Use of titanium and zirconium in centrifugally cast heat resistant steel

Low carbon 25Cr-35Ni steel (HP type steel) modified with titanium and zirconium has been produced by centrifugal casting. The different phases present in the as cast and aged conditions were described by light optical and scanning electron microscopy with secondary electron imaging and energy dispersive spectroscopy. Results suggest that the use of titanium as a microalloying element reduces secondary precipitation during aging. Moreover, secondary precipitates in the microalloyed steel are much finer and more evenly distributed. On the other hand, zirconium oxides was found to be potential nucleation sites for primary titanium rich carbides contributing to an optimum distribution of these carbides in the tubes. These differences together with the higher stability of the titanium containing primary carbides are responsible for the improvement on ductility and creep resistance found in the present work.