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There is a wide spectrum of cast ferrous heat resistant alloys available for exhaust component applications such as exhaust manifolds and turbocharger housings. Generally speaking, the ferrous alloys can be divided into four groups including: ferritic cast irons, austenitic cast irons, ferritic stainless steels, and austenitic stainless steels. Selection of a suitable alloy usually depends on a number of material properties meeting the requirements of a specific application. Ferritic cast irons continue to be an important alloy for exhaust manifolds and turbocharger housings due to their relatively low cost. A better understanding of the alloying effects and graphite morphologies of ferritic cast irons are discussed and their effect on material behavior such as the brittleness at medium temperatures is provided. The nickel-alloyed austenitic cast irons, also known as Ni-resist, exhibit stable structure and improved high-temperature strength compared to the ferritic cast irons.

The cyclic plasticity of a typical exhaust manifold material has been successfully characterized using a unified constitutive model based on the models developed by Sehitoglu and his co-workers [1-2]. Both monotonic tensile and cyclic strain controlled fatigue tests were performed at temperatures ranging from ambient to 800 °C to evaluate the material constants in the model. In this model, the isotropic hardening is ignored due to its minor effect upon the selected cast iron, which simplified the data processing. The model predictions are satisfactory for a wide temperature range (23-800 °C), and the strain rates covered (0.5-50 %/min).

Strain-controlled low-cycle fatigue (LCF) experiments were conducted on ductile cast iron at total strain rates of 1.2/min, 0.12/min and 0.012/min in a temperature range of RT ~ 800°C. An integrated creep-fatigue (ICF) life prediction framework is proposed, which embodies a deformation mechanism based constitutive model and a thermomechanical damage model. The constitutive model is based on the decomposition of inelastic deformation into plasticity and creep mechanisms, which can describe both rate-independent and rate-dependent cyclic responses under wide strain rate and temperature conditions. The damage model takes into consideration of i) plasticity-induced fatigue, ii) intergranular embrittlement, iii) creep and iv) oxidation. Each damage form is formulated based on the respective physical mechanism/strain.