Arcelormittal

Coralie Magar

Astrid Perlade

Kangying Zhu

A cold-rolled and heat-treated steel sheet, having a composition comprising, 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 amongst 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%, A remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure consists of, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite comprises Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, the surface fraction of said Mn-enriched austenite with respect to the whole microstructure being comprised between 2% and 12%; and Mn-poor austenite, having a Mn content comprised between 0.5*Mn % and 1.3*Mn %.

Resistance spot welded joint and a process for producing a resistance spot welded joint

A cold-rolled and heat-treated steel sheet, having a composition including, by weight percent: 0.10%&#x2264;C&#x2264;0.40%, 3.5%&#x2264;Mn&#x2264;8.0%, 0.5%&#x2264;Si&#x2264;2.5%, 0.003%&#x2264;Al&#x2264;3.0%, with Si+Al&#x2265;0.8%, 0.001%&#x2264;Mo&#x2264;0.5%, S&#x2264;0.010%, P&#x2264;0.020%, N&#x2264;0.008%, and optionally one or more elements selected from a group comprising Cr, Ti, Nb, V and B, such that: 0.01%&#x2264;Cr&#x2264;2.0%, 0.010%&#x2264;Ti&#x2264;0.080%, 0.010%&#x2264;Nb&#x2264;0.080%, 0.010%&#x2264;V&#x2264;0.30%, 0.0005%&#x2264;B&#x2264;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 %.

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Schwerdorff, France

Coralie Magar