Fracture initiation by local brittle zones in weldments of quenched and tempered structural alloy steel plate
- Idaho National Engineering Lab., Idaho Falls, ID (United States)
- Bethlehem Steel Corp., PA (United States)
- Colorado School of Mines, Golden, CO (United States). Dept. of Metallurgical and Materials Engineering
The heat-affected zone (HAZ) embrittlement of an API 2Y Grade 50T quenched and tempered offshore structural steel plate, welded by the submerged-arc process at a heat input of 4.5 kJ/mm, was investigated from the viewpoint of identifying the local brittle zone (LBZ) microstructure and the metallurgical factors associated with its formation. Microstructural and fractographic analysis showed the LBZ microstructure to be dual phase martensite-austenite (M-A) constituent. The formation of M-A constituent was found to be related to microstructural banding of the hot-rolled base plate. When the banded base plate was welded, M-A constituent formed only within the band microstructure which penetrated the intercritically-reheated coarse-grain HAZ (IRCGHAZ). The chemistry of the band microstructure in conjunction with the thermal cycle of the IRCGHAZ provided the critical conditions for the formation of M-A constituent in the API 2Y Grade 50T steel investigated. The influence of local brittle zones (i.e., M-A constituent) on the HAZ fracture toughness was evaluated by means of Crack-Tip Opening Displacement (CTOD) tests. These tests showed the steel to suffer embrittlement when the fatigue precrack sampled an intercritically-reheated coarse-grain HAZ which contained M-A constituent, confirming that M-A constituent is the major microstructural factor controlling the HAZ toughness of this particular steel.
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC07-94ID13223
- OSTI ID:
- 566599
- Report Number(s):
- CONF-9606178-; TRN: IM9805%%210
- Resource Relation:
- Conference: 28. ASTM national symposium on fatigue and fracture mechanics, Saratoga Springs, NY (United States), 25-27 Jun 1996; Other Information: PBD: 1997; Related Information: Is Part Of Fatigue and fracture mechanics: 28. volume; Underwood, J.H.; Macdonald, B.D.; Mitchell, M.R. [eds.]; PB: 704 p.; ASTM special technical publication, 1321
- Country of Publication:
- United States
- Language:
- English
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