Steel Cleanliness Control and Fluid Flow in Continuous Casting Strands

Transcription

1 CCC ANNUAL MEETING June 15, 2006 UIUC Steel Cleanliness Control and Fluid Flow in Continuous Casting Strands Lifeng Zhang Professor at Dept. of Materials Sci. & Engr. Norwegian University of Science & Technology (NTNU) Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 1 Inclusions in Steel Dendritic alumina 10μm Alumina cluster Flower-like plate alumina Inclusions from mold flux 400μm Slag inclusions Refs: 1. T. B. Braun, J. F. Elliott and M. C. Flemings: Metal. Trans. B, (1979), 10B(6), L. Zhang, B. Thomas. ISIJ 2003, No.3, pp L. Zhang, B. Thomas, B. Rietow. Investigation of Ingot Inclusions Using Microscope and SEM. ISIJ, No.5, R. Dekkers, B. Blanpain and P. Wollants: Metall. mater. trans., (2003), 34B, 161. Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 2

2 Size and Sources of Inclusions in Steel Indigenous inclusions Exogenous inclusions Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 3 Wire Break due to Inclusions Typical inclusions (Al 13.40%, Si 44.24%, S 2.79%, K 11.28%, Ca 2.60%, Fe ) observed on weir break Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 4

3 Steel Cleanliness at Different Period Total oxygen in the steel at different steps T[ O]/ bef or e LF af t er LF t undi sh sl ab head sl ab dur i ng l adl e change slab steady st at e sl ab Tai l amount i ncl usi ons, mg/10kg stee bef or e LF af t er LF t undi sh t hi n sl ab >50µm inclusions at every step from ladle to slab Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 5 Casting Transition Control - Inclusion amount control - Transition duration control - Inclusion level should be more focused on unsteady casting state - Case 1 is better due to smaller transition duration and fewer inclusions Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 6

4 Cleanliness Variation due to Accidental Disruption of Mold Automatic Level Control Fig.9 ] Jacobi, 1998 Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 7 Slab/coil defects and the optimum steel meniscus velocities Dauby, 1998 Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 8

5 Mold Powder Entrainment and Critical Velocity for Entrainment Iguchi, 2002 Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 9 Powder Entrainment by Bubble Rupture (Water Models) Iguchi, 2002 Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 10

6 Critical Waves for Mold Slag Entrainment and Surface Velocity Suzuki, 2001 Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 11 EMBr on Inclusions and Bubbles in CC Slab Abbel, 1996 Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 12

7 Effect of SEN Outport Angle on Inclusion Removal (Inclusions) Speed (m/s) Down 15 o, no Steps up 15 o, no Steps Inclusion removal fraction to top (%) Down 15 o, 2 Steps step 0 15 SEN outport angle ( o ) - With more upwards SEN outport angle, more inclusions can be removed from CC mold; - Steps in SEN can help remove more inclusions from CC mold. Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 13 Particle Motion in SEN and CC Mold Conditions: - 300mm submergence depth m/min casting speed - no gas injection pathline 50μm inclusions 300μm inclusions Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 14

8 Speed (m/s) Turbulent energy dissipation rate (m 2 /s 3 ) Fluid Flow in SEN and CC Mold Conditions: - 300mm submergence depth m/min casting speed - no gas injection Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 15 Effect of SEN Submergence Depth on Inclusion Removal (Inclusions) Inclusion removal fraction to top (%) μm 200μm 50μm Submergence depth (mm) After some critical value of SEN submergence depth, inclusion removal from CC mold is independent of SEN submergence depth. Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 16

9 Effect of Casting Speed on Steel Cleanliness (Inclusions) 50μm 200μm 300μm Casting speed (m/min) Inclusion remaining fraction in the slab (%) Industrial Measurement ( 250μm inclusions), (Kodama, 1982) Simulation (Lifeng Zhang, 2006) With casting speed increasing, more > 50µm inclusions can be removed, and almost no removal of < 50µm inclusions Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 17 Steel Cleanliness under Casting Speed Variation - Casting speed decreases from 1.4 m/min to 0.6 m/min in 5 minutes with a variation rate of 0.15 m/min - Steel cleanliness in is detected by automatic 2D image analysis - Steel cleanliness is worse at larger casting speed (>1.2m/min) Q. Zhang, X. Wang and L. Zhang: Baosteel BAC 2006-The Second Baosteel Biennial Academic Conference, L.X. Qihua Xie, (2006), 1, Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 18

10 Steel Cleanliness under Casting Speed Variation - Casting speed increases from 0.6 m/min to 1.4 m/min in 5 minutes with a variation rate of 0.15 m/min - Steel cleanliness is detected by automatic 2D image analysis - Steel cleanliness is worse at larger casting speed (>1.2m/min) Q. Zhang, X. Wang and L. Zhang: Baosteel BAC 2006-The Second Baosteel Biennial Academic Conference, L.X. Qihua Xie, (2006), 1, Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 19 Level Fluctuation Versus Casting Speed Variation (Simulation) Q. Zhang, X. Wang and L. Zhang: Baosteel BAC 2006-The Second Baosteel Biennial Academic Conference, L.X. Qihua Xie, (2006), 1, Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 20

11 Level Fluctuation Versus Casting Speed Variation (Simulation) Q. Zhang, X. Wang and L. Zhang: Baosteel BAC 2006-The Second Baosteel Biennial Academic Conference, L.X. Qihua Xie, (2006), 1, Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 21 Level Fluctuation Versus Casting Speed Variation (Industrial Data) 6 Level fluctuation (m) With casting speed change, the level fluctuation does not change too much Casting speed (m/min) Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 22

12 Level Fluctuation Versus Casting Speed Variation (Industrial Data) Level fluctuation (mm) Casting time (min) Casting speed (m/min) Cast time (min) With casting speed change, the level fluctuation does not change too much Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 23 Level Fluctuation Versus Casting Speed Variation (Industrial Data) Level fluctuation (mm) Casting speed (m/min) Casting time (min) Cast time (min) With casting speed change, the level fluctuation does not change too much Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 24

13 Inclusions in Slab Versus Casting Speed with EMLS S.-H. Lee, S.-M. Lee and J.-S. Kim: Baosteel BAC The Second Baosteel Biennial Academic Conference, (2006), 1, EMLS improves steel cleanliness under high casting speed. Norwegian University of Science and Technology (NTNU) University of Illinois at Urbana-Champaign Lifeng Zhang 25