Abstract: The P92 steel plate of 6 mm thickness was welded by plasma welding process. High-resolution scanning electron microscope with dynamic stretching table was used to examine the micro-cracking behavior of the welded joint. Fracture processes of welding joints were observed by in-situ tensile tests, and fracture mechanism was also analyzed. The results show that the microcracks initiated at the intermediate phase M23C6 after the earlier passivation zone, and the entire crack expansion path of the weld area was along the intermediate phase M23C6, forming a tea-ring ridge on the section. The fracture behavior of the welded zone was a translayer fracture morphologies. The heat-affected zone was the weakest area of the P92 welding joint, and microcracks initiated at the middle phase M23C6 without previous passivation, that is the extended length of the plastic crack in the early stage Xf=0. With loading increasing, the microcracks extended in the layer fracture mode and there was a layering phenomenon at the fault. The fracture behavior of the heat-affected zone was cleavage mode. After the in-situ tensile specimen in the base metal zone undergoed passivation stretch zone, the cracks propagated in a plastic fracture mode. As the expansion of the crack, there were many microvoid nucleated when the formation of stress concentration and the cracks propagating in the base metal changed from dimple fracture mode to shear fracture mode. The fracture behavior of the base metal zone was the layer fracture mode.
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2021, Vol. 35 
