Dependence of Accelerated Creep Rate at 580 °C and Room Temperature Yield Stress for Two Creep Resistant Steels

Two creep resistant steels, P91 and X20, were tempered for 17520 h at 650 °C or 8760 h at 750 °C to study the growth and redistribution of carbide precipitates in martensite. On specimens annealed for a different time, yield stress at room temperature and accelerated creep rate at 580 °C were determined. With increasing yield stress in the range from 350 to 650 MPa the accelerated creep rate decreased continuously by about 2 orders of magnitude from 8·10^?7 s^?1 to 5·10^?9 s^?1. For equal yield stress, the creep rate was slightly lower for the steel P91 than for the steel X20.     

Effect of Microstructure on the Accelerated Creep of 20CrMoV12‐1 and P 91 Steels

In the initial part the change of microstructure for steel X20 CrMoV 121 is discussed in terms of the distribution of carbide precipitates and its effects on accelerated creep resistance and hardness are presented. In the following, experimental results of microstructure and accelerated creep resistance are presented for the steels X20CrMoV 121 and P91 annealed for up to 8760 hours at 650°C and 750°C before the testing. A similar evolution of the distribution of carbide particles of a size above 102 nm is found for both steels, while the accelerated creep resistance is diminished much stronger for the steel X20CrMoV 121. This difference is due to a greater stability of NbC than that of VC precipitates, both related to the evolution of the chemical composition of complex chromium, molybdenum and iron carbide particles.