High-temperature mechanical- and fatigue properties of cast alloys intended for use in exhaust manifolds

In the present work materials for use in exhaust manifolds of heavy-duty diesel engines were tested in air from 20 to 1000 °C with respect to mechanical properties. Two cast irons, SiMo51 and Ni-resist D5S, four austenitic cast steels, HF, A3N, HK30 and HK-Nb, and one ferritic cast steel, 1.4509 were studied. The experimental work included thermal conductivity, thermal expansion, uniaxial stress–strain testing, low-cycle fatigue testing up to 30,000 cycles and fractography. Below 500 °C, SiMo51 is superior. At higher temperatures, a transition from elastic to plastic strain dominance was observed for the cast irons, reducing their performance. Carbide-forming elements increase heat conductivity and result in a dendrite-like fracture surfaces during fatigue testing. The austenitic steels are superior only at higher temperatures.