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利用热压缩实验,研究了中碳钢回火马氏体在700℃/0.01 s~(-1)条件下变形时的组织演变规律,分析了渗碳体粒子状态的影响。实验结果表明:中碳钢回火马氏体热变形过程中,发生了渗碳体粒子粗化和铁素体动态再结晶,形成由微米级的等轴铁素体晶粒与均匀分布的渗碳体粒子组成的超细化(α+θ)复相组织。与静态回火相比,形变促进Fe原子和C原子的扩散,使渗碳体粒子粗化动力学提高2—3个数量级。渗碳体粒子的粗化主要来自铁素体晶界上粒子尺寸的增加,铁素体晶粒内部的细小粒子尺寸无明显变化但数量减少,前者有助于以多粒子协同方式实现粒子激发形核,后者减小了晶界迁移的阻力,两者均有利于铁素体动态再结晶的发生。随着初始组织中渗碳体粒子尺寸的减小,发生动态再结晶所需应变量增大,但所得复相组织更加均匀、细化。
By means of hot compression experiment, the microstructure evolution of tempered martensite of medium carbon steel under 700 ℃ / 0.01 s ~ (-1) deformation was studied, and the influence of cementite particle state was analyzed. The experimental results show that during the hot deformation of tempered martensite of medium carbon steel, the coarsening of the cementite particles and the dynamic recrystallization of the ferrite occur, resulting in the formation of microstructures consisting of micron-sized equiaxed ferrite grains and uniformly distributed infiltration Ultrafine (α + θ) Complex Structure of Carbon Particles. Compared with static tempering, the deformation promotes the diffusion of Fe atoms and C atoms, increasing the coarsening kinetics of cementite particles by 2-3 orders of magnitude. The coarsening of cementite particles mainly comes from the increase of particle size on the ferrite grain boundaries. The size of fine particles in ferrite grains has no obvious change but the number decreases. The former is helpful to achieve the particle excitation shape in multi-particle synergy The latter reduces the resistance to grain boundary migration, both of which favor the dynamic recrystallization of ferrite. As the size of cementite particles in the initial microstructure decreases, the amount of strain required for dynamic recrystallization increases, but the resulting composite phase becomes more uniform and refined.