Sensitization of inconel 600. II. Analytical electron microscopy

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Abstract
Analytical electron microscopy has been used to study the effect of trace impurity elements, such as carbon, phosphorus, boron and silicon, on the microstructural characteristics of Inconel 600. Sulphide particles, rich in manganese and chromium, have been detected in association with both titanium nitride and chromium carbide, and the structure, lattice parameters and crystallographic orientation relationship between the γ-M23C6 and sulphide determined. Additions of carbon to the base alloy caused extensive precipitation of carbides, mainly of the M7C3 type. In the annealed alloy, these carbides were found to outline prior austenite grain boundaries and, on subsequent ageing, precipitated at the existing boundaries. Trace additions of boron to the base alloy increased the twin frequency by enhancing precipitation at non-coherent twin boundaries. These new precipitates were rich in chromium but also contained some iron and nickel. Additions of silicon did not alter the microstructure of the base alloy.