Laves Phase Formation and Its Effect on Mechanical Properties in P91 Steel

Abstract

Effect of Laves phase formation on mechanical properties in a pressurized T-junction of P91 steel pipe at 849 K for 58,000 h with 25.65 MPa vapor pressure was studied. Thermodynamic calculations had been performed by using the software Thermo-Calc to study the phase at equilibrium state. Counter plot of von Mises stress in the pipe during service life was calculated by finite element analysis to study the effect of the operated stress distribution on the evolution of Laves phase. The change in the microstructure and mechanical properties in the sites with different stress was also studied. The results indicated that the formation of Laves phase in P91 steel was a thermodynamically possible process due to enrichment of Mo and depletion of C adjacent to M 23 C 6 particles or along martensite lath and packet boundaries. The formation of Laves phase had a detrimental influence on the mechanical properties in P91 steel. The mean size of Laves phase would be significantly increased with increasing operated stress, leading to a reduction in tensile properties and impact energy. In particular, crack initiation energy and crack growth energy during impact test rapidly decreased with increasing the mean size and volume fraction of Laves phase.

Controlling microstructure and mechanical properties of Ti-V-Cr-Nb-Ta refractory high entropy alloys through heat treatments

“…The effect of Laves phase on the mechanical properties, beneficial or detrimental, mainly depends on the volume fraction and mean size of Laves phase in the RHEAs. With increasing mean size and volume fraction of Laves phase, crack initiation and crack growth would rapidly increase [48]. In this study, small cracks can be observed around the indentations employed for the 1200 °C homogenised Ti-V-Cr-Nb-Ta sample, but not for the 800 °C homogenised Ti-V-Cr5-Nb-Ta sample, Fig.…”

Development of Oxidation Resistant Refractory High Entropy Alloys for High Temperature Applications: Recent Results and Development Strategy

“…These converse effects of the Cr additions on strength/ductility were attributed by the authors to the formation of the Laves phase that is expected from the thermodynamic point of view [6,7]. Several studies have clearly proven that the Laves phase is inherently brittle at lower temperatures [8,9]. In a very recent study, Senkov et al investigated the microstructure and mechanical properties of the alloy Al-Mo 0.5 -Nb-Ta 0.5 -Ti-Zr [10].…”

Laves phase formation in Fe-based alloys from strengthening particle to self-healing agent: a review

“…Most of the factors influencing precipitation strengthening depend on the particle size obtained during the nucleation and growth stages [90]. On the other hand, during exposure to high temperatures under constant load, high chromium ferritic steels have been found to have high intermetallic stability, unlike the rapid growth observed in 9%-12%Cr ferritic/martensitic steels.…”

“…On the other hand, during exposure to high temperatures under constant load, high chromium ferritic steels have been found to have high intermetallic stability, unlike the rapid growth observed in 9%-12%Cr ferritic/martensitic steels. In both cases, the creep conditions tend to increase the diffusion of the elements that form Laves-phase, affecting the growth and coarsening of the particulate, decreasing the anchoring on the high-angle grain boundaries [90,91]. Initially, the fine Laves-phase adopt the shape of a needle, maintaining a semi-coherent (or coherent) interface with the matrix.…”