Application of hydrostatic integration parameter for free-forging and rolling

Steel bars and billets may have pores at the center originating from solidification shrinkage in continuous or ingot casting. In this study, the authors discuss the integration of the hydrostatic stress, Gm, which is usually used in free forging, as a parameter to describe the closure of the center pores. The hydrostatic integration, Gm, is assessed in a model rolling experiment. It is found that the cross-sectional area of the pore was in proportion with the hydrostatic integration Gm in single-pass rolling. By introducing a coefficient C, the hydrostatic integration is modified, image, to reproduce the result of the industrial continuous rolling sequence. In this case, the value C is 0.024, and the threshold of the summation of image is 0.25. In addition, this new parameter image has been used to plan an industrial mill modification. The new pass schedule of larger image has been introduced to the plant successfully. It is confirmed that the new pass is effective to produce larger diameter bars without pores.