Application of ADI with Improved Fracture Toughness for Structural Members of Heavy Duty Trucks 942311

Production cost saving is the main subject of process control of all automobile industries. Recently introduced ADI is a suitable material for those issues, but usefulness is restricted because of its poor fracture toughness. In the study, the effect of casting and austempering conditions on the fracture toughness of ADI were determined in order to develop a suitable material which can replace forged alloy steel.
For casting of DCI, sandwitch method was conducted as inoculation process involving spheroldizing treatment with calballoy. Austempering was carried out in a salt bath with a composition of 50% KNO3 and 50% NaNO3 and then cooled in air. Two main parameters, namely austempering temperature and time, were selected as variables and structural changes of ADI with initial casting conditions was monitored with them.
According to the casting results, it was confirmed that the mechanical properties of ADI, especially fracture toughness, depends strongly on casting conditions of DCI.
From the test results, it was confirmed that the fracture toughness of ADI obeyed strongly to the austempering conditions such as time because the bainitic reaction depends on them. Crack growth rate with upper bainitic microstructured ADI was slower than that of lower bainitic ADI, which showed a highest fracture toughness of the materials. To improve fracture toughness of ADI, control of microstructural constituents during austempering is most important, which were affected by initial casting conditions such as addition of alloying elements, nodularity and counts of graphite.
The test results in that replacement of some structural members made of forged alloy steel with ADI is accountable successfully and benefit for saving production cost.


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