Study On Thermal Fatigue Behavior Of A Kind Of Heat-resistant Ductile Iron

Ductile iron as an excellent, inexpensive materials, has good resistance to fatigue andhigh temperature, making it ideal for use in high temperature, hot and cold cyclicenvironment. Study on thermal fatigue damage mechanism of ductile iron under differentconditions contribute to further improving the thermal fatigue properties of ductile iron,develop their potential, and make it more widely used.This article combined finite element analysis and experimental, studying thermalfatigue crack initiation and extension situations of QT400-18under different upper limittemperature. Then compared the microstructure and hardness of the material before andafter experiment, and studied on thermal fatigue crack initiation and propagationmechanism of ductile iron. The main results of this study are as follows:This article established the thermal-structural coupling model, got the temperaturedistribution and stress distribution of the test specimens, discovered that the thermal stressis the biggest in the bottom of the V-type notch. And the thermal stress increased as theupper limit of temperature rise, plastic deformation happened at the stress concentrationparts.Thermal fatigue crack initiation in the bottom of the V-type notch generally, and thecrack initiation life decreased and crack propagation velocity increased as the upper limitof temperature rise. Finite Element Analysis on stress distribution, fatigue life results fittedthe experimental results, and found that fatigue crack along the perpendicular to thedirection of maximum stress components extended. Finite Element Simulation results wasagree with the experiments.Found that Oxidation and corrosion, graphite morphology and phase transition werethe main factors affecting thermal fatigue performance of ductile iron. The hardness ofthermal fatigue test specimens increased, and when the upper limit temperature was higherthan transformation temperature, the hardness improved a lot.Fe-safe software predicted the fatigue life under different upper limit temperature inwater and air accurately, which was consistent with the experimental results. Air-cooledfatigue life was much longer than cooled in the water. Finite element analysis is a new practical and effective method to study thermalfatigue and prediction of Crack Initiation life. The research on the anti-thermal fatigueperformance of ductile iron, the mechanism of thermal fatigue damage, and thermalfatigue life of materials, can provide theory guidance and experimental support forengineering practice, and avoid the loss caused by the thermal fatigue damage.