Fabrication of graded surfacing layer for the repair of failed H13 mandrel using submerged arc welding technology

摘要

A graded surfacing layer for repairing a failed mandrel was prepared on the surface of H13 steel using the homemade flux-cored wires via submerged arc welding technology. The microstructure of the designed surfacing layer was controlled by modifying its chromium content based on the Fe-Cr binary phase diagram. The as welded microstructure, phases, chemical composition, microhardness and wear resistance of the resultant surfacing layer were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), direct reading spectrometry, Vickers hardness testing and dry sliding wear testing. These results showed that the surfacing sample could be divided into seven zones based on cross sectional micrographs of the substrate, sublayer, wear layer and four fusion zones. The sublayer consists of a large amount of ferrite, lower bainite and carbides, which showed the lowest microhardness of 237 HV0.2. The wear layer was composed of martensite, lower bainite, residual austenite and carbides with a microhardness of 356 HV0.2 that was 80 HV0.2 higher than that of the H13 steel substrate. The weight loss of the H13 steel substrate after wear testing for 20 min was 25.3 mg, which was around 1.7 times that of the wear layer (15.1 mg), whilst wear scar with smaller width and depth was observed on the surface of the wear layer. This indicates that the wear resistance of the wear layer was better than for the H13 steel substrate. No appreciable cracks were observed in the four fusion zones after the surfacing process, suggesting that good fusion had occurred between the H13 steel substrate, sublayer and wear layer.