Splat quenching of austenitic steels containing niobium and carbon

Rapid quenching from the melt has been used to obtain significant increases in the solid solubility of carbon in a Fe-20% Cr-25% Ni austenitic steel with and without the presence of niobium. Both X-ray techniques and transmission electron microscopy were employed to study the solidification structures and subsequent decomposition on aging between 5000-8000C. M23C6 carbide was found on ageing all steels and was confined to areas of high chromium content or grain boundaries. NbC particles similarly grew at these sites but also formed a dense matrix carbide. The nature and formation of these carbides are discussed in terms of solidification structure and a possible precipitation sequence for NbC is outlined in terms of a vacancy-solute clustering model. (author)