Effect Of Sn On Microstructure And Properties Of Vermicular Graphite Iron

Vermicular Graphite Iron (VGI), with unique morphology of graphite, is a novel type of engineering materials. However, sufficient attentions and interests were always absent on related researches about VGI due to the misunderstanding of its characteristic microstructure and properties. Until recently, the rapid progress of human society and amazing development of industrial technology awakens people to realize the advantages and adaptability of VGI in severe working condition consisted of thermal shock and mechanical loads, especially on cylinder liners, manifolds, ingot molds and brake discs. While because of the difficulty to accurately control the vermicular ratio, there is few research activities conducted on VGI, included alloying elements and relationships between microstructure and properties, which seriously slowed down the improvements and widespread applications of this inexpensive and efficient kind of materials.In the current research, effects of Sn in the range of Owt.%to0.121wt.%on microstructure and properties were investigated and the mechanisms were also analyzed with the help of optical microscope (OM), scanning electron microscope (SEM), and X-ray Diffractometer (XRD). And the purpose of this research is to supply some theoretical foundations and practical experiences for imminent research activities on VGI.The results of the present study showed that Sn barely affects the vermicular ratio but abates the amount of vermicular graphite and refines them At the same time, pearlite is promoted and refined by addition of Sn. With addition of0.057wt.%Sn, pearlite accounts for more than95%in the matrix and the lamellar spacing of pearlite obviously narrows to troosites level (83nm). With further increment of Sn, percentage of pearlite remains more than95%, and free cementite was observed in the samples containing0.121wt.%Sn Furthermore, Sn shows a homogeneous distribution in the matrix, which positively influences the combination properties of VGI.More specifically, tensile strengths of VGI showed a fluctuation and the samples containing0.057wt.%Sn performed the best tensile strength of410.7MPa. Existence of free cementite critically destroyed the samples and the tensile strength sharply declined to334.0MPa with0.121wt%Sn. While the Brinell Hardness increased gradually from192HBW with0.003wt.%Sn to227HBW with0.121wt.%Sn Impact toughness increased to maximum value of9.11J with0.057wt.%Sn and then decreased sharply to5.08J when Sn was excessively added.Wear resistance of samples also experienced a fluctuant increase and the samples containing0.057wt.%and0.121wt%Sn displayed impressive wear resistance owing to the narrow lamellar spacing ofpearlite and high hardness and stability of cementite. Samples containing0.057wt.%Sn performed the best thermal fatigue resistance, which comes from the refined graphite morphology and reduced lamellar spacing of pearlite.In conclusion, appropriate addition of Sn could effectively refine the micro structure and properties of VGI. And samples containing0.057wt.%performed the best combination of microstructure and properties with pearlite lamellar spacing of83nm, tensile strength of410.7MPa and impact toughness of9.11J. Sn is an effective and inexpensive alloying element in VGI which is strongly suggested to be applied in industrial production.