Análise quantitativa da fração de austenita presente na ZAC do aço ASTM A333 Gr. 8 (9% Ni).

Abstract

The aim of this study was to evaluate the effect of the welding heat input on the amount of retained austenite, as well as reversed austenite, present in different regions of the heat affected zone (HAZ) of the ASTM A333 Gr. 8 (9% Ni) steel, including the effect of superposing of heating cycle caused by multiples welding passes. Due to the complexity of multi pass welded joints, the analysis was performed for the finishing, filling and root passes. Specimens of weld cross section extracted from different pipes welded with 0.7 kJ/mm, 1.5 kJ/mm and 2.5 kJ/mm were evaluated. Afterwards, they were submitted to a metallographic preparation followed by a chemical etching using a modified Lepera reagent, and subsequently analyzed using the scanning electron microscopy technique (SEM), operating in SE mode. The austenite present in microstructure was quantified by using SVRNA image analysis software, which segmented and quantify the amount of this particular phase. Statistical analysis of the effect of heat input on the amount of austenite phase was carried out by analysis of variance. The results obtained from the analysis of the variance diagrams show that an increase in the welding heat input leads to a decrease in the amount of austenite present in different HAZ regions for the different passes. In general, even being observed a difference in the amount of austenite present for different regions (finishing, filling and root passes), the tendency to decrease the amount of austenite with increasing the heat input was maintained.