Saarstahl AG, Völklingen, Germany:

Thome R., Dr. Eng., Head of Research and Development, Continuous Casting, ralf.thome@saarstahl.com 

Harste K., Dr. Eng., Chairman of the Voard

Richter K.-J., Dr. Eng., Head of Production of Liquid Phase

Ney G., Mag. Eng., Head of Casting Shop, LD-Steel Making

The production of steel grades with excellent mechanical and technological properties is under the existing cost pressure only possible if appropriate procedures are available to produce a solidification structure in the as-cast strand which is more homogeneous and largely free of segregation and defects. Internal quality of the as-cast billets is evaluated by different methods. Appearance and effects of center segregation and center porosities are displayed. Influence of mechanical soft reduction on the solidification process is shown as well as operational range end effectiveness of the soft reduction process are analyzed in the range between of solid fraction and liquid pool thickness in order to define centerline segregation index and crack index. Layout of the billet caster S0 and technical data for the mechanical soft reduction unit is observed. Chemical composition of the produced steel grades fabricated in soft reduction production process is compared and microstructure of the ball bearing steel 100Cr6 is presented for the cases with and without soft reduction. Process-dependent appearance of center segregation and level of center segregation for ball-bearing grade 100Cr6 are considered. The results presented in the following paper show that the mechanical soft reduction is a suitable technology to significantly improve center segregation and center porosity also in billet casting 150 mm х 150 mm. It is shown that for steels with carbon content in the range 0.3–1.0%, solidification structure becomes more uniform in comparison with conventional production and in its center area is close to the material structure produced by ingot casting.

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2. Ameling, D.; Litterscheidt, H.; Schwerdtfeger, K.; Senk, D.: Effect of sharp cooling on the structure and macrosegregation of continuously cast billets, Proc. 69. Steelmaking Conf. AIME-ISS, Warrendale, USA, 6.–9. April 1986, S. 387/95.

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4. Suzuki, M.; Kimura, K.; Kawami, A.; Mizutani, M.:  Rev. de Mét. CIT 89 (1992) Nr. 1, S. 83/92.

5. Isobe, K.; Kusano, Y.; Nogushi, S.; Ishiyama, K.; Yamanaka, A.; Horie, T.; Uehara, M.: Improvement of segregation of continuously cast billets by soft reduction, Proc. Intern. Sympos. on near–netshape casting in the minimills, Vancouver, Kanada, 19.–23. Aug. 1995, S. 179/92.

6. Ito, Y.; Yamanaka, A.; Wanatabe, T.: Rev. de Mét. CIT 97 (2000) Nr. 10, S. 1171/76.

7. Thome, R.; Harste, K.: steel res. 75 (2004) Nr. 10, S. 693/700.

8. Thome, R.; Harste, K.: ISIJ Intern. 46 (2006) Nr. 12, S. 1839/44.

9. Ney, G.; Korte, E.; Richter, K.; Rüppel, F.: The new billet caster S0 at Saarstahl AG Voelklingen, Proc. 5. Continuous Casting Conf., Nizza, Frankreich, 20.–22. Juni 2005, S. 374/81.

10. Thome, R.; Ostheimer, V.; Ney, G.; Rüppel, F.; Girgensohn, A.; Plociennik, U.; Schmitz, W.; Geerkens, C.; Becker, M.: stahl u. eisen 127 (2007) Nr. 2, S. 43/50.