Speaker
Description
Cementite decomposition is crucial in microstructural degradation in steels subjected to fatigue/wear loading conditions. Examples include the deformation and decomposition of cementite in pearlitic rail steels and in the formation of white etching areas (WEAs), which cause premature failures of wind turbine gearbox bearings (WTGBs). Therefore, it is worthwhile to study the fundamentals of cementite decomposition by using model severe plastic deformation (SPD) conditions in a controlled high-pressure torsion (HPT) setup.
In this study, the 100Cr6 steel which is normally used in the hardened condition for bearing applications is intentionally modified by adjusting the heat treatment to create two types of precipitates - spherical and lamellar cementite - which are embedded in a softer ferrite matrix instead of a bainitic or martensitic matrix in the hardened condition. The two types of precipitates differ in morphology (spherical vs. lamellar), and also in size (100-1000 nm diameter vs. 40-100 nm thickness) and composition (Cr partitioning: ~11 at. % and ~7.5 at. %). We aim at separating the effect of these precipitate characteristics on decomposition behavior. The emerging difference in decomposition behavior upon HPT was examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). We also discuss the role of matrix microstructure by comparing the present work with the decomposition behavior of spherical cementite precipitates surrounded by a martensitic matrix.
We conclude that the cementite size and morphology, as well as the matrix mechanical properties predominantly influence the decomposition behavior of cementite, whereas the compositional effects of Cr and Mn are minor in the HPT deformation scenario.
Keywords: Severe plastic deformation, Cementite decomposition, Pearlite, High-pressure torsion
| Speaker Country | India |
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