Abstract
The metallographic characteristics of prior austenite grain boundary (PAGB) reheat cavitation have been examined in a range of low-alloy steels using high-resolution electron probe fractography and optical techniques. There is an intimate association with two microstructural features, namely the presence of a fine (∼0.1 μm dia.) dispersion of PAGB manganese sulphide and the concentration of the overall deformation into PAGB deformation zones. Reprecipitated PAGB sulphides are incoherent and behave virtually as pre-existing nuclei. Their presence can be controlled by compositional modification of the primary matrix sulphides. It is shown that the removal of PAGB sulphides greatly reduces the ability to cavitate, even in the presence of high levels of otherwise deleterious residuals. Ways of modifying sulphide dispersions are considered and promise a viable means of controlling cavitation in steels of high residual element content. PAGB zone shear is seen as a necessary though insufficient condition for cavitation. Zone deformation values have been obtained for a large number of steels and the beneficial effect of chromium can be related to its influence in reducing the matrix/zone strength differential.
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