Probabilistic fracture toughness of a duplex stainless steel in the transition range

The fracture toughness of a 2205 duplex stainless steel (DSS) heavy section forged bar in the transition range (between 0 degrees C and -60 degrees C) was investigated. Experimental results were used to estimate the reference temperature T-0 and to define a Master Curve according to the ASTM E 1921-11 Standard. Following this Standard, that assumes the Weibull exponent b fixed and equal to 4, the reference temperature obtained using data at T=-60 degrees C is T-0=-110 degrees C; using data at T=-40 degrees C is T-0=-103 degrees C and using data at T=-20 degrees C is T-0=-110 degrees C. As the description of the experimental data distribution does not follow the theoretical Weibull slope of b = 4, the slope obtained by the best fit of the experimental data was also measured and its influence on the assessment of the toughness scatter in the transition range by the weakest link approach ascertained. The recalculated reference temperatures T-0 for the data at -60 degrees C, -40 degrees C and -20 degrees C are -114 degrees C (with b = 6.5), -107 degrees C (with b = 6), and -113 degrees C (with b = 4.8) respectively. Experimental data are well fitted by the Master Curve for all the chosen temperatures. Fracture mechanisms were also investigated by means of scanning electron microscope in order to discuss the application of the ASTM E 1921-11 Standard to duplex stainless steels whose microstructure is only partially ferritic and whose fracture transition does not result in a completely cleavage fracture at low temperatures because of the ductile behaviour of the austenite phase. (C) 2012 Elsevier Ltd. All rights reserved.