Abstract
The effect of cold working on the creep rupture strength of Alloy617 was investigated. The creep rupture tests were conducted at temperatures of 700 to 800°C, under stresses from 100 to 350 MPa. At high stress conditions, the creep rupture time of the non-pre-strained samples are similar to those of the pre-strained samples. On the other hand, at low stress conditions, the creep rupture time of the pre-strained samples are longer than those of the non-pre-strained samples. The amount of precipitates near the grain boundaries in the pre-strained sample is higher than that in the non-pre-strained sample. Weak regions such as PFZ and recrystallization grains in the non-pre-strained sample are formed in the early stage of creep compared to the pre-strained sample. At low stress conditions, the precipitates near the grain boundaries in the pre-strained sample play an effective role to pin the grain boundaries and they delay the formation of the weak regions resulting in extension to the creep rupture time.
Highlights
For coal-fired power plants, the high temperature steam conditions are required for the reduction of CO2 emissions and high efficiency of the plants
No significant difference was seen in the creep rupture strength between the pre-strained and non-pre-strained samples
At low stress conditions, the pre-strained samples exhibited higher creep rupture strength compared to the non-pre-strained samples
Summary
For coal-fired power plants, the high temperature steam conditions are required for the reduction of CO2 emissions and high efficiency of the plants. It is reported that the creep strength is affected considerably by the precipitation of γ’ phase at temperatures below approximately 800°C [9,10,11,12] This alloy has high creep-rupture strength for up to 100,000 hours at 700°C and the strength is approximately 100 MPa. Ni based alloys have not been used in boilers far. There are some reports about the effect of cold working on creep rupture strength of ferritic heat-resistant steels and austenitic heat-resistant steels [15,16,17], but very few reports exist about that of Alloy617. The purposes of this paper are to clarify the effect of cold working on the creep rupture strength, the creep deformation behavior and the change in microstructure of pre-strained Alloy617. The pre-strained Alloy617 was prepared via interrupted tensile test and was used for the creep rupture and interruption tests
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