EFFECT OF THERMAL COOLING CONDITIONS ON THE MICROSTRUCTURE AND HARDNESS OF MEDIUM CHROMIUM FERRITIC STAINLESS STEEL

Abstract

The characterization of the heat affected zone (HAZ) of medium chromium ferritic
stainless steel (FSS) welds in terms of phases has not been exhaustive due to the
dynamics of the cooling cycle from the peak temperature in the transformation range.
Consequently, the relative contribution of the phases to weld property is difficult to
determine. In the present work, attempt was made to approximate the HAZ of medium
chromium FSS via the characterization of the effect of thermal cooling conditions
on the microstructure of medium chromium FSS base metal. Two thermal cooling
scenarios from four transformation temperatures-500; 800; 900; and 1100oC- were
considered; and the resulting microstructure characterized using light optical

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microscopy (LOM), X-ray diffraction (XRD) and microhardness evaluation was

compared with the HAZ of a weld of the same metal. The characterization indicated
that the transformation te7?lperature determines the types and distribution of phases
present in the microstructure of medium chromium FSS. III comparison to fusion
welded FSS of the same grade, the low temperature heat affected zone (LTHAZ)
was approximated in the annealing temperature of 50aoC while that of the high
temperature heat affected zone (HTHAZ) was identified as 1100e.