Effect of Thermal Aging on Microstructure and Mechanical Properties of P92 Steel

Microstructure and mechanical properties of P92 steel in the normalized and tempered, and thermal aged at 923 K for 5,000 h conditions have been investigated. Laves phase (size of similar to 0.160 mu m) was observed in the thermal aged steel. Tensile tests were carried out at a strain rate of 3 x 10(-4) s(-1) and in the temperature range of 300-923 K. Both in the normalized and tempered, and thermal aged conditions, yield stress and ultimate tensile strength of the steels were found to decrease with increase in test temperatures. Tensile strengths of the thermal aged steel were decreased significantly in all test temperatures in comparison with normalized and tempered condition. Tensile strengths of thermal aged steel decreased due to sub-structure recovery and loss of solid solution strengthening from tungsten. Creep tests were conducted at 923 K in the stress range of 130-110 MPa. Lower creep rupture life has been observed in the thermal aged steel than normalized and tempered steel at higher stress level. Creep rupture life of thermal aged steel was comparable with steel in the normalized and tempered condition at lower stress levels. The presence of Laves phase precipitates in thermal aged steel has compensated the creep strength decrement due to loss of tungsten and sub-structure recovery in the steel.