J. Mater. Sci. Technol. ›› 2018, Vol. 34 ›› Issue (4): 720-731.DOI: 10.1016/j.jmst.2017.06.015
• Orginal Article • Previous Articles Next Articles
Xiongfei Wanga, Chendong Shaoa, Xia Liub, Fenggui Lua*()
Received:
2017-01-03
Revised:
2017-04-25
Accepted:
2017-06-08
Online:
2018-04-20
Published:
2018-05-04
Contact:
Lu Fenggui
Xiongfei Wang, Chendong Shao, Xia Liu, Fenggui Lu. Transition and fracture shift behavior in LCF test of dissimilar welded joint at elevated temperature[J]. J. Mater. Sci. Technol., 2018, 34(4): 720-731.
Material | C | Si | Mn | Co | Cr | Mo | Ni | V | S | P |
---|---|---|---|---|---|---|---|---|---|---|
CrMoV | 0.19-0.3 | 0.12 | 0.31-1.04 | - | 0.9-1.25 | 1.08 | 0.47-0.98 | 0.2-0.3 | 0.005 | 0.015 |
Modified 9Cr | 0.12-0.15 | ≤0.1 | 0.3-0.5 | 0.9 | 9-9.4 | 0.4-0.6 | 0.1-0.2 | 0.15-0.25 | ≤0.005 | ≤0.001 |
Filler metal | 0.11 | 0.12 | 0.51 | - | 2.67 | 1.02 | 0.13 | 0.27 | 0.001 | 0.0032 |
Table 1 Chemical composition of the base metals and the filler wire (wt%).
Material | C | Si | Mn | Co | Cr | Mo | Ni | V | S | P |
---|---|---|---|---|---|---|---|---|---|---|
CrMoV | 0.19-0.3 | 0.12 | 0.31-1.04 | - | 0.9-1.25 | 1.08 | 0.47-0.98 | 0.2-0.3 | 0.005 | 0.015 |
Modified 9Cr | 0.12-0.15 | ≤0.1 | 0.3-0.5 | 0.9 | 9-9.4 | 0.4-0.6 | 0.1-0.2 | 0.15-0.25 | ≤0.005 | ≤0.001 |
Filler metal | 0.11 | 0.12 | 0.51 | - | 2.67 | 1.02 | 0.13 | 0.27 | 0.001 | 0.0032 |
Welding current (A) | Welding Voltage (V) | Welding speed (mm/min) | Heat input (kJ/cm) | PWHT Temperature (°C) | PWHT Holding time (h) |
---|---|---|---|---|---|
500 | 30 | 600 | 15.0 | 560 | 30 |
Table 2 Parameters for NG-SAW process and PWHT process.
Welding current (A) | Welding Voltage (V) | Welding speed (mm/min) | Heat input (kJ/cm) | PWHT Temperature (°C) | PWHT Holding time (h) |
---|---|---|---|---|---|
500 | 30 | 600 | 15.0 | 560 | 30 |
Fig. 1. Schematic of the dissimilar welded joint and fatigue test specimen: (a) specimens for LCF test and microstructure observation chipped from the welded joint; (b) geometry of the specimen for LCF test.
△εp/2 | σ′f(MPa) | b | ε′f | c | n′ | K′ |
---|---|---|---|---|---|---|
<0.15% | 901.12 | -0.104 | 24.67 | -2.110 | 0.067 | 478.5 |
≥0.15% | 901.12 | -0.104 | 12.77 | -0.622 | 0.184 | 599.8 |
Table 3 Fatigue parameters determined by the modified fitting.
△εp/2 | σ′f(MPa) | b | ε′f | c | n′ | K′ |
---|---|---|---|---|---|---|
<0.15% | 901.12 | -0.104 | 24.67 | -2.110 | 0.067 | 478.5 |
≥0.15% | 901.12 | -0.104 | 12.77 | -0.622 | 0.184 | 599.8 |
Fig. 5. Microstructure across the modified 9Cr/CrMoV dissimilar welded joint: (a) overall microstructure of the dissimilar welded joint; (b) detailed microstructure of CrMoV-BM; (c) detailed microstructure of 9Cr-BM; (d) microstructure of WM; (e) detailed microstructure of the fine grain zone in WM.
Fig. 6. Microstructure of the HAZ in CrMoV side: (a) overall microstructure of CrMoV-HAZ; (b) detailed microstructure of over-tempered zone; (c) detailed microstructure of fine grain zone; (d) detailed microstructure of coarse grain zone.
Fig. 7. Microstructure of the HAZ in modified 9Cr side: (a) overall microstructure of 9Cr-HAZ; (b) detailed microstructure of fine grain zone; (c) detailed microstructure of coarse grain zone; (d) carbon-enriched zone between the 9Cr-HAZ and WM.
Fig. 8. Specimen failed at CrMoV-BM at 500 °C at △εt/2 = 0.35%: (a) fracture location, (b) optical image adjacent to the fracture location, (c) microstructure near the fracture location.
Fig. 9. Specimen failed at CrMoV-HAZ at 500 °C at △εt/2 = 0.5%: (a) fracture location, (b) optical image adjacent to the fracture location, (c) microstructure near the fracture location.
Fig. 10. Microhardness distribution of the 9Cr/CrMoV dissimilar welded joint: (a) before the test; (b) microhardness comparison on CrMoV side of specimen before test, after test at △εt/2 = 0.35% and 0.5%; (c) the corresponding locations of the microhardness measurement.
Fig. 11. Fracture morphology of the specimen failed at CrMoV-BM at △εt/2 = 0.35%: (a) the overall micrograph of the fracture surface; (b) magnified micrograph of the a surface crack initiation; (c) fatigue striations near the multiple surface crack initiation sites; (d) magnified micrograph of the internal crack initiation; (e) internal inclusion in higher magnification; (f) fatigue striations near the internal crack initiation.
Fig. 12. Fracture morphology of the specimen failed at CrMoV-OTZ at △εt/2 = 0.5%: (a) the overall micrograph of the fracture surface; (b) magnified micrograph of the surface crack initiation; (c) fatigue striations induced by surface crack initiation; (d) internal inclusion in the ultimate fracture area; (e) internal inclusion in higher magnification; (f) dimples near the internal inclusion.
Fig. 13. (a-1) (a-2) Inverse pole figure, (b-1) (b-2) local misorientation maps, (c-1) (c-2) deformed grains fraction maps, (d-1) (d-2) strain contouring maps, (e-1) (e-2) the legend of deformed grains fraction, (f-1) (f-2) the legend of strain contouring for the sample at △εt/2 = 0.35% in OTZ and BM, respectively.
Fig. 14. (a-1) (a-2) Inverse pole figure, (b-1) (b-2) local misorientation maps, (c-1) (c-2) deformed grains fraction maps, (d-1) (d-2) strain contouring maps, (e-1) (e-2) the legend of deformed grains fraction, (f-1) (f-2) the legend of strain contouring for the sample at △εt/2 = 0.5% in OTZ and BM, respectively.
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