Pre-study on centre defects and porosity in rolled and forged bars

Purpose and goal

The project has resulted in answers regarding causes for center defects during hot-rolling and open-die forging of bars. During production of larger dimensions, defects and porosities can remain throughout the production chain. In this study a literature survey, results from FE-analysis and practical trials on rolling and forging are presented. It identifies ways to improve the production and satisfy customer demands on improved quality and extended dimensional ranges.

Results and expected effects

This study shows how porosities and inclusions are the result of enrichment in segregated volumes, how segregations are related to the solidification process and how carbides are dissolved. Compression trials show how hydrostatic pressure causes plastic deformation of pores into closed void interfaces or cracks that can be healed through a self-diffusion process. An internal pore-closure index can be calculated to optimise the process. The expected result is that the casting process can be optimised and that critical rolling parameters to improve pore closure can be applied.

Approach and implementation

Within the project a committee was formed that included the executing and industrial partners. During a workshop the project was presented and then the industry informed about current problems within this field. The project planning regarding literature survey, industrial investigations and FE-analysis was settled. The tasks were distributed among the executing partners and the results were discussed within the committee. Finally, during a concluding workshop the results were presented to the industrial partners and these results are included in the final report of the project.