Repair Welding Procedure for P460NH Grade Steel Making Ladles

Abstract

P460NH steels are extensively used in steel plants as ladle fabrication material. However, fusion welding of these steels leads to the problems such as cold cracking, residual stress, distortion and fatigue damage, these steels may require welding of the cracks that can develop during fabrication, handling and transportation stages, or during the service life of the plant. Present work explains repair welding procedure used for P460NH steel ladles welded by using shielded metal arc (SMA) welding and flux cored arc (FCW) welding processes and evaluation of its weld metal and heat affected area (HAZ) microstructure. Butter bead tempered bead technique followed to fill the joint groove and simulated repair welding of SMA and FCA welds was carried out at the weld/base metal interface, i.e. at the location at which cracks are usually reported to occur during fabrication. SMA repair welding procedure conforming to the ASME Boiler and pressure Vessel Code were used followed by post heating of welds at 300°C for 2 hours per 25mm thickness of the weld. Tensile properties, bend tests, hardness profiles, impact tests and metallography studies using scanning electron microscope (SEM) were determined for both SMA and FCA welds to evaluate simulated repair welds. Analysis of the test results showed that the cooling rate maintained by means of preheating, interpass and post heating plays an important role in repairing of P460NH steel weld cracks.