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对3.55C-1.95Si-0.36Mn-3.58Ni-0.708Cu-0.92Mo-0.65Cr (质量分数, %)低合金贝氏体球墨铸铁实施等温淬火及不同温度的回火热处理工艺, 采用OM, EPMA, SEM, TEM以及XRD研究了回火温度对等温淬火低合金贝氏体球墨铸铁的组织演变过程的影响, 并对力学性能和耐磨性进行了测试与分析. 结果表明, 回火过程组织演变的物理机制包括孪晶马氏体及其位错亚结构的回复与再结晶软化、残余奥氏体分解、马氏体中过饱和碳的脱溶与相变以及共晶渗碳体的转变等过程. 随着回火温度的升高, 等温淬火低合金贝氏体球墨铸铁基体的显微硬度和宏观硬度及抗压强度逐渐降低. 在450 ℃回火后, 共晶渗碳体的显微硬度出现最低值, 其原因是, 在此温度下共晶渗碳体的亚片层有α相析出, 此时, 低合金贝氏体球墨铸铁的压缩率最高, 塑性提高; 在600 ℃回火时, 其力学性能明显恶化. 在干砂/橡胶轮磨损条件下, 450 ℃回火后的等温淬火低合金贝氏体球墨铸铁具有较好的耐磨性. 磨损形貌观察表明, 其磨损机制为塑性变形疲劳磨损和显微切削, 塑性变形疲劳机制对耐磨性的贡献大于切削破坏机制, 在450 ℃回火析出的弥散Mo₂C对耐磨性也有一定贡献.

Austempered bainitic ductile iron has been widely used in machinery components and parts due to its low fabrication cost, excellent mechanical properties, and abrasive wear resistance. In order to get a fine bainitic matrix, austempering process is usually adopted which consists of austenitizing temperature, austempering temperature and time. For quenched ductile cast iron, tempering plays an important role in subsequent heat treatment process. However, less attention has been paid on the microstructural evolution and mechanical properties of the austempered bainitic ductile iron after tempering treatment. Thus, in this work, 3.55C-1.95Si-0.36Mn-3.58Ni-0.708Cu-0.92Mo-0.65Cr (mass fraction, %) bainitic ductile iron was subjected to austempering and subsequent tempering treatment, and the effect of tempering on microstructures and properties has been investigated by using OM, EP MA, SEM, TEM and XRD. The microstructural evolution during tempering has been investigated, and mechanical properties and wear resistance have also been measured and analyzed. The results show that microstructural evolution of the bainitic ductile iron during tempering contains recovery and recrystallization softening processes of twin martensite and dislocation substructure, decomposition of retained austenite, dissolution of supersaturated carbon and phase transformation in martensite and transformation in eutectic cementite. With increasing tempering temperature, there is a gradual decrease in micro- and macro-hardness of substrate microstructure and compressive strength of austempered low alloyed bainitic ductile iron. When the bainitic ductile iron was tempered at 450 ℃, the eutectic cementite has the lowest micro-hardness value due to the precipitation of α phase in its slice layer and the compressive ratio is thus higher. The mechanical properties of the austempered low alloyed bainitic ductile iron was even worse when tempered at 600 ℃. Under the wear condition of dry sand/rubber wheel, the austempered low alloyed bainitic ductile iron possesses the best wear resistance when tempered at 450 ℃. The worn morphology observation by SEM indicates that the worn surfaces were caused by plastic deformation and micro-cutting. The plastic deformation plays an important role in wear process, while the precipitated and finely distributed Mo₂C contributes a lot to the improvement of wear resistance when tempered at 450 ℃.