Method for producing a cold-rolled flat steel product with high yield strength and flat cold-rolled steel product

US10435763B2 · kind B2 · utility

Assignees

• ThyssenKrupp Steel Europe AG · DE
• JFE Steel Corporation · JP

Inventors

• Brigitte Hammer · Voerde, DE
• Frank Hisker · Bottrop, DE
• Thomas Heller · Pittsburgh, US
• Almir Dzafic · Dortmund, DE
• Richard G. Thiessen · Malden, NL
• Shinjiro Kaneko · Tokyo, JP
• Fusae Shiimori · Tokyo, JP

Key dates

• Filing date: Apr 14, 2015
• Grant date: Oct 8, 2019
• Expiry date: Nov 24, 2035

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C21D2211/008
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A method for producing a cold-rolled steel strip with a yield ratio Re/Rm of at least 0.7, the cold-rolled steel product including iron, unavoidable impurities and (in wt. %) C: 0.05-0.20%, Si: 0.25-1.00%, Mn: 1.0-3.0%, Al: 0.02-1.5%, Cr: 0.1-1.5%, N: <0.02%, P: <0.03%, S: <0.05% and optionally one or more of Ti, Mo, Nb, V, and B, Ti: up to 0.15%, Mo: <2%, Nb: <0.1%, V: <0.12%, and B: 0.0005-0.003%. The cold-rolled flat steel product undergoes heat treatment for 4.5-24 hours at a temperature of 150-400° C. Also, a cold rolled flat steel product discussed above having a structure including at least two phases, selected from (in vol. %) at least 10% tempered martensite, <10% bainite, <10% residual austenite and remainder ferrite, a yield ratio of at least 0.7, a tensile strength of ≥750 MPa and a hole expansion of at least 18%.