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The mechanical and thermal properties of ferritic–pearlitic ductile irons vary widely according to their silicon and pearlite contents. Thus, different combinations of silicon and pearlite affect components’ lifetime under mechanical and thermal stress. An excellent example of the usage of such irons is combustion engine cylinder heads. They experience transient thermal loading (heating and cooling) during starting and stopping in addition to mechanical loading (combustion) during engine operation. An optimization approach and calculation models for the estimation of the optimal ductile iron composition are presented in this study. The approach allows selection of the most suitable base composition for subsequent analyses, such as casting simulation and final accurate finite element modelling and fatigue calculations.
Abstract The mechanical and thermal properties of ferritic–pearlitic ductile irons vary widely according to their silicon and pearlite contents. Thus, different combinations of silicon and pearlite affect components’ lifetime under mechanical and thermal stress. An excellent example of the usage of such irons is combustion engine cylinder heads. They experience transient thermal loading (heating and cooling) during starting and stopping in addition to mechanical loading (combustion) during engine operation. An optimization approach and calculation models for the estimation of the optimal ductile iron composition are presented in this study. The approach allows selection of the most suitable base composition for subsequent analyses, such as casting simulation and final accurate finite element modelling and fatigue calculations.
Abstract The usage of ductile irons at thermo mechanically loaded components is increasing, necessitating more knowledge of material properties in elevated temperatures. A study of elevated temperature mechanical properties was done, investigating the effect of different pearlite fractions along with silicon content tests in fully ferritic microstructure. Effect of pearlite fraction and silicon content to tensile and yield strength were measured in different temperatures from room temperature up to 450°C. Models were developed, based on those measurements. These resulting regression models were tested with data gathered from literature. These can be used in various design tools, such as FEM calculations and in the optimisation of thermally and cyclic loaded ductile iron components.
Abstract The influence of ferritic and pearlitic microstructures to dynamic strain aging (DSA) of ductile iron was investigated by means of strain-controlled cyclic tests performed at temperatures ranging from room temperature to 450°C, strain rates of 10−5 to 10−2 s−1 and at three different strain amplitudes along with tensile tests. Results indicated that all tested microstructures exhibit strain aging effects at elevated temperatures in some form, similar to ferritic-pearlitic steels. Additionally, static tensile tests show hardening at intermediate temperatures, minima in elongation and serrations in stress–strain curves. Cyclic data indicates DSA related changes in stresses at 250°C and 350°C at smaller strain rates, while the effects become more suppressed at higher strain rates.
Abstract The microstructure and nodule count of large-size nodular cast iron components vary spatially. These variables are qualitatively known to affect the fatigue limit, yet no model exists to quantify the effects. Some of the physical aspects, such as the clustering of graphite nodules and the role of ferrite microhardness in ferritic–pearlitic nodular cast iron fatigue, have been unclear in the literature. This paper aims to clarify and quantify these aspects. In the absence of casting defects, the largest ferrite with a crack initiating graphite is shown to be the physical, and statistical, explanation for the mixed grade fatigue limit.