Effect of Mn and Si on the microstructure and mechanical properties of medium manganese hot-rolled high-strength steel

To study the effects of manganese and silicon contents on the microstructure and mechanical properties of medium manganese hot-rolled high-strength steel,different C-Si-Mn tested steels with different manganese and silicon contents were designed.The phase transformation point,microstructure,retained austenite content,and mechanical properties were measured and analyzed using dilatometric simulation,scanning electron microcopy,transmission electron microcopy,X-ray diffraction,and tensile testing.The obtained results indicate that the final microstructure of specimens can be greatly affected by the contents of manganese and silicon.The microstructure of low-silicon and high-manganese specimens consists of granular bainite. The microstructure of high-silicon and high-manganese specimens consists of bainite-ferrite,martensite,and retained austenite. The microstructure of high-silicon and low-manganese specimens consists of quasi-polygonal ferrite,bainite,martensite,and retained austenite. The results show that the best comprehensive mechanical properties of newly designed medium manganese hot-rolled high-strength steel are obtained in high Si and high Mn specimens. The ultimate tensile strength is in excess of 1200 MPa,the total elongation is 16%,and the product of tensile strength and elongation is about 20 GPa·%. The high strength and ductility of the tested high-silicon and high-manganese steel can be explained by the ultrafine grain microstructure and TRIP effect.