A metallographic study of the high-temperature decomposition of austenite in alloy steels containing Mo and Cr

• Published in: Metallography 1979-01, Vol.12 (1), p.3-21
• Main Authors: Bee, J.V., Edmonds, D.V.
• Format: Article
• Language: English
• ISSN: 0026-0800
• DOI: 10.1016/0026-0800(79)90015-6

Optical and electron microscopy have been used to study the complex microstructures developed during the isothermal decomposition of austenite above 550°C in Fe-4Mo-0.2C and Fe-10Cr-0.4C alloy steels. As the transformation temperature is decreased, the decomposition products change from the disordered growth of nodular alloy pearlites to blocky ferrite structures containing fine dispersions of alloy carbide, and finally to acicular ferrite structures also containing alloy carbide. The branched M 6C and M 23C 6 of the high-temperature pearlite is replaced by Mo 2C and M 7C 3 with a fibrous or lath morphology in the lower temperature structures. The decomposition microstructures are explained in terms of a model which takes account of the growth of particular alloy carbides at the interfaces of ferrite allotriomorphs, where the growth mechanism, and hence the morphology, is sensitive to transformation temperature.