Cellular Growth of Delta-Pearlite Formed by Carburization of Ternary Iron Alloys

Abstract

Eutectoid composition and microstructure of δ-pearlite were studied in the carburized Fe–Cr–M and Fe–W–M ternary alloys, where M is the third element. The chromium or tungsten content in the eutectoid alloy decreases with addition of a ferrite-stabilizing element and increases with addition of an austenite-stabilizing element.
The alloying element causes the change in shape of δ-ferrite/δ-pearlite interface from planar to cellular. Measurements of solute distribution in front of the cellular interface have revealed that a spike of substitutional solute concentration ahead of the tip of the cell is produced and solute segregation occurs at the cell boundary. The formation of the cellular structure is caused by the generation of the carbon-supersaturated region in δ-ferrite due to the presence of the spike.