Microstructure characteristics and mechanism of strength and plasticity of complex phase steel based on the TRIP effect
Microstructure of complex phase steel was characterized using scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)technique and transmission electron microscopy(TEM),and its mechanism of strength and plasticity based on the transformation induced plasticity(TRIP)effect was studied.The results show that when the annealing temperature is in the single-phase austenite zone and the(γ+α)two-phase critical zone,there are significant differences in the mechanical properties of the experimental steel due to the different microstructure characteristics.When the annealing temperature is 915 ℃ which is in the single-phase austenite zone,the microstructure of the experimental steel consists of 27％proeutectoid ferrite,56％block bainite and 17％retained austenite distributed at grain boundaries.the proeutectoid ferrite in the microstructure has better plasticity than the recrystallized ferrite,which is more conducive to coordinating deformation and effectively exerting its TRIP effect by relieving the effect of stress on the retained austenite.At the same time,blocky retained austenite with a aspect ratio greater than 2.0 uniformly distributed at grain boundaries is hindered by the phase interface and blocky hard phase bainite during the deformation process,and the TRIP effect contributes significantly and can continue to occur throughout the entire strain stage.Under the combined effects of grain size,microstructure,crystallographic structure,V(C,N)precipitation and dislocation packing,as well as TRIP effect,the comprehensive mechanical properties of the complex phase steel annealed at 915 ℃ are the best,with yield strength and tensile strength of 756 and 1135 MPa,respectively,and product of strength and plasticity reaching 26.446 GPa·％.At the same time,it has excellent elongation and expansion performance,which are 23.3％and 56％,respectively.
complex phase steelTRIP effectmechanism of strength and ductilityretained austenite stabilitycoordinate deformation
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