Enhancing microstructure and mechanical properties of carbidic austempered ductile iron via Ti-Y-Zr microalloying

In order to improve the microstructure and mechanical properties of carbidic austempered ductile iron (CADI), the synergistic effect of Ti-Y-Zr ternary microalloying on its microstructure and mechanical properties has been systematically investigated in this study. The results show that Ti-Y-Zr ternary microalloying can significantly refine the diameter of graphite nodules, so that the average size is significantly smaller than that of the matrix material without microalloying. At the same time, the morphology and distribution of carbides can be effectively controlled, which not only inhibits the formation of coarse or unevenly distributed carbides, but also promotes the formation of fine and uniformly dispersed carbides. The optimization of these microstructures significantly improves the mechanical properties of the material: compared with the matrix material without microalloying, when the addition amounts of Ti, Y and Zr are 0.1 wt.%, 0.04 wt.% and 0.06 wt.%, respectively, the comprehensive mechanical properties of CADI reach the optimal level, in this case, the hardness of the material is increased by 5.8%, the impact toughness is increased by 22.22%, and the wear loss of CADI is reduced by 16.67%. • The synergistic effect of Ti-Y-Zr ternary microalloying on carbidic austempered ductile iron (CADI) was systematically studied for the first time, which broke through the limitations of single element or traditional alloying methods. • The synergistic effect of Ti-Y-Zr optimizes the microstructure of CADI: the average diameter of graphite spheres is refined from 25μm to 15μm, and the spheroidization rate is increased from 85% to 95%. The carbide morphology is improved, and the bainite structure is obviously refined. • The synergistic improvement of mechanical properties of CADI is realized: under the optimum addition amount of Ti-Y-Zr, the hardness is increased by 5.8%, the impact toughness is increased by 22.22%, and the wear loss is reduced by 16.67%, which solves the problem that the strength and toughness are difficult to balance. • The multi-scale synergistic regulation mechanism is clarified: Ti/Zr achieves heterogeneous nucleation and dispersion strengthening by forming fine carbides, and Y improves graphite morphology by purifying the melt. The synergistic regulation of the evolution from atomic scale to microstructure provides a theoretical support for the performance optimization of CADI.