| The microstructure and fracture toughness of weld heat affected zone of ductile cast iron have been investigated by using thermal cycle simulator on the assumption of practical welding process. The matrix structure of heat-affected zone was transformed to martensite, martensity ＋ pearlite, pearlite and pearlite including small amount of ferrite, by turns, with increasing the cooling time from 800℃ to 500℃. The use of a proper preheat temperatures prevented the formation of martensite. The instrumented charpy impact test has been carried out on a welded ductile cast iron. Result showed that dynamic fracture touhghness, k_(Id) was increased slightly with preheat temperature and heat input In this work, it was shown that apparent impact energy includes contributions other than that of the true deflection of specimen. We found that a compliance energy correction was always needed to determine the true specimen energy. For this purpose, elastic compliance value of testing machine was measured dynamically by the low blow test to correct the apparent impact energy. From this result, true specimen energy was nearly 62 percent of apparent of apparent impact energy value, Therefore, machine compliance corrections must be adapted to load-deflection curves in instrumented impact testing. |
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