Microstructure and Mechanical Properties of the Weld Joint of Small Diameter Glass-Lined Metal Pipe with Inner Surface Layer

Abstract

The width of 36mm of inner surface layer was formed by Ni625 welding wires in the ends of glass-lined 20# metal pipe, and the metal tubes were welded. The microstructure and the distribution of the main alloying elements of the weld joints were analyzed by optical microscope (OM) and electron probe microscope analysis (EPMA). The mechanical property and nondestructive inspection tests of the welded joints were carried out. The results show that the welded joints were divided into three layers including root layer, transition layer and cap layer. The microstructure in root layer was characterized by the cellular-dendrite structure. The transition layer contained martensite and retained austenite. The capping layer included acicular ferrite and pearlite. The defect free joint was produced and performed well. The concentration of nickel and chromium element in weld root were higher than inner surface layer which proves that welding wire of transition layer protects the major alloying elements in welding root.