Abstract
A short review of modern theories of bainitic transformations has been undertaken and it has been shown that the usually medium high silicon content of ‘unalloyed’ grey and nodular iron is an effective controlling factor for austempering such materials. Malleable iron has a lower silicon content but a new alloy of the same class has been developed, which contains ∼ 2 wt-%Si and responds to austempering. New quenching media (molten + solid zinc, or a combination of cold and hot water) and the ‘short quenching’ method have been developed as operations before carrying out the final bainitic transformation in an ordinary air furnace. Some new ideas on bainitic quenching of different cast irons and graphitic steel are analysed, including the combination of graphitising annealing and austenitisation into a single operation before quenching. Hot knocking out of castings and their subsequent heat treatment using the accumulated heat as well as quenching from the austenite + ferrite critical temperature interval have been considered.
Get full access to this article
View all access options for this article.