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Abstract:
X-ray diffractometry and light microscopy have been used as tools to characterize the constitution and austempering kinetics of 13 ductile iron alloys containing various amounts of Mn, Mo, Ni, and Si. One-inch Y-block castings of each alloy were produced. Specimens were austenitized at 927 C (1700 F) and 871 C (1600 F) and austempered at 316 C (600 F) and 371 C (700 F) for times from 2 to 10,000 minutes. X-ray diffraction yielded measurements of the matrix carbon content (C(sub gamma)(o)), the metastable high carbon austenite volume fraction (X(sub gamma)) and carbon content (C(sub gamma)), and the martensite volume fraction (X(sub alpha')). Light microscopy yielded estimates of the untransformed austenite volume, (UAV). It was observed that the rate of the stage I process for both upper and lower bainite was determined by the carbon content difference between the matrix and the high carbon austenite C(sub gamma)-C(sub gamma)(o). As C(sub gamma)-C(sub gamma)(o) increased, the rate of stage I increased. Moreover, as C(sub gamma)-C(sub gamma)(o) decreased, the tendency to form "residual" UAV increased, a result promoted by Mn segregation and higher austenitizing temperatures. It was also observed that the rate of the stage II process for both upper and lower bainites was decreased with additions of all the alloying elements Si, Mn, Mo, and Ni.
| Description: |
Journal article |
| Pages: |
24 |
| Report Date: |
87 |
| Report Number: |
D656941 |
Report Unavailable |
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