Toughening and its Application of Austempered Ductile Cast Iron by Thermomechanically Treatment

1998财政年度，研究了热机械处理中轧制压下、等温回火温度和回火时间对ADI韧性的影响。1999会计年度，为了优化和提高热处理条件的效率，研究了石墨直径和等温回火温度对韧性的影响。在2000财政年度，评估了奥氏体的轧制压下和稳定性对强度和韧性的影响。已经证明，石墨尺寸对ADI断裂韧性的影响几乎可以忽略不计。另一方面，根据伽玛池与韧性的关系分析，伽玛池对ADI的断裂韧性性能起主导作用。虽然石墨结核之间形成的剪切带有效地充当了贝氏体铁素体的形核位置，但有时也会在那里造成断裂。结果表明，更大的石墨结节更适合实际应用。在吸收能量方面，当轧制压下量为40%、等温回火时间为14.4ks时达到最大值，而断裂韧性在轧制压下量为60%时达到最大值。当轧制收缩率为0 ~ 40%时，拉伸强度超过1000MPa，伸长率在收缩率为40%时达到最大值。残余奥氏体在高压下范围内减少，稳定性提高，变形诱发马氏体相变消失。综合考虑，从强度和韧性平衡的角度来看，轧制压下率为40%是最佳状态。轧制压下侧强度增大，压下侧韧性增大。利用所获得的知识，使各部分的特性优化以及近净形状成形成为可能。在上述概念的基础上对球墨铸铁进行显微组织和部件设计，可以识别出球墨铸铁优于传统钢的优势，从而可以替代传统钢。少

In the fiscal year 1998, effects of rolling reduction, austempering temperature and its time during thermo-mechanical treatments on toughness of the ADI were investigated. In the fiscal year 1999, in order for the optimization and efficiency of the thermo-mechanical treatment conditions, effects of graphite diameter and austempering temperature on toughness were investigated. In the fiscal year 2000, effects of rolling reduction and stability of Austenite on strength and toughness were evaluated.It has been certified that the effects of the graphite size on the fracture toughness of the ADI is almost negligible.. On the other hand, according to the analysis of the relationship between the gamma pool and toughness, the gamma pool is predominant over the fracture toughness properties of the ADI.Although shear bands which are formed in-between the graphite nodules act as a nucleation site for the beinitic ferrite effectively, it sometimes causes fracture there. It has been concluded that … More large graphite nodules are preferable for the practical application of the thermo-mechanical treatment. As for the absorbed energy, the maximum value was obtained for the rolling reduction of 40% and austempering time of 14.4ks, while the fracture toughness reached maximum for the rolling reduction of 60%. The tensile strength exceeds 1000MPa when the rolling reduction ranges 0 to 4O%, and the elongation reached the maximum for the 4O% reduction. The residual Austenite decreased and its stability increased within the range and deformation-induced Martensite transformation disappeared in the high rolling reduction range.Comprehensively speaking, the rolling reduction of 40% is concluded as the best condition from a viewpoint of the balance between strength and toughness. Strength becomes higher in the lower rolling reduction side, while toughness becomes superior in the higher side. The optimization of characteristics of respective portion becomes possible together with near-net-shape forming by utilizing the knowledge obtained above. By performing microstructural and component designs of the ductile cast irons on the basis of the above-mentioned concepts, predominance over the traditional steel can be recognized which enables substitution from the steels. Less