Abstract Scope |
The high alloying content of the recently developed hyper duplex stainless steel (HDSS) provides remarkable corrosion resistance, PREn > 49, and a balanced ferrite austenite microstructure. However, due to the Cr and Mo content, this alloy is susceptible to sigma phase formation. An extensive sigma phase formation study was conducted on HDSS developing precipitation experimental data, JMAK analytical calculations, and a computational kinetic model. Isothermal heat treatments produced specimens for SEM characterization. The quantified sigma volume fraction developed a TTT map to adjust and validate the computational model and the JMAK calculations. We found that sigma kinetics is highest at 900 oC -920oC in isothermal conditions. However, in conditions of continuous cooling processes, cooling rates faster than 4oC/s do not cause sigma precipitation. The established kinetic model allows the prediction of sigma formation based on the applied cooling rates. Hence, allowing optimization of the welding parameters to avoid sigma presence. |