Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds

Pertti Aaltonen, Hannu Hänninen, Anssi Brederholm, Aki Toivonen, Ulla Ehrnsten

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

Abstract

Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulfate and fluoride at 400 °C. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. High susceptibility to crack initiation and growth was observed with Alloy 182 and 82 weld metals, while Alloy 152 and 52 weld metals showed high resistance to crack initiation. No extension of the hot cracks was observed in the doped steam test in any of the studied materials. Fractography of the broken Alloy 182 and 82 samples showed both nickel deposition and presence of NiO in addition to the continuous spinel type Cr-rich oxide film on the fracture surface inside the crack. Fracture path was intergranular in all the studied samples. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FE-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed.
Original languageEnglish
Title of host publicationBaltica VIII
Subtitle of host publicationLife Management and Maintenance for Power Plants
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Pages384-400
Volume1
ISBN (Electronic)978-951-38-7592-3
ISBN (Print)978-951-38-7591-6
Publication statusPublished - 2010
MoE publication typeB3 Non-refereed article in conference proceedings
EventBALTICA VIII - International Conference on Life Management and Maintenance for Power Plants - Helsinki-Stockholm, Finland
Duration: 18 May 201020 May 2010

Publication series

SeriesVTT Symposium
Number264
ISSN0357-9387

Conference

ConferenceBALTICA VIII - International Conference on Life Management and Maintenance for Power Plants
CountryFinland
CityHelsinki-Stockholm
Period18/05/1020/05/10

Fingerprint

Dissimilar metals
Welds
Crack initiation
Metals
Fractography
Steam
Cracks
Nickel
Metallography
Oxide films
Solidification
Energy dispersive spectroscopy
Crack propagation
Hydrogen
Microstructure
Scanning electron microscopy

Cite this

Aaltonen, P., Hänninen, H., Brederholm, A., Toivonen, A., & Ehrnsten, U. (2010). Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds. In Baltica VIII: Life Management and Maintenance for Power Plants (Vol. 1, pp. 384-400). Espoo: VTT Technical Research Centre of Finland. VTT Symposium, No. 264
Aaltonen, Pertti ; Hänninen, Hannu ; Brederholm, Anssi ; Toivonen, Aki ; Ehrnsten, Ulla. / Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds. Baltica VIII: Life Management and Maintenance for Power Plants. Vol. 1 Espoo : VTT Technical Research Centre of Finland, 2010. pp. 384-400 (VTT Symposium; No. 264).
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abstract = "Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulfate and fluoride at 400 °C. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. High susceptibility to crack initiation and growth was observed with Alloy 182 and 82 weld metals, while Alloy 152 and 52 weld metals showed high resistance to crack initiation. No extension of the hot cracks was observed in the doped steam test in any of the studied materials. Fractography of the broken Alloy 182 and 82 samples showed both nickel deposition and presence of NiO in addition to the continuous spinel type Cr-rich oxide film on the fracture surface inside the crack. Fracture path was intergranular in all the studied samples. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FE-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed.",
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Aaltonen, P, Hänninen, H, Brederholm, A, Toivonen, A & Ehrnsten, U 2010, Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds. in Baltica VIII: Life Management and Maintenance for Power Plants. vol. 1, VTT Technical Research Centre of Finland, Espoo, VTT Symposium, no. 264, pp. 384-400, BALTICA VIII - International Conference on Life Management and Maintenance for Power Plants, Helsinki-Stockholm, Finland, 18/05/10.

Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds. / Aaltonen, Pertti; Hänninen, Hannu; Brederholm, Anssi; Toivonen, Aki; Ehrnsten, Ulla.

Baltica VIII: Life Management and Maintenance for Power Plants. Vol. 1 Espoo : VTT Technical Research Centre of Finland, 2010. p. 384-400 (VTT Symposium; No. 264).

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

TY - GEN

T1 - Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds

AU - Aaltonen, Pertti

AU - Hänninen, Hannu

AU - Brederholm, Anssi

AU - Toivonen, Aki

AU - Ehrnsten, Ulla

PY - 2010

Y1 - 2010

N2 - Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulfate and fluoride at 400 °C. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. High susceptibility to crack initiation and growth was observed with Alloy 182 and 82 weld metals, while Alloy 152 and 52 weld metals showed high resistance to crack initiation. No extension of the hot cracks was observed in the doped steam test in any of the studied materials. Fractography of the broken Alloy 182 and 82 samples showed both nickel deposition and presence of NiO in addition to the continuous spinel type Cr-rich oxide film on the fracture surface inside the crack. Fracture path was intergranular in all the studied samples. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FE-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed.

AB - Environment-assisted cracking (EAC) susceptibility of dissimilar metal mock-up welds of Alloy 182 and 82 as well as Alloy 152 and 52 were studied with four-point bending specimens in steam doped with hydrogen, chloride, sulfate and fluoride at 400 °C. The doped steam environment accelerated the crack initiation process and the susceptibility of the studied weld metals to EAC was obtained and ranked. High susceptibility to crack initiation and growth was observed with Alloy 182 and 82 weld metals, while Alloy 152 and 52 weld metals showed high resistance to crack initiation. No extension of the hot cracks was observed in the doped steam test in any of the studied materials. Fractography of the broken Alloy 182 and 82 samples showed both nickel deposition and presence of NiO in addition to the continuous spinel type Cr-rich oxide film on the fracture surface inside the crack. Fracture path was intergranular in all the studied samples. The same dissimilar metal welds were exposed to Varestraint hot cracking tests and their hot cracking susceptibility was also ranked and determined as a function of the amount of strain. The microstructures of the weld metals were fully characterized by optical metallography and a modern FE-SEM/EDS system. Hot cracking susceptibility was related to the solidification mechanism and segregation of Nb, Si, P and Mn in the weld metals. Fractography of the EAC and hot cracks was compared and their characteristic features are demonstrated. Finally, the mechanisms of hot cracking and EAC of nickel-base alloy dissimilar metal welds are identified and discussed.

M3 - Conference article in proceedings

SN - 978-951-38-7591-6

VL - 1

T3 - VTT Symposium

SP - 384

EP - 400

BT - Baltica VIII

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Aaltonen P, Hänninen H, Brederholm A, Toivonen A, Ehrnsten U. Environment-assisted cracking and hot cracking of Ni-base alloy dissimilar metal welds. In Baltica VIII: Life Management and Maintenance for Power Plants. Vol. 1. Espoo: VTT Technical Research Centre of Finland. 2010. p. 384-400. (VTT Symposium; No. 264).