蠕墨铸铁综合了球墨铸铁和灰铸铁的性能优势，是理想的发动机缸盖材料。在温度较高的服役过程中，缸盖材料需要具备良好的疲劳性能来承受大的机械载荷和热载荷。而高温疲劳性能不仅需要考虑抗拉强度，还要具备好的延伸率和热导率。目前蠕墨铸铁的延伸率普遍不高于4%，大多在2%左右，且热导率也普遍低于40 W?m-1•K-1。为了提高高温疲劳性能，蠕墨铸铁的延伸率和热导率需进一步提高。降低合金含量是同时提高这两种性能的可行途径，但这会降低抗拉强度。针对这一问题，本文研究了延伸率≥4%、热导率≥40 W?m-1•K-1所对应的蠕墨铸铁的微观组织，并依次探讨Si、Sn、Mo和Ni元素对铁素体分数和热导率的影响。研究发现蠕化率与延伸率负相关，而铁素体分数与延伸率正相关。为了保证高的热导率，至少需要保证蠕化率大于80%，因此通过提高铁素体分数的方式使延伸率高于4%，即铁素体分数要高于60%。通过金相观察、性能测试和DSC测试研究了Si、Sn、Mo和 Ni元素对铁素体分数的影响，发现Si显著提高铁素体分数，但高Si会降低抗拉强度和延伸率，不能通过增Si的方式来提高铁素体分数。Sn降低铁素体分数的能力最强，Mo对铁素体分数的影响很小，微量的Ni对铁素体分数的影响也较小，但当Ni含量超过0.5%时，铁素体分数下降幅度较大，延伸率也下降。同时Mo提高抗拉强度的能力强于Ni，这一方面是固溶强化的作用，另一方面是由于Mo会导致碳化物特别是大片状渗碳体的析出，既提高了强度又抑制了裂纹的扩展。因此各元素抑制铁素体生成的能力依次为：Sn＞Ni＞Mo＞Si。一定条件下，蠕化率要大于85%，蠕墨铸铁的热导率才可达到40 W?m-1•K-1以上。通过热导率测试，发现Si、Sn、Mo和Ni均会降低热导率，并根据影响程度将其排序为：Sn＞Si，Sn＞Mo＞Ni。同时结合各元素对铁素体维氏硬度的影响间接验证这个规律。蠕墨铸铁热导率的温度依存性与溶质原子在基体中引起的畸变有关，溶质含量越大，热导率随温度升高而上升的幅度越大，同时热导率极大值所对应的温度也可能越高。通过合金优化，基本达到了蠕墨铸铁组织性能的目标值。在三组试样中，高延伸率、高热导率的蠕墨铸铁具有最佳的高温疲劳性能。疲劳裂纹起源于石墨与基体的界面，且有多个裂纹源，扩展过程中主要穿过石墨，并且伴有氧化现象。

Possessing the comprehensive advantages of the ductile iron and the grey cast iron, compacted graphite cast iron (CGI) is an ideal material of cylinder head, especially for high power density diesel engines. Since the cylinder head is bearing with massive stress and heat, it is required to have a higher the fatigue property at high temperature. To attain this object, high tensile strength, as well as high elongation and thermal conductivity should be considered. At present, the elongation of the commercial CGIs is generally less than 4%, mostly distributed at about 2%, and the thermal conductivity is lower than 40 W?m-1•K-1. In order to improve the thermal fatigue property and broaden the application, the elongation and the thermal conductivity of CGI need to be improved. It is feasible to improve these properties by reducing the alloy content, but the tensile strength.will be reduced Aiming at this problem, this paper studied the microstructure corresponding to the elongation of more than 4% and the thermal conductivity of more than 40 W?m-1•K-1, and then the effects of the chemical elements, i.e. Si, Sn, Mo, and Ni, on the ferrite percent and thermal conductivity were discussed.It is found that the vermicularity is negatively correlated with the elongation, while the ferrite fraction has a positive effect on the elongation. To reach a high thermal conductivity, the vermicularity should be more than 80%. So it is the only way to improve the elongation (>4%) by increasing the ferrite percent, i.e., the ferrite percent is more than 60%. Then the influence of Si, Sn, Mo, and Ni on the ferrite percent is studied by metallography, mechanical test, and DSC experiment. It is found that Si increases ferrite percent significantly. However, a high addition of Si is detrimental to the tensile strength and the elongation. So it is not a good way to increase ferrite percent by increasing the content of Si. Sn has a strong negative effect on ferrite percent, while Mo has few effects on ferrite percent. Besides, a small amount of Ni has few effects on ferrite percent, but when the content of Ni exceeds 0.5%, the ferrite percent decreases, as well as the elongation. At the same time, Mo can improve the tensile strength obviously, which is higher than that of Ni. This phenomenon can be attributed to solid solution strengthening. On the other hand, there are Mo-carbides and sheet cementite when Mo is added, which inhibit the propagation of crack and contribute to the higher tensile strength. Therefore, the ability of each element to decrease ferrite percent, can be concluded as Sn>Ni>Mo>Si. Under certain conditions, the thermal conductivity of CGI cannot reach 40 W?m-1•K-1 unless the vermicularity is more than 85%. Through thermal conductivity test, it is found that Si, Sn, Mo, and Ni reduce the thermal conductivity, and the order among the negative effects of these elements on thermal conductivity can be ranked as Sn>Si and Sn>Mo>Ni, which is indirectly verified by testing the Vickers hardness of ferrite. The temperature dependence of the thermal conductivity of CGI is related to the distortion caused by solute atoms in the matrix. As the addition of solute increases, the rise of thermal conductivity and the characteristic temperature corresponding to the maximal of thermal conductivity increase. The target value of the microstructure and properties of CGI are basically achieved through the optimization of composition. Among the three samples, the CGI with high elongation and thermal conductivity has the best fatigue property at high temperature. There are multiple crack sources, which originates from the interface between the graphite and the matrix. The propagation of cracks mainly passes through graphite and is usually accompanied by oxidization.