In order to solve key challenges in lightweight transportation and safe infrastructures stronger steels with high ductility are urgently needed. In this work we introduce a new unique chemical boundary engineering (CBE) approach, which enables us to create a material with an ultrafine hierarchically heterogeneous microstructure even after heating to high temperatures.
Grain boundary engineering has been for long the most effective approach to tailor mechanical properties of metallic materials. There are limits to the fineness and types of microstructures achievable because of the low thermal stability of crystallographic boundaries, which leads to a rapid increase of grain size after exposure to thermal loads. Our unique chemical boundary engineering approach (CBE) enables us to create a material with an ultrafine hierarchically heterogeneous microstructure even after heating to high temperatures. For plain steels with a carbon content only up to 0.2 weight% ultimate strength levels over 2.0 GPa in combination with good ductility (>20%) can be achieved. The CBE design approach, shown here for plain carbon steels, can also be used for other alloys.