INFLUENCE OF MICROSTRUCTURE ON THE FRACTURE-TOUGHNESS AND FRACTURE TOPOGRAPHY OF A DUPLEX STAINLESS-STEEL

The effect of heat treatment on the fracture toughness and fracture topography of a duplex stainless steel has been studied. Samples treated above 1050-degrees-C exhibit just a slight decrease in toughness in good agreement with the metallographic and fractographic analyses. However, in those coupons annealed between 675 and 900-degrees-C a marked loss of toughness was detected. This embrittlement is maximum in samples treated at 825-degrees-C and has been associated with sigma phase precipitation clearly seen in the metallographic examination. Elongated splits of brittle walls are present in their fracture surfaces. Specimens treated at lower temperatures for short times show a certain decrease in toughness. The almost featureless surfaces of the fissures present in these samples suggest a delamination along the austenite-ferrite interfaces. Longer exposure times produce a greater loss of toughness and fracture morphologies similar to those in 825-degrees-C treated specimens. Treatment at 475-degrees-C produces an embrittlement attributed to alpha-prime phase.