The present invention relates to steel used for a sash component and the like of a vehicle and, more specifically, to a hot-rolled steel sheet for a high-strength electric resistance welded steel pipe having excellent expandability and a method for manufacturing same, the hot-rolled steel sheet having a smaller decrease in the strength of a welding heat-affected zone (HAZ) formed during electric resistance welding, in comparison with a base material.

The disclosed martensitic stainless steel is defined in its composition is by specified ranges of weight percentages of C; Mn; Si; ≤Mn+Si; ≤S; 10,000×Mn×S; P; Cr, with [Cr−10.3−80*(C+N).sup.2]≤(Mn+Ni); Ni; Mo; Mo+2W; Cu; Ti; V; Zr; Al; O; Ta; Nb; (Nb+Ta)/(C+N); Nb; N; Co; Cu+Co; Cu+Co+Ni; B; rare earths+Y; Ca; the remainder being iron and impurities resulting from processing. Its microstructure includes at least 75% martensite, at most 20% ferrite and at most 0.5% carbides, the size of the ferrite grains being between 4 and 80 μm, preferably between 5 and 40 μm. Also disclosed is a method of manufacturing such steel.

A cold rolled and annealed steel sheet includes by weight: 0.6≤C≤1.3%, 15.0≤Mn≤35%, 5≤Al≤15%, Si≤2.40%, S≤0.03%, P≤0.1%, N≤0.1%, possibly one or more optional elements chosen among Ni, Cr and Cu in an respective amount of up to 4.0%, up to 3.0% and up to 3.0% and possibly one or more elements chosen among B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, the microstructure of the sheet including optionally up to 3% of kappa carbides, optionally up to 10.0% of granular ferrite, the remainder being made of austenite, the average grain size and average aspect ratio of the austenite being respectively below 6 μm and comprised between 1.5 and 6 and the average grain size and average aspect ratio of the ferrite, when present, being respectively below 5 μm and below 3.0.

An embodiment of the present invention provides a steel material, for a pressure vessel, comprising, in weight %, 0.06-0.25% of carbon (C), 0.05-0.50% of silicon (Si), 1.0-2.0% of manganese (Mn), 0.005-0.40% of aluminum (Al), 0.010% or less of phosphorus (P), 0.0010% or less of sulfur (S), 0.001-0.03% of niobium (Nb), 0.001-0.03% of vanadium (V), 0.001-0.03% of titanium (Ti), 0.01-0.20% of chromium (Cr), 0.05-0.15% of molybdenum (Mo), 0.01-0.50% of copper (Cu), 0.05-0.50% of nickel (Ni), 0.0005-0.0050% of magnesium (Mg), 0.0005-0.0050% of calcium (Ca), 0.0020% or less of oxygen (O), and the remainder being Fe and other unavoidable impurities. A microstructure comprises in terms of area fraction 30% or less of pearlite and the remainder being ferrite. A non-metallic inclusion contains Mg—Al—Ca—O composite oxide.

A cold rolled and heat treated steel sheet having a composition including the following elements, expressed in % by weight: 0.1%≤carbon≤0.6% 4%≤manganese≤20% 5%≤aluminum≤15% 0≤silicon≤2% aluminium+silicon+nickel≥6.5% and can possibly contain one or more of the following optional elements: 0.01%≤niobium≤0.3%, 0.01%≤titanium≤0.2% 0.01%≤vanadium≤0.6% 0.01%≤copper≤2.0% 0.01%≤nickel≤2.0% cerium≤0.1% boron≤0.01% magnesium≤0.05% zirconium≤0.05% molybdenum≤2.0% tantalum≤2.0% tungsten≤2.0% the remainder being composed of iron and unavoidable impurities caused by processing, wherein the microstructure of said steel sheet includes in area fraction, 10 to 50% of austenite, the austenite phase optionally including intragranular kappa carbides, the remainder being regular ferrite and ordered ferrite of D03 structure (Fe,Mn,X).sub.3Al, optionally including up to 2% of intragranular kappa carbides (Fe,Mn).sub.3AlC.sub.x said steel sheet presenting a ultimate tensile strength higher than or equal to 900 MPa. It also deals with a manufacturing method and with use of such grade for making vehicle parts.

The present invention relates to steel used for a sash component and the like of a vehicle and, more specifically, to a hot-rolled steel sheet having excellent durability and a method for manufacturing same, the hot-rolled steel sheet having no cracks formed on a material and a welding heat-affected zone (HAZ) even after pipemaking and molding due to a smaller decrease in the strength of the welding heat-affected zone formed during electric resistance welding in comparison with the strength of the material (base material).

The present invention relates to a steel for mold, containing: 0.28 mass %≤C≤0.65 mass %, 0.01 mass %≤Si≤0.30 mass %, 1.5 mass %≤Mn≤3.0 mass %, 0.5 mass %≤Cr≤1.4 mass %, 1.9 mass %≤Mo+W/2≤4.0 mass %, 0.2 mass %≤V≤1.0 mass %, and 0.01≤N≤0.10 mass %, with the balance being Fe and inevitable impurities, in which, in a state after quenching and tempering, the steel has: a (Mo, W) carbide having a diameter of 0.2 μm or less being in an amount of 1.2 mass % or more, a ratio (mass ratio) of the amount of the (Mo, W) carbide to an amount of a Cr carbide being 11 or more, and a hardness change of 15 HRC or less.

A cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, the retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of the Martensite Austenite islands having a size above 0.5 μm, at most 1% of fresh martensite, at most 50% of tempered martensite, and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A method for manufacturing the cold-rolled and heat-treated steel sheet is also described.

The present invention relates to a manganese steel alloy having a heat-treated microstructure comprising: (a) an alloy composition of: manganese: 12 to 30 wt %; carbon: 1.0 to 2.0 wt %; chromium: 4.5 to 7.0 wt %; molybdenum: 0.0 to 3.0 wt %; and iron and impurities: balance, and (b) an austenitic ferrous matrix; and (c) formed refractory particles dispersed throughout the austenitic ferrous matrix such that ≥10% of the formed refractory particles are located within crystallites of the austenitic ferrous matrix, as opposed to being located at grain boundaries between the crystallites, wherein the formed refractory particles are compounds of carbides and/or borides and/or nitrides of any one or more of chromium, zirconium, hafnium, tantalum, molybdenum, and tungsten. The invention further relates to equipment adapted for high-stress gouging abrasion that includes the manganese steel alloy of the invention, and a method of producing the manganese steel alloy of the invention.

A steel sheet has a predetermined chemical composition, in which a microstructure in a ¼ width portion, a microstructure in a ½ width portion, and a microstructure in a ¾ width portion, include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, in which a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, and Expressions (2) to (5) are satisfied.

Δ.sub.SF/μ.sub.SF≤0.10  (2)

Δ.sub.dF/μ.sub.dF≤0.20  (3)

Δ.sub.SUF≤20  (4)

Δ.sub.dC/μ.sub.dC≤0.50  (5)