Mechanical and fatigue properties of pearlitic ductile iron castings characterized by long solidification times

Abstract In this paper, the fatigue behaviour of heavy section pearlitic ductile iron castings has been investigated. The inoculation treatment has been changed for each casting in order to investigate its influence on the mechanical and fatigue properties of the materials. Tensile tests and axial fatigue tests under nominal ratio R = 0.01 have been performed on specimens taken from the core of casting components characterized by long solidification times. Scanning Electron Microscopy has been used to investigate the fracture surface of the broken samples in order to identify crack initiation points and fracture mechanisms. Metallographic analyses have been carried out to measure nodule count and nodules dimensions and to identify matrices structures. It has been found that fatigue behaviour is strongly influenced by defects, such as microshrinkages or degenerated graphite particles near to specimens' surface. It has been also found that inoculation process influences the microstructure and the fatigue resistance of heavy section pearlitic ductile iron castings.

[1]  Gunnar Härkegård,et al.  Fatigue life prediction of components made of spheroidal graphite cast iron , 2010 .

[2]  Tobias Melz,et al.  Fatigue strength of nodular cast iron with regard to heavy-wall applications , 2015 .

[3]  Mervin T. Rowley,et al.  International Atlas of Casting Defects , 1974 .

[4]  H. Hänninen,et al.  Influence of chunky graphite on mechanical and fatigue properties of heavy‐section cast iron , 2009 .

[5]  Yi Niu,et al.  Classification of degenerate graphite and its formation processes in heavy section ductile iron , 1989 .

[6]  C. Carollo,et al.  Effect of inoculant containing rare earth metals and bismuth on microstructure and mechanical properties of heavy-section near-eutectic ductile iron castings , 2013 .

[7]  F. Berto,et al.  Experimental investigation of the multiaxial fatigue strength of ductile cast iron , 2014 .

[8]  Filippo Berto,et al.  Fatigue properties of ductile cast iron containing chunky graphite , 2012 .

[9]  Fatigue crack growth analysis in porous ductile cast iron microstructure , 2014 .

[10]  Influence of casting defects on fatigue crack initiation and fatigue limit of ductile cast iron , 2011 .

[11]  Nadot,et al.  Fatigue life assessment of nodular cast iron containing casting defects , 1999 .

[12]  G. Härkegård,et al.  Self-arresting fatigue cracks at notches in nodular cast iron , 2010 .

[13]  G. Härkegård,et al.  A review on fatigue design of heavy section EN-GJS-400-18-LT ductile iron wind turbine castings , 2014 .

[14]  Gunnar Härkegård,et al.  Large scale axial fatigue testing of ductile cast iron for heavy section wind turbine components , 2011 .

[15]  G. Meneghetti,et al.  Notch Fatigue and Fracture Mechanics of Austempered Ductile Irons , 2010 .

[16]  G. Härkegård,et al.  Fracture toughness and growth of short and long fatigue cracks in ductile cast iron EN‐GJS‐400‐18‐LT , 2012 .

[17]  Gunnar Härkegård,et al.  Fatigue life distribution and size effect in ductile cast iron for wind turbine components , 2011 .

[18]  Ch. Guster,et al.  Influence of micro-shrinkage on the fatigue behavior of ductile iron , 2013 .