Arcelormittal

Narayan Subramaniam Pottore

Nina Michailovna Fonstein

Hyun Jo Jun

Rongjie Song

Oleg N Yakubovsky

A martensitic steel alloy is provided. The martensitic steel alloy includes carbon from 0.22 to 0.36 wt. %, manganese from 0.5% to 2.0% wt. %, and chromium in an amount less than 0.10 wt. %. and a carbon equivalent Cof less than 0.44 in which C=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15. Cis the carbon equivalent, C, Mn, Cr, Mo, V, Ni, and Cu are in wt. % of the elements in the alloy. The alloy has an ultimate tensile strength of at least 1700 MPa.

Martensitic steels with 1700 to 2200 MPa tensile strength

A method for producing a dual phase steel sheet is provided. The method includes providing a dual phase hot rolled steel sheet having a microstructure including ferrite and martensite and a composition including 0.1 to 0.3 wt. % C, 1.5 to 2.5 wt. % Si and 1.75 to 2.5 wt. % Mn. The steel sheet is annealed at a temperature from 750 to 875&#xb0; C., water quenched to a temperature from 400 to 420&#xb0; C. and subject to overaging at the temperature from 400 to 420&#xb0; C. to convert the martensite in the hot rolled steel sheet to tempered martensite. The overaging is sufficient to provide the hot rolled steel sheet with a hole expansion ratio of at least 15%.

Method for producing high silicon dual phase steels with improved ductility

A cold rolled and annealed martensitic steel sheet is provided. The steel sheet includes by weight percent, 0.30&#x2264;C&#x2264;0.5%, 0.2&#x2264;Mn&#x2264;1.5%, 0.5&#x2264;Si&#x2264;3.0%, 0.02&#x2264;Ti&#x2264;0.05%, 0.001&#x2264;N&#x2264;0.008%, 0.0010&#x2264;B&#x2264;0.0030%, 0.01&#x2264;Nb&#x2264;0.1%, 0.2&#x2264;Cr&#x2264;2.0%, P&#x2264;0.02%, S&#x2264;0.005%, Al&#x2264;1%, Mo&#x2264;1% and Ni&#x2264;0.5%. The remainder of the composition includes iron and unavoidable impurities resulting from melting. The microstructure is 100% martensitic and a prior austenite grain size is lower than 20 &#x3bc;m. The steel sheet has a delayed fracture resistance of at least 24 hours during an acid immersion U-bend test. A method, part, structural member and vehicle are also provided.

Martensitic steel with delayed fracture resistance and manufacturing method

A dual phase steel (martensite+ferrite) having a tensile strength of at least 980 MPa, and a total elongation of at least 15%. The dual phase steel may have a total elongation of at least 18%. The dual phase steel may also have a tensile strength of at least 1180 MPa. The dual phase steel may include between 0.5-3.5 wt. % Si, and more preferably between 1.5-2.5 wt. % Si.

High silicon bearing dual phase steels with improved ductility

A cold rolled, annealed TRIP steel sheet which has a composition including (in wt. %): C: 0.1-0.3; Mn: 4-10, Al: 0.05-5, Si: 0.05-5; and Nb: 0.008-0.1, the remainder being iron and inevitable residuals. The cold rolled sheet has an ultimate tensile strength of at least 1000 MPa, and a total elongation of at least 15%. The cold rolled sheet may have at least 20% retained austenite in its microstructure and may have greater than 50% lath-type annealed ferrite structure. The cold rolled sheet may have an ultra fine grain size of less than 5 micron for the retained austenite and ferrite.

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Munster, IN, United States of America

Narayan Subramaniam Pottore