A macro- and micromechanics investigation of hot cracking in duplex steels

• Published in: Acta materialia Vol. 60; no. 11; pp. 4646 - 4660
• Main Authors: Martin, Guilhem, Yerra, Sampath Kumar, Bréchet, Yves, Véron, Muriel, Mithieux, Jean-Denis, Chéhab, Béchir, Delannay, Laurent, Pardoen, Thomas
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2012; Elsevier
• Subjects: Applied sciences; Chemical Sciences; Crack propagation; Cracking (fracturing); Damage; Duplex stainless steels; Essential work of fracture; Exact sciences and technology; Ferrite; Fracture mechanics; Fractures; High temperature deformation; Material chemistry; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Micromechanics; Microstructure; Steels; Strain; Micromechanics; High temperature deformation; Duplex stainless steels; Essential work of fracture; Crack propagation; Hot cracking; Temperature; Deformation; Austenitic ferritic steel; Rupture; Mechanical properties; High temperature; Stainless steel; Duplex stainless steel; Dual phase steel
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2012.03.040

The relationship between microstructure and high temperature ductile tearing in duplex stainless steels has been investigated. Several grades were considered corresponding to different chemical compositions, different volume fractions and morphologies of the ferrite and austenite phases and different oxide inclusion contents. The high temperature cracking resistance has been quantified using both the essential work of fracture (EWF) and the fracture strain. The EWF discriminates the different grades of duplex steels and the different microstructures in terms of hot tearing resistance better than does the fracture strain. Metallographic characterization reveals that damage preferentially nucleates near inclusions at the austenite/ferrite boundary. Voids grow inside the ferrite until they coalesce. Damage develops more rapidly when increasing either the mismatch of rheology between the phases, which was evaluated by micro-scale strain measurements, or the inclusion content. The cracking resistance is related to the plastic work performed in the fracture process zone whereas the fracture strain depends on the damage kinetics. Both processes involve length scales related to the morphology and to the microstructure dimensions. Guidelines for improving the hot cracking resistance of duplex steels are formulated.