt % of chrome (Cr), 15 to 30 wt % of nickel (Ni), and 5 to 15 wt % of aluminum (Al) and has a multiplex structure in which an austenite phase accounting for high ductility, a ferrite phase accounting for high strength, and an NiAl(B2) phase providing both strength and high-temperature steam oxidation resistance, exist in combination. The multiplex stainless steel can secure necessary fabricability and mechanical strength even if for/in a thin state, can maintain integrity as a structural member in a normal operation condition of a light-water reactor thanks to the formation of a chrome oxide layer thereon, and can form a stable oxide layer including alumina under a high-temperature steam environment, which is plausible in a high-temperature nuclear accident, thereby providing exceptionally improved resistance to serious accidents.

Provided are a laminate shaped article made of a maraging steel and having excellent toughness, a method for manufacturing the same, and a metal powder for laminate shaping. The laminate shaped article is made of a maraging steel comprising 0.1-5.0 mass % of Ti. When sis is performed on concentration distribution of Ti in a cross section parallel to a lamination direction of the above laminate shaped article, a length of a linear Ti-rich portion having a Ti concentration B of (1.5×A) or more with respect to an average Ti concentration A in the cross section is 15 μm or less. In addition, the method for manufacturing the laminate shaped article uses a metal powder made of a maraging steel comprising 0.1-5.0 mass % of Ti, and a heat source output is set to 50-330 W and a scanning speed is set to 480-3000 mm/sec during the laminate shaping.

This steel sheet has a predetermined chemical composition, Ex. C that is obtained by Ex. C = (%C) - 12 ( (%Ti*)/48 + (%V)/51 + (%Nb)/93 + (%Mo)/96 + (%W)/184} is 0.020% or less, a microstructure at a ¼ depth position of a sheet thickness from a surface contains 60% or more of ferrite, 0% to 5% of MA and a total of 0% to 5% of pearlite and cementite with a remainder of bainite in terms of area fractions, in the microstructure, the average crystal grain diameter is 10.0 .Math.m or less, the average aspect ratio of crystal grains is 0.30 or more, the standard deviation of a Mn concentration is 0.60 mass% or less, a Ti-based carbide having a Baker-Nutting orientation relationship in the ferrite is precipitated in a semi-coherent state, and a tensile strength is 980 MPa or more.

Provided is a steel sheet for low-temperature service, which can be used at a wide temperature range from low temperature to room temperature in liquefied gas storage tanks and transport facilities. The steel sheet for low-temperature service has an excellent surface processing quality even after a processing processes is performed, such as a tension process. The a steel sheet contains manganese (Mn, 15-35 wt %), carbon (C, satisfying 23.6C+Mn≧28 and 33.5C—Mn≦23), copper (Cu, 5 wt % or less (excluding 0 wt %)), chrome (Cr, satisfying 28.5C+4.4Cr≦57 (excluding 0 wt %)), titanium (Ti, 0.01-0.5 wt %), nitrogen (N, 0.003-0.2 wt %), the balance iron (Fe), and other inevitable impurities. Ti and N satisfy relational expression 1 below. [Relational expression 1] 1.0≦Ti/N≦4.5 (Mn, C, Cr, Ti, and N in the respective expressions mean wt % of respective ingredient contents).

A high-strength spring steel coil spring of a vehicle suspension, having excellent corrosion resistance, may include 0.4 to 0.9 wt % of C, 0.9 to 2.3 wt % of Si, 0.5 to 1.2 wt % of Mn, 0.6 to 1.5 wt % of Cr, 0.01 to 0.5 wt % of Mo, 0.01 to 0.9 wt % of Ni, 0.5 wt % or less (excluding 0 wt %) of V, 0.5 wt % or less (excluding 0 wt %) of Nb, 0.3 wt % or less (excluding 0 wt %) of Ti, 1.0 wt % or less (excluding 0 wt %) of Co, 0.1 wt % or less (excluding 0 wt %) of B, 0.3 wt % or less (excluding 0 wt %) of W, 0.3 wt % or less (excluding 0 wt %) of Cu, 0.3 wt % or less (excluding 0 wt %) of Al, 0.03 wt % or less (excluding 0 wt %) of N, 0.003 wt % or less (excluding 0 wt %) of O, and a remainder of Fe and inevitable impurities.

A plastic forming mold made from a stainless steel, having in weight % (wt. %): C 0.32-0.50, Si 0.1-1.0, Mn 0.1-0.8, Cr 11-14, Mo 1.8-2.6, V 0.35-0.70, N 0.05-0.19, optional elements, and a balance of Fe apart from impurities. The stainless steel is hardened and tempered and has a matrix comprising ≥90 vol. % martensite.

Provided are: a boron-added high strength steel for bolt excellent in delayed fracture resistance even having a tensile strength of 1100 MPa or more without addition of large amounts of expensive alloy elements such as Cr and Mo: and a high strength bolt made from the boron-added high strength steel for bolt. The high strength steel for bolt contains C of 0.23% to less than 0.40%, Si of 0.23% to 1.50%, Mn of 0.30% to 1.45%, P of 0.03% or less (excluding 0%), S of 0.03% or less (excluding 0%), Cr of 0.05% to 1.5%, V of 0.02% to 0.30%, Ti of 0.02% to 0.1%, B of 0.0003% to 0.0050%, Al of 0.01% to 0.10%, and N of 0.002% to 0.010%, with the remainder being iron and inevitable impurities. The steel has a ratio ([Si]/[C]) of the Si content [Si] to the C content [C] of 1.0 or more and has a ferrite-pearlite mixed microstructure.