Transformation Kinetics of M23C6 Carbide Lattice Parameters in Low Alloyed Steel

Abstract

Power plant steel 12X1MФ, taken from the as-installed condition through to 270000 h service-exposed and accelerated aged in laboratory conditions, have been characterized with optical microscopy and X-ray diffraction. Microscopy showed that during heat treatment a number of microstructural changes occurs. Initially formed pearlite disappeared and carbide coarsening also is detectable in steel exploited for long periods and during accelerated ageing. X-ray diffraction revealed that carbide M23C6 crystal lattice parameter changes as a function of service time or heat exposure in laboratory conditions. Johnson-Mehl-Avrami law was adapted to express the dependence of carbide M23C6 crystal lattice parameter changes in a double logarithmic plot. The obtained linear relationship could be applied for steel real state assessment.