Characterization of precipitates in a 7.9Cr–1.65Mo–1.25Si–1.2V steel during tempering
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Date
2009-03-11
Authors
H. Djebaili
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Abstract
In this paper, the precipitates formed during the tempering after quenching from temperature
1150 °C for 7.90Cr–1.65Mo–1.25Si–1.2V steels are investigated using an analytical transmission
electron microscope (A-TEM).The study of this tempering is carried out in isothermal and
anisothermal conditions, by comparing the results given by dilatometry and hot hardness.
Tempering is performed in the range of 300–700 °C. Coarse primary carbides retained after
heat treatment are V-rich MC and Cr–Mo-rich M7C3 types. In turn, it gives a significant
influence on the precipitation of fine secondary carbides, that is, secondary hardening
during tempering. The major secondary carbides are Cr–Mo–V-rich M′C (and/or) Cr–Mo-rich
M2C type. The peak hardness is observed in the tempering range of 450–500 °C. In the end,
we observe between 600 and 700 °C, that this impoverished changes the phase. At these high
temperatures of tempering, we observe that there is a carbide formation of the types M6C
developing at the expense of the fine M7C3 carbides previously formed