High-temperature phase transformations in strongly metastable austenitic-martensitic CrMnNi-N-C cast steels

The influence of carbon on the melting behavior and solid-solid state phase transformations in highly alloyed cast stainless steels (Fe-15Cr-3Mn-3Ni-0.1N-(0.05-0.25)C) was studied using differential thermal analysis (DTA). The temperatures of the transformations from alpha'-martensite to gamma-austenite and from gamma-austenite to delta-ferrite as well as the solidus temperatures were determined. The investigations using scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM/EDX) showed that at high carbon content (0.25 mass.%) the character of crystallization changes from ferritic-austenitic to austenitic. According to the thermodynamic calculations, the character of the crystallization should be ferritic-austenitic for all studied alloys. The calculated temperature of the alpha' to gamma transformation is in reasonable agreement with the DTA results, but only in the two samples with the lowest C content alpha'-martensite fraction was sufficiently large to detect this transformation predicted by calculations. Both, gamma to delta transformation temperatures and solidus temperatures were lower in the calculation than experimentally measured. The probable reasons for the inconsistency between the results of calculations and experiments are discussed. (C) 2016 Elsevier B.V. All rights reserved.