Effect of microstructural evolution on high-temperature strength of 9Cr-3W-3Co martensitic heat resistant steel under different aging conditions

Evolution of microstructures and high-temperature strength at 650 degrees C of 9Cr-3W-3Co martensitic heat resistant steel after aging at 650 degrees C and 700 degrees C for different time durations have been experimentally investigated using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM) and post-aged tensile tests. The results show that after aging at 650 degrees C, the high-temperature strength and the microstructures of 9Cr-3W-3Co steel keep almost stable with increasing aging time from 300 h to 3000 h. In comparison, after aging at 700 degrees C, there are obvious changes in the high-temperature strength and the microstructures. The strengthening mechanisms of the 9Cr-3W-3Co steel were also discussed and the athermal yield stresses were calculated. The change of the high-temperature strength is mainly affected by the evolution of dislocations and laths. The precipitates mainly act as obstacles against motion of dislocations and lath boundaries. (C) 2013 Elsevier B.V. All rights reserved.