Application of hot strength and ductility test to optimization of secondary cooling system in billet continuous casting process

By means of Gleeble-1500 dynamic thermomechanical simulator, the continuous casting process for HRB335C steel was simulated using solidifying method and hot ductility and strength of the steel were determined. The test results indicate that there are three temperature regions of brittleness for HRB335C billet in the temperature range from 700 degrees C to solidification point; the first temperature region of brittleness is 1 300 degrees C to solidification point of the billet, the second temperature region of brittleness is 1 200- 1 000 degrees C, and the third temperature region of brittleness is 700-850 degrees C; the steel is plastic at 850-1 000 degrees C. The cracking sensitivity was studied in the different temperature zones of the brittleness for steel HRB335C and the target surface temperature curve for the secondary cooling is determined.' With optimized process, the mathematical model of the steady temperature field with two-dimensional heat transfer for 150 mmX 150 mm HRB335C steel billet was established to optimize the secondary cooling process. The conic relation of water distribution between secondary cooling water flux and casting speed is regressed. Keeping the surface temperature of billet before the straightening point above 1 000 degrees C, the results of billet test indicate that there is free central shrinkage cavity. The billet defect is decreased greatly, and the quality of billet is obviously improved.