Effect of aging temperature on phase decomposition and mechanical properties in cast duplex stainless steels

Abstract

The microstructure and mechanical properties in unaged and thermally aged (at 280 o C, 320 o C, 360 o C, and 400 o C to 4300 h) CF-3 and CF-8 cast duplex stainless steels (CDSS) are investigated. The unaged CF-8 steel has Cr-rich M 23 C 6 carbides located at the δ-ferrite/γaustenite heterophase interfaces that were not observed in the CF-3 steel and this corresponds to a difference in mechanical properties. Both unaged steels exhibit incipient spinodal decomposition into Fe-rich α-domains and Cr-rich α'-domains. During aging, spinodal decomposition progresses and the mean wavelength (MW) and mean amplitude (MA) of the compositional fluctuations increase as a function of aging temperature. Additionally, G-phase precipitates form between the spinodal decomposition domains in CF-3 at 360 o C and 400 o C and in CF-8 at 400 o C. The microstructural evolution is correlated to changes in mechanical properties.

Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels: Under Real Low-Temperature Service Conditions

“…[15,[23][24][25][26][27][28][29][30][31][32] With developments in both experimental and computational tools, it is now also more tangible to investigate the nanostructure evolution in duplex alloys quantitatively, even during the early stages of the PS phenomenon. [26,33] Phase separation in commercial grade duplex alloys [9,14,17,22,34,35] has only been investigated to a limited extent, especially for test conditions emulating operando conditions, i.e., low temperatures where the embrittlement takes years. [17,36] Furthermore, there is a lack of comprehensive bulk characterization of PS and often measurements are made on a limited volume of the material using techniques such as atom probe tomography.…”

Effects of Electromagnetic Stirring on the Cast Austenitic Stainless Steel Weldments by Gas Tungsten Arc Welding

“…When the spinodal decomposition occurs, the ferrites start to decompose into nano-meter scale Fe-rich (α-domains) phases, Cr-rich (α'-domains) phases, and G-phases [1,21,22]. With the formation of these phases, the ferrites become brittle and increase in hardness.…”

Determination of the phase-orientation relationship and a quantitative microstructure analysis for ASTM A351 stainless steel

“…No major difference can be observed between the non-aged and aged conditions at this magnification. The differences can, however, be seen at much higher magnifications, at the nano level, inside the d-ferrite grains, observed under a high-resolution transmission electron microscope 15 or using atom-probe microscopy [6][7][8]16 due to the spinodal decomposition.…”

“…300°C), which are similar to the operating temperatures of the vital parts of a power plant's coolant system. 2,[4][5][6][7][8] The formation of two phases with the same crystal structure but different lattice parameters can cause high internal elastic stresses. This might be one of the reasons for a significant hardness increase and a decrease of the impact toughness.…”