Cast structure and mechanical properties of fine grained superalloy K4169 by addition of refiners

Grain size and microstructural features of cast superalloy K4169 were investigated under various melting and casting conditions together with the addition of grain refiners. It is found that lowering the pouring temperature and adding refiners to the melt before pouring can lead to grain refinement of gamma matrix and improve the proportion of equiaxed grains. At a conventional pouring temperature of 1400 degrees C, the average size of equiaxed grains could be refined to the order of ASTM 3.2 (0.17 mm), the proportion of equiaxed grains at the transverse cross-section could be improved from 56% to 99% with addition of a trace intermetallic compound into the melt. The results also indicate that the length of primary dendrite is shortened with the addition of refiners, but the secondary dendrite arm spacing keeps almost unchanged. Meanwhile, the microsegregation of main elements such as Fe, Cr, Nb, Mo and Ti is alleviated with the decrease in grain size, and the grains have transformed from dendrite to granulation in fine-grained castings. The amount of microporosity in samples with the addition of refiners can be greatly reduced. The mechanisms of grain refinement and increase in equiaxed grain proportion were proposed. Tensile properties at room temperature and at 700 degrees C were tested. The rupture strength, yield strength, elongation and reduction of area for refined grains are all more superior to those of coarse ones. Whereas the elongation and reduction of area of fine grained samples decrease at 700 degrees C. Low cycle fatigue (LCF) properties of refined grain samples at room temperature are improved significantly. In addition, the degree of dispersion of LCF data of fined grain samples is diminished.