EUTECTIC CRYSTALLIZATION OF Fe-C ALLOYS WITH HYPERCEMENTITE CARBIDE

Abstract

Рurpose. To investigate the peculiarities of the structure formation in white cast irons with the participation of Fe3C and Fe7C3 carbides.
 Methods of research. By the comparing detailed both microscopic and thermal (DSC) kinetics of the melting and crystallization process to determine the regularities of the eutectic transformation of the white cast iron under significant undercooling of the liquid phase.
 Microscopic analysis of samples using a light microscope Jenaphot 2000 (Carl Zeiss, Germany). Thermal analyses using differential scanning calorimeter (DSC) STA 449C “Jupiter” (Netzsch Geratebau GmbH, Germany).
 Results. It is shown that eutectic crystallization of white cast irons with great undercooling of the melt is a complex process that consists of crystallization and simultaneous dissolution of crystalline phases: γ austenite and two metastable carbides Fe3C and Fe7C3. In general, crystallization proceeds according to scheme L → L+ Fe7C3 +γ → L++ Fe7C3 + γ + Fe3C→ Fe7C3 +γ+ Fe3C. As a result, two eutectics are formed, one Fe7C3 +γ (plate-like) with austenitic, second ledeburite γ+ Fe3C with cementite matrix.
 Scientific novelty. The microscopic kinetics of nucleating and growth of plate-like Fe7C3 +γ eutectics was investigated and relative stability of Fe7C3 carbide under normal conditions was found. A scheme of metastable phase equilibria with the participation of Fe7C3 carbide in system Fe-Fe3C-Fe7C3 is proposed.
 Practical value. A simple liquid phase processing technology is proposed in order to generate significant undercooling of the melt that causes formation a natural composite material with both a matrix of transformed austenite and carbide reinforcing phases.