The present invention relates to a motor vehicle crash box with a working direction in vehicle's longitudinal axis manufactured out of a tube which is expanded into different zones, wherein the zones are different in strength and diameter by using steel after forming a homogenous austenitic microstructure with a strain hardening effect. The present invention further relates to the manufacturing method of such a component.

A cold rolled and coated steel sheet having a composition including of the following elements, 0.12%≤Carbon≤0.2%, 1.7%≤Manganese≤2.10%, 0.1%≤Silicon≤0.5%, 0.1%≤Aluminum≤0.8%, 0.1%≤Chromium≤0.5%, 0%≤Phosphorus≤0.09%, 0%≤Sulfur≤0.09%, 0%≤Nitrogen≤0.09%, Nickel≤3%, Niobium≤0.1%, Titanium≤0.1%, Calcium≤0.005%, Copper≤2%, Molybdenum≤0.5%, Vanadium≤0.1%, Boron≤0.003%, Cerium≤0.1%, Magnesium≤0.010%, Zirconium≤0.010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet including in area fraction, 10 to 60% Bainite, 25 to 55% Ferrite, 5% to 15% Residual Austenite wherein carbon content in residual austenite is between 0.7% and 1% and 5% to 18% Martensite, wherein the cumulated amount of Bainite and Ferrite is at least 70%.

A steel sheet including a chemical composition in mass %: C: 0.14-0.60%, Si+Al≤3.00, P 0.030%, S≤0.0050%, N 0.015%, B≤0.0050%, C×Mn≤0.80, Mn+Ni+Cu+1.3Cr+4(Mo+W)≥0.80, 0.003≤Ti+Zr+Hf+V+Nb+Ta+Sc+Y≤0.20, Sn+As+Sb+Bi≤0.020, Mg: 0 to 0.005%, Ca: 0 to 0.005%, REM: 0 to 0.005%, with the balance: Fe and impurities, and satisfying Ms=546 ×exp(−1.362 x C)−11 ×Si−30 ×Mn−18 ×Ni−20 ×Cu−12×Cr −8(Mo+W)≥200.

An austenitic heat resisting steel includes, as a chemical composition, by mass %: C: 0.04% to 0.12%; Si: 0.10% to 0.30%; Mn: 0.20% to 0.80%; P: 0% to 0.030%; S: 0.0001% to 0.0020%: Sn: 0.0005% to 0.0230%; Cu: 2.3% to 3.8%; Co: 0.90% to 2.40%; Ni: 22.0% to 28.0%; Cr: 20.0% to 25.0%; Mo: 0.01% to 0.40%; W: 2.8% to 4.2%; Nb: 0.20% to 0.80%; B: 0.0010% to 0.0050%; and N: 0.16% to 0.30%, and a remainder of Fe and impurities, optionally further includes one or more selected from Al, O, V, Ti, Ta, C, Mg, and REM, in which 0.0012%≤[% S]+[% Sn]≤2.5×[% B]+0.0125% is satisfied.

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 high-strength steel sheet includes a steel structure with: ferrite being 35% to 80%, martensite being 5% to 35%, and tempered martensite being 0% to 5% in terms of area fraction; retained austenite being 8% or more in terms of volume fraction; an average grain size of: the ferrite being 6 μm or less; and the retained austenite being 3 μm or less; a value obtained by dividing an area fraction of blocky austenite by a sum of area fractions of lath-like austenite and the blocky austenite being 0.6 or more; a value obtained by dividing, by mass %, an average Mn content in the retained austenite by an average Mn content in the ferrite being 1.5 or more; and a value obtained by dividing, by mass %, an average C content in the retained austenite by an average C content in the ferrite being 3.0 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.

A steel sheet having a tensile strength (TS) of 780 MPa or more and less than 1180 MPa, high LME resistance, and good weld fatigue properties. The steel sheet has a specific chemical composition and a specific steel microstructure. Crystal grains containing an oxide of Si and/or Mn in a region within 4.9 μm in a thickness direction from a surface of the steel sheet have an average grain size in the range of 3 to 10 μm, the lowest Si concentration L.sub.Si and the lowest Mn concentration L.sub.Mn in the region within 4.9 μm in the thickness direction from the surface of the steel sheet and a Si concentration T.sub.Si and a Mn concentration T.sub.Mn at a quarter thickness position of the steel sheet satisfy a specified formula.

An austenitic stainless steel consists of 0.010 to 0.200% by mass of C, 2.00% by mass or less of Si, 3.00% by mass or less of Mn, 0.035% by mass or less of P, 0.0300% by mass or less of S, 6.00 to 14.00% by mass of Ni, 20.0 to 26.0% by mass of Cr, 3.00% by mass or less of Mo, 0.01 to 3.00% by mass of Cu, 1.000% by mass of less of Ti, 0.200% by mass or less of Al, 0.1000% by mass or less of Ca, 0.100 to 0.250% by mass of N, and 0.0080% by mass or less of 0, the balance being Fe and impurities.