Acta Metallurgica Sinica (English Letters) ›› 2015, Vol. 28 ›› Issue (10): 1238-1246.DOI: 10.1007/s40195-015-0318-5

• Orginal Article • Previous Articles     Next Articles

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

Zhi-Xin Xia1(), Chuan-Yang Wang2, Yan-Fen Zhao3, Guo-Dong Zhang3, Lu Zhang3, Xin-Ming Meng3   

  1. 1 Shagang School of Iron and Steel, Soochow University,Suzhou 215021, China
    2 School of Mechanical and Electric Engineering, Soochow University, Suzhou 215021, China
    3 Suzhou Nuclear Power Research Institute, Suzhou 215004,China
  • Received:2015-06-25 Revised:2015-08-13 Online:2015-09-25 Published:2015-10-20


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 M23C6 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.

Key words: Heat-resistant steels, Laves phase, Creep, Precipitation, Phase stability