Microstructure of as cast reinforced ductile iron

Local hardening of parts made of ductile iron may be achieved by having carbides appearing in appropriate locations. The present work focuses on the study of the as cast microstructure of parts reinforced by Cr containing steel inserts. The presence of such inserts in the mold cavity results in localised chemical changes during the casting process, constituents of the insert (principally chromium) being transferred to the cast iron while carbon penetrates the insert. This leads to the formation of various carbides within and in the surroundings of the insert

Wear property of ductile iron locally reinforced with Cr-containing steel inserts

The influence on the wear properties of ductile iron with Cr-containing steel inserts has been investigated before and after austempering. The microstructure of locally reinforced ductile iron, with and without an austempering treatment, has been characterized using optical microscopy, scanning and transmission electron microscopy and secondary ion mass spectrometry. The introduction of such inserts during casting leads to the precipitation of carbides M3C, M7C3 and M23C6 (M stands for Fe and/or Cr) inside the inserts and to M3C and M7C3 in the region surrounding the inserts. After austempering, a partial dissolution of these latter carbides and transformation of the matrix to ausferrite occur. The wear properties of these materials have been evaluated under reciprocating sliding motion using cylinder-on-disc line contact configuration. The results of the present investigation show a better wear behavior of the reinforced material related to the microstructural changes observed

A SIMS and TEM investigation of the microstructure of wear-resistant ductile cast iron

The benefit of the presence of Cr containing inserts inside ductile iron on the tribological properties of these materials has been recently demonstrated. In order to understand these improved properties, a secondary ion mass spectrometry (SIMS) and transmission electron microscopy investigation of these wear-resistant ductile cast irons has been performed. The results indicate that the principal change in the microstructure induced by inserts occurs in the inserts and in their surroundings where the formation of carbides with different sizes and compositions is observed: M3C, M7C3 and M23C6 (M stands for Fe and/or Cr). These are not pure binary carbides since among the different elements studied by SIMS, Cr, Fe, Mn and, to a lesser extent, Ni are soluble in these carbides

Friction and wear performance of functionally graded ductile iron for brake pads

Due to its wear resistance, functionally graded ductile iron (FGDI) is a potential material for automotive brake pads. In this investigation it was studied (i) under well controlled sliding conditions in a typical tribological model-test to show in detail the mechanism behind improved wear resistance, namely the "property on-demand" functionality in the sub-surface zone and (ii) in a validation experiment on a disc-brake machine that mimic realistic brake-contact conditions, at various elevated temperatures against a carbon-reinforced ceramic disc in order to understand its tribological behaviour in a real automotive brake application. The results revealed a positive e ff ect of the functional gradient zone (FGZ) on the wear performance of the functionally graded ductile- iron pads. Most notably, improved wear resistance was observed under sliding model-test conditions as well as a more-stable wear and wear that is less sensitive to the contact temperature during a disc-brake test. In addition, the sliding model-tests revealed that FGZ leads to faster running in and a more stable coe ffi cient of friction. The disc-brake tests also show that FGZ ensures a relatively constant coe ffi cient of friction for all contact temperatures. Surface analysis of the pads further revealed that oxidized, smoothened plateaus containing graphite nodules were formed on the pads. On the other hand, a patchy and layered transfer fi lm resulting from the pads was formed on the disc\u27s surface