Effect of Nb Addition on Compact Microstructure and Mechanical Properties of Gray Cast Iron for Cylinder Liner

To improve the mechanical properties and the strengthening mechanism, gray cast irons (Nb content is 0 wt.%, 0.15 wt.%, 0.2 wt.%, 0.25 wt.%, 0.3 wt.%, and 0.35 wt.%, simplify as Nb0, Nb1.5, Nb2, Nb2.5, Nb3, Nb3.5, respectively) were prepared using a medium-frequency induction furnace. The results show that the interlamellar spacing in the microstructure of the gray cast iron matrix is refined by the addition of Nb, and the spacing decreases from 530 nm to 210 nm. The A-type graphite decreases in size and gets distributed more homogeneously. With the addition of Nb, the Vickers hardness and tensile strength of the gray cast iron increases. The Nb2.5 has excellent structural uniformity and refines the pearlite spacing to 210 nm, showing stable mechanical properties. The Nb3.5 gray cast iron exhibits the best mechanical properties, the Vickers hardness and tensile strength are 389 HV and 537 MPa, respectively. The improvement in Vickers hardness and tensile strength is attributed to second-phase strengthening, solid solution strengthening, and fine-grain strengthening. This work will provide experience for the material design of high-performance gray cast iron cylinder liners.