Degradation Characteristics of Microstructure and Mechanical Properties for 9Cr-1MoVNb Steel aged under High-Temperature

Thermal aging was conducted at 650 degrees C until 1,000 h under the atmospheric environment to evaluate the degradation characteristics of microstructure and mechanical properties of 9Cr-1MoVNb steel. The analysis of the microstructure and carbide of aged specimens was conducted by scanning electron microscopy and energy dispersive X-ray spectroscopy. The mechanical properties were evaluated by tensile and Vickers hardness tests. In addition, fractured tensile specimens were characterized by using scanning electron microscopy and energy dispersive X-ray spectroscopy to observe the changes in fracture mode with aging time. As a result, loss of martensite lath, coarsening of M23C6 carbide, and precipitation of Laves phase were observed after aging for 100 h. Degradation leads to deterioration in mechanical properties due to the effect of the nucleation and coarsening of Cr-rich M23C6 carbide. However, the change in fracture mode was more affected by the Laves phase (Fe2Mo) than the M23C6.