Abstract
AbstractThis 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 M23C6andσphase; 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 theβ′ 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 ofβ′ 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.
Highlights
In the electric utility industry, there is a growing demand for reduction of energy consumption and CO2 gas emission in power stations
This study investigated the evolution of precipitates and the change of micro-hardness of the TP347HFG
The matrix of TP347HFG was composed of the equiaxed austenite grains with the average size of nearly 22 μm, but the size of grains is heterogeneous, Table 1: The chemical composition of TP347HFG steel
Summary
In the electric utility industry, there is a growing demand for reduction of energy consumption and CO2 gas emission in power stations. Materials that possess the higher heat resistance are required to meet the demands of such severe service conditions [1,2,3]. 9% Cr ferritic heat-resistant steels, such as the T/P91 (9Cr–1Mo–V–Nb) steel and T/P92 (9Cr–0.5Mo–1.8W–V–Nb) steel, have been recognized as the ideal materials for USC components because they possess high creep resistance, good ductility, and corrosion resistance. When the service temperature was more than 620°C, it has been reported that there was limited resistance of 9% Cr steels to steam oxidation and gas-side corrosion. The austenitic heat-resistant steels often possess a higher Cr content (>18%) [4,5,6]; they have a stronger oxidation resistance, which could be employed at the high-temperature section of the pipeline system
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