Arcelormittal

Wei Xu

Artem Arlazarov

A method for manufacturing a high-strength sheet including the steps of (i) providing a steel having a chemical composition consisting of, in percent by weight: 0.1%≤C≤0.4%, 4.5%≤Mn≤5.5%, 1%≤Si≤3%, and 0.2%≤Mo≤0.5%, a remainder being Fe and unavoidable impurities; (ii) annealing a rolled sheet made of the steel by soaking the rolled sheet at an annealing temperature AT higher than an Actransformation point of the steel; (iii) quenching the sheet by cooling it down to a quenching temperature QT between the Ms transformation point of the steel and 130° C.; (iv) heating the sheet up to an overaging temperature PT between 300° C. and 500° C. and maintaining the sheet at said overaging temperature PT for an overaging time Pt greater than 10 s; and (v) cooling the sheet down to ambient temperature.

Method for manufacturing a high strength steel sheet having improved formability and sheet obtained

A method is for manufacturing a high-strength steel sheet having a tensile strength of more than 1100 MPa and a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation of at least 10%, made of a steel containing in percent by weight: 0.1%&#x2264;C&#x2264;0.25%, 4.5%&#x2264;Mn&#x2264;10%, 1%&#x2264;Si&#x2264;3%, 0.03%&#x2264;Al&#x2264;2.5%, the remainder being Fe and impurities resulting from the smelting, the composition being such that CMnIndex=C&#xd7;(1+Mn/3.5)&#x2264;0.6. The method includes annealing a rolled sheet made of said steel by soaking it at an annealing temperature TA higher than the Actransformation point of the steel but less than 1000&#xb0; C., cooling the annealed sheet to a quenching temperature QT between 190&#xb0; C. and 80&#xb0; C. at a cooling speed sufficient to obtain a structure just after cooling containing martensite and retained austenite, maintaining the steel sheet at an overaging temperature PT between 350&#xb0; C. and 500&#xb0; C. for an overaging time Pt of more than 5 s cooling the sheet down to the ambient temperature.

Method for manufacturing a high-strength steel sheet and sheet obtained by the method

A method for manufacturing a high-strength steel sheet having a tensile strength of more than 1100 MPa and a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation of at least 10%, made of a steel containing in percent by weight: 0.1%&#x2264;C&#x2264;0.25%, 4.5%&#x2264;Mn&#x2264;10%, 1%&#x2264;Si&#x2264;3%, 0.03%&#x2264;Al&#x2264;2.5%, the remainder being Fe and impurities resulting from the smelting, the composition being such that CMn Index=Cx(1+Mn/3.5)&#x2264;0.6, the method comprising the steps of annealing a rolled sheet made of said steel by soaking it at an annealing temperature TA higher than the Ac transformation point of the steel but less than 1000&#xb0; C., cooling the annealed sheet to a quenching temperature QT between 190&#xb0; C. and 80&#xb0; C. at a cooling speed sufficient to obtain a structure just after cooling containing martensite and retained austenite, maintaining the steel sheet at an overaging temperature PT between 350&#xb0; C. and 500&#xb0; C. for an overaging time Pt of more than 5 s cooling the sheet down to the ambient temperature. Sheet obtained.

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Zelzate, Belgium

Wei Xu