Influence of Keyhole Mode of Plasma Arc Welding on Microstructure and Mechanical Properties of Similar Butt-Welded Incoloy 800H

The keyhole mode of plasma arc welding (K-PAW) was employed to weld Incoloy 800H plates of 6 mm thickness. A nickel–chromium-based superalloy, Incoloy 800H is a fully austenitic face-centered cubic structure and imparts better tensile strength, fatigue strength, and creep properties at higher temperatures. Full-penetration weld was achieved by a single-pass welding, and no defects were observed in X-ray radiography testing. Microstructural studies revealed fine equiaxed dendritic structure present in the weld metals due to the steep temperature gradient induced by the K-PAW. Due to fine grain structure, no solidification cracking was observed in the weldment. Mechanical properties studies confirmed that weldments attained the minimal requirements of tensile strength, hardness, ductility, and toughness as per the boiler pressure vessel fabrication requirement norms.