THE EFFECT OF WELDING PARAMETERS ON THE FRACTURE TOUGHNESS OF MANUAL METAL-ARC WELDED MILD STEEL PLATES

Abstract

Investigations have been carried out to find the influence of welding current on the fracture toughness values of mild steel weldments at ambient temperature. MMAW process was used to obtain full penetration welds in mild steel plates with compatible electrodes. Fracture toughness testing was conducted using a CT specimen as per ASTM specifications. From the tests carried out it is established that the fracture toughness of weld metal depends on the net heat input values. The fracture toughness decreases with increase in heat input values in the range of 929- 1320 .l/mm. The change in fracture toughness values has been attributed to the changes in microstructures of the fusion zone. As the plates used are quite thick and full penetration welding has been carried out by laying 8- 10 beads, keeping the interpass temperature the same as the ambient temperature, rate of cooling has been sufficiently high. It has been observed that the weld metal microstructure comprises of -a mixture of blocky ferrite, accicular ferrite, pearlite and martensite. The microstructure might also contain bainite which however could not be identified.