STUDY ON PREDICTION OF MECHANICAL PROPERTIES OF LARGE RING-SHAPED FORGING DEPENDING ON COOLING RATE

Large ring-shaped forgings manufactured by ring rolling, as heavy as 10 tons, are greatly affected by cooling. In the present study, controlled cooling was performed to improve the mechanical properties of large ring-shaped forgings. To quantify cooling rate, thermocouples were used to measure the cooling rate and the microstructures of the products were observed during still air cooling, fan cooling, mist control cooling, and water quenching. The temperature distribution measured in the four cooling methods was used to calculate the heat transfer coefficient in each cooling method by the inverse method. The mechanical properties were tested with specimens obtained from the test block for each cooling method, and continuous cooling transformation (CCT) curves were obtained by using measured microstructure contents. The mechanical properties of the regions corresponding to the regions of the specimens were calculated on the basis of the CCT curves and the heat transfer coefficients. The experimental values and the analytical values of the strength of the products manufactured by each cooling method were compared to verify that the mechanical properties at each region of the products depending on the cooling methods may be predicted