Silicon and molybdenum (SiMo) alloyed cast irons with spherical graphite are used for exhaust manifolds for service at high temperatures in air and combustion atmospheres containing water vapor. Analysis of degraded surfaces of in-service manifolds indicates existence of a combined oxidation and de-carburization (de-C) phenomena. Therefore, sequential high-temperature tests in air and combustion atmosphere with recording weight change together with carbon analysis at each time step were utilized to quantify the kinetics of both processes. The recorded weight change was related to weight gain due to oxidation and weight loss due to de-C. Carbon analysis was used to de-couple these two processes. SEM measured thicknesses of de-C layers were used to verify kinetics obtained from changes in carbon concentration during oxidation. It was shown that the oxidation and de-C kinetics have different sensitivities to testing temperature and the type of oxidizing atmospheres. At 700 °C and above, there are several significant mutual effects between scale formation and de-C processes which affect the kinetics of these processes and activation energy. The tested experimental methodology for decoupling these processes can be used for alloy optimization.

具有球形石墨的硅和钼（SiMo）合金铸铁用于排气歧管，可在空气和含有水蒸气的燃烧气氛中在高温下使用。对在役歧管退化表面的分析表明，存在着氧化和脱碳（de- C）现象的结合。因此，在空气和燃烧气氛中进行连续的高温测试，记录重量变化，并在每个时间步骤进行碳分析，以量化这两个过程的动力学。记录的重量变化与由于氧化引起的重量增加和由于de C引起的重量损失有关。碳分析被用来分离这两个过程。SEM测量的de- C厚度层用于验证由氧化过程中碳浓度变化获得的动力学。结果表明，氧化和de- C动力学对测试温度和氧化气氛的类型具有不同的敏感性。在700°C或更高温度下，结垢形成和de- C过程之间存在一些重要的相互影响，这会影响这些过程的动力学和活化能。用于解耦这些过程的经过测试的实验方法可用于合金优化。