An Overview of the Development of Austempered Cast Irons for Railway Brake Shoe

摘要

Austempered cast irons possessing high strength, ductility and toughness, are good alternative for applications where wear resistance is of great importance. Brake shoe in railway transportations, already made of phosphorous pearlitic gray iron, is main concern of this investigation. In this respect, first a dimensional analysis was derived and applied on similitude to determine required properties and relevant wear test method. Thus two series of alloys I.e. Austempered Gray Iron (AGI) and Austempered Vermicular/compacted graphite Iron (AVI) were adopted. Proper alloy design was fulfilled in relation to shoe geometry to ensure fully bainitic structure of final product. Experimental specimens were produced and tested to specify the optimum processing parameters. Laboratory wear testing was conducted upon specimens. Then final parts were produced based on optimum results. Finally, field testing was conducted to verify functionality of new brake shoes in practice. Metallographic examinations and electron micrography were carried out on worn specimens and parts to verify response of the materials in laboratory testing and field service. Having consistent results, both laboratory and field tests revealed enhanced performance and remarkable longer lives of austempered parts as high as five times for AVI and twice for AGI with respect to conventional shoes.