Henrik Sieurin: Fracture toughness properties of a welded duplex stainless steel (Abstract)
Supervisor: Rolf Sandström
Department of Materials Science and Engineering
Good toughness properties in base and weld material enable the use of DSS in critical applications such as pressure vessels. By using DSS a reduction of wall thickness can be accomplished together with a reduction of cost, welding time and transportation weight, contributing to ecological and energy savings. However, although DSS have been used successfully in many applications the last decades, the full utilisation in pressure vessels has been restricted due to conservative design rules. The consequences of failure in a pressure vessel are often very severe and it is accordingly important to verify a high ductility and fracture toughness. The duplex stainless steels need for this purposes further testing and evaluation.
In this study fracture toughness data has been generated which has been used to analyse the brittle failure model in the European pressure vessel code EN 13 445. The evaluation of the fracture toughness results has been done successfully by the master curve analysis, previously applied to ferritic steels. Both the base and the weld material provide very high fracture toughness at tested temperatures (-60 to -105°C) and reference temperatures of-143°C and -101°C were obtained for the base and the weld material, respectively. The reference temperature is the temperature at which the fracture toughness is 100 MPaVm, which characterizes the onset of cleavage cracking.
Calculations of the heat distribution and the austenite reformation in the heat affected zone have been performed to theoretically verify satisfactory toughness properties in that zone. The reformed austenite fraction agrees with the fraction measured by microstructure analysis. Cooling DSS (2205) weldments (SAW) in air using ordinary welding parameters provides a satisfactory phase balance and avoidance of brittle intermetallic precipitates.
Keywords: duplex stainless steel, fracture toughness, brittle fracture, heat affected zone, austenite reformation
Dennis Andersson 2005-08-16