Effect of Chemical Compositions on Properties of Root Bead Surface in TIG Arc Welding

Effect of Chemical Composititons on Weldability in Fabrication in High Alloyed Steel (Report IV)

Abstract

The effects of chromium and silicon contents on the roughness of root bead surface in gas tungsten inert gas arc welding without inert gas backing was investigated from a point of view of the oxide layer formed on root bead surface. Test welding was carried out on plates containing various contents of chromium and silicon. The roughness of root bead surface was measured by observation of a cross section of weld metal. The thickness of the oxide layer was also measured and chemical compositions were analyzed by EPMA. The roughness of root bead surface increased in weld metals with higher chromium content as a result of the random formation of thick and porous oxide on the root bead surface. The increase of silicon content improved the roughness of root bead surface. The thickness of oxide on root bead surface was thinned by increasing the silicon content and the high silicon concentration was detected at the interface of oxide and the weld metal. From these results, the improvement of roughness of root bead surface by silicon was considered to be due by preventing the random growth of oxide by the formation of a dense silicon oxide layer as a barrier of oxygen diffusion at the interface of oxide and weld metal. The increase of roughness by increasing the chromium content was also considered to be caused by the formation of thick and porous oxide as a result of the prevention of the formation of uniform and dense oxide layer of silicon.