Abstract
About this talk
There has been a significant effort to develop steels with sub-micron grain size, since they will possess high strength and toughness, which makes them promising candidates for light-weighting technologies and contribute to strategies for energy savings. However, there has been no industrial fabrication of true ultrafine-grained steels. The finest grain size steels have a microstructure that is developed through phase transformation with a limit on the grain size that can be developed to a few microns. Here, we present a new method to produce a copper bearing ultrafine-grained structured steel that can be manufactured through conventional manufacturing routes. The key to achieving a sub-micron grain size is to induce simultaneous recrystallization and copious quantities of intragranular nanoprecipitation. The rapid and plentiful nanoprecipitation prevents the growth of the fine freshly recrystallized grains, leading to an equiaxed ultrafine-grained structure. Precipitation is from fine, coherent, disordered Cu based precipitates throughout the structure. Importantly, the precipitates do not provide precipitation hardening, rather they exhibit weak interactions with dislocations, which is key to achieving high ductility. Sustained work hardening arises from twinning-induced plasticity, with the fine grain size and the presence of fine precipitates leading to the formation of extremely fine twins. This results in a large uniform ductility of 45% with tensile strengths of 2000 MPa. The current grain refinement concept can be easily extended to other alloy systems, and the manufacturing processes are compatible with existing industrial production lines.
Audience Take Away Notes:
- Understand the latest state-of-the-art in steel
- Understand how microstructure can be manipulated by processing
- Understand the origins of high strength
Speaker
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