Investigation of hot cracking resistance of 2205 duplex steel

Austenitic duplex steel of the brand 2205 according to Avesta Sheffield is used for welded constructions (pipelines, tanks) in the petrol industry, chemical industry and food industry. It is important to know the range of high-temperature brittleness in designing welding technology for constructions made of this steel type. There is no data in literature concerning this issue. High-temperature brittleness tests using the simulator of heat flow device Gleeble 3800 were performed. The tests results allowed the evaluation of the characteristic temperatures in the brittleness temperature range during the joining of duplex steels, specifically the nil-strength temperature (NST) and nil-ductility temperatures (NDT) during heating, the strength and ductility recovery temperatures (DRY) during cooling, the parameter (R-f = (T-liquidus - NDT)/NDT) describing the duplex steel inclination for hot cracking, and the brittleness temperature range (BTR). It has been stated that, for the examined steel, this range is wide and amounts to ca. 90 degrees C. The joining of duplex steels with the help of welding techniques creates a significant risk of hot cracks. After analysis of the DTA curves a liquidus temperature of T-L = 1465 degrees C and a solidus temperature of T-s = 1454 degrees C were observed. For NST a mean value was assumed, in which the cracks appeared for six samples; the temperature was 1381 degrees C. As the value of the NDT temperature 1367 degrees C was applied while for DRT the assumed temperature was 1375 degrees C. The microstructure of the fractures was observed using a Hitachi S-3400N scanning electron microscope (SEM). The analyses of the chemical composition were performed using an energy-dispersive X-ray spectrometer (EDS), Noran System Six of Thermo Fisher Scientific. Essential differences of fracture morphology type over the brittle temperature range were observed and described.