Assessment of thermal embrittlement in duplex stainless steels 2003 and 2205 for nuclear power applications

Abstract

Duplex stainless steels are desirable for use in power generation systems due to their attractive combination of strength, corrosion resistance, and cost. However, thermal embrittlement at intermediate homologous temperatures of ~475°C and below, limits upper service temperatures for many applications. New lean grade duplex alloys have improved thermal stability over standard grades and potentially increase the upper service temperature or the lifetime at a given temperature for this class of material. The present work compares the thermal stability of lean grade, alloy 2003 to standard grade, alloy 2205, through a series of isothermal agings between 260°C and 482°C for times between 1 and 10,000 hours. Aged samples were characterized by changes in microhardness and impact toughness. Additionally, atom probe tomography was performed to illustrate the evolution of the α-α′ phase separation in both alloys at select conditions. Atom probe tomography confirmed that phase separation occurs via spinodal decomposition for both alloys and identified the presence of Ni-Cu-Si-Mn-P clusters in alloy 2205 that may contribute to embrittlement of this alloy. The impact toughness model predictions for upper service temperature show that alloy 2003 may be viable for use in 288°C applications for 80 year service lifetimes based on a Charpy V-notch criteria of 47 J at room temperature. In comparison, Alloy 2205 should be limited to 260°C applications for the same room temperature toughness of 47 J. © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 Keywords: duplex stainless steels, 475°C embrittlement, spinodal decomposition, atom probe tomography 1.0 Introduction Duplex stainless steels (DSS) comprise a unique class of materials that possess desirable properties of both the face-centered cubic (austenitic) and body-centered cubic (ferritic) phases within their microstructures. The ferrite and austenite phases are present in roughly equal volume fractions,typically ranging from 30-70% ferrite. Relative to their austenitic counterparts, DSS tend to have higher strength, higher toughness, improved corrosion resistance (especially to localized corrosion), and exceptional resistance to halide stress corrosion cracking [1,2]. Additionally, their relatively low nickel content lowers the cost of these alloys and helps ensure price stability.DSS are widely used in chemical processing, desalination, pulp and paper, storage, and transportation industries due to their high strength and good corrosion resistance [1]. Components commonly manufactured from DSS include storage tanks, pipes, pressure vessels, heat exchangers, seawater systems, rotors, and structural members. However, DSS have had little application in power generation industries, in part due to concerns with thermal embrittlement. The thermal embrittlement that limits broader applications of DSS generally occurs at temperatures between 204°C and 538°C with a peak embrittlement rate near 475°C. ...

Effect of spinodal decomposition on the pitting corrosion resistance of Z3CN20.09M duplex stainless steel

“…A number of studies showed that the impact property of DSSs decreased significantly with increasing thermal aging time, and the hardness of the ferrite in the DSSs increased significantly . The studies confirm further that the Cr‐rich, Fe‐rich, and G phases formed during a spinodal decomposition process impede the dislocations movement and harm the plastic deformation ability of the DSSs, resulting in an increase and a decrease for the hardness and impact property, respectively.…”

Influence of Microstructure on the Corrosion Resistance of AISI 317L (UNS S31703)

“…It is worth noting that the Cr-rich precipitate produced by spinodal decomposition and the magnetic martensite produced by cold working are usually cited with the same symbol (α') [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] , but these are phases completely distinct. For this reason, in this paper, the Cr-rich precipitate produced by spinodal decomposition was called α 1 .…”

“…By using Reed and Schramm empirical formula, a SFE of ~ 63 mJ/m 2 is found for the AISI 317L 19 steel. Therefore, α'-martensite formation in this steel is expected to be ruled by reaction (5).…”

Martensitic transformation and fractographic analysis of lean duplex stainless steel during low temperature tension deformation

“…The grain refinement promoted by the duplex structure and the alloying elements provide higher mechanical strength than austenitic and ferritic grades such as AISI 304 and AISI430, respectively [1][2][3][4][5][6][7].…”