Study On Strengthening And Toughening Mechanism Of Iron-based Nanocrystalline Alloys

In recent years,bimodal grain structure in ferrite-carburized steel has been extensively studied.Through research,multi-scale layered nanocrystalline/ultra-fine grained steel was prepared by multi-pass hot rolling of different initial microstructure steels.SEM and EBSD were used to observe the microstructure change of the material after warm rolling and annealing,and the tensile test and impact were observed.Experiments were conducted to investigate the changes in the properties of materials after different treatment processes,and the mechanism of their toughness was analyzed.The research found that a multi-scale structure including a pro-eutectoid ferrite phase,a fracture phase with a large degree of fracture and a small phase with a small degree of fracture was obtained after the pseudo-eutectoid steel was warm rolled at 450℃,550℃ and 650℃.After the warm rolling,the strength and total elongation of the pseudoeutectoid steel decreased with the increase of the rolling temperature,and the uniform elongation first increased and then decreased which reached the highest at 550℃.When the 550℃ warm rolled pseudo-eutectoid steel was annealed at 600℃,it was found that the multi-scale structure began to weaken when the experimental steel was annealed for 30 min,and disappeared completely after annealing for 60 min.The contribution of each strengthening mechanism to the yield strength of the material was investigated by comparing the effects of annealing time on material properties.By establishing a mathematical model,an empirical formula for estimating the yield strength of pseudoeutectoid steel after warm rolling and annealing is obtained.Comparing the 550℃ warm rolling samples of martensitic steel,it is found that the two phases after warm rolling are not obvious,and more carbides are precipitated,and some grains are equiaxed,the grain boundaries are obvious,the small grains are less,and the small-angle grain boundaries are relatively low.Annealing at 600℃ showed that the ductility of the martensitic steel was significantly improved,but the strength was impaired.And the comprehensive performance is best when annealing for 30 min.Figure 36;Table 14;Reference 58...