Microstructure control and enhancement mechanism of strength-plasticity for ultra-high strength complex phase steel
The comprehensive mechanical properties of ultra-high strength complex phase steel were optimized fur-therly by regulating the microstructure morphology and the ratio of each phase structure.The enhancement mecha-nism of strength-plasticity was studied by characterization methods of scanning electron microscopy(SEM),elec-tronic probe micro-analysis(EPMA)and transmission electron microscopy(TEM).The results show that the mi-crostructure is composed of about 37％ferrite,49％bainite and 14％retained austenite(volume fraction)when the annealing temperature is 820 ℃ which is in the(γ+α)two-phase critical region.The ferrite structure is composed of recrystallized ferrite and proeutectoid ferrite,bainite is blocky.Retained austenite is irregularly granular and mainly distributed at the ferrite grain boundary or between the ferrite and bainite phase interface,and its grain size is basically proportional to the BCC structure of the"carbon-poor region"around it.When the annealing temperature is 910 ℃ which is in the single-phase austenite region,the microstructure is composed of about 19％proeutectoid fer-rite,61％lath-like bainite ferrite and 20％lamellar retained austenite with a thickness of 60-130 nm.The bainite ferrite is a massive reference unit with recrystallized austenite grains as the phase transition and distributes in differ-ent directions.The proportion of high angle grain boundaries reaches 85.4％.The second phase particles of V(C,N)in the matrix are interphase precipitated,the diameter of the precipitated particles is 3-9 nm,the average column spacing is about 31 nm,and the calculated contribution to the strength of the material is about 281 MPa.The com-prehensive mechanical properties of ultra-high strength complex phase steel are closely related to its micro-morpholo-gy,crystal structure and crystal orientation,second-phase precipitated particles,high-density dislocations and the TRIP effect contribution of retained austenite.When the annealing temperature is in the single-phase austenite re-gion,the tensile strength of the complex phase steel reaches 1 226 MPa,while the elongation and hole expansion rate increase to 19.1％and 51％,respectively,and the product of strength and plasticity reaches 23.42 GPa·％.The research results can provide a reference for improving the comprehensive performance of high-strength materi-als.
complex phase steelmicrostructure controlmechanism of strength-plasticityinterphase precipitationcrystallography structure
NETL
NSTL
万方数据
维普
