Fracture toughness of the lean duplex stainless steel LDX 2101

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DUPLEX stainless steels (DSS) offer an attractive combination of properties, including high strength, excellent resistance to chloride stress corrosion cracking, and good weldability. The high strength of DSS enables both cost and weight savings and DSS are increasingly used as an alternative to conventional austenitic steels. Typical applications can be found in the chemical, offshore, oil, and gas industries. The mechanical properties of DSS are satisfactory but anisotropic. The anisotropic behavior of the tensile strength is a texture effect,[1] while the toughness also is influenced by the elongated phase distribution in the worked condition. LDX 2101 (EN 1.4162, UNS S32101) is a recently developed low alloyed (lean) DSS with low addition of nickel in order to reduce and stabilize the cost. The low nickel content is compensated by an increased amount of manganese and nitrogen to assure a balanced microstructure with approximately equal amounts of ferrite and austenite. The strength of this material is comparable with DSS 2205 (EN 1.4462, UNS S32205) and the corrosion properties are in general better than for austenitic 304 (EN 1.4301).[2] The low nickel content of the grade makes it important to verify satisfactory fracture toughness. The master curve method has been developed to determine fracture toughness in the brittle-to-ductile transition range.[3] The fracture toughness is described by only one parameter, T0, which characterizes onset of cleavage cracking at elastic or elastic-plastic instabilities. The master curve method provides a description for the fracture toughness scatter, size effect, and temperature dependence. This ¨ M, HENRIK SIEURIN, Postdoctoral Candidate, and ROLF SANDSTRO Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, S-100 44 Stockholm, Sweden. Contact e-mails: [email protected] and [email protected] ELIN M. WESTIN, Master of Science and IWE, is with Outokumpu Stainless AB, Avesta Research Centre, S-774 22, Avesta, Sweden. Manuscript submitted April 10, 2006. METALLURGICAL AND MATERIALS TRANSACTIONS A

method is the basis for the American testing and analysis standard ASTM E1921-97.[4] The aim of the current study was to analyze the fracture toughness properties of LDX 2101, for both base and weld materials.

II.

MATERIALS

The specimens were extracted transverse to the rolling direction of a 30-mm-thick hot-rolled plate. The material was solution treated at 1100 °C and quenched in water. The chemical composition of the base material can be found in Table I. The material was etched with a Murakami etching solution containing 7 g K3FE(CN)6, 15 g KOH, and 30 mL distilled water. The base material microstructure in the L- and S-planes can be found in Figure 1. The L-plane is perpendicular to the longitudinal (rolling) direction, the S-plane is perpendicular to the short-transverse direction, and the T-plane is perpendicular to the transverse direction. The etching solution colors the ferrite dark and the austenite white. The austenite fraction

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