Hot dip galvanising of transformation induced plasticity and other intercritically annealed steels

Conventional transformation induced plasticity (TRIP) steels have high Si levels, which makes it difficult to coat them satisfactorily by hot dip galvanising. As a consequence, new low Si TRIP steels in which Al or P substitutes for the Si are being examined. The compositions, processing, and properties of these new steels are discussed and compared with those of dual phase steels at the same strength level. It is shown that although the presence of retained austenite always gives some benefit to ductility, it is very difficult to produce hot dipped galvanised TRIP steels with very high (> 30%) elongations by a commercial processing route. In contrast, dual phase steels, although having worse properties, still give relatively good formability and can at present be more readily coated.