AFS/FEF Student Technology ContestThermal Fatigue Behavior of Cast Irons Used in the Automotive Industry

Cast irons are widely used to manufacture automotive components such as brake discs, cylinders heads, crankshaft, engine block. Typically, these components are subjected to sudden changes in temperature that induce stresses of tension and compression. The cyclic stresses are due to restriction in the thermal contraction or expansion caused by the temperature changes. The previous phenomenon known as thermal fatigue is one of the causes of failure of iron parts. To study the thermal fatigue behavior of gray iron (GI) and compacted graphite iron (CGI) samples, experimental laboratory equipment was built. The results show that the CGI exhibits a higher thermal fatigue strength than that of the GI, and in addition the gray iron presents a pronounced relaxation of the stress level during the first 5 cycles of the test, whereas in the CGI samples this occurs until the cycle 35 is reached. Scanning electron microscopy showed that microcrack initiation occurred in the graphite, and it is propagating through the matrix.