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

在1998财政年度，研究了轧制变形量、等温温度及其在形变热处理过程中的时间对ADI韧性的影响。在1999财政年度，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温度对韧性的影响。2000财年对奥氏体压下量和稳定性对强度和韧性的影响进行了评价，结果表明，石墨尺寸对奥氏体钢断裂韧性的影响几乎可以忽略不计。另一方面，根据伽马池与韧性之间的关系分析，伽马池对ADI的断裂韧性性能起主导作用。虽然石墨球间形成的剪切带有效地起到贝氏体铁素体形核的作用，但有时也会导致断裂。已经得出结论，…对于热机械处理的实际应用来说，较大的石墨球体是可取的。在吸收能量方面，轧制变形量为40%、等温时间为14.4K时达到最大值，而断裂韧性在变形量为60%时达到最大值。轧制变形量为0~4O%时，抗拉强度超过1000 MPa，延伸率在变形量为4O%时达到最大。在高变形量范围内，残余奥氏体量减少，稳定性增加，形变诱发马氏体相变消失。从强韧性平衡的角度出发，综合考虑，轧制变形量为40%是最佳工艺条件。压下率越低，强度越高，而压下量越高，韧性越好。通过利用上面获得的知识，各个部分的特性的优化与近净成形一起成为可能。通过根据上述概念进行球墨铸铁的组织和成分设计，可以认识到相对于传统钢的优势，这使得可以从钢中进行替代。较少

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