High strength and high formability steel sheet and manufacturing method

US11434541B2 · kind B2 · utility

Assignee

• ArcelorMittal · LI

Inventors

• Coralie Magar · Cottendorff, FR
• Kangying Zhu · Metz, FR
• Astrid Perlade · Le Ban-Saint-Martin, FR

Key dates

• Filing date: Sep 15, 2017
• Grant date: Sep 6, 2022
• Expiry date: Jan 23, 2038

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C22C38/32
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A cold-rolled and heat-treated steel sheet, having a composition including, by weight percent: 0.10%≤C≤0.40%, 3.5%≤Mn≤8.0%, 0.5%≤Si≤2.5%, 0.003%≤Al≤3.0%, with Si+Al≥0.8%, 0.001%≤Mo≤0.5%, S≤0.010%, P≤0.020%, N≤0.008%, and optionally one or more elements selected from a group comprising Cr, Ti, Nb, V and B, such that: 0.01%≤Cr≤2.0%, 0.010%≤Ti≤0.080%, 0.010%≤Nb≤0.080%, 0.010%≤V≤0.30%, 0.0005%≤B≤0.003%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure includes, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite includes Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, a surface fraction of the Mn-enriched austenite with respect to the whole microstructure is between 2% and 12%, and Mn-poor austenite, having an Mn content between 0.5*Mn % and 1.3*Mn %.