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  • A micromechanism-based probabilistic approach for prediction of toughness scatter in HAZ of thick-plate welds of thermomechanically treated structural steels

Abstract

The present research work studies the effect that typical heat affected zone (HAZ) microstructural phases can have on the fracture behaviour of a welded joint. Two different heat treatments have been used to obtain two fragile microstructures characterized by their content of martensite-retained austenite (MA) and large bainite packets. An API X65 grade plate steel for linepipe use was used. Fracture mechanical tests, microstructural and fractographic examinations and a computer model have been used to characterize our microstructures. The computer model used was developed by the research center of CEIT in San Sebastian. It can calculate the probability of fracture of a given specimen starting from the test conditions and the microstructure knowledge. The most important results of the present work can be summarized as follows:

- The MA islands are nucleation sites. They can substitute the carbides if these are too small;
- The bainite packets sizes are too large to arrest crack propagation; consequently only the nucleation steps trigger material failure;
- The computer model used is able to predict the material toughness but it is too conservative.
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Additional information

Authors: DEMOFONTI G, Centro sviluppo materiali SpA, Roma (IT);ANDENNA C, Centro sviluppo materiali SpA, Roma (IT)
Bibliographic Reference: EUR 16633 IT (1997) 73pp., FS, ECU 13.50
Availability: Available from the (2)
ISBN: ISBN 92-828-0324-4
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