This article reports the microstructure evolution in TP347HFG austenitic steel during the aging process. The experiments were carried out at 700°C with different aging time from 500 to 3,650 h. The metallographic results show that the coherent twin and incoherent twin are existed in the original TP347HFG grains, while they gradually vanished with the increase of the aging time. After aging for 500 h, a lot of fine, dispersed particles precipitated from the matrix, but they disappeared after aging for 1,500 h. When the aging time extend to 3,650 h, the precipitates appeared apparently coarse in TP347HFG steel, which include the M 23 C 6 and σ phase; besides, the micro-hardness of TP347HFG also changes during the aging, which was closely related to the effect of dispersion strengthening and solution strengthening. The results of the nonlinear ultrasonic measurement reveal that the β ′ of TP347HFG steel was also changed with the aging time. It first increased at 0–500 h, then reduced later, and increased finally at 1,500–3,650 h. The variation of β ′ in TP347HFG was influenced by a combined effect of the twin microstructure and the precipitate phase, which indicate that the nonlinear ultrasonic technique can be utilized to characterize the microstructure evolution in TP347HFG.

中文翻译：

---

TP347HFG奥氏体钢在700°C时组织演变的研究及其表征方法

本文报道了TP347HFG奥氏体钢在时效过程中的组织演变。实验在700°C下进行，老化时间从500到3,650 h不等。金相分析结果表明，原始TP347HFG晶粒中存在相干孪晶和不相干孪晶，但随着时效时间的增加逐渐消失。老化500小时后，许多细小的分散颗粒从基体中沉淀出来，但在老化1500小时后它们消失了。当时效时间延长到3,650 h时，TP347HFG钢中的析出物明显变粗，其中包括M 23 C 6和σ相。此外，TP347HFG的显微硬度在时效过程中也会发生变化，这与分散强化和固溶强化的效果密切相关。非线性超声测量结果表明，TP347HFG钢的β′也随着时效时间的变化而变化。它首先在0–500 h时增加，然后减少，最后在1,500–3,650 h时增加。孪晶组织和析出相的共同作用影响了TP347HFG中β'的变化，表明非线性超声技术可用于表征TP347HFG中组织的演变。