Influence of Casting Materials on the Microstructure and Mechanical Properties of Gray Cast Iron for Cylinder Liners

In this paper, four different casting materials were used to get gray cast iron samples, the effects of different cooling rates caused by different casting materials on graphite distribution, matrix structure and mechanical properties were investigated. The experimental results show that as the cooling rate increases, the graphite form of gray cast iron changed from coarse flake A-type graphite to rosette shaped B-type graphite, graphite increased in quantity and was more evenly distributed. The interlayer spacing of pearlite in matrix decreased with the increase of cooling rate, four different mold casting of cast iron material sample of pearlite lamellar spacing is CO₂ sodium silicate bonded sand mold, 340 nm, oxide ceramic mold, 275 nm, cast iron mold, 141 nm, graphite casting mold, 135 nm, respectively. The reduction of the interlayer spacing of pearlite also significantly improves the tensile strength, compressive strength and hardness. The tensile strength of cast iron specimens cast in graphite casting molds is the highest, at 421 MPa, while the tensile strength of cast iron specimens cast in CO₂ sodium silicate bonded sand molds is the lowest, at 346 MPa. The graphite cast iron sample has the highest compressive strength of 2165 MPa, and the oxide ceramic cast iron sample has the lowest compressive strength of 1115 MPa. The Brinell hardness of the samples cast in cast iron molds is the highest, at 409 HB, while the samples cast in CO₂ sodium silicate bonded sand molds have the lowest Brinell hardness, at 255 HB. In addition, increasing the cooling rate inhibited the diffusion of elements in the melt, reduced the final solidification interval and also reduced the shrinkage porosity and other defects. Fracture analysis shows that cleavage fracture is the main fracture mode of castings. The higher the cooling rate, the smoother the fracture morphology.