Thermal Fatigue Characteristics of Plasma Duplex Treated Ductile Cast Iron

摘要

This paper reports an investigation of the characteristics of plasma duplex treated ductile cast irons during thermal fatigue tests on a thermal cycling rig. The thermal fatigue cracking behaviors and microstructure of untreated and plasma surface treated ductile cast irons have been investigated. Both ferrite and pearlite matrix ductile cast irons were evaluated. During the tests, 60 mm long cylinders with 20 mm diameter were subjected to 1,000 high frequency induction heating and water cooling cycles, lasting 7 and 5 sec, respectively. The thermal fatigue damage was evaluated by analyzing different crack dimensions and distribution by light microscopy. The results showed that the plasma surface treatment increased thermal fatigue cracking resistance. When thermal fatigue cracking occurs, the cracks always initiate at the surface of the specimen. The major path of crack propagation is generally along the ferrite grain boundaries. The hardened layer had an effect on the thermal fatigue property. In addition, the ductile cast iron with an pearlite matrix has a better resistance to thermal fatigue than that of ferrite matrix.