Transformations in Cr-Mo-Si steels with a specific addition of Vanadium have been characterized
precisely as well as their effect on the hardness of the materials. A preliminary treatment in
the austenitic field leads to a limited enrichment of the matrix as well as temperature is less
than 1050°C : only M3C and M23C6 carbides may then be dissolved. On the contrary, the dissolution
of M7C3 and MC carbides is observed over 1100°C but is only partial even after treatment
at 1150°C. After quenching from three distinct temperatures (1050-1100 and 1150°C), the
microstructure consists of martensite, residual austenite and primary carbides (mainly M7C3
and MC type) ; different tempering treatments have been performed (isochronal, isothermal or
on continuous heating) using various physical methods (dilatometry, DTA and magnetic measurements,
TEM observations and hot hardness testing). According to the maximum θR temperature
reached, the following structural evolutions were observed :•ε carbide precipitates at θR < 250° C in the a’ matrix, then M3C carbide forms between 250 and 350°C which transforms in M7C3 carbide from 450 to 500°C. At the same time (300-
500°C) a secondary hardening occurs linked to the formation of very fine V4C3 carbides : a
progressive increase in hot hardness is observed while holding isothermally at 300-450°C.•From 450 to 600°C, the residual austenite is destabilized owing to the precipitation of small
carbides in α'/γ interfaces and may be transformed on cooling either in bainite or secondary
martensite. On the other hand that impoverished austenite may be transformed in (α + carbides)
between 600-700°C. Besides in the same temperature range, M6C and M23C6 may be
formed at the expense of fine M7C3 carbides previously formed.
Effect of Electric Current Pulse on Microstructure and Corrosion Resistance of Hypereutectic High Chromium Cast Iron
