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Title: Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments

Abstract

The microstructural features that influenced the room and elevated temperature fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination of fatigue fracture surfaces revealed that operative fatigue mechanisms were dependent on microstructure, temperatures and stress intensity factor. All specimens exhibited three basic fracture surface appearances at temperatures up to 538{degrees}C: crystallographic faceting at low stress intensity range ({Delta}K) levels, striation, formation at intermediate values, and dimples coupled with striations in the highest ({Delta}K) regime. At 649{degrees}C, the heat-treated welds exhibited extensive intergranular cracking. Laves and {delta} particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused on overall acceleration in crack growth rates at intermediate and high {Delta}K levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material was attributed to compressive residual stresses introduced by the welding process. 19 refs., 16 figs.

Authors:
;
Publication Date:
Research Org.:
Hanford Engineering Development Lab., Richland, WA (United States)
Sponsoring Org.:
USDOE; USDOE, Washington, DC (United States)
OSTI Identifier:
5493647
Report Number(s):
HEDL-TME-81-13
ON: DE91015594
DOE Contract Number:  
AC06-76FF02170
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; INCONEL 718; CRACK PROPAGATION; MICROSTRUCTURE; WELDED JOINTS; FATIGUE; HEAT TREATMENTS; LMFBR TYPE REACTORS; MICROSCOPY; REACTOR MATERIALS; STRESS INTENSITY FACTORS; ALLOY-NI53CR19FE19NB5MO3; ALLOYS; ALUMINIUM ADDITIONS; ALUMINIUM ALLOYS; BREEDER REACTORS; CHROMIUM ALLOYS; CORROSION RESISTANT ALLOYS; CRYSTAL STRUCTURE; EPITHERMAL REACTORS; FAST REACTORS; FBR TYPE REACTORS; HEAT RESISTANT MATERIALS; HEAT RESISTING ALLOYS; INCONEL ALLOYS; IRON ALLOYS; JOINTS; LIQUID METAL COOLED REACTORS; MATERIALS; MECHANICAL PROPERTIES; MOLYBDENUM ALLOYS; NICKEL ALLOYS; NICKEL BASE ALLOYS; NIOBIUM A; REACTORS; 360103* - Metals & Alloys- Mechanical Properties; 210500 - Power Reactors, Breeding; 360102 - Metals & Alloys- Structure & Phase Studies

Citation Formats

Mills, W.J., and James, L.A. Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments. United States: N. p., 1981. Web. doi:10.2172/5493647.
Mills, W.J., & James, L.A. Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments. United States. doi:10.2172/5493647.
Mills, W.J., and James, L.A. Fri . "Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments". United States. doi:10.2172/5493647. https://www.osti.gov/servlets/purl/5493647.
@article{osti_5493647,
title = {Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments},
author = {Mills, W.J. and James, L.A.},
abstractNote = {The microstructural features that influenced the room and elevated temperature fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination of fatigue fracture surfaces revealed that operative fatigue mechanisms were dependent on microstructure, temperatures and stress intensity factor. All specimens exhibited three basic fracture surface appearances at temperatures up to 538{degrees}C: crystallographic faceting at low stress intensity range ({Delta}K) levels, striation, formation at intermediate values, and dimples coupled with striations in the highest ({Delta}K) regime. At 649{degrees}C, the heat-treated welds exhibited extensive intergranular cracking. Laves and {delta} particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused on overall acceleration in crack growth rates at intermediate and high {Delta}K levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material was attributed to compressive residual stresses introduced by the welding process. 19 refs., 16 figs.},
doi = {10.2172/5493647},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri May 01 00:00:00 EDT 1981},
month = {Fri May 01 00:00:00 EDT 1981}
}

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