| Summary: | 碩士 === 逢甲大學 === 機械工程學所 === 99 === With the increasing of serious environmental pollution, the importance of environmental protection is imperative. The alloying element chromium (Cr) which is regarding as class B carcinogen by U.S. EPA, is often added to cast iron, thus it deserves to make more effort on looking for replacement alloying elements so as to make contribution on environmental protection.
The objective of this research is to adopt the alloying element vanadium (V) which has the similar properties with chromium (Cr) as the replacement target. Then the effect of alloying element vanadium(V) (0.02~0.5wt％) and chromium(Cr) (0.2~1.0wt％) on the mechanical properties and metallographic microstructure(matrix structure, morphology and size of graphite etc.) of the flake graphite and spheroidal cast iron will be investigated. Also, this research is to evaluate the homogeneity and differences of these two alloying elements.
The result of the experiment shows that with the increasing of the alloying elements Cr, V added, the pearlite in the microstructure will be refined. For example of flake graphite cast iron FC350, when added with 0.2wt%Cr, the average lamella thickness of cementite and ferrite is 343.1nm and 1500nm respectively. But when the addition amount of Cr is increased to 0.9wt%, the average lamellar thickness of cementite and ferrite is 161.6nm and 296.9nm. When 0.02wt%V was added, the average lamella thickness of cementite is 223.4nm, and ferrite is 270.2nm. But when V wt% was increased to 0.5wt%, the average lamella thickness of cementite and ferrite is decreased to 132.8nm and 168.7nm respectively. In addition, by SEM/EDS and Line scan can find that, with the increasing of the alloying elements wt%, Cr is easy to segregate on the pearlite grain boundary, and solid solution into cementite, then generate complex carbides(Fe, Cr)3C,but V will generate carbide independently(MC(M=
Fe, V)).
In the mechanical properties of flake and spheroidal graphite cast iron shows that with the same trend. When adding alloying element Cr, hardness gradually increased, but the impact value and elongation gradually reduced, with the increasing of Cr wt%. For tensile strength, it will increases gradually at first, but when the wt% of the alloying elements chromium Cr is greater than a certain value, the trend of the tensile strength will decrease obviously.
Adding alloying element V, ranging from 0.02wt% to 0.5wt%,the tensile strength, hardness showed a gradual upward trend, while the impact value and elongation is shown a downward trend.
For the tensile strength of flake graphite cast iron FC350, addition amount of 0.2wt% V has the same effect with 0.5wt% Cr addition. For the tensile strength of spheroidal graphite cast iron FC450-10, addition amount of 0.08wt% V has the same effect with 0.2wt% Cr addition. In addition, this research also uses the obtained experiment result data, to calculate the regression equation of the alloy addition amount respect to mechanical properties. Its accuracy is high, and should be able used to predict the relationship between the alloying elements Cr, V addition amount and the mechanical properties of flake and spheroidal graphite cast iron castings in the future.
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