The Substructure of Quenched High-Carbon Pearlite in Fe–C Alloys

Abstract

After a brief review of the history of pearlite structures in carbon steels, particularly on the pearlite formation mechanism, recent experimental investigations on the pearlite substructure are presented to express a distinct point of view. The water-quenched high-carbon pearlite substructure is investigated in detail by means of scanning electron microscopy and transmission electron microscopy. In the experimental observation results, it is shown that the cementite layer or ferrite layer in pearlite is composed of fine grains, which cannot be simply explained by traditional nucleation and grain growth mechanisms. However, the fine grain structure can be explained by the martensitic transformation products (twinned martensite with ultrafine grains of α–Fe and twinning boundaries ω–Fe (or ω–Fe₃C)) and detwinning process. Upon tempering or detwinning, recrystallization of the ultrafine grains of both crystalline phases occurs to form the initial pearlite structure, while the grain size of both phases is still fine. The twinned martensite can be treated as the precursor of pearlite structure (pearlite nucleation stage), and the detwinning process can be regarded as the growth of the pearlite structure. Thus, the pearlite reaction can be described as follows: austenite → twinned martensite → pearlite.