Zr-containing precipitates in a TiNb microalloyed HSLA steel containing 0.016 wt.% Zr addition

The effects of an 0.016 wt.% Zr addition on precipitation in a TiNb microalloyed HSLA steel were studied by analytical electron microscopy (AEM). Complex Zr-containing oxides and complex TiZr and TiNbZr nitrides (carbonitrides) were found, but no single ZnN precipitates were observed. Microanalysis and lattice parameter measurements showed that in these complex Zr-containing nitrides, Zr and N were intermixed with either Ti or Ti and Nb rather than present as an isolated ZrN phase. Four groups of complex Zr-containing nitride were observed in terms of microchemistry, morphology and size. All the TiZr and TiNbZr nitrides observed were greater than 100 nm in size. However, the majority of the Zrfree TiNb precipitates were smaller than 100 nm. Therefore, the precipitation of these TiNb particles was not affected by an 0.016 wt.% Zr addition. It appears that the Zr addition increased the microsegregation in TiNb steel, which would have an adverse effect on toughness. As a comparison the lattice parameters of the TiNb precipitates in TiNb microalloyed steels were measured. Finally, the potential application of ZrN particles in Nbbearing HSLA steels is discussed.