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过共析钢在奥氏体化温度下加热后空冷或炉冷将会产生片状珠光体组织和网状渗碳体,在超细晶条件下得到了不遵循这一规律的固态相变新现象。本实验采用高能球磨快速烧结方法制备了超细晶过共析钢块体试样,通过控制球磨时间控制烧成试样晶粒度。结果表明:当球磨时间超过40 h,烧结后试样晶粒细化到2～4μm的量级,试样空冷无法得到片状珠光体,经共析转变得到纳米级球状渗碳体和铁素体组织,渗碳体球的尺寸在10～100 nm范围。热力学分析表明,晶粒细化导致原奥氏体中碳化物形核率增加,尺寸较小的粒状碳化物相对于片状碳化物具有更大的形核动力;动力学分析表明,晶粒细化导致钢中碳扩散速度提高,层片状珠光体的长大受到抑制,共析转变中珠光体更易长成为粒状。
Hypereutectic steel heated at austenitizing temperature after air cooling or furnace cooling will produce lamellar pearlite and reticular cementite, obtained in the ultrafine grain solid state transformation does not follow this new phenomenon. In this experiment, ultra-fine grain hypereutectoid steel block samples were prepared by high-energy ball milling rapid sintering method, and the grain size of the sintered samples was controlled by controlling the milling time. The results show that when the ball milling time exceeds 40 h, the grain size of the sample after sintering is reduced to the order of 2 ~ 4 μm. The flake pearlite can not be obtained by air cooling. After the eutectoid transformation, nanoscale spherical cementite and ferrite Body tissue, cementite sphere size in the 10 ~ 100 nm range. Thermodynamic analysis shows that grain refinement leads to the increase of carbide nucleation rate in the former austenite. The smaller size carbide has more nucleation kinetics than the flake carbide. Kinetic analysis shows that the grain size is fine As a result, the diffusion rate of carbon in steel is increased, the growth of lamellar pearlite is inhibited, and the pearlite in eutectoid transformation is more likely to become granular.