Issue 48

C. Bellini et alii, Frattura ed Integrità Strutturale, 48 (2019) 740-747; DOI: 10.3221/IGF-ESIS.48.67 743 at laboratory temperature for 2 minutes and then they are dried for 10 minutes at 100 °C. After this procedure, they are immediately dipped into the galvanizing bath, at 440 ± 2 °C for different time (respectively 15, 60, 180, 360 and 900 seconds) and cooled in air. In order to identify the thermal damaging mechanisms for each investigated dipping duration, longitudinal sections of the bent specimens are metallographically prepared and observed by means of both an optical microscope (LOM) and a scanning electron microscope (SEM). C OATING FORMATION KINETICS alvanized specimens are analysed by means a LOM with and without chemical etching in order to evaluate the role of graphite nodules during the coating formation (without etching) and the intermetallic phases formation kinetic (by nital 2% etching for 60 s). Considering the observation of unetched coating sections (Figure 2) it is possible to underline that the presence of graphite nodules is observed also in the coating for each investigated dipping time [19]. 15 s 60 s 180 s 360 s 900 s Figure 2 : Unetched section of galvanized GS500 at different dipping time. Starting from 180 s up to 900 s, it is observed the presence of many dark round zones which can be the effect of carbon dispersed in the zinc. These zones can be the effect of coalescence of carbon and/or the effect of CO2 or CO due to the high temperature interaction of graphite to the oxide dispersed in the bath. G