EFFECT OF Nb AND Ti ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 30% Ni / 18% Cr CAST STEEL AFTER ANNEALING

The study discusses the microstructure and mechanical properties of eight tested 0.3 % C -30 % Ni 18 % Cr cast steels stabilized with niobium and titanium after annealing in the cycle of 900 °C / 300 h. The niobium content in the cast steels varied from 0.0 to 2.0 % and that of titanium from 0.0 to 1.2 % by weight. Microstructure was examined using both light microscope and a scanning electron microscope with Link IS-IS attachement as well as an X-ray diffractometer. Depending on the chemical composition of cast steel, the following phases were identified: carbides of MC and M23C6 type and a phase rich in silicon, nickel, niobium and / or titanium, which was supposed to be a phase G. Relationships between the microstructure and mechanical properties of cast steel at 20 and 900 °C were examined as well.