Arcelormittal

Pavan C Venkatasurya

Hyun Jo Jun

Hassan Ghassemi-Armaki

Anirban Chakraborty

Véronique Hebert

Maya Gospodinova

A method produces a steel sheet having a microstructure including, in area fraction, 20% to 50% intercritical ferrite, 10% to 20% retained austenite, 25% to 45% tempered martensite, 10% to 20% fresh martensite, and bainite. The sum of tempered martensite and bainite is between 30% and 60%. A cold-rolled steel sheet provided includes 0.18% ≤C≤0.25%, 0.9% ≤Si≤1.8%, 0.02% ≤Al≤1.0%, with 1.00% ≤Si+Al≤2.35%, 1.5% ≤Mn≤2.5%, 0.010% ≤Nb ≤0.035%, 0.10% ≤Cr≤0.40%. The steel sheet is annealed to obtain 50% to 80% austenite and 20% to 50% of ferrite, quenched at a cooling rate between 20° C/s and 50° C/s to between Ms-50° C. and Ms-5° C., heated to a partitioning temperature between 375° C. and 450° C. and maintained at the partitioning temperature for at least 50s, then immediately cooled to room temperature.

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

A method for producing a steel sheet is provided. The method includes providing a cold-rolled steel sheet including in weight %: 0.15%≤C≤0.23%, 1.4%≤Mn≤2.6%, 0.6%≤Si≤1.5%, 0.02%≤Al≤1.0%, with 1.0%≤Si+Al≤2.0%, 0≤Nb≤0.035%, 0≤Mo≤0.3%, 0≤Cr≤0.3%, and a remainder of Fe and unavoidable impurities, annealing the steel sheet at an annealing temperature between Ac1 and Ac3 to obtaining at least 40% austenite and at least 40% intercritical ferrite, quenching the sheet from at least 600° C. at a cooling rate of at least 20° C./s to a quenching temperature between 180° C. and 260° C., heating the sheet to a partitioning temperature between 375° C. and 470° C. and maintaining the sheet at this partitioning temperature for a partitioning time Pt between 25 s and 440 s, then cooling the sheet to room temperature. A steel sheet is also provided.

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

A method for producing a high-strength steel sheet having high ductility, formability and weldability includes providing a cold-rolled sheet, with a composition containing: 0.15% &#x2264;C&#x2264;0.23%, 1.4% &#x2264;Mn&#x2264;2.6%, 0.6% &#x2264;Si&#x2264;1.3%, with C+Si/10&#x2264;0.30%, 0.4% &#x2264;Al&#x2264;1.0%, with Al&#x2265;6(C+Mn/10)&#x2212;2.5%, 0.010% &#x2264;Nb&#x2264;0.035%, 0.1% &#x2264;Mo&#x2264;0.5%, annealing the sheet at 860&#xb0; C.-900&#xb0; C. to obtain a structure consisting of at least 90% austenite and at least 2% intercritical ferrite, quenching to a temperature between Ms-10&#xb0; C. and Ms-60&#xb0; C. at a rate Vc higher than 30&#xb0; C./s, heating to a temperature PT between 410&#xb0; C. and 470&#xb0; C. for 60 s to 130 s, hot-dip coating the sheet, and cooling to room temperature. The microstructure includes 45% to 68% of martensite, consisting of 85% to 95% partitioned martensite having a C content of at most 0.45%, and fresh martensite; 10% to 15% retained austenite; 2% to 10% intercritical ferrite; 20% to 30% lower bainite.

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

A method for producing a steel sheet having a microstructure including 71% to 91% martensite and bainite, 9% to 13% retained austenite, and at most 20% ferrite is provided. The method includes providing a cold-rolled steel sheet including, in weight percent: 0.13%&#x2264;C&#x2264;0.22%, 1.2%&#x2264;Si&#x2264;2.3%, 0.02%&#x2264;Al&#x2264;1.0%, with 1.25%&#x2264;Si+Al&#x2264;2.35%, 2.4%&#x2264;Mn&#x2264;3%, Ti&#x2264;0.05%, Nb&#x2264;0.05% and a remainder of Fe and unavoidable impurities, annealing the steel sheet to obtain 80% to 100% austenite and 0% to 20% ferrite, quenching the steel sheet at a cooling rate between 20&#xb0; C./s and 50&#xb0; C./s to a quenching temperature between 240&#xb0; C. and 310&#xb0; C., heating the steel sheet to a partitioning temperature between 400&#xb0; C. and 465&#xb0; C. and maintaining the steel sheet at the partitioning temperature for 50 to 250 seconds, then immediately cooling the sheet to room temperature. Steel sheets are also provided.

Growing community of inventors

Highland, IN, United States of America

Pavan C Venkatasurya