Overview of Advanced High-Strength Steels

Steels are backbone materials of civilization since more than 3000 years. They retrieve their properties not from expensive chemical compositions but rather from complex nano- and microstructures. They cover a wider spectrum of properties than any other material.

We have cast some recent progress in the understanding of the microstructure–property relations of advanced high-strength steels into a viewpoint paper. These alloys constitute a class of high-strength, formable steels that are designed mainly as sheet products for the transportation sector. They have often complex and hierarchical microstructures consisting of ferrite, austenite, bainite, or martensite matrix or of duplex or even multiphase mixtures of these constituents, sometimes enriched with precipitates. This complexity makes it challenging to establish reliable and mechanism-based microstructure–property relationships.

We review progress in microstructures and alloy design, placing attention on the deformation and strain hardening mechanisms of steels that utilize complex dislocation substructures, nanoscale precipitation patterns, deformation-driven transformation, and twinning effects. Recent developments on microalloyed nanoprecipitation hardened and press hardening steels are also reviewed. Besides discussing their microstructures and properties, features such as hydrogen embrittlement and damage formation are also evaluated. We also present progress in characterization and modeling techniques applied to these steels. Emerging topics such as machine learning, through-process simulation, and additive manufacturing are also presented.

Figure:  Correlative FIM and APT analysis revealing the enrichment of Mn to defects such as a grain boundary (black arrows) and a dislocation (red arrow). The four images with varying transparency of concentration map are shown to emphasize the location of defects and enhanced Mn concentration.

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