Using Thermomechanical Conditioning Cycles to Improve Fracture Toughness of Low Carbon Steel

The improvement of material toughness has significant industrial applications. In this article, the thermomechanical conditioning (TMC) cycle (which involves simultaneous application of heat to a moderate temperature combined with a tensile load, followed by unloading and cooling to room temperature) was used to improve the fracture toughness of the material. Apparent fracture toughness (K a ) is denoted to represent the fracture toughness of cracked components after the application of TMC cycles. The TMC cycles result in a significant increase in the apparent fracture toughness (K a ) of AS 1548 grade 7-460R steel as compared to the fracture toughness (K IC ) of the original material. It is found that the improvement in the apparent fracture toughness of the material was due to the increase in plastic strain and the plastic zone size ahead of the crack tip that occurred after applying TMC. In this study, both the apparent and original fracture toughness (K a and K IC ) are evaluated using the cylindrical notched tensile (CNT) technique, which is considerably cost effective over the standard compact tension specimens (ASTM E399).