Date

November 1981

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science

Institution

Oregon Graduate Center

Abstract

Electroslag weldments, while economically attractive, exhibit low impact toughness and lack of reliable non-destructive inspectability. The purpose of this investigation was to improve the reliability and integrity of electroslag weldments through control of welding process variables, improvements in as-welded microstructure and weld metal alloy additions. The influence of process variables including electrode position, slag level, welding current, voltage, guide tube geometry and joint spacing on A588 structural steel consumable guide electroslag weldments were investigated. Plate grounding and electrode positioning were critical to control the weld symmetry, and proper slag level maintenance was necessary to control the process stability and weld microstructure. The welding current vs. wire feed rate relationship was influenced by the guide tube design and joint spacing, and the use of a winged guide tube enabled lower welding voltages. The high current/narrow gap/winged guide tube weld provided a 50% reduction in specific heat input and heat affected zone width and a 67% reduction in weld time. Grain refinement in the as-welded condition was achieved by shielding the consumable guide tube with either a mullite or fused quartz sleeve combined with a supplemental vibration of the consumable guide tube in the case of mullite. Several other weld puddle agitation techniques were also studied. A hypothesis for the grain refinement mechanism is presented. Alloy additions were made through either elemental wires welded on to the guide tube or alloyed filler electrodes. Weld metal alloy additions provided a better control over the proeutectoid ferrite films bordering grain boundaries in standard welds. Both standard and fatigue precracked CVN toughness tests were carried out for several electroslag welds. Standard electroslag welds possessed least toughness at mid-thickness weld centerline location (4 ft.lbs. at 0°F). Crack propagation along proeutectoid ferrite films was observed. High current/narrow gap welds posted an improvement in mid-thickness weld centerline toughness (11 ft.lbs. at 0°F). Both grain refined and alloyed welds showed limited variations in toughness across their width. The high current/narrow gap weld made with chromium and molybdenum alloyed filler wire possessed much improved mid-thickness weld centerline toughness (17 ft.lbs. at 0°F). Optical, scanning and transmission electron microscopy were carried out for weld microstructure evaluations.

Identifier

doi:10.6083/M49C6VBH

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