Arcelormittal

Arcelormittal France

Sebastien Allain

Thierry Iung

Audrey Couturier

Christine Colin

Jean-Christophe Hell

Marie-Christine Theyssier

Gerard Petitgand

Nicolas Charbonnier

Gérard Petitgand

A method for the manufacture of a TWIP steel is provided including: (A) feeding of a slab comprising by weight: 0.5&#x3c;C&#x3c;1.2%, 13.0&#x2264;Mn&#x3c;25.0%, S&#x2264;0.030%, P&#x2264;0.080%, N&#x2264;0.1%, Si&#x2264;3.0%, 0.051%&#x2264;Al&#x2264;4.0%, 0.1&#x2264;V&#x2264;2.5%, and on a purely optional basis, one or more of Nb&#x2264;0.5%, B&#x2264;0.005%, Cr&#x2264;1.0%, Mo&#x2264;0.40%, Ni&#x2264;1.0%, Cu&#x2264;5.0%, Ti&#x2264;0.5%, 0.06&#x2264;Sn&#x2264;0.2%, the remainder of the composition being made of iron and inevitable impurities resulting from the elaboration, (B) reheating the slab and hot rolling the slab to provide a hot rolled slab, (C) coiling the hot rolled slab to provide a coiled slab, (D) first cold-rolling the coiled slab to provide a first cold rolled slab, (E) recrystallization annealing the first cold rolled slab such that an annealed steel sheet having an UTSis obtained and (F) second cold-rolling the annealed steel sheet with a reduction rate CR % that satisfies the following equation A: 1216.472&#x2212;0.98795*UTS&#x2264;(&#x2212;0.0008*UTS+1.0124)*CR %+(0.0371*UTS&#x2212;29.583)*CR %.

Method for the manufacture of TWIP steel sheet having an austenitic matrix

The invention relates to a hot-rolled steel sheet having a tensile strength of greater than 1200 MPa, an R/Rratio of less than 0.75 and an elongation at break of greater than 10%, the composition of which contains, the contents being expressed by weight: 0.10%&#x2264;C&#x2264;0.25%; 1%&#x2264;Mn&#x2264;3%; Al&#x2265;0.015%; Si&#x2264;1.985%; Mo&#x2264;0.30%; Cr&#x2264;1.5%; S&#x2264;0.015%; P&#x2264;0.1%; Co&#x2264;1.5%; B&#x2264;0.005%; it being understood that 1%&#x2264;Si+Al&#x2264;2%; Cr+(3&#xd7;Mo)&#x2265;0.3%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to or greater than 5% and martensite in an amount equal to or greater than 2%.

Process for manufacturing steel sheet

The invention relates to the manufacture of a cold-rolled steel sheet having a strength of more than 900 MPa, an elastic limit of more than 700 MPa and distributed elongation of more than 12%, the composition of which includes, the contents being expressed as weight percentages: 0.26%&#x2264;C&#x2264;0.45%, 1.0%&#x2264;Mn&#x2264;3.0%, 1.0%&#x2264;Si&#x2264;3.0%, Al&#x2264;0.10%, 0%&#x2264;Cr&#x2264;1.5%, S&#x2264;0.005%, P&#x2264;0.020%, Nb&#x2264;0.1%, Ti&#x2264;0.020%, V&#x2264;0.015%, N&#x2264;0.01%, the remainder of the composition being iron and inevitable impurities resulting from the production process. The microstructure, given in surface proportions, comprises 13% to 25% residual austenite and 13% to 30% MA islands, the remainder consisting of bainite and possibly ferrite.

Steel sheet having very high mechanical properties of strength and ductility

The invention relates to a hot-rolled steel sheet having a tensile strength of greater than 1200 MPa, an R/Rratio of less than 0.75 and an elongation at break of greater than 10%, the composition of which contains, the contents being expressed by weight: 0.10%&#x2266;C&#x2266;0.25%; 1%&#x2266;Mn&#x2266;3%; Al&#x2267;0.015%; Si&#x2266;1.985%; Mo&#x2266;0.30%; Cr&#x2266;1.5%; S&#x2266;0.015%; P&#x2266;0.1%; Co&#x2266;1.5%; B&#x2266;0.005%; it being understood that 1%&#x2266;Si+Al&#x2266;2%; Cr+(3&#xd7;Mo)&#x2267;0.3%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to or greater than 5% and martensite in an amount equal to or greater than 2%.

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Metz, France

Sebastien Allain