Effect of nodularity on resonant vibration fracture behavior in upper bainitic and ferritic cast irons

Abstract

This work examines resonant vibration fatigue fracture behavior. According to those results, the region I section of the D-N curve (deflection amplitude vs number of vibration cycles) declined with decreasing graphite nodularity or a changing of the matrix to a bainitic structure. Resonant vibration fatigue cracks were often initiated at graphite particles on the surface and grew into the body of the specimen. Initiation and propagation of these cracks were promoted by lowering the graphite nodularity, but no significant difference in deflection amplitude was observed with a bainitic or ferritic matrix microstructure. Bainitic cast iron specimens proved to have a higher initial deflection amplitude and would simply drop almost without displaying region I as the cycle numbers of vibration increased.

Effect of Nodular Graphite on the Deterioration of Vibration Fracture Resistance of Ferritic Cast Iron under an Aqueous Environment

“…[8][9][10] In our previous investigations on the vibration behavior of nodular graphite cast iron, vibration cracks initiated from the surface took place either from nodular graphite or along the ferritic boundary. 7,11,12) However, the ambient environmental effect on vibration fracture resistance remains unclear. Therefore, this study aimed to investigate the effect of an aqueous environment on the occurrence of intergranular fractures with regard to the deterioration of vibration fracture resistance.…”

Effect of Si Content on the Deterioration of Vibration Fracture Resistance of Ferritic SG Cast Iron under an Aqueous Environment

“…Moreover, from our previous results, the cracks tended to nucleate from and propagate toward the prior-eutectic cell-wall regions where a fair amount of MgO inclusions embedded inbetween the nodular graphite. 5,9) Figure 1, also reveals that the silicon content will affect the microstructural feature, and although the MgO inclusion clustered 10,11) region is an inevitable route for vibration crack propagation, little influence can be recognized in this study. However, more detailed investigation is needed.…”

“…4.4Si Based on our earlier investigations, 5,6) the resonant vibration samples, resembling the reverse bending fatigue test, suffer from alternate bending stress. It can be deduced that the alternate tensile-compressive stresses should be correlated to the existence of nodular graphite which actually plays an important role in causing deterioration in vibration fracture resistance.…”

“…In our previous investigations on the vibrational fracture behavior of ferritic nodular graphite cast iron under aqueous conditions, vibration cracks initiating from the surface took place either from nodular graphite or sequently along the ferritic boundary, also causing embrittlement, although microstructural refinement or damping capacity improved the vibration fracture resistance. [4][5][6] On the other hand, it has been recognized that increasing silicon content will improve thermal and weather-resistance of SG cast iron, the solid solution strengthening effect of Si atoms often were found to be the main controlling factor. As to the silicon affected microstructural evolution, however, why or how these metallurgical factors affected vibration fracture behavior has still not been clarified.…”

“…1 Relation between silicon content and logarithmicdecrement value with respect to initial deflection amplitude Based on our previous report, 5) the vibration life (L x ) is affected primarily by crack propagation resistance and initial deflection amplitude (D I ). The former is directly proportional to its yield strength (YS), and this can be correlated with silicon content and recognized as a positive effect.…”