Abstract
Quenching and tempering are mostly employed to tune the mechanical properties of the high-carbon steels. In the present study, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) are used to examine the microstructural evolution in quenched and tempered high carbon steels. In quenched specimens, the ω-Fe(C) phase is a common substructure in twinned martensite and its diffraction spots are located at 1/3 and 2/3 (21¯1)α-Fe positions along the [011]α-Fe zone axis (ZA). When specimens are in-situ heated in TEM, few additional diffraction spots are observed at 1/6, 3/6 and 5/6 (21¯1)α-Fe positions along the [011]α-Fe ZA. Moreover, martensite decomposes into a lamellar structure and ω-Fe(C) phase transforms into θ-Fe3C cementite during tempering. The TEM and electron diffraction analysis reveals that diffraction spots of θ-Fe3C cementite phase are located at 1/6, 2/6, 3/6, 4/6 and 5/6 (222¯)α-Fe and (21¯1)α-Fe along [112]α-Fe and [011]α-Fe ZAs. Furthermore, the orientation relationships between θ-Fe3C cementite and α-Fe are indexed as: [013]θ//[112]α-Fe, [001]θ//[011]α-Fe, [1¯13]θ//[111]α-Fe and [1¯02]θ//[131]α-Fe, which are related to the transformation of ω-Fe to θ-Fe3C cementite. The current study provides a baseline to understand the microstructural evolution in high carbon steels during heat treatment processes.
Highlights
Quenched high carbon steel renders excellent strength but suffers from high brittleness
A highly complex microstructural evolution occurs in quenched martensite during tempering, including the formation of fine carbides, the decomposition of retained austenite and the nucleation and growth of cementite
The martensite phase exhibits a plate-like morphology, whereas the retained austenite can be identified from the dislocation contrast close to the martensite
Summary
Quenched high carbon steel renders excellent strength but suffers from high brittleness. Heat treatments, such as tempering or aging, are carried out to obtain a desirable combination of strength and toughness.. The strength of steel generally decreases, whereas the toughness increases, with increasing tempering temperature and time. Lots of studies have reported different heat-treatment processes and tempering parameters.. A highly complex microstructural evolution occurs in quenched martensite during tempering, including the formation of fine carbides, the decomposition of retained austenite and the nucleation and growth of cementite.. The type and morphology of carbides play a critical role in determining the structural characteristics and mechanical properties of tempered steels. Lots of studies have reported different heat-treatment processes and tempering parameters. Usually, a highly complex microstructural evolution occurs in quenched martensite during tempering, including the formation of fine carbides, the decomposition of retained austenite and the nucleation and growth of cementite. The type and morphology of carbides play a critical role in determining the structural characteristics and mechanical properties of tempered steels.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call