Influence of cooling rate on microstructure and phase composition of HAZ of duplex (DSS) 2205 steel in wet underwater welding

Abstract

The article shows the results of the analysis of changes in the microstructure and volumetric particles of phase components of HAZ metal in modeling of welding thermal cycles, inherent in wet underwater welding and welding in air, with the use of the Gleeble-3800 system. The value of cooling rate of different areas of weld metal in wet underwater welding and welding in air was determined. It is shown that as a result of cooling impact of water environment, the cooling rate in wet underwater welding is almost by an order higher than that of welding in air (w13/8 = 8.21 °C/s — air, in the middle of the weld, and in wet underwater welding it is accordingly w13/8 = 81.70 °C/s in the middle of the weld, w13/8 = 165.85 °C/s at the beginning of the weld and w13/8 = 320.51 °C/s in the weld crater). The change in volumetric particles of phase components of ferrite, austenite and excess phases (chromium Cr2 N nitrides) was determined in the microstructure of HAZ metal depending on the cooling rate. Phase transformations almost completely occur in the high-temperature heat-affected zone (HHAZ) in the temperature range T = 1300‒800 °С. Contribution of low-temperature heat-affected zone (LHAZ), temperature range T = 800‒500 °С on the change in phase components is negligible. The amount of ferritic and austenitic components and especially the morphology of austenite in the microstructure of HHAZ depend on the cooling rate, as well as the amount of precipitation of excess phases (probably, chromium Cr2 N nitrides).