Microharndess enhancement of steel weldments using mechanical oscillation of the welding joint

Mechanical vibration applied to solidifying metals is a proven method to create finer and uniform microstructure. However, its application toward welding of ferrous joints as those used in the oil and gas industry is not fully utilized. Several shielded metal arc welding (SMAW) experiments of mild steel plates were conducted at the following three levels of vibration frequency: 50 Hz, 500 Hz, and 5 kHz. Metallographic examination revealed that the average grain size of the center of the welds was reduced compared to the conventional welding by 29%, 11%, and 20% when vibration with frequencies of 50 Hz, 500 Hz, and 5 kHz were used respectively. The center of the welds recorded hardness in the range of 210-225 HV for the 50 Hz vibrated welds, 205-219 HV for the 500 Hz vibrated welds, and 200-235 HV for the 5 kHz welds against 180-190 HV for the unvibrated welding samples.