Splitting in dual-phase 590 high strength steel plates: Part II. Quantitative analysis and its effect on Charpy impact energy

The influence of splitting on Charpy impact energy was investigated by analyzing the primary fracture (from the Charpy V-notch) and splitting (secondary fracture) surfaces at different test temperatures quantitatively. The morphology of splitting at the primary fracture surface of Charpy impact specimens made of dual-phase (DP) 590 hot-rolled steel in TL direction at +60 °C and −30 °C were surveyed by scanning electron microscope (SEM). The broken Charpy impact specimens in both TL and LT directions at different test temperatures were studied by examining sliced images obtained from micro-radiography imaging system. Three-dimension (3D) and plane sliced images of specimens were analyzed using GEHC microview software. Results show that fracture appearance inside the splitting is cleavage. The length and depth of the splitting increased with decreasing test temperature. Splitting width decreased first then the trend becomes irregular when test temperature falls due to variation of steel ductility and reaction between splitting and the primary crack. The surface areas of splitting and primary crack changed with test temperature as well. Splitting area increased with decreasing test temperature, while the surface area of the primary crack decreased as the test temperature was lowered. Influence of splitting on the impact energy in upper shelf of DP590 hot-rolled steel is small. In the ductile-to-brittle transition temperature (DBTT) range, splitting tends to increase the Charpy impact energy and consequently reduced the DBTT of DP590 hot-rolled steel.