Ordinary gray cast iron is a kind of material with low price and wide application. Due to its poor corrosion resistance and low mechanical properties, its application in some important fields is limited, especially in the fields of shipbuilding and automobile manufacturing. Therefore, how to improve the properties of ordinary gray cast iron has attracted more and more attention. Adding rare earth for inoculation treatment in the melting process of gray cast iron can greatly improve and improve the properties of gray cast iron and expand the scope of practical application of gray cast iron.
- When the content of rare earth alloy is 0.1%, it can effectively improve the casting properties of low carbon equivalent gray cast iron. The addition of rare earth alloy in the melting process can effectively improve the fluidity of low carbon equivalent gray cast iron. The fluidity of low carbon equivalent gray cast iron first increases and then decreases with the increase of rare earth alloy. When the addition of rare earth alloy is 0.1%, the fluidity of molten iron is the best; The shrinkage rate of low-carbon equivalent gray cast iron is large. With the increase of rare earth alloy, the shrinkage of low-carbon equivalent gray cast iron decreases first and then increases, and the shrinkage rate is the smallest when the amount of rare earth alloy is 0.1%.
- Rare earth alloy has obvious effect on changing the morphology of graphite. It is found that the microstructure of graphite is mainly in the form of flake graphite and coarse graphite with the addition of rare earth, and the microstructure of graphite gradually changes to the form of spherical graphite with the addition of E and graphite. It is found that the microstructure of graphite is mainly in the form of flake graphite and coarse graphite with the addition of rare earth.
- Rare earth alloy can effectively refine the matrix structure. By comparing the matrix structure of different rare earth alloys, it can be found that in a certain range, rare earth can greatly reduce the content of cementite in low carbon equivalent gray cast iron, increase the content of pearlite and greatly improve the mechanical properties of gray cast iron; When the amount of rare earth alloy is 0.1% and 0.2%, the amount of pearlite is more and flake, and rare earth can effectively reduce the spacing of pearlite flakes; After the modification of rare earth alloy, the number of eutectic clusters per unit area increases with the increase of the amount of rare earth alloy; After eutectic refinement, the mechanical properties of gray cast iron can be effectively improved under the same matrix conditions.
- Rare earth alloy can change the lattice constant of gray cast iron and cause character distortion. With the increase of rare earth addition, α- The Fe lattice constant also increases gradually. Among them, the lattice constant reaches the maximum when the addition amount of rare earth alloy reaches 0.25%, and the lattice constant of low carbon equivalent gray cast iron reaches the maximum when the addition amount of rare earth alloy is 0.1% and 0.3% respectively α- There is little difference in Fe lattice constants; In general, low carbon equivalent gray cast iron before modification α- The lattice constant of Fe is obviously higher than that of Cast Iron Inoculated with rare earth alloy α- Fe lattice constant is small. This shows that the addition of rare earth alloy in the melting process makes the gray cast iron with low carbon equivalent α- The distortion of Fe lattice significantly increases the microhardness of the matrix structure of gray cast iron, and then increases the tensile strength of gray cast iron.
- Rare earth alloy has obvious double inoculation effect on low carbon equivalent gray cast iron. When the addition amount of rare earth alloy is 0.1% – 0.2%, it can promote the graphitization of low carbon equivalent gray cast iron, reduce the tendency of white cast iron, refine graphite and have obvious inoculation effect. However, with the increase of the amount of rare earth, the role of rare earth alloy in hindering graphitization is gradually strengthened, the white tendency of low carbon equivalent gray cast iron is significantly increased, and the ledeburite structure is significantly increased. When the amount of rare earth is more than 0.25%, the graphite appears creep and spheroidization.
- When the content of rare earth alloy is 0.1%, the comprehensive mechanical properties of low carbon equivalent gray cast iron are significantly improved. When the amount of rare earth alloy is 0.1%, the tensile strength is the largest and the hardness is in a reasonable range. With the increase of rare earth alloy, the tensile strength of gray cast iron decreases, and reaches the lowest when the amount of rare earth ferrosilicon is 0.2%. When the amount of rare earth exceeds 0.2%, the hardness of low carbon equivalent gray cast iron increases greatly with the increase of the amount of rare earth alloy.
The experiment mainly studied the effect of rare earth on the microstructure and properties of low-carbon equivalent gray cast iron. The direction was relatively single, and the effect of rare earth on the microstructure and properties of high-carbon equivalent gray cast iron was not studied. At the same time, the gray cast iron used in the experiment was only HT250, and other gray cast iron models were not included in the research scope due to the large amount of experiments. Therefore, the study of rare earth treatment of high carbon equivalent gray cast iron and the effect of rare earth on the microstructure and properties of different types of gray cast iron will become the focus of future work.
With the in-depth study on the method and mechanism of rare earth inoculation treatment of low carbon equivalent gray cast iron and the continuous development of inoculation technology, the application of rare earth in ordinary gray cast iron will be more and more abundant and expanded. Rare earth treatment of gray cast iron will have great practical application value and good development prospects.