Investigation On Microstructural Evolution And Synergistic Strengthening Mechanism Of Fe-Mn-Al-C Lightweight Steel Under Static Deformation Condition

Using lightweight materials to reduce weight is an important way to reduce CO₂ emission and improve energy efficiency.Among them,Fe-Mn-Al-C lightweight steel has the advantages of low density,high strength,good plastic toughness,etc.It has become the advantage material of steel used in the field of vehicle and other carrying equipment in the future,and has a broad application prospect.At present,some achievements and progress have been made in the research of Fe-Mn-Al-C lightweight steel,but the specific deformation and strengthening mechanism still need to be further explored.In this paper,we took Fe-27Mn-10Al-1C（wt.%）lightweight steel as the research object,systematically studied the mechanical properties and microstructure evolution of test steel before and after solution,clarified the microstructure evolution and cooperative strengthening mechanism during plastic deformation,and revealed the relationship between strain hardening behavior and microstructure.The main conclusions are as follows:（1）The matrix structure of cold-and hot-rolled test steel before and after solution treatment at 1000℃is composed of austenite and ferrite.The recrystallization of the microstructure was induced by the solution treatment.Compared with before solution treatment,the strength and hardness of the test steel decreased,and the elongation at room temperature increased.The value of product of strength and ductility over 51.9 GPa%.（2）Under static deformation conditions at room temperature,the microstructure of the test steel during plastic deformation is dominated by dislocation slip and dislocation substructure evolution.With the increase of strain,the dislocation of austenite with higher stack fault energy（～96.2 m J·m²）occurs plane slip.The slip band spacing of Taylor Lattice is refined from low strain to medium strain,and microband is formed at high strain.At high compression deformation,the dislocation in austenite will cross slip and form the structure of dislocation cell.The dislocation in ferrite has wavy slip,forming dislocation cell.（3）The microstructural evolution of the test steel shows that different types of dislocations form different substructures in different deformation stages and refine the grain.The deformation of soft ferrite precedes that of austenite,resulting in a strain gradient at the interface of two phases,and a large number of dislocations are deposited at the interface.In austenite grains,two deformation mechanisms,“dynamic slip band refinement induced plasticity”and“microband induced plasticity”,are activated.The synergistic strengthening mechanism of the test steel results in excellent strain hardening ability and good strong plastic combination.