富C和富(Al,Ti)的617B合金750℃时效组织与硬度及冲击吸收能量的研究

Study on Microstructure,Hardness and Impact Energy Absorption of Alloy 617B with High Content of C/(Al,Ti) After Being Aged at 750℃

研究了C和(Al,Ti)质量分数不同的2种617B合金在750℃时效5 000h、7 500h和10 000h后的硬度和冲击吸收能量。利用OM和SEM/TEM观察其显微组织并结合EDS+MPST方法进行相定量分析。结果表明:与Al、Ti质量分数较高的合金B相比,C质量分数较高的合金A固溶处理后晶粒较细,沿晶界析出的M23C6相连续分布,其冲击吸收能量较低。5 000～10 000h时效后,合金A的γ′相体积分数虽然较低,但晶内均匀分布极细条状M_(23)C_6相和γ′相的复合组织,其硬度基本不变;合金B中γ′相体积分数虽然较高,但仅在晶界附近分布有较少的M_(23)C_6相和γ′相的复合组织,其硬度明显降低;随时效时间的延长,合金A晶界上M_6C相略有增加,其冲击吸收能量较高。而合金B晶界上μ相明显增加,因此合金B的冲击吸收能量明显较低。晶界析出影响原始晶粒大小及其冲击吸收能量,而晶内均匀分布的M_(23)C_6相和γ′相的复合组织可提高其硬度的稳定性,C和(Al,Ti)的添加量对上述现象起决定性作用。

Hardness and Charpy energy absorption of two 617B alloys with different contents of C, A1 and Ti were investigated after being aged at 750℃ for 5 000, 7 500 and 10 000 hours, respectively. The microstructures were observed by OM, SEM and TEM, while their phase parameters were determined with the use of SEM/TEM-EDS＋MPST（multiphase separation technology）. Results show that compared with high A1/Ti-containing alloy B, the impact value of high C-containing alloy A is relatively samller with M23C6 phase continuously distributed along the finer grain boundaries after solution heat treatment. After being aged for 5 000-10 000 hours, alloy A with a relatively low volume fraction of γ′ phase basically keeps its hardness unchanged due to the existence of multiphase microstructure of very fine M23 C6 and γ′ particles distributed throughout the grain interiors; whereas alloy B with a relatively high volume fraction of γ′ phase has a significantly reduced hardness due to the lack of multiphase miscrostructure of Mza C6 and γ′particles in the vicinity of grain boundaries. With the rise of aging time, the amount of M6C phase increases slightly on the grain boundary of alloy A, while that of γ′ phase increases evidently on the boundary of alloy B, resulting in obviously reduced energy absorption of alloy B. In brief, the precipitates scattered along the grain boundary influence the grain size and then determine the impact energy absorption of the allong. In addition, the multiphase microstructure of M23C6 and γ′particles distributed throughout the grain interiors helps to keep the alloy hardness unchanged. It is evident that the contents of C6 A1 and Ti play a decisive role in the orignation and development of above phenomena.