Super304H耐热钢的热稳定性

Thermal stability of super304H heat-resistant steel

通过在650℃下直至3000h高温时效后的显微组织和力学性能的研究,评价Super304H耐热钢的热稳定性能。结果表明,供货态Super304H钢为奥氏体单相组织,高温时效后其中除奥氏体基体相外,还生成了ε富铜相、Nb(C,N)相和M7C3相。在时效初期,M7C3相大量在晶界析出,导致Super304H钢强度、硬度显著增加,但冲击韧性显著降低;随时效时间的延长,M7C3相逐渐粗化,在晶界处呈连续状分布,割裂基体,导致其强度、硬度及韧性降低。长期高温时效过程中ε富铜相和Nb(C,N)相在晶内持续析出且弥散分布,是Super304H耐热钢具有良好热稳定性的主要原因。

The thermal stability of heat-resistant steel Super304H was evaluated by microstructure observation and mechanical property testing after aging at 650 ℃ for times till 3000 h. The results indicate that the as-supplied Super304H steel is of single austenitic state. After aging, except austenitic phase, Cu-rich e-phase, Nb（C, N） and M7C3 are also formed. In the early aging stage, many M7C3 particles precipitate along the austenitic grain boundaries, leading to the increases of tensile strength and hardness, but the decrease of impact toughness of the steel, apparently. As the aging time increasing, the M7C3 particles gradually coarsen, continuously distribute along the austenitic grain boundaries, and separate the austenitic matrix, leading to the decreases of tensile strength, hardness and impact toughness of the steel. During long-term aging, the continuous precipitation and the dispersive distribution of Cu-rich e-phase and Nb（C, N） are beneficial to the thermal stability of Super304H steel.