The influence of warm rolling on the fracture toughness of bainitic steels

The effect of warm rolling on upper bainitic structures is to promote the development of a spherodized carbide structure and a clearly defined dislocation substructure. An investigation of the mechanical properties of as transformed and warm rolled structures in SAE 4340 steel revealed that the microstructural changes result in an increase in the strain to fracture and in fracture toughness for the plate thickness studied in this work. These factors are related using a simple model based on the critical strain to fracture. The detailed microstructural features are incorporated by examining the strain to cause void nucleation and growth at carbide particles in terms of their size shape and volume fraction.