Microstructure of Spray Formed 2.9C-22Cr High Chromium White Cast Iron

摘要

In the present work a 2.9%C-22%Cr white cast iron was processed by spray forming aiming to investigate the potential of achieving novel microstructure by the high cooling rate involved in this process. Two gas flow rate to metal flow rate ratios (0.12 and 0.23) were used. The microstructural characterization was performed by using X-ray diffractometry, optical and scanning electron microscopy. The conventional microstructure of this alloy shows M_7C_3 carbides (about 300 μm in length) embedded in a matrix of austenite and martensite dendrites; on the other hand the spray formed deposit showed a microstructure formed by fine M_7C_3 carbides (less than 10 μm in length) in a martensitic matrix. The overspray powders showed a microstructure composed mainly by carbides and austenite; the relatively rapid solidification of the droplets enhanced the chromium and carbon solubility in austenite changing the M_s temperature.