Microstructure-Aided Analysis of Fatigue Thresholds in Duplex Stainless Steel
High fatigue threshold values of duplex ferritic-martensitic steels are interpreted by using a unified model of roughness- and plasticity induced crack closure. Complex metallographical and fractographical analysis was performed in order to obtain characteristics of tortuous crack paths produced by crack deflection and branching mainly at austenite/ferrite interfaces. Calculated values of effective thresholds are in a good agreement with experimental data. The total level of extrinsic toughening (closure + shielding) induced by the duplex microstructure was determined to be as much as 70% of measured fatigue threshold values. This is the main reason for the high resistance to propagation of long fatigue cracks in the near-threshold region.
J. Pokluda et al., "Microstructure-Aided Analysis of Fatigue Thresholds in Duplex Stainless Steel", Materials Science Forum, Vols. 567-568, pp. 101-104, 2008