Influence of heat treatment on the microstructure and mechanical properties of Alloy 718 base metal and weldments

Technical Report · Fri Jun 01 04:00:00 EDT 1979

DOI:https://doi.org/10.2172/6016371· OSTI ID:6016371

Mills, W J

Effect of heat treatment on the metallurgical structure and tensile properties of three heats of Alloy 718 base metal and an Alloy 718 GTA weldment were characterized. Heat treatments employed were the conventional (ASTM A637) precipitation treatment and a modified precipitation treatment designed to improve the toughness of the weldments. The GTA weldments were characterized in the as-welded condition. Light microscopy, thin foil, and surface replica electron microscopy revealed that the microstructure of this superalloy was sensitive to heat treatment and heat-to-heat variations. The modified aging treatment resulted in a larger grain size and a more homogeneous microstructure than the conventional treatments. The morphology of the primary strengthening ..gamma.. phase was found to be finer and more closely spaced in the conventionally treated condition. Room and elevated temperature tensile testing revealed that the strength of the conventionally treated alloy was generally superior to that of the modified material. The conventional aging treatment resulted in greater heat-to-heat variations in tensile properties. This behavior was correlated with variations in the microstructure resulting from the precipitation heat treatments. The precipitate morphology of the GTA weldments was sensitive to heat treatment. The Laves phase was present in the interdendritic regions of both heat-treated welds. The modified aging treatment reduced the amount of Laves phase present in the weld zone. Room and elevated temperature tensile properties of the precipitation hardened weldments were relatively insensitive to heat treatment, suggesting that reduction in Laves phase from the weld zone had essentially no effect on tensile properties. As-welded GTA weldments exhibited lower strength levels and higher ductility values than heat-treated welds.

• Research Organization: Hanford Engineering Development Lab., Richland, WA (USA)
• DOE Contract Number: EY-76-C-14-2170
• OSTI ID: 6016371
• Report Number(s): HEDL-TME-78-54
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE
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360103* -- Metals & Alloys-- Mechanical Properties
AGING
ALLOYS
ARC WELDING
CHEMICAL COMPOSITION
CHROMIUM ALLOYS
CRYSTAL STRUCTURE
DIAGRAMS
FABRICATION
FILLER METALS
FRACTURE PROPERTIES
GAS TUNGSTEN-ARC WELDING
HARDENING
HEAT TREATMENTS
INCONEL 718
INCONEL ALLOYS
JOINING
JOINTS
LAVES PHASES
MECHANICAL PROPERTIES
MICROSTRUCTURE
MODIFICATIONS
MOLYBDENUM ALLOYS
MORPHOLOGY
NICKEL ALLOYS
NICKEL BASE ALLOYS
NIOBIUM ALLOYS
PRECIPITATION HARDENING
SURFACES
TESTING
WELDED JOINTS
WELDING