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摘要
A New Test Procedure to Investigate the Cracking Behaviour of Hot-Dip Galvanised Steel. A new test procedure has been developed for systematic research into the conditions conducive to liquid metal-assisted cracking (LMAC), a phenomenon which can occur when steel is hot-dip galvanised. U-bend specimens are used to achieve different tensile stress gradients and to allow an investigation of the influence of any pre-deformation. The procedure was used to test steels with different levels of susceptibility to LMAC, although the main focus was on S355 J2. Having established a broad range of parameters, closer attention was paid to the effect of the alloying elements of lead, tin and bismuth during zinc smelting on the potential risk posed by LMAC. Of the various procedures studied, the test involving constant stress (stress/time-to-rupture test) and the test where stress was continually increased (tensile test) offered the greatest indication of existing risk potential. Irrespective of the test procedure and of the variable used for the indication (time to crack formation, engineering stress or strain), comparable results were obtained with comparable risk potential for tests lasting between 5 min and 1 h. One important insight is that before any damage becomes evident on the basis of load curves and their analysis, micro-cracks occur in the outer layer which is subject to high stress, and these minute cracks cause an increase in the expansion as compared to a crack-free specimen subject to similar levels of stress. This must be factored into the calculation of the plastic expansion which can be withstood during the galvanising process as measured from the specimen expansion.
- 出版日期2010
