EFFECTS OF WELDING VARIABLES ON PROPERTIES OF SUBMERGED ARC WELDS

Abstract

This study was carried out to investigate the effects of welding variables such as voltage, cunent & speed in terms of heat input and to clarify the influence of titanium in weld metals, added in a form of Fe-Ti to the flux during submerged welding process, on structure and properties of boron micro- alloyed steel welds. Two welding conditions have been carried out, first welding condition was performed with varying heat inputs and without the addition of titanium to the flux, second welding condition was prepared with varying heat inputs as that were used in the first condition and with the addition of titanium to the weld metal via the flux. Radiography (using Gamma rays) of the weldments has been done to be sure that they are free of discontinuities and other internal defects. The heat input 840 Jlmm showed lack of penetration while heat inputs 1260 & 1320 Jlmm showed severe under cut and burn through respectively. Chemical composition of the weld metal, mechanical tests and metallographic investigation were carried out. The results showed increase in manganese, silicon and titanium content in the weld metals with the increase of heat input. Hardness and toughness increased with the increase in heat input and they were higher in case of adding titanium to the weld metal. An increase in acicular ferrite with increasing heat input was observed. The percentage of acicular ferrite was higher when titanium was added to the weldment. Addition of titanium to the weld metal enhanced the mechanical properties especially the toughness due to the formation of Ti- containing inclusions which work as nucleation sites for acicular ferrite formation and hence higher performance in lower temperatures.