Effect of activating flux on the weld bead geometry and microstructure in TIG Welding of AISI 4140 steel

The Activated flux TIG (A-TIG) is an effective way for improving the penetration of TIG welding. This paper presents the effect of welding current and thickness of activating flux layer on the weld bead geometry. Three oxides Cu2O, ZnO and Cr2O3 were used to investigate the effect of activating flux on the weld bead geometry, microstructure and hardness of AISI 4140 steel. The effect of activated flux on metallurgical properties of the welds was discussed using result of scanning electron images and EDS graphs of the weld zone for welds with or without fluxes. Vickers microhardness tests with 500g force was performed. Experimental results showed that maximum depth of weld was obtained by using Cr2O3 activated flux but this flux can reduce the depth to width ratio of the beads. Zinc oxide powder causes arc spraying due to high humidity absorption, which is its intrinsic property. Copper oxide, even in small amounts, produces arc blow and does not have a significant effect on penetration depth. All welds had martensite microstructure. Despite the high percentage of carbon in the steel which weakens the weldability, applying ceramic powder on the surface improved the penetration depth and the depth-to-width ratio comparing to TIG.

Keywords:

42CrMo4 heat treatable low alloy steel , TIG welding , Weld geometry , Activated oxide flux.