GH690合金管材热处理工艺优化

以国外Inconel 690成品管的显微组织为参照对象,对国产GH690合金管材在不同工艺条件下的固溶处理与TT处理工艺进行了研究;采用OM、SEM和TEM等表征手段分析了工艺参数对其晶粒度、晶界碳化物形貌和贫Cr区的影响。结果表明:国产GH690合金管在固溶处理过程中,随着固溶温度的提高,尺寸较大晶粒所占比例逐渐升高,长大激活能为265 kJ/mol。当固溶温度超过1100℃时,保温时间对晶粒尺寸影响显著。国产GH690合金管析出细小半连续晶界碳化物的TT处理工艺参数为680℃/10~20 h,715℃/10~20 h,750℃/5~15 h。经1090~1110℃/5 min固溶处理以及715℃/10 h或15 h的TT处理后,国产GH690合金管晶粒尺寸分布、晶界碳化物形貌特征和贫Cr区演化特征与国外Inconel 690成品管非常相似;而其TiN颗粒数量和尺寸明显少于和小于后者,贫Cr区的最低Cr浓度高于后者。通过对显微组织特征的综合评价,表明国产GH690合金管的显微组织总体优于国外Inconel 690成品管。同时,兼顾实际生产中的成本问题,提出国产GH690合金管热处理工艺优化的建议。

Optimization on Heat Treatment Processes of GH690 Tubes

The solution treatment and thermal treatment (TT) processes of GH690 tube made in China were investigated with different processing parameters including temperature and time. The microstructural features, consisting of the grain size, carbide morphology along grain boundary and chromium-depleted zone of the investigated GH690 tube, were characterized through OM, SEM and TEM and evaluated based on Inconel 690 commercial tube. The results indicate that the proportion of large grains in the investigated GH690 tube increases gradually with increasing the solution temperature. The activation energy of grain growth is 265 kJ/mol. The influence of time on grain size becomes significant once the solution treatment is above 1100 °C. Thermal treatment processes for promoting the formation of fine semi-continuous carbides along grain boundaries are 680 °C/10~20 h, 715 °C/10~20 h and 750 °C/5~15 h. Similar microstructural features, including grain size, carbide morphology along grain boundaries and chromium depletion profile, are observed in both the investigated GH690 tube and the Inconel 690 commercial tube after solution treatment at 1090~1110 °C for 5 min followed by thermal treatment at 715 °C for 10 h or 15 h. Nonetheless, the size and density of TiN are lower and the minimum chromium content is higher in the investigated GH690 tube than those in the Inconel 690 commercial tube. Overall, microstructural features in GH690 tube made in China are superior to those in Inconel 690 commercial tube. The optimized heat treatment process is suggested based on microstructure analyses as well as the consideration of economic cost in production.