Microstructure and high-temperature tensile properties of HR3C heat- resistant steel after annealing at 650 ℃

Microstructure and high-temperature tensile properties of HR3C steel after annealing at 650 ℃ for long-time till 3000 h were studied. High-temperature tensile fracture mechanism of the annealed steel was also investigated. The results show that the hightemperature mechanical properties of the HR3C steel change remarkably with annealing time due to the comprehensive effects of grain boundary strengthening,dispersion strengthening of precipitated phases and weakening of austenite matrix by precipitation in the annealing process. In the initial annealing stage( 500 h),the high-temperature mechanical properties of the HR3C steel are nearly unchanged. As increasing the annealing time from 500 h to 1000 h,high-temperature tensile strength of the HR3C steel increases rapidly,however, plasticity of the steel decreases continuously. In the final annealing stage( 1000 h),microstructure of the HR3C steel does not change with the annealing time,so,both high-temperature strength and plasticity of the annealed steel remain to be unchanged. High-temperature tensile fracture mechanism of the HR3C steel changes from the normal mode to the shear mode as the annealing time increased.