ABSTRACT
This study aims to characterize the welds obtained by submerged arc welding using pulsed current in ultrasonic frequencies (above 20 kHz). To this end, welds were made on ASTM A36 carbon steel plates, varying the current and the frequency of the ultrasonic pulse in 25 to 50 A and 20, 50 and 80 kHz, respectively. Optical and scanning electron microscopy analysis were performed, as well as mechanical tests of Vickers hardness and Charpy. As a result, it was found that the use of ultrasonic pulse of current results in the appearance of side plates of secondary Widmanstätten ferrite in the melt zone while the HAZ-GG, besides the emergence of this microstructure it was grain growth with increasing frequency ultrasonic pulse. Regarding the results of Charpy tests at room temperature the energy absorbed in the impact has been increasing with increasing current amplitude and frequency of the ultrasonic pulse, while for the subzero temperature this increased level of absorbed average energy was noticeable only to the extent of 25 A. These results reinforce the hypothesis that the grain growth may be due to the slower cooling of the weld, while the microstructural changes, may be related to the effect of ultrasonic energy in the material.
Keywords:
Submerged arc; pulsed current; Ultrasonic frequencies; ASTM A36; Microstructural changes
