Papers by Author: Jian Xin Dong

Abstract: A 700 advanced ultra-supercritical (A-USC) power plant technology project was initiated in China in the year of 2011. The highest temperature components in A-USC boiler are superheater and reheater tubes. The fire-side metal temperature can reach 750 (even higher). Based on the very long time service (30-40 years) these important high temperature tubes require 10⁵h long time stress rupture strength higher than 100MPa and the corrosion/oxidation layer loss less than 2mm for 2×10⁵h. The highest temperature components in 700 steam turbine are the buckets of different stages and require very long service time. At this severe condition only superalloys can fulfill these unusual requirements. This paper reviewed Fe-Ni and Ni-base superalloys from the view point of structure stability and long term mechanical properties and corrosion/oxidation resistance for 700 A-USC power plant materials selection.

Abstract: The Cu-containing austenitic heat-resistant steel 18Cr-9Ni-3CuNbN has been widely used as superheater and reheater tube material for modern ultra-super-critical (USC) power plants in the world. High temperature structure stability is considered to be an important factor for long-term service. Long-term aging at 650°C for this steel was conducted from 100 to 10,000hours. Effect of aging time on microstructure was studied by means of SEM, TEM and 3DAP (three dimensional atom probe). Micro-hardness tests were carried out after aging at 650°C for different times to be considered as a representative of strength. Experimental results show that Cu-rich phase, MX and M23C6 are major strengthening precipitates in this steel. With on increasing of aging time, fine nano-size Cu-rich phase particles precipitate in the grains and its size is in the range of several nanometers to 35nm till 10,000h at 650°C. The fraction of MX also increases with aging time and its average size is about 100nm till 10,000h. Carbide M23C6 mainly precipitates at grain boundaries and coarsens quickly. Investigation results show that the most important strengthening effect for 18Cr-9Ni-3CuNbN steel is contributed by Cu-rich phase and MX in the grains and M23C6 carbide at the grain boundaries.

Abstract: Super304H, a Cu-containing 18Cr-9Ni-3CuNbN heat-resisting steel is wildly used as an superheater/reheater tube material for ultra-super-critical (USC) power plants all over the world. It is recognized that the Cu-rich phase is an important strengthening phase for Super304H. However, the detail precipitation behaviour and its strengthening effect are still not very clear. Investigated material was taken from routine production and was aged at 650°C for different times. The precipitation of Cu-rich phase in Super304H was studied by three dimensional atom probe (3DAP) and TEM. Experimental results show that Cu-rich clusters have been formed at very early stage of 650°C aging. The Cu-rich particle images have been clearly caught just after 650°C aging for 5h. The Cu atoms gradually concentrate to Cu-rich particles and the other elements (such as Cr, Ni etc) diffuse away from Cu-rich particles to γ-matrix with the increasing of aging time. The Cu-rich particle size and its density have been determined as a function of aging time. Cu-rich particles still keep nano-size and distribute homogenously in grains even after long time (1,000h) aging, which is one of the most important reasons for keeping good strength of Super304H heat-resistant steel at high temperatures.