Precipitate Characteristic of T91 Ferritic/Martensitic Steel During Short-Term Creep

The precipitates and their distribution characteristic of T91 heat resistant steel have an important influence on the service life of components. At the same time, tuning the precipitation and distribution of precipitates is also an important means to improve the properties. Ascertaining the growth behavior of precipitates is essential to tune their distribution and properties of materials more accurately. In the present study, the precipitate characteristic of T91 heat resistant steel during short-term creep at 650 °C was investigated using transmission electron microscope (TEM) and transmission Kikuchi diffraction (TKD). TEM results showed that M 23 C 6 carbide, Laves phase, MX carbonitride and modified Z phase would precipitate during short-term creep. Nanoscale MX carbonitrides are uniformly distributed within the matrix. The Laves phase grew gradually by consuming M 23 C 6 carbide during creep, which resulted in the Laves phase being larger than the M 23 C 6 carbide. However, a minority of Laves phases co-existing with M 23 C 6 carbides has also been found. On the other hand, TKD results showed the M 23 C 6 carbide and Laves phase precipitated at lath boundaries. In particular, Laves phase formed in the vicinity of the Cr-rich M 23 C 6 carbides and obeyed a specific orientation relationship with the M 23 C 6 carbide, i.e. , (110) M 23 C 6 // ( 10 1 ¯ 3 ) Laves and [ 03 3 ¯ 1] Laves// 1 1 ¯ 1 M 23 C 6 . Furthermore, M 23 C 6 carbide exhibits the double Kurdjumov–Sachs (DKS) relation with adjoining parent grains, and the Laves phase also demonstrates the near DKS relation with adjoining grains. The presence of these DKS/near DKS relations reduced the interfacial energy between the precipitate and two/three adjoining grains. Graphical Abstract