Abstract
Choosing the appropriate heat treatment condition of large forging is important for reducing production cost and to guarantee the quality. This is due to the fact that the strength and the accuracy of large forging are greatly influenced by the residual stress. The residual stress is the stress that remains after the heat treatment and is the cause of cracks and reduces the lifetime of materials. The stress is brought about by strain that occurs due to phase transformation and unbalanced temperature distribution. The unbalanced temperature distribution is caused by the difference in cooling rates within the material. A method for quantitative evaluating the residual stress of large forging has not been fully established. In this research, the analytical cooling curves are determined by optimizing heat transfer coefficient between steel and the circumferential fluid, so the difference to the experimental cooling curves are minimized. Using the obtained cooling curves, residual stress is analyzed. Finite element analysis software ANSYS 13.0 is using. The parameters using in the analyses are temperature dependent considering phase transformation of austenite to bainite. The analytical results of the residual stresses compared to the experimental ones, and the validity is examined.
