HIGH TEMPERATURE CREEP DEFORMATION MECHANISM OF BSTMUF601 SUPERALLOY
SUN Chaoyang1(), SHI Bing1, WU Chuanbiao1, YE Naiwei2, MA Tianjun3, XU Wenliang3, YANG Jing1
1 School of Mechanical and Engineering, University of Science and Technology Beijing, Beijing 100083 2 Ningbo Baoxin Stainless Steel Co. Ltd., Ningbo 315807 3 Special Steel Business Unit, Baoshan Iron & Steel Co. Ltd., Shanghai 200940
Cite this article:
SUN Chaoyang, SHI Bing, WU Chuanbiao, YE Naiwei, MA Tianjun, XU Wenliang, YANG Jing. HIGH TEMPERATURE CREEP DEFORMATION MECHANISM OF BSTMUF601 SUPERALLOY. Acta Metall Sin, 2015, 51(3): 349-356.
Muffle tube is the core component in a large bright annealing muffle furnace. A lot of defects will be found on the muffle tube after long-term application under high temperature, self-weight and uneven temperature conditions, and among them creep deformation is serious, directly affecting the usability and life expectancy of muffle tube. High temperature creep and rupture properties are important indicators of the muffle tube material, and BSTMUF601 nickel-based superalloy materials are commonly used in a muffle tube. Because of good oxidation resistance at high temperatures, high strength and good creep resistance, nickel-base superalloy materials are taken seriously especially its creep mechanism. For different alloys or alloys in different conditions, the conclusions about creep mechanism are different. So the research of each alloy is necessary. Creep tests of BSTMUF601 superalloy for elevated temperature were carried out under different temperatures and stresses. The creep deformation characteristic of BSTMUF601 superalloy was investigated based on the creep curves. And then, a creep constitutive model for elevated temperature was proposed by introducing a modified θ projection method, which contained three stages of creep. The predicted results by using the model are in good agreement with the experimental results. The average relative error of the model fitted is 1.86%. Compared with the model ignored the second stage of creep and the model ignored the first stage of creep, the average relative error is reduced 0.10% and 6.02%, respectively. It is indicated that the model will be a wider range of application whereas the prediction precision is not reduced. Dislocation structure and its distribution for creep specimens and void evolution for creep rupture specimens have been carried by analyzing the microscopic structure. The results show that the creep stress index is close to 5 during the steady-state creep stage for different temperatures. The dislocation climb mechanism controlls the creep deformation process. There is no stacking fault or microtwin observed in phase or matrix. Cracks originate from the cavities at grain boundary and along the boundary, which lead to fracture. Grain boundary fracture is the main creep rupture mechanism.
Fund: Supported by National Natural Science Foundation of China (Nos.50831008 and 51105029) and National Science and Technology Major Project (No.2014ZX04014-51)
Fig.1 Microstructures of BSTMUF601 alloy before creep (a) and crept at 1095 ℃ under applied stress of 5.7 MPa (b)
Fig.2 Experimental and predicted creep curves of BSTMUF601 alloy crept at 1095 ℃ (a), 980 ℃ (b) and 870 ℃ (c) under different applied stresses
Fig.3 Predicted creep curves with different models compared with experimental results of BSTMUF601 alloy crept at 1095 ℃ under applied stress of 7.7 MPa
Creep temperature
Creep stress
Steady creep rate
℃
MPa
10-2 h-1
1095
5.7
0.00855
1095
6.7
0.02180
1095 980 980 980
7.7 12.4 14.4 16.4
0.03690 0.06800 0.10000 0.25000
870
20.0
0.01300
870
32.0
0.18000
870
40.0
0.45000
Table 1 Steady-state creep rates of BSTMUF601 alloy at different conditions
Fig.4 lnε?s - lnσ curves of BSTMUF601 alloy at differenttemperatures(σ—appliedstress, ε?s —seady-state creep rate, n—creep stress index)
Fig.5 TEM images of BSTMUF601 alloy crept at 1095 ℃ under applied stress of 5.7 MPa
(a) dislocation in γ matrix (b) dislocation tangle (c) dislocation pile-up around γ′ particles (d) dislocation climb
Fig.6 OM image of BSTMUF601 alloy crept at 870 ℃ under applied stress of 32 MPa after creep rupture
Fig.7 Morphologies on the longitudinal (a, b) and cross (c, d) sections with cavity nucleation (a, c) and microcrack (b, d) at grain boundaries near the fracture of BSTMUF601 alloy crept at 1095 ℃ under applied stress of 7.7 MPa
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