A CONTEMPORARY MONOGRAPH ON SILICON CAST IRONS MICROSTRUCTURE. From atom scale to casting.

This monograph finds its foundation in a simple fact: there is a paradigm with cast irons, which is that these alloys are produced and cast to shape since thousands of years but are amongst the most complicated metallic alloys when considering the formation of their microstructure by solidification and solid-state transformations. In turn, this complexity opens a wide range of possibilities for shaping their microstructure and engineering their service properties. 

The first cast irons were mostly Fe-C alloys and as such solidified mainly in the metastable system, leading to hard and brittle parts that were heat treated for graphite precipitation to give malleable cast irons. The introduction of silicon into the melt increased the temperature difference between the stable and metastable systems, thus promoting the formation of graphite instead of cementite during solidification. This gave rise to the silicon cast irons that are the subject of this monograph. With the advent of metallographic observations, it was realized that cast iron also often contained phosphides related to the origin of iron ores. A good control of the metallic charge allowed to improving the mechanical properties, in particular by ensuring a minimum elongation before rupture under tensile stress. 

The essential step, however, was the discovery that it is possible to change the shape of graphite by transforming the interconnected lamellae into discrete spheroids. Cast irons thus became a material for safety parts and were no more restricted to construction. This historical evolution and the research effort during the first part of the 20th century are described in the vast review carried out by Merchant in the 1960s. At that time, there was an explosion of research on cast irons with the aim of describing and understanding the formation of graphite during solidification and, to a lesser extent, during heat treatment. As far as solidification is concerned, the review by Lux of this research effort is an important step that already contained most of the questions and provisional answers that are still referenced in more recent works. It is worth mentioning here Zhou’s comprehensive literature review on solidification of different types of cast iron. 

This monograph is not intended to be an exhaustive review of the literature as those mentioned above, but rather to provide a coherent view of the formation of the microstructure of silicon cast irons. In fact, the authors felt it was very important to present how various aspects of microstructure formation could be related to each other using schemes based on known physical phenomena, and sometimes supported by ad hoc modelling. Consequently, the works that will be referenced first are those that contain information that has proven to be essential for the development of these schemes. 

Where appropriate, controversies will be mentioned but not discussed, with reference to the works where they are detailed. Instead, emphasis will be on open questions. The main text containing basic information and descriptions appears on odd-numbered pages, while details and more in-depth descriptions are limited to even-numbered pages. All references are listed at the end of the monograph, which also contains a glossary of acronyms and unusual terms and an index of the parameters used in the equations and the values employed for physical parameters. 

The authors acknowledge the dynamism of the European Cast Iron (ECI) group. The exchanges within this group, as well as the discussions and controversies that have taken place at its annual meetings have been renewed stimuli. We would like to thank the participants, both academics and industrialists, for their continued contribution to this group.