Effect of deformation modes and heat treatment on microstructure and impact property restoration of internal crack healing in SA 508 steel

摘要

In this study, the effects of deformation modes and quenching and tempering (Q&T) process on the crack healing and percentage recovery of impact properties were studied. The microstructure, Charpy impact properties and fracture surface morphology of the crack zones at different healing stages were evaluated. When the healing temperatures was 950 ℃ and 1050 ℃, percentage recovery of impact properties of the internal crack healing by multi-pass thermal deformation (twice upsetting and once drawing) was lower than that by uniaxial compression. After deformed by twice upsetting and once drawing at 1150 ℃, the 'Z type' newly formed grain belt was observed in the crack healing zone, which showed high resistance to the dynamic load. After Q&T process, the microstructure was evolved into the tempered bainite, and residual austenite decomposed gradually to carbides, precipitating out mainly along the grain boundaries. After Q&T process, the impact toughness of the crack healing zones were improved, but the percentage recovery decreased, it is because that in the crack healing zone, the carbides aggregated in the line, which has a lower resistance to applied force than the matrix.