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Numerous high-performance steels with various compositions and mechanical properties were developed to enable a safe and light-weight automotive body-in-white (BIW). However, this multisteel scheme creates substantial challenges, including the resistance spot welding of dissimilar steels, processing optimization, and recycling. Here, we propose a revolutionary unified steel (UniSteel) concept, i.e., using a single chemistry to produce multiple steel grades for the entire BIW. The tensile strengths of various UniSteel grades are ranging from 600 to 1680 MPa, encompassing the strengths of typical commercial counterparts while exhibiting competent ductility. The prototype parts made of UniSteel press-hardened steel (PHS) grade demonstrate superior side-intrusion resistance over the commercial PHS, and the satisfactory weldability is verified. The UniSteel reduces the resistivity difference within the sheet stack-ups, allowing the simplification of welding processes. The UniSteel concept could potentially revolutionize the manufacturing of BIW for the global automotive industry and contribute to carbon neutrality.