Effect on properties and microstructure of bainitic steel crossing joint with thermit welding by normalizing

The properties and microstructure of normalized thermit welding heat-affected zone(HAZ) of bainitic steel crossing were investigated, by simulating different thermal curves in HAZ with a Gleeble-3500 thermal simulator. The simulated results show that the bainite structure can be regained in the thermit welding HAZ by 900 ℃ normalizing. After normalizing, the toughness is improved, the hardness is more uniform, and the tensile strength is reached closely to the level of base metal. Based on the thermal simulated result, bainitic steel crossing and U75V rail were welded by thermit welding. The results showed that, the hardness and tensile strength of the weld and soft zone in HAZ were significantly improved when the joint was normalized at 900 ℃, which was very important to the life of the joint.