Processing, Microstructures and Mechanical Properties of Ultra-high Strength Steel Sheet

An ultra-high strength steel sheet with a tensile strength over 1500 MPa and excellent low-temperature impact toughness was obtained by either using controlled rolling plus air cooling (CR+AC) or laboratorial thermo-mechanical controlled processing (TMCP). The effects of CR+AC and the TMCP processes were then examined on the microstructures and mechanical properties of this steel sheet. The results showed that by using CR+AC technology a uniformly distributed bainitic ferrite microstructure could be produced in this steel sheet under the appropriate reheating and rolling condition. By using TMCP technology, a lath bainite and martensitic microstructure with superior mechanical properties could also be generated. A microstructural analysis was made to interprete the strengthening-toughening mechanisms in association with the processes.