Development of ferritic weldments for grain-refined ferritic steels for 4. 2K service
The weldability of grain-refined ferritic nickel steels designed for structural use in liquid helium was investigated. Plates of interstitial-free Fe-12Ni-0.25Ti alloy and carbon-containing 9Ni steel were welded with 14Ni ferritic fillers using a gas tungsten arc welding (GTAW) process with pure argon gas shielding. The ferritic weldments made have a strength closely matching those of the base plates without a significant loss in base metal toughness at temperatures as low as 4.2K. The comparable toughness obtained in the welded region is attributed to three factors; the defect-free weldment, the chemical cleanliness of the GTAW weld deposit, and the in-process formation of an appropriate microstructure in the welded region. Special emphasis in this study was placed on changes in microstructures with respect to the characteristic of the weld thermal cycles and the effect of the resultant microstructures on low temperature toughness. In the heat-affected zone (HAZ) of multipass welded 9Ni steel, the retained (or precipitated) austenite is removed by the weld heat cycles but the sequential rapid heat cycles to successively lower peak temperatures associated with succeeding weld passes re-establish high toughness by sequentially refining the grain size and gettering carbon in the form of cementite precipitates. On the other hand, the high toughness in the HAZ of the 12Ni alloy and in the weld deposit is a direct consequence of repeated grain refinement through the overlapped austenitizing cycles and is not affected by the tempering cycles because of the carbon-free nature of these materials.
- Research Organization:
- California Univ., Berkeley (USA)
- OSTI ID:
- 6834351
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
IRON BASE ALLOYS
WELDABILITY
NICKEL ALLOYS
NICKEL STEELS
TITANIUM ALLOYS
ARGON
GAS TUNGSTEN-ARC WELDING
HELIUM
WELDED JOINTS
ALLOYS
ARC WELDING
ELEMENTS
FABRICATION
FLUIDS
GASES
IRON ALLOYS
JOINING
JOINTS
NONMETALS
RARE GASES
STEELS
WELDING
360101* - Metals & Alloys- Preparation & Fabrication