Arcelormittal

Arcelormittal France

Audrey Couturier

Thierry Iung

Sebastien Allain

Christine Colin

Christian Moretto

Nicolas Pethe

Sébastien Allain

A method for the regulation of at least one of the parameters (&#x3b1;) of a hot rolling process of a semi-finished metal product in at least one rolling mill stand having at least two work rolls is provided. The regulation method includes calculating a forward slip ratio (FWS) with the following equation: where vis the speed of the semi-finished product at the exit of the respective stand and vis the linear velocity of the work rolls; calculating an estimated coefficient of friction (&#x3bc;) as a function of a measured value of the screwdown force (F) of the work rolls in the stand and of the forward slip ratio (FWS); and regulating at least one of the parameters (&#x3b1;) based on the calculated estimated coefficient of friction (&#x3bc;).

Hot rolling method

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 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%.

Process for manufacturing steel sheet having very high strength, ductility and toughness characteristics, and sheet thus produced

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Metz, France

Audrey Couturier