Arcelormittal

Dongwei Fan

Hyun Jo Jun

Rashmi Ranjan Mohanty

Pavan K C Venkatasurya

John A Rotole

Pavan K Venkatasurya

Stavros Fountoulakis

Josée Drillet

Jean Philippe Masse

Gregory Inacio Da Rosa

Lijia Zhao

Xiang (frank) Chen

Narayan Pottore

A method is for producing a high strength coated steel sheet having an improved ductility and an improved formability, and a chemical composition containing: 0.13%&#x2264;C&#x2264;0.22%, 1.9%&#x2264;Si&#x2264;2.3%, 2.4%&#x2264;Mn&#x2264;3%, Al&#x2264;0.5%, Ti&#x2264;0.05%, Nb&#x2264;0.05%, the remainder being Fe and unavoidable impurities. The sheet is annealed at temperature TA higher than Ac3 but less than 1000&#xb0; C. for a time of more than 30 s, quenched by cooling to a quenching temperature QT between 200&#xb0; C. and 280&#xb0; C. in order to obtain a structure consisting of austenite and at least 50% of martensite, the austenite content being such that the final structure can contain between 3% and 15% of residual austenite and between 85% and 97% of the sum of martensite and bainite, without ferrite, heated up to a partitioning temperature PT between 430&#xb0; C. and 490&#xb0; C. and maintained at this temperature for a time Pt between 10 s and 100 s, hot dip coated and cooled to the room temperature.

Method for producing a high strength coated steel sheet having improved strength, formability and obtained sheet

A method for producing a high strength steel sheet having a yield strength YS of at least 850 MPa, a tensile strength TS of at least 1180 MPa, a total elongation of at least 14% and a hole expansion ratio HER of at least 30%. The chemical composition of the steel contains: 0.15%&#x2264;C&#x2264;0.25%, 1.2%&#x2264;Si&#x2264;1.8%, 2%&#x2264;Mn&#x2264;2.4%, 0.1%&#x2264;Cr&#x2264;0.25%, Nb&#x2264;0.05%, Ti&#x2264;0.05%, Al&#x2264;0.50%, the remainder being Fe and unavoidable impurities. The sheet is annealed at an annealing temperature TA higher than Ac3 but less than 1000&#xb0; C. for more than 30 s, by cooling it to a quenching temperature QT between 275&#xb0; C. and 325&#xb0; C., at a cooling speed sufficient to have, just after quenching, a structure consisting of austenite and at least 50% of martensite, the austenite content en.) being such that the final structure can contain between 3% and 15% of residual austenite and between 85 and 97% of the sum of martensite and bainite, without ferrite, heated to a partitioning temperature PT between 420&#xb0; C. and 470&#xb0; C. and maintained at this temperature for time between 50 s and 150 s and cooled to the room temperature.

Method for producing a high strength steel sheet having improved strength, ductility and formability

A method for producing a high strength uncoated steel sheet having an improved strength and an improved formability, including the steps of: providing an uncoated steel sheet; annealing the sheet at an annealing temperature TA higher than 865&#xb0; C. but less than 1000&#xb0; C. for a time of more than 30 s; cooling the sheet down to a quenching temperature QT between 310&#xb0; C. and 375&#xb0; C., at a cooling speed of at least 30&#xb0; C./s; heating the sheet up to a partitioning temperature PT between 370&#xb0; C. and 470&#xb0; C. and maintaining the sheet at the partitioning temperature for a partitioning time Pt between 50 s and 150 s; and cooling the sheet down to the room temperature.

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

A method is for producing a high strength coated steel sheet having a yield stress YS&#x3e;800 MPa, a tensile strength TS&#x3e;1180 MPa, and improved formability and ductility. The steel contains: 15%&#x2264;C&#x2264;0.25%, 1.2%&#x2264;Si&#x2264;1.8%, 2%&#x2264;Mn&#x2264;2.4%, 0.1%&#x2264;Cr&#x2264;0.25%, Al&#x2264;0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature higher than Ac3 and lower than 1000&#xb0; C. for a time of more than 30 s, then quenched by cooling it to a quenching temperature QT between 250&#xb0; C. and 350&#xb0; C., to obtain a structure consisting of at least 60% of martensite and a sufficient austenite content such that the final structure contains 3% to 15% of residual austenite and 85% to 97% of martensite and bainite without ferrite, then heated to a partitioning temperature PT between 430&#xb0; C. and 480&#xb0; C. and maintained at this temperature for a partitioning time Pt between 10 s and 90 s, then hot dip coated and cooled to the room temperature.

Method for producing a high strength coated steel sheet having improved strength, ductility and formability

A method for producing a cold rolled and hot dip coated steel sheet is provided. The method includes casting a steel into a slab, reheating, hot rolling, cooling, coiling, descaling and cold rolling the slab. The cold rolled steel sheet is annealed so a layer of iron oxide forms on the surface with an internal oxidation underneath. The sheet is then heated so the surface is oxidized and the layer of iron oxide is fully reduced to obtain an internally oxidized depth between 200 nm and 100 &#x3bc;m which includes one or more of Si, Mn, Al, Ti containing oxides. The sheet is then hot dip coated and cooled.

Method for making a high strength multiphase steel

A method for producing a high strength coated steel sheet having a yield strength YS of at least 800 MPa, a tensile strength TS of &#x3e;1180 MPa, a total elongation &#x3e;14% and a hole expansion ratio HER &#x3e;30%. The steel contains in weight %: 0.13%&#x2264;C&#x2264;0.22%, 1.2%&#x2264;Si&#x2264;1.8%, 1.8%&#x2264;Mn&#x2264;2.2%, 0.10%&#x2264;Mo&#x2264;0.20%, Nb&#x2264;0.05%, Al&#x2264;0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature TA higher than Acbut less than 1000&#xb0; C. for more than 30 s, then quenched by cooling temperature QT between 325&#xb0; C. and 375&#xb0; C., at a cooling speed sufficient to obtain a structure consisting of austenite and at least 60% of martensite, the austenite content being such that the final structure can contain between 3% and 15% of residual austenite and between 85 and 97% of the sum of martensite and bainite, without ferrite, then heated to a partitioning temperature PT between 430&#xb0; C. and 480&#xb0; C. and maintained at this temperature for a partitioning time Pt between 10 s and 90 s, then hot dip coated cooled to the room temperature. Coated sheet obtained.

Method for producing a high strength coated steel sheet having improved strength and ductility and obtained sheet

A method for producing a high strength coated steel sheet having an improved ductility and an improved formability, the chemical composition of the steel containing: 0.13%&#x2264;C&#x2264;0.22%, 1.9%&#x2264;Si&#x2264;2.3%, 2.4%&#x2264;Mn&#x2264;3%, Al&#x2264;0.5%, Ti&#x3c;0.05%, Nb&#x3c;0.05%, the remainder being Fe and unavoidable impurities. The sheet is annealed at temperature TA higher than Ac3 but less than 1000&#xb0; C. for a time of more than 30 s, quenched by cooling to a quenching temperature QT between 200&#xb0; C. and 280&#xb0; C. in order to obtain a structure consisting of austenite and at least 50% of martensite, the austenite content being such that the final structure can contain between 3% and 15% of residual austenite and between 85% and 97% of the sum of martensite and bainite, without ferrite, heated up to a partitioning temperature PT between 430&#xb0; C. and 490&#xb0; C. and maintained at this temperature for a time Pt between 10 s and 100 s, hot dip coated and cooled to the room temperature.

The invention deals with a cold rolled and hot dip steel sheet, with a tensile strength of at least 980 MPa, with yield strength above or equal to 500 MPa, with total elongation above or equal to 8%, the composition consisting by weight percent: 0.05&#x3c;C&#x3c;0.15%, 2&#x3c;Mn&#x2264;3%, Al&#x3c;0.1%, 0.3&#x3c;Si&#x3c;1.5%, 0.01%&#x3c;Nb&#x3c;0.05%, N&#x3c;0.02%, 0.1&#x3c;Cr+Mo&#x3c;1%, 0.0001&#x3c;B&#x3c;0.0025, Ti&#x3c;0.5%, V&#x3c;0.01%, S&#x3c;0.01%, P&#x3c;0.05% the remainder of the composition being iron and unavoidable impurities resulting from the smelting and the microstructure contains, in surface fraction: between 50 and 95% of martensite and between 5 and 50% of the sum of ferrite and bainite, wherein the ferrite grain size is below 10&#x3bc;&#x3b9;&#x3c4;&#x3b9;, and wherein the aspect ratio of the ferrite grain size is between 1 and 3. The steel according to the invention is oxidized and subsequently reduced during heating, soaking and cooling steps of the annealing.

High strength multiphase steel, production method and use

A multipurpose continuous processing line able for heat treating and hot dip coating a steel strip containing:

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East Chicago, IN, United States of America

Dongwei Fan