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The research activity carried out is aimed at a more careful investigation of the mechanical and behaviour specifications of the cleavage fracture's micro mechanism; it is referred to high tensile steels for pipeline, produced by lamination under accelerated cooling and control.
The objective of the work is to study how the variation of the several micro structural phases conditions our steels' cleavage and to investigate the micro cracks initiation and propagation mechanisms.
Persuing this objective, we chose 6 selected steels; all of them are industrial and about X80 grade (except one that is X65); their micro structures having different polygonal ferrite percentages. On these materials, we carried out toughness measurements; cleavage critical tension and nil ductility transition (NDT) tests. At the same time we carried out the micro structure quantitative study and a careful analysis of the various specimens' fracture surfaces. We analysed the experimental results in terms of cleavage critical tension compared to the most reliable theoretical models. More practically, according to the above mentioned outcomes, the following direction can be given: as regards the cleavage resistance, to maximize the exploitation of the fine carbides and composite structure combination in TMCP high grade steels, it is necessary to control the grains' maximum size, and then their dimensional distribution, rather than the polygonal ferrite percentage. .

Additional information

Authors: DEMOFONTI G, Centro Sviluppo materiali SpA, Roma (IT);ANDENNA C, Centro Sviluppo materiali SpA, Roma (IT)
Bibliographic Reference: EUR 15733 IT (1996) 85pp., FS, ECU 11.50
Availability: Available from the (2)
ISBN: ISBN 92-827-6547-4
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