EFFECT OF LAVES PHASE PRECIPITATION ON REDISTRIBUTION OF ALLOYING ELEMENTS IN P92 STEEL
WANG Xue1,2(), LI Yong1, REN Yaoyao1, LIU Hongwei3, LIU Hong3, WANG Wei4
1 School of Power and Mechanics, Wuhan University, Wuhan 430072 2 Key Laboratory of Accoutrement Technique in Fluid Machinery & Power Engineering, Hubei Province, Wuhan University, Wuhan 430072 3 DongFang Boiler Group Co. Ltd., Zigong 643001 4 Electric Power Research Institute of Guangdong Power Grid Corporation, Guangzhou 510080
Cite this article:
WANG Xue, LI Yong, REN Yaoyao, LIU Hongwei, LIU Hong, WANG Wei. EFFECT OF LAVES PHASE PRECIPITATION ON REDISTRIBUTION OF ALLOYING ELEMENTS IN P92 STEEL. Acta Metall Sin, 2014, 50(10): 1203-1209.
The P92 steel specimens were aged at 650 ℃ for 0~5000 h, and precipitates of the aged specimens were extracted from the matrix using carbon extraction replicas and potentiostatic electrolysis. The amount of alloy elements in extracted precipitates was determinded by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and EDS, then the redistribution of alloying elements owing to Laves phase formation was analyzed. The hardness of aged specimens was taken using a Brinell hardness tester. The damage evolution equation owing to solute depletion was obtained from the redistribution characteristic of alloying elements and its influence on the creep life of P92 steel was evaluated based on the physical CDM model. The results are as follows. Before aging, about 86% contents of W and Mo in P92 steel are supersaturated in matrix and the remains are in M23C6 carbides. The removing of alloy elements take place due to the precipitation of Laves phase during aging. The formation of Laves phase consumes mainly W and Mo in matrix, and has little effect on the compositions of M23C6 cabides and MX carbonitrides precipitated before aging. The partition coefficients of these two elements supersaturated in matrix reduce up to 50% on the completion of Laves phase precipitation, and the Cr content in the matrix decreases about 3.6% because the formation of the Laves phase consumes Cr. The precipitation of Laves-phase contributes to the significant decreasing of solution hardening, causes the creep life of P92 steel reduction of about 24% at 650 ℃, 100 MPa.
Fund: Supported by National Natural Science Foundation of China (Nos.51074113 and 51374153) and Sichuan Province Fundamental Research Project (No.2013JY0123)
Fig.1 TEM images of precipitates in the replica of P92 steel as received (a) and aged at 650 ℃ for 500 h (b), 2000 h (c) and 5000 h (d) (Inset in Fig.1c shows the SAED pattern of Laves phase)
Aging time / h
Cr
Fe
Mo
W
500
14.50±1.72
47.97±1.45
8.54±0.79
28.95±1.04
2000
17.07±3.42
47.25±1.75
8.15±0.90
27.53±1.48
5000
13.46±2.15
49.36±1.59
8.12±0.56
29.06±1.28
Table 1 EDS analysis results of Laves phase in P92 steel aged at 650 ℃ for different times
Aging time / h
Cr
Fe
Mo
W
Mn
V
500
67.61±1.12
22.72±0.90
2.0±0.24
5.29±0.33
1.35±0.28
1.03±0.62
2000
68.09±1.80
22.41±1.37
1.91±0.16
5.40±0.36
1.41±0.24
0.78±0.27
5000
69.86±1.25
19.71±0.76
1.97±0.22
5.64±0.46
1.35±0.26
1.47±0.96
Table 2 EDS analysis results of metallic element of M23C6 carbides in P92 steel aged at 650 ℃ for different times
Aging time
V-rich MX
Nb-rich MX
h
V
Nb
V
Nb
500
89.52±4.95
10.48±2.71
30.11
69.89
2000
88.45±4.99
11.55±2.74
24.71
75.29
5000
88.30±8.05
11.70±4.41
28.28
71.72
Table 3 EDS analysis results of metallic element of MX carbonitrides in P92 steel aged at 650 ℃ for different times
Fig.2 Amount of extracted residues and alloy elements as a function of aging time for P92 steel at 650 ℃
Fig.3 Partition coefficient curves of Mo and W supersaturated in matrix of P92 steel aged at 650 ℃ for different times
Fig.4 Hardness curve of the steel P92 aged at 650 ℃ for different times
Fig.5 Comparison of creep curves of P92 steel with or without solute depletion damage (Applied stress is 100 MPa and temperature is 650 ℃)
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