| Summary: | 碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 97 === The study was carried out to change austempering temperature (300℃~400℃), and the content of chromium (0.3~1.5wt%). The flake graphite cast iron were austenitized at 900℃ for 2 hours, and then quenched to the austempering temperature and holded the temperature for 2 hours. The study was to examine the influence of the austempering temperature and the percent of chromium on the mechanical properties and the microstructure of the austempered flake graphite cast iron.
The result of the study showed that the matrix were composed of ferrite and block and a few of string-type of austenite. When the austempering temperature were low temperature, the structure of ferrite were to grow and coarse, and the retained austenite content and the value of retained austenite content multiplied by the carbon content of austenite rises with rising austmpering temperature. The Heat treatment in the same conditions, when the chromium content was lower, the retained austenite volume fraction was decrease; when the chromium content was higher, there was formation of carbide precipitation in the matrix, caused to increased austenitic volume fraction, the ratio of chromium content of carbide and the matrix, it will decrease as the temperature increases.
When the tempering temperature increased, the mechanical properties of the casting iron, the hardness and tensile strength will be drop, and the ultimate tensile strength occurs in the 1.5wt% Cr, and austempering temperature at 300 ℃ to 1448 MPa.
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