Failure mechanisms during galvanising
The overall objective of the Famega project was to identify the mechanisms controlling liquid metal assisted cracking (LMAC) of high-strength structural steels during hot-dip galvanising. Sixteen steel sections were obtained and classified in terms of chemical composition, microstructure and mechanical properties, including high-temperature properties as inputs for FE modelling. Measurements of web residual stress showed predominantly compressive values of up to 50 % of yield. In contrast, welding processes resulted in tensile residual stresses close to yield near the weld. Details of the galvanising process considered important to FE models were obtained from operators in Germany, Spain, Luxembourg and the United Kingdom. Eighty full-scale galvanising tests were carried out on 2 m long beams with welded half-cover plates. Beams without welded plates did not crack. Techniques to reduce LMAC showed that thermal stress relief with a hand-held torch was highly effective, while sand blasting, ultrasonic peening and additional weld beads proved ineffective with compressive stresses confined to surface layers. LMAC tests in three laboratories were carried out using newly developed and conventional test piece types and a variety of Zn alloys. Factors which contributed to LMAC included: Zn-Sn baths, lower strain rates and steel. High hydrogen levels were found at the steel/zinc alloy interface but did not contribute to cracking. Combining threshold stress and stress intensity using an FAD approach showed that fracture mechanics was only appropriate for cracks > 2 mm. Modelling of welding and galvanising showed the importance of stress concentration near the half cover plate, residual stress, dipping speed and angle, and the heat transfer coefficient associated with a Zn-Sn alloy bath.
Bibliographic Reference: EUR 23195 EN (2008), 138 pp. Free of charge
Availability: Catalogue Number KI-NA-23195-EN-S The PDF version can be downloaded from: http://bookshop.europa.eu
ISBN: ISBN 978-92-79-08171-2
Record Number: 200910395 / Last updated on: 2009-10-07
Original language: en
Available languages: en