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采用冷弯实验、等温热处理结合硬度测量、光学金相技术和透射电子显微术观测分析了微合金钢中贝氏体组织在A1以下温度受热时的组织演化历程。结果表明,提高微合金钢的碳铌浓度积可以显著延缓贝氏体组织趋于平衡的演变,阻碍钢的软化进程。冷变形在增加钢的初始硬度的同时也加快了随后的受热过程中钢的软化和显微组织向平衡组织演化的进程。张应变和压应变这两种不同类型的应变对组织演变的促进效果几乎相同。冷变形提高了钢中位错密度,也加剧了位错分布的不均匀性,后者是预应变加速组织演变的直接原因。在等温受热过程中贝氏体组织的演变首先是贝氏体板条内的位错发生重新分布,在板条边界附近形成高位错密度区,并同时伴随有低位错密度区出现,然后低位错密度区跨越板条边界形成铁素体晶核并不断吞噬高位错密度区,最终完全演变为平衡组织多边形铁素体。
Cold rolling test, isothermal heat treatment combined with hardness measurement, optical metallography and transmission electron microscopy were used to analyze the microstructure evolution of bainite in microalloyed steel heated below A1. The results show that increasing the carbon-niobium concentration product of microalloyed steel can significantly delay the evolution of bainite structure and impede the softening process of steel. Cold deformation increases the initial hardness of the steel and also accelerates the softening of the steel and the evolution of the microstructure to the equilibrium structure in the subsequent heating process. The two types of strains, tensile strain and compressive strain, have almost the same effect on the evolution of the structure. Cold deformation increases the dislocation density in steel and also exacerbates the inhomogeneity of dislocation distribution, which is the direct cause of pre-strain accelerated microstructure evolution. The evolution of bainitic structure during isothermal heating is primarily the redistribution of dislocations within the bainite lath, the formation of high dislocation density zones near the slab boundary, accompanied by low dislocation density zones, and the subsequent low dislocation The density zone forms ferrite nuclei across the slab boundary and continues to engulf high dislocation density zones, eventually completely evolving into a balanced tissue polygonal ferrite.