The present invention relates to the application of at least partially bainitic or interstitial martensitic heat treatments on steels, often tool steels or steels that can be used for tools. The first tranche of the heat treatment implying austenitization is applied so that the steel presents a low enough hardness to allow for advantageous shape modification, often trough machining. Thus a steel product is obtained which can be shaped with ease and whose hardness can be raised to a higher working hardness with a simple heat treatment at low temperature (below austenitization temperature).

Adopted are a hot-rolled steel sheet having a predetermined chemical composition, in which a region, where a rotation angle between a normal line of a surface and a (011) pole near the normal line becomes 5° or less, is 0.150 or less from the surface in terms of a sheet thickness direction position standardized by a sheet thickness, and a region, where the rotation angle becomes 20° or more, is 0.250 or more from the surface in terms of the sheet thickness direction position standardized by the sheet thickness and a manufacturing method thereof.

A packaging sheet metal product from a cold-rolled steel sheet with a thickness of less than 0.6 mm has a specified composition. The packaging sheet metal product during biaxial deformation in a bulge test has a lower yield strength (Sb.sub.eL) of more than 300 MPa and a corresponding elongation at break (Ab) of more than 10% and in the plastic region between the Lüders elongation (Ab.sub.e) and an upper (plastic) elongation limit of ε.sub.max=0.5.Math.Ab.Math.(Sb.sub.eL/Sb.sub.m) has a biaxial stress/strain diagram σ.sub.B(ε) that can be represented by a function ε.sub.B=b.Math.ε.sup.n, with: σ.sub.B is the true biaxial stress in MPa; ε is the amount of true elongation in the thickness direction in %; Sb.sub.m is the absolute strength; b is a proportionality factor; and n is a strain-hardening exponent. A strengthening of the packaging sheet product in the thickness direction is characterized by a strain-hardening exponent of n≥0.353-5.1.Math.Sb.sub.eL/10.sup.4 MPa.

Provided is a high-strength steel sheet including: 0.12% to less than 0.17% of carbon (C), 0.3% to 0.8% of silicon (Si), 2.5% to 3.0% of manganese (Mn), 0.4% to 1.1% of chromium (Cr), 0.01% to 0.3% of aluminum (Al), 0.01% to 0.03% of niobium (Nb), 0.01% to 0.03% of titanium (Ti), 0.001% to 0.003% of boron (B), 0.04% or less of phosphorus (P), 0.01% or less of sulfur (S): 0.01% or less of nitrogen (N), and a balance of iron (Fe) and inevitable impurities. The contents of C, Si, and Al satisfy: [C]+[Si]+[Al])/5≤0.35 wt. A microstructure includes more than 1% to 4% or less of retained austenite, more than 10% to 20% or less of fresh martensite, 5% or less (excluding 0%) of ferrite, more than 50% to 70% or less of tempered martensite, and a balance of bainite.

A steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, in terms of area fraction, ferrite: 20% or more and 60% or less, a total of bainite and tempered martensite: 25% or more and 60% or less, retained austenite: 7% or more and 20% or less, fresh martensite: 8% or more and 40% or less, and the remainder: 5% or less. Cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less, and the steel sheet has a tensile strength of 980 MPa or more.

A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm.sup.2, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

Disclosed is a clad steel plate with further improved low temperature toughness along with excellent HIC resistance while ensuring a tensile strength of 535 MPa or more. A clad steel plate includes: a base steel; and a clad metal made of a corrosion resistant alloy bonded to one surface of the base steel, in which the base steel has: a chemical composition with appropriately controlled values of ACR and P.sub.HIC; and a steel microstructure in which bainite is present in an area fraction of 94% or more at a ½ thickness position in a thickness direction of the base steel, and with an average crystal grain size of 25 μm or less, and shear strength at a bonded interface between the base steel and the cladding metal is 300 MPa or more.

A galvannealed steel sheet having a steel substrate coated with a first alloy layer with iron and nickel directly topped by a second alloy layer based on zinc, the first and second alloyed layers being alloyed through diffusion such that the second alloy layer includes from 5 to 15 wt.% of iron, from 0 to 15 wt.% of nickel, a balance being zinc.

Steel for glass lining, comprising the following chemical elements in mass percent: C: 0.015-0.060%, Si: 0.01-0.50%, Mn: 0.20-1.5%, P: 0.005-0.10%, Al: 0.010-0.070%, Ti: 0.10-0.30%, and the balance of Fe and other inevitable impurities. The microstructure of the steel for glass lining is a ferrite or a combination of a ferrite and a cementite. In addition, also disclosed is a production method for steel for glass lining, comprising the steps of (1) smelting, refining, and continuous casting to obtain a slab; (2) heating, the heating temperature being 1050-1250° C.; (3) hot rolling, the final temperature of hot rolling being controlled to be 800-920° C.; (4) cooling; and (5) thermal treatment. The steel for glass lining has excellent machinability and low temperature toughness, and also has excellent lining performance.

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 %).