Innovative square cogging to enhance void closure efficiency during forging of continuously cast round blooms

The use of continuously cast round blooms as a substitute for cast ingots has attracted wide interest because it can improve yields and reduce operating costs through continuous operation. However, central voids and segregations, which are the most common internal defects in continuously cast round blooms, must be eliminated through the cogging process to ensure adequate mechanical properties. In general, because the diameter of a round bloom is not large owing to the limited facility capacity, the permissible amount of forging reduction may be insufficient to completely close the internal defects. Accordingly, it is necessary to apply a more efficient cogging method to eliminate internal defects, particularly central voids, in a round bloom. Therefore, an innovative square cogging process using a square-shaped billet was implemented in this study to concentrate deformations within the central region of a Ø 1000 mm round bloom. A comparison of shop-floor operations between round and square cogging processes for the manufacture of main shafts shows that the square cogging operation noticeably increases the void closure efficiency with a reduced number of forging blows. Furthermore, the square-cogged products show improved mechanical properties as a result of the enhanced forging effect. Finite element simulations of the square cogging process also confirm the experimental results and validate the feasibility of the square cogging process.