Abstract
Different austenitizing temperatures were used to obtain medium-carbon low-alloy (MCLA) martensitic steels with different lath martensite microstructures. The hierarchical microstructures of lath martensite were investigated by optical microscopy (OM), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM). The results show that with increasing the austenitizing temperature, the prior austenite grain size and block size increased, while the lath width decreased. Further, the yield strength and tensile strength increased due to the enhancement of the grain boundary strengthening. The fitting results reveal that only the relationship between lath width and strength followed the Hall–Petch formula of. Hence, we propose that lath width acts as the effective grain size (EGS) of strength in MCLA steel. In addition, the carbon content had a significant effect on the EGS of martensitic strength. In steels with lower carbon content, block size acted as the EGS, while, in steels with higher carbon content, the EGS changed to lath width. The effect of the Cottrell atmosphere around boundaries may be responsible for this change.
Highlights
Medium-carbon low-alloy (MCLA) steel has an excellent combination of strength, toughness and hardenability and is widely used in structural components with large sections, such as generator spindles and automotive crankshafts [1,2,3]
We studied the effect of martensite microstructures on the strength of MCLA steel
When increasing the the austenitizing temperature, Prior austenite grains (PAGs) size sizeand andblock block size become larger, while the lath width decreases in the experimental
Summary
Medium-carbon low-alloy (MCLA) steel has an excellent combination of strength, toughness and hardenability and is widely used in structural components with large sections, such as generator spindles and automotive crankshafts [1,2,3]. Research on low-carbon steel [8,9,10,11,12,13,14] draws the conclusion that the block/packet size is the key structural parameter in controlling the strength of lath martensite, while research on medium-carbon steel [16,18]. It is necessary to study the relationship between the martensite multi-level microstructure and strength in medium-carbon steel in order to verify the above finding. In this work, austenitizing temperatures of 850–940 ◦ C were used to obtain different sizes of PAG, block, and lath in the experimental MCLA steel. PAG size, block width, and lath width respectively in order to clarify the EGS that governs the strength in the experimental MCLA steel. The influence of carbon content on the effective grain size of strength is summarized and further elucidated based on the above results as well as data from published research
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