Metallic materials that have enabled progress for ages now face severe limits set by sustainability, as global production of metals accounts for 8% of the total energy consumption and 30% of industrial CO2 equivalent emissions. In contrast, the accelerated demand for critical areas such as energy, infrastructure, medicine, safety, construction and transportation will create huge growth rates of up to 200% until 2050. Therefore, the steel and automotive industries are responsible for energy saving and emission reduction. Promoting green short-process lightweight bodies and structural components is an important direction for the automotive manufacturing industry.

Multiphase steels with multiple microstructures significantly increase the strength, usually at the expense of flangeability because of a lack of microstructure homogeneity. To further improve the strength-flangeability of multiphase steel, the microstructural homogeneity was advanced by adjusting the hard martensite/austenite (M/A) islands. This strategy has been achieved by compact steel production (CSP), a near-net-shape steel manufacturing technology that omits the reheating procedure, and the mechanical properties of its products are at a good level with the steels produced by cold-rolling, thus mitigating the energy consumption and amount of CO2 emission.

The case shows that the adjusted multiphase steel achieves an excellent ultimate tensile strength (~800 MPa) and flangeability (~135% hole expansion ratio in milling conditions). A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600 ℃. This microstructure consists of soft polygonal ferrite, blocky bainitic ferrite and hard M/A islands. The volume fraction of M/A islands is around 5%, and the average size is less than one μm. Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity. Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late, which resulted in a positive flangeability. Moreover, avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance. This work not only demonstrates the great potential of short-process green production for developing and producing high-performance metallic materials but also provides a viable solution for developing materials with high requirements for local formability.