Abstract
Steel components working in extreme conditions require materials presenting the highest performances. Nowadays, nanoengineering is being applied to the development of ultra-high strength steels as a key-enabling technology in the steel sector. The present article describes the multiscale structure of nano-grained steels designed using atomic transformation theory and processed by a simple heat treatment. Outstanding mechanical properties for these novel steels are reported, and strain-hardening mechanisms are discussed.
Highlights
Steel components working in extreme conditions require materials presenting the highest performances
Metals 2019, 9, 426 ultra-fine plate-like structures to minimize the large elastic strain energy [8]. It applies to bainite, where the shape change is partially accommodated by plastic deformation, and the introduced defects limit the final size of formed plates, becoming thinner at low temperatures when the austenite is harder [9]
Applying these fundamental concepts and reducing bainite reaction temperatures drastically by high-carbon (0.6–1.0 wt.%) and high-silicon (1.5–3.0 wt.%) alloying additions [10], industrial components with bainitic structures consisting of nano-scale plates of ferrite and retained austenite, were manufactured by a simple isothermal heat treatment at low temperatures (125–325 ◦ C), using dry gas technology for small components (20 cm × 2 cm × 3 cm) and a conventional salt bath for large components (70 cm × 40 cm × 20 cm) [11]
Summary
Reducing the grain size is the most common approach to improving the strength of polycrystalline materials. It applies to bainite, where the shape change is partially accommodated by plastic deformation, and the introduced defects limit the final size of formed plates, becoming thinner at low temperatures when the austenite is harder [9] Applying these fundamental concepts and reducing bainite reaction temperatures drastically by high-carbon (0.6–1.0 wt.%) and high-silicon (1.5–3.0 wt.%) alloying additions [10], industrial components with bainitic structures consisting of nano-scale plates of ferrite and retained austenite, were manufactured by a simple isothermal heat treatment at low temperatures (125–325 ◦ C), using dry gas technology for small components (20 cm × 2 cm × 3 cm) and a conventional salt bath for large components (70 cm × 40 cm × 20 cm) [11]. The rationalization to their unprecedented mechanical performances was possible only after the comprehensive examination of the structure at several length scales
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