Fatigue propagation of long cracks in ferritic thin wall ductile iron castings

M. CALDERA; M. CHAPETTI; J. MASSONE; J. SIKORA

MATERIALS SCIENCE AND TECHNOLOGY

Maney Publishing

Lugar: Londres; Año: 2010 vol. 26 p. 1102 - 1107

0267-0836

The present work focuses on the fatigue propagation of long cracks in ferritic ductile iron parts of varied thickness. Samples were taken from Thin Wall Ductile Iron (TWDI) plates and standard "Y" blocks with nodule counts ranging from 250 to 2200 nodmm-2, and ferrite grain sizes from 70 to 150 m. Fatigue crack propagation threshold ( Kth) and Paris law constants ("C" and "m") were measured, and the influence of the microstructure refinement (established through nodule count and grain size) on the characteristics of the fatigue fracture surface was analyzed. The results show that once the crack is initiated, the fatigue crack growth threshold diminishes as the microstructure is refined, while the rate of growth remains practically unaltered. The crack path preferentially intersects graphite nodules and is mostly transgranular through the ferrite grains. Nevertheless, at low levels of K, a low percentage of intergranular fracture was also observed.m. Fatigue crack propagation threshold ( Kth) and Paris law constants ("C" and "m") were measured, and the influence of the microstructure refinement (established through nodule count and grain size) on the characteristics of the fatigue fracture surface was analyzed. The results show that once the crack is initiated, the fatigue crack growth threshold diminishes as the microstructure is refined, while the rate of growth remains practically unaltered. The crack path preferentially intersects graphite nodules and is mostly transgranular through the ferrite grains. Nevertheless, at low levels of K, a low percentage of intergranular fracture was also observed.