A Study on Microstructure of Ductile Ni-Resist Cast Iron for Exhaust Manifolds and Mechanical Property at the Condition of Altermative Thermal Cycles

The kind of ductile Ni-resist cast iron which will be used to exploit the exhaust manifold in First Automotive Works mainly contains up to 29 wt% Nickel, 4.9 wt% silicon and 1.7 wt% chromium. The main part of this study focused on the microstructure characterization of the as-cast condition and mechanical property at the condition of alternative thermal cycles. In the cast state, the alloy consists of the austentic matrix and carbides. The carbides contain M6C and M7C3. And FeNi3 phase is found in the austentic matrix. After alternative thermal cycles at 900 degrees C, the hardness value gradually descends from 203 HV to 170 HV.